Transitions to more sustainable urban water management … faculteit...Transitions to more sustainable urban water management and water supply Rutger de Graaf April, 2005 Expansion

Transitions to more sustainable urban water management and

water supply

Rutger de Graaf April, 2005

Expansion valve

Water is pumped from the lake to the heat pump.

Ground loop releases heat to cool earth

In the cold zone, the working fluid absorbs heat from circulating lake water.

Hot working fluid in the coil, releases heat to the closed ground loop.

Cooled lake water is released again to the lake to decrease water temperature.

Compressor

Pump

Sun provides heat to the surface water

Transitions to more sustainable urban water management and water supply

MSc Thesis Report 2


MSc Thesis Report 3

Transitions to more sustainable urban water management and

water supply

MSc Thesis Report Living with water project P1002

Report nr. 1.2005

Rutger de Graaf April, 2005

Delft University of Technology Faculty of Civil Engineering and Geosciences

Section of Water Resources Stevinweg 1

2600 GA Delft

Graduation Committee Dr. ir. F.H.M. van de Ven - Delft University of Technology Prof. dr. ir. N.C. van de Giesen - Delft University of Technology Prof. ir. F.H.L.R. Clemens - Delft University of Technology Drs. P.J.A. Baan - WL|Delft Hydraulics Drs. R. van der Brugge - Erasmus University Rotterdam Drs. P.L.G.M. Hesen - Kiwa Water Research Drs. D. Loorbach - Erasmus University Rotterdam


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Preface This MSc thesis report is an exploration and feasibility study to future urban water systems. In this report two future water systems are elaborated and the feasibility of these water systems is determined. The preparation of this report has been a long and interesting project that would not have been possible without the help of encouragement of my family, friends and supervisors. I would like to thank the following people in particular for their contributions: my supervisor Frans van de Ven for his encouragement, enthusiasm and clear vision on water management. The other members of the graduation committee Paul Baan, Peter Hesen, François Clemens and Nick van de Giesen for their constructive criticism and valuable remarks and suggestions. Rutger van der Brugge and Derk Loorbach, for teaching me about transitions and watch over the societal component of my report. And last but certainly not least, my girlfriend Anna van Dinther for being there and for listening to my stories about this graduation project. Rutger de Graaf April, 2005


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Summary Introduction The current state of the urban water system and urban water supply is the result of ages of measures, which have resulted from societal demands of the past. Urban water management supports a wide range of functions and needs. As a result, various interests such as ecology, public health, safety and economy should be balanced in the design of an urban water system. In this report concepts for future urban water systems are developed. For this purpose, first an analysis has been made of the needs and functions of urban water systems. Subsequently, problems, threats and opportunities have been studied and the system lay out has been analysed. Moreover, this report contains an analysis of the regime of organisations, to indicate actors and importance of actors. Besides, a vision has been extracted from the most important policy documents, technology developments, autonomous trends and needs. The feasibility of two future water systems, the Closed City and the Two Layer City has been studied as well as the implications of these systems for organisations. At last, obstacles for realization of future water systems have been indicated and both concepts have been evaluated. Transition process In urban water management, there is no agreement about the problem and the solution. Moreover, urban water management is characterized by a variety of interests, which may conflict with each other. Consequently, technical optimisation only, does not lead to the desired objective. In such a situation another approach is required, the transition approach is an example of such an approach. The transition approach is an approach, which describes broad societal changes and the mutual relations and complexity of these changes. A transition is a structural change in the way a societal system operates. A transition is a long-term process (25-50 years). Such a transition process in water management is already taking place and is focused on more sustainable and integrated water management. This transition process can be recognized by new approaches such as, ‘Room for rivers’, ‘Water as guiding principle’ and the retain-store-discharge principle. The transition process in water management is currently in the take off phase. In order to shape the transition process, objectives and ideas for a future sustainable water system are needed. In this thesis technically feasible future urban water systems are described, which can play a role in developing transition paths. Problem exploration For the transition process, in this report research has been conducted to find out if it is possible to make use of the following opportunities.

�� Available water may be used more efficiently, while the water system still contributes to public health, environmental and ecological quality and the living environment. An example is the use of runoff for useful purposes such as groundwater and surface water storage. In particular at places where urban water supply leads to groundwater depletion in surrounding areas, it would be an advantage if local water resources were used more efficiently.

�� Use of materials, energy and space may be decreased if local water resources are used more efficiently, for instance, the required dimensions of sewer systems become smaller if rainwater is no longer transported by the sewer system. Moreover, less dilution of wastewater takes place.


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�� A better balance between rainfall, storage and water shortage may be achieved by retaining and storing water within the city borders, for instance by infiltration facilities.

�� Groundwater and surface water levels may be adapted to prevent rotting of pile foundations, flooding of cellars and balance water surplus and water shortage.

Problem statement

�� Can urban water systems in the future be a feasible and more sustainable alternative for the present urban water systems?

�� Are future urban water systems (1) technically feasible (2) socially feasible and (3) preferable above current urban water systems?

Demands and needs The most important demands on urban water systems are sustainability, safety, housing conditions, public health, ecological quality and a high quality living environment. To balance these needs sustainability can be defined in a broad sense which consists of social, economic and ecological components. These components of sustainability can be subdivided further in the following objectives for future water systems. Future generations

�� Sustainable use of water �� Sustainable use of energy �� Sustainable use of space

Economic aspects �� Economic sustainability

Ecological aspects �� Clean water �� Varied morphology of water system �� Self-supporting system �� Connections with other ecosystems

Present generation

�� Reliable, clean and healthy water supply �� Reliable system to collect and transport wastewater �� Reduce water nuisance �� High quality living environment

The components of sustainability have been used to systematically analyse problems, threats and opportunities. These can be used to define a vision on urban water systems. There appear to be four influence fields on vision development, these are society, policy, technology and autonomous trends. If these are brought together, a ideal future water system could be defined as a water system that focuses on solving problems at a local scale, provides good surface water and groundwater quality, offers good possibilities for nature, secures public health, saves water and energy and is flexible for autonomous trends. Consequently, two future water systems can be defined. The first is the Closed City. The Closed City is a city that does not have adverse effects on its surroundings, such as water depletion or emission of pollution. The Closed City uses local rainfall as the only source for water use, improves water quality by self-purification processes and copes with water nuisance at a local scale. The second future water system that has been


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developed is the Two Layer City. The Two Layer City is a city that makes use of the water system to save energy. The Closed City The feasibility of the Closed City in average Dutch circumstances has been studied for three components, namely water quantity, water quality and water nuisance. The conclusion of the feasibility study is that the Closed City is technically feasible. For water quantity the ‘One house city schematisation’ has been developed, which, together with the water system analysis, is the base for a water quantity model. Results from this model show that local rainfall can compensate water use in a new residential district. However, there are a number of conditions. At first, the housing density should be low. At second, most rainfall should be kept in the urban water system, as a result, the stormwater infiltration or disconnection percentage should be high. To secure water supply during dry years, a part of effluent from wastewater treatment plants should be discharged back to the urban water system during dry spells. Another possibility is management of water demand by demand management measures, for instance the use of water saving technology, water pricing or public campaigns. Use of water saving technology only, can already decrease water use with 20%. This amount increases the feasibility and robustness of the Closed City to a large extent. Discharging effluent back to the urban water system is possible, although there are strict conditions. The possibility to discharge effluent back to the urban water system is a water quality issue; concentrations of oxygen, nitrogen, phosphorus and heavy metals must comply with water quality standards. For this purpose water quality calculations have been made to determine the effect of effluent on surface water quality. It appears that discharging effluent back is possible, although natural and artificial purification processes should be improved considerably. The nutrients removal efficiency of wastewater treatment plants should be increased as well as the efficiency of runoff purification processes, for instance by making use of infiltration, settling basins or reed bed filters. Moreover, the self-purifying capacity of the urban water system should be increased by circulation and adjusted morphology, for example by applying vegetation in canals and adjusting side slopes. Moreover, the oxygen demand of the bed sediments should be low, because it appears that the internal waste load has a determining influence on water quality. It is possible to cope with water nuisance locally without shifting problems to surrounding areas. The amount of storage, which has to be installed to cope with water nuisance problem can be realised in various ways, for instance by constructing an inundation area percentage of 15% combined with 500 mm allowable water level fluctuation. The inundation area consists of both surface water and area that is suitable for inundation such as parks. The water level fluctuation must be realized in addition to the seasonal fluctuation. Such a level fluctuation is only possible if the built environment is adjusted to this fluctuation. Because groundwater levels will fluctuate a lot, houses and other buildings should be able to cope with this. Another important aspect is the runoff collection system. This system should be able to collect and transport runoff effectively. In the Closed City, a surface runoff collection system is used combined with a wadi system. The combination of these systems offers good possibilities for purification of runoff and to keep water within the water system, which is needed for water use purposes. Some pumping capacity will be needed and consequently some water will discharge to the surrounding areas, however, because of its large storage capacity the Closed City has also the ability to accommodate water nuisance problems from surrounding areas. By installing a small pumping capacity in the Closed City, adjacent water systems and the Closed City can have mutual advantage by shifting problems on purpose to the place where it causes no problems. Other measures have also been evaluated. Increasing overland flow length, using permeable pavements and green rooftops lead to a larger time of concentration and consequently to smaller


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dimensions of the runoff collection system. However, these measures are not useful to decrease the required amount of storage in the Closed City. The Closed City is all about managing fluctuations and adjusting the city to these fluctuations. By varying level differences and drainage capacity according to the function of the urban area, water nuisance can be managed and a resilient urban water system can be designed. Adjusted building technology plays a crucial role to achieve such a water system and make groundwater and surface water fluctuation possible. The Two Layer City In the Two Layer City, groundwater heat pumps are used to supply heat to houses. Consequently, less conventional energy is needed. Groundwater is a very suitable heat source because it is a lowly valued energy source, thus it cannot be used for other purposes than heating. Contrarily, conventional energy sources such as gas or electricity are highly valued energy sources because a large amount of these energy sources can be converted into work. Therefore, these sources are suitable for other more useful purposes. From the viewpoint of efficiency, it is preferable to use groundwater for heating of houses. Very high efficiencies can be achieved, up to 400% of the electrical input is supplied as heat to the building, which is a much better efficiency than the conventional central heating systems. Energy use of houses can be decreased about 50% if heat pumps are applied. Heat pumps can be applied nearly everywhere in the Netherlands, however in less suitable circumstances, larger ground loops are required and consequently costs are higher. Less suitable circumstances are for instance, soils with a low thermal conductivity or a very low groundwater table. Extracting heat from surface water in summer, storing it in groundwater and extracting this heat in winter to heat houses, is possible and provides about 40% of the total residential room heating demand. Extracting large amounts of heat from aquifers leads to a structural decrease of groundwater temperature, especially if many buildings within a relatively small area make use of heat pumps. A decrease of temperature of an aquifer is undesirable from an ecological point of view and because effects of such a decrease are still uncertain. Integration with the surface water system provides a source of heat to reload the aquifer. In urban areas the air temperature and surface water temperature are about 1.5 oC higher, in summer the high water temperature leads to problems, for instance, algae bloom, anaerobic conditions and turbidity. Cooling the surface water to 19oC during August and July has a beneficial influence on the water quality and can provide heat to the aquifer. Heat balance calculations show that this amount is almost 40% of the total heat demand for room heating of houses. The heat pumps operation energy is added to this amount as well as the heat flow that results from cooling houses in summer. Deeper groundwater layers and the surface should supply the remaining part of the required heat. Implications If future urban water systems would be realized in practice, there would be a number of implications for involved organisations and inhabitants. First of all, water chain and water system are integrated in the Closed City, the urban groundwater and surface water are the source for the urban drinking water supply. Consequently, there are more dependencies between the municipality, the water board and the drinking water company. Expected obstacles are the distribution of costs and responsibilities. Consequently, more cooperation is required between the involved organisations in the Closed City. Also the formation of one water organisation that is responsible for all water tasks such as, water quantity management, water quality management, runoff collection, sewer system, waste water treatment and drinking water supply could be an alternative. The Closed City will involve inhabitants more because inhabitants experience their drinking water supply in their own living area and have influence on their drinking water supply. This asks for responsible behaviour, more involvement and managing of risks. More knowledge



is required for these aspects because failure on these points could be a major obstacle for the realization of the Closed City. The Two Layer City results in integration of water system and energy supply. Therefore, organisations, which used to have no relation, will now have to cooperate. By integrating the energy supply with the water system, the water board, being the manager of the water system, gets involved in the energy supply. Heat from surface water is extracted in summer, stored in an aquifer and extracted in winter. Consequently, cooperation between the water board and the energy supplier is needed. Another possibility is a situation where the water board takes up the responsibility to supply heat to households in the city, or even the situation where the inhabitants themselves are responsible for their individual groundwater heat supply. Obstacles for the realization of future water systems are the costs that are probably higher and the fact that not all effects, both positive and negative, of future water systems are known and quantified. Evaluation To evaluate future water systems an assessment has been made on the general feasibility of these systems. General feasibility includes technical feasibility, effectiveness, costs, desirability, preferability and contribution to sustainable development. Both alternatives contribute to sustainability in a positive way by reducing use of energy and materials, improving water quality and efficient water use of scarce water. The Closed City reduces external water supply almost entirely, whereas the Two Layer City provides about 50% of the total room heating demand of a residential district by extracting heat from surface water. Moreover, both future water systems use space for multiple functions. The preferability of the future water systems cannot yet been determined because information about costs and relevant effects is still lacking. Therefore, more research is needed and these innovations should be protected and developed further in applications. If technology proceeds and risks can be managed, future water systems can be preferable in the future.





Table of contents

PREFACE.......................................................................................................................5

SUMMARY .....................................................................................................................7

TABLE OF CONTENTS................................................................................................13

LIST OF FIGURES........................................................................................................18

LIST OF TABLES .........................................................................................................20

INTRODUCTION...........................................................................................................21

1 DEMANDS ON URBAN WATER SYSTEMS.....................................................26

1.1 The importance of water.................................................................................................26

1.2 Overall aim of water management.................................................................................26

1.3 Needs for sustainability...................................................................................................26

1.4 Safe and habitable country .............................................................................................28

1.5 Needs for public health ...................................................................................................29

1.6 A high quality living environment .................................................................................29

1.7 A healthy ecosystem ........................................................................................................29

1.8 Balance between needs....................................................................................................30

1.9 Water management policy ..............................................................................................30 1.9.1 National policy..............................................................................................................30 1.9.2 European policy ............................................................................................................30

2 FUNCTION ANALYSIS .....................................................................................32

2.1 Surface water ...................................................................................................................33 2.1.1 Water quantity functions...............................................................................................33 2.1.2 Water quality functions.................................................................................................33 2.1.3 Nature functions............................................................................................................34 2.1.4 Social functions.............................................................................................................34 2.1.5 Other functions..............................................................................................................34

2.2 Groundwater....................................................................................................................35 2.2.1 Water quantity functions...............................................................................................35



2.2.2 Water quality functions.................................................................................................37 2.2.3 Foundation ....................................................................................................................37 2.2.4 Nature............................................................................................................................38

2.3 Drinking water.................................................................................................................38 2.3.1 Household water supply................................................................................................39 2.3.2 Industrial water supply..................................................................................................40 2.3.3 Other functions..............................................................................................................40

2.4 Rainwater .........................................................................................................................40 2.4.1 Recharge........................................................................................................................40 2.4.2 Household water supply................................................................................................40

3 PROBLEM ANALYSIS......................................................................................41

3.1 Sustainable use of water..................................................................................................43 3.1.1 Present situation ............................................................................................................43 3.1.2 Threats...........................................................................................................................43 3.1.3 Opportunities.................................................................................................................44

3.2 Sustainable use of energy................................................................................................44 3.2.1 Present situation ............................................................................................................44 3.2.2 Threats...........................................................................................................................45 3.2.3 Opportunities.................................................................................................................45

3.3 Sustainable use of space ..................................................................................................45 3.3.1 Present situation ............................................................................................................46 3.3.2 Threats...........................................................................................................................46 3.3.3 Opportunities.................................................................................................................46

3.4 Economic sustainability ..................................................................................................47 3.4.1 Present situation ............................................................................................................47 3.4.2 Threats...........................................................................................................................48 3.4.3 Opportunities.................................................................................................................48

3.5 Clean water ......................................................................................................................48 3.5.1 Present situation ............................................................................................................48 3.5.2 Threats...........................................................................................................................51 3.5.3 Opportunities.................................................................................................................51

3.6 Varied morphology of water system..............................................................................51 3.6.1 Present situation ............................................................................................................52 3.6.2 Threats...........................................................................................................................52 3.6.3 Opportunities.................................................................................................................52

3.7 Self supporting system ....................................................................................................52 3.7.1 Current situation............................................................................................................52 3.7.2 Threats...........................................................................................................................53 3.7.3 Opportunities.................................................................................................................53

3.8 Connections with other systems .....................................................................................53



3.8.1 Present situation ............................................................................................................53 3.8.2 Threats...........................................................................................................................53 3.8.3 Opportunities.................................................................................................................53

3.9 Reliable, clean and healthy water supply ......................................................................54 3.9.1 Present situation ............................................................................................................54 3.9.2 Threats...........................................................................................................................54 3.9.3 Opportunities.................................................................................................................55

3.10 System to collect and transport wastewater..................................................................55 3.10.1 Present situation........................................................................................................55 3.10.2 Threats ......................................................................................................................55 3.10.3 Opportunities ............................................................................................................55

3.11 Reduce water nuisance....................................................................................................56 3.11.1 Present situation........................................................................................................57 3.11.2 Threats ......................................................................................................................58 3.11.3 Opportunities ............................................................................................................58

3.12 High quality living environment ....................................................................................59 3.12.1 Present situation........................................................................................................59 3.12.2 Threats ......................................................................................................................59 3.12.3 Opportunities ............................................................................................................59

4 SYSTEM ANALYSIS.........................................................................................61

4.1 Natural Resource system ................................................................................................61 4.1.1 Combined system..........................................................................................................61 4.1.2 Separated system...........................................................................................................62 4.1.3 Disconnected system.....................................................................................................62

4.2 Social Economic system ..................................................................................................64 4.2.1 Private organisations .....................................................................................................64 4.2.2 Social organisations ......................................................................................................65

4.3 Administrative and Institutional system .......................................................................66 4.3.1 Government organisations ............................................................................................67 4.3.2 Relation between watermanagement and spatial planning ...........................................68 4.3.3 Legal aspects .................................................................................................................68

4.4 Regime analysis................................................................................................................69 4.4.1 Critical actors ................................................................................................................69 4.4.2 Structural characteristics of the regime.........................................................................72 4.4.3 Development of the regime...........................................................................................73

5 A VISION ON FUTURE URBAN WATER SYSTEMS........................................75

5.1 The city system approach ...............................................................................................75

5.2 A vision as a result of four influence fields....................................................................76



5.3 Two future water systems...............................................................................................78

6 FUTURE WATER SYSTEMS: ’THE CLOSED CITY’ ........................................79

6.1 Ideas for Closed City Concepts ......................................................................................79

6.2 Water quantity analysis ..................................................................................................82 6.2.1 Schematisation of a new housing district......................................................................82 6.2.2 Schematisation of the water system ..............................................................................83 6.2.3 Water quantity model....................................................................................................84 6.2.4 Calculation of flows ......................................................................................................85 6.2.5 Water quantity assessment for several circumstances...................................................92 6.2.6 Influence of design parameters on water availability....................................................96 6.2.7 Sensitivity analysis........................................................................................................99 6.2.8 Demand management..................................................................................................100

6.3 Water quality analysis...................................................................................................100 6.3.1 Pollution sources .........................................................................................................100 6.3.2 Oxygen management...................................................................................................103 6.3.3 Phosphorus management.............................................................................................109 6.3.4 Nitrogen management .................................................................................................112 6.3.5 Heavy metals management .........................................................................................114

6.4 Water nuisance ..............................................................................................................116 6.4.1 Precipitation ................................................................................................................116 6.4.2 The urban water system ..............................................................................................117 6.4.3 Demands on the urban water system...........................................................................119 6.4.4 Design of storage and discharge capacity ...................................................................119 6.4.5 Design of gutters and wadi..........................................................................................123 6.4.6 Influence rainfall runoff process .................................................................................127 6.4.7 Design of drainage ......................................................................................................131 6.4.8 Variation of level difference and inundation frequencies ...........................................132 6.4.9 Make use of adjusted building technology..................................................................133

6.5 Concluding remarks......................................................................................................133

7 FUTURE WATER SYSTEMS: ’THE TWO LAYER CITY’................................135

7.1 Energy conservation......................................................................................................135 7.1.1 How a heat pump works..............................................................................................136 7.1.2 Types of groundwater heat pump systems ..................................................................137 7.1.3 Efficiency of heat pumps ............................................................................................138 7.1.4 Working fluids ............................................................................................................139 7.1.5 Heat pumps for residential use....................................................................................139 7.1.6 Applicability of groundwater heat pumps...................................................................140 7.1.7 System response of groundwater ................................................................................141

7.2 Integration with the surface water system ..................................................................143 7.2.1 Equilibrium temperature of surface water...................................................................144 7.2.2 Heat balance of surface water .....................................................................................145



7.2.3 Required pump capacity..............................................................................................149 7.2.4 Influence of further temperature decrease...................................................................150 7.2.5 Implications for design................................................................................................150


8 IMPLICATIONS OF FUTURE WATER SYSTEMS ..........................................152

8.1 Implications of the Closed City ....................................................................................152 8.1.1 Implications for organisations.....................................................................................152 8.1.2 Implications for inhabitants.........................................................................................154 8.1.3 Obstacles and advice for realization of the Closed City .............................................154

8.2 Implications of the Two Layer City .............................................................................155 8.2.1 Implications for organisations.....................................................................................155 8.2.2 Implications for inhabitants.........................................................................................156 8.2.3 Obstacles and advice for realization of the Two Layer City.......................................156

9 EVALUATION OF FUTURE WATER SYSTEMS ............................................157

9.1 Contribution to sustainable development ...................................................................157

9.2 Effectiveness...................................................................................................................158

9.3 Technical feasibility.......................................................................................................159

9.4 Desirability .....................................................................................................................159

9.5 Affordability...................................................................................................................159

9.6 Preferability ...................................................................................................................159


10 CONCLUSIONS AND RECOMMENDATIONS................................................161

10.1 Conclusions ....................................................................................................................161

10.2 Recommendations .........................................................................................................163

11 REFERENCES ................................................................................................165

APPENDIX A: SIMPLIFICATIONS FOR WATER SYSTEMS .....................................172

APPENDIX B: ELABORATION OF FOUR CALCULATION STEPS GROUNDWATER AND SURFACE WATER LEVELS .............................................................................175

APPENDIX C: INPUT VALUES FOR OXYGEN DEFICIT CALCULATION.................178



List of figures Figure 0-1: Flooding in Delft in 2002 (Min van V&W, 2003) .......................................................21 Figure 0-2: Four phases in the transition process (Rotmans et al, 2002) .....................................23 Figure 0-3: Interaction between different scale-levels (Geels and Kemp, 2000)..........................23 Figure 0-4: Structure and results of the report ..............................................................................25 Figure 1-1: ICIS triangle with three domains of sustainability (Rotmans, 1998)..........................28 Figure 1-2: Houses for handling fluctuating water levels in Maasbommel (Min van V&W, 2000)........................................................................................................................................................28 Figure 1-3: The waterchain in the hydrological cycle (DWI, 2004)..............................................29 Figure 2-1: Phase and results of chapter 2....................................................................................32 Figure 2-2: The influence of the city on groundwater (Lerner, 2004, Barett et al. 1999) .............35 Figure 2-3: Groundwater and rainwater recharge by precipitation..............................................40 Figure 3-1: Position in the report and results of chapter 3 ...........................................................41 Figure 3-2: Scheme of the objective tree for sustainable water management................................42 Figure 3-3: Urbanisation of the Netherlands.................................................................................46 Figure 3-4: Nature quality of regional waters compared to 1950 level (RIVM, 2004) .................48 Figure 3-5: Sources of surface water pollution (Water in Focus, 2004) .......................................49 Figure 3-6: Phosphorus in surface water.......................................................................................50 Figure 3-7: Nitrogen in surface water ...........................................................................................50 Figure 3-8: Zinc in surface water ..................................................................................................50 Figure 3-9: Copper in surface water..............................................................................................50 Figure 3-10: Nickel in surface water .............................................................................................50 Figure 3-11: Surface water without many variations ....................................................................51 Figure 3-12: Varied morphology in floatlands………….. .......................................................53 Figure 3-13: Development number of wildlife friendly banks (RIVM, 2004) ................................52 Figure 3-14: Disconnection of paved area in Barneveld ...............................................................53 Figure 3-15: Fragmentation of the landscape (RIVM, 2004) ........................................................54 Figure 3-16: Simplified structure of water nuisance problems and possible intervention points..56 Figure 3-17: Disconnection of paved surfaces from the sewer system ..........................................57 Figure 3-18: Delaying run-off process to reduce water nuisance .................................................59 Figure 3-19: The use of surface water to improve living quality ..................................................60 Figure 4-1: Position in the report and results of chapter 4 ...........................................................61 Figure 4-2: Schematisation of the urban water system with a combined sewer system.................62 Figure 4-3: Schematisation of the urban water system with a separate sewer system ..................63 Figure 4-4: Schematisation of the urban water system with disconnected paved surface .............63 Figure 4-5: Multilevel approach in transitions (Geels and Kemp, 2000)......................................69 Figure 4-6: Interactions in the regime between critical actors when realizing an innovation ......72 Figure 5-1: Position in the report and results of chapter 5 ...........................................................75 Figure 5-2: Flows to and from the city, which have impact on the surrounding area...................76 Figure 5-3: Four influence fields on the development of a vision..................................................77 Figure 6-1: Position in the report and results of chapter 6 ...........................................................79 Figure 6-2: Closed city concepts....................................................................................................81 Figure 6-3: Percentage of terrain types in a city ...........................................................................83 Figure 6-4: Water system schematisation ......................................................................................83 Figure 6-5: Structure of closed city with a combined system for water quantity model ................84 Figure 6-6: Structure of closed city with a separated system for water quantity model................85 Figure 6-7: Surface water level and groundwater level fluctuation for situation 1.......................92



Figure 6-8: Surface water level and groundwater level fluctuation for situation 2.......................93 Figure 6-9: Surface water level and groundwater level fluctuation for situation 3.......................95 Figure 6-10: Surface water level and groundwater level fluctuation for situation 4.....................96 Figure 6-11: Water availability vs. disconnection percentage for a combined sewer system .......97 Figure 6-12: Water levels vs. disconnection percentage for a separated sewer system ................97 Figure 6-13: Water availability vs. surface water percentage.......................................................98 Figure 6-14: Water availability vs. housing density ......................................................................98 Figure 6-15: Routes of pollution to the urban surface water.......................................................101 Figure 6-16: Development of oxygen concentration in one circulation.......................................106 Figure 6-17: Development of oxygen concentration in one circulation.......................................106 Figure 6-18: Development of oxygen concentration in one circulation.......................................107 Figure 6-19: Development of oxygen concentration in one circulation.......................................107 Figure 6-20: Development of oxygen concentration in one circulation.......................................108 Figure 6-21: Acceptable load of phosphorus ...............................................................................110 Figure 6-22: Influence of water depth on phosphorus load.........................................................110 Figure 6-23: Strategy of the two networks (Tjallingii, 1995)......................................................115 Figure 6-24: Rainfall depth duration curves for three return periods.........................................117 Figure 6-25: System layout of the closed city...............................................................................119 Figure 6-26: Rainfall duration curve with water use and evaporation........................................121 Figure 6-27: Rainfall duration curve with water use, evaporation and additional discharge ....122 Figure 6-28: Realisation of storage capacity by alternative water system design......................123 Figure 6-29: The intensity duration frequency curve..................................................................124 Figure 6-30: Street surface runoff collection system ...................................................................126 Figure 6-31: Wadi dimensions .....................................................................................................127 Figure 6-32: Influence of overland flow length on time of concentration....................................128 Figure 6-33: Increasing storage capacity by applying adjusted building technology .................133 Figure 7-1: Position in the report and results of chapter 7 .........................................................135 Figure 7-2: Schematisation of a heat engine................................................................................136 Figure 7-3: Schematisation of a heat pump .................................................................................136 Figure 7-4: System components of a heat pump (modified after Groen-Holland, 2004).............137 Figure 7-5: A vertical closed loop system (left) and an open loop system ..................................138 Figure 7-6: The Itho Energy house (itho, 2004) ..........................................................................140 Figure 7-7: Soil temperature as function of time and distance (IF technology,1997) .................142 Figure 7-8: Use of surface water in a lake to deliver heat to aquifer ..........................................143 Figure 7-9: The use of the circulation concept to extract heat from the surface water ...............144 Figure 7-10: Temperature of air and surface water ....................................................................145 Figure 7-11: The amount of extracted energy per house ............................................................150 Figure 8-1: Position in the report and results of chapter 8 .........................................................152 Figure 9-1: Position in the report and results of chapter 9 .........................................................157 Figure 10-1: Position in the report and results of chapter 10 .....................................................161 Figure a-0-1: Simplifications of water system for calculations ...................................................172 Figure a-0-2: Simplifications of water system for calculations ...................................................173 Figure b-0-1: New water level after groundwater drainage .......................................................175 Figure b-0-2: New surface water level after water use and precipitation .................................176 Figure b-0-3: Groundwater level after adjustment .....................................................................176 Figure b-0-4: New groundwater level after groundwater recharge and compensation .............177



List of tables Table 2-1: Functions of the urban surface water ...........................................................................33 Table 2-2: Functions of the urban groundwater water ..................................................................35 Table 2-3: Demands on drainage depth and discharge for various functions ..............................37 Table 2-4: Functions of drinking water..........................................................................................38 Table 2-5: Sources of drinking water in the Netherlands (Vewin, 2004) .......................................39 Table 2-6: Average water use in the Netherlands in 2001 (Vewin, 2004)......................................39 Table 2-7: Functions of drinking water..........................................................................................40 Table 3-1: Costs per household for various services .....................................................................47 Table 3-2: Types and percentages of sewer systems ......................................................................55 Table 4-1: Economic importance of water recreation (Hiswa,2005).............................................66 Table 4-2: Importance and proposed level of involvement of government organisations .............70 Table 4-3: Importance and proposed level of involvement of social organisations.......................71 Table 4-4: Importance and proposed level of involvement of private organisations.....................71 Table 6-1: Differences of the closed city concepts .........................................................................80 Table 6-2: Build up of private and public area in a residential district.........................................82 Table 6-3: Area of terrain type per house ......................................................................................83 Table 6-4: Average monthly precipitation (KNMI, 2004) ..............................................................86 Table 6-5: Results of Penman Eo calculation by Cropwat (FAO, 1998)........................................86 Table 6-6: Average monthly evaporation Makkink (KNMI, 2004) and Penman...........................87 Table 6-7: Thorntwaite and Mather calculation of evaporation with S0=100mm .........................88 Table 6-8: Discharge coefficients for various terrain types...........................................................88 Table 6-9: Estimations of discharge, infiltration and evaporation at a yearly timescale ..............89 Table 6-10: Estimation of average monthly evaporation..............................................................89 Table 6-11: Summary of methods, as being used in this chapter ..................................................90 Table 6-12: Water balance of an ’one house city schematisation’ in situation 1 ..........................93 Table 6-13: Waterbalance of an ’one house city schematisation’ in situation 2 ...........................94 Table 6-14: Waterbalance of an ’one house city schematisation’ in situation 3 ...........................95 Table 6-15: Waterbalance of an ’one house city schematisation’ in situation 4 ...........................96 Table 6-16: Predicted changes in Dutch climate ...........................................................................99 Table 6-17: Influence of climate change on water availability......................................................99 Table 6-18: Water quality figures of pollution sources for urban water systems ........................101 Table 6-19: Purification efficiency for various facilities .............................................................102 Table 6-20: Purification efficiency of wastewater treatments plants...........................................103 Table 6-21: Pollution sources on national scale (Water in Data, 2004) .....................................114 Table 6-22: Rainfall quantities for various return periods and durations...................................116 Table 6-23: The 95% confidence interval of figures from table 6.25...........................................117 Table 6-24: Runoff coefficient of a street block ...........................................................................125 Table 6-25: Runoff coefficient of green rooftops..........................................................................129 Table 6-26: Runoff coefficient on a yearly timescale of green rooftops (Rüngeler, 1998) .........129 Table 6-27: Runoff coefficient standards for green rooftops .......................................................130 Table 6-28: Runoff coefficient for closed city ..............................................................................131 Table 7-1: Residential energy use if EPC=1.0 (Duurzame-energie.nl, 2004) .............................139 Table 7-2: Indication of thermal capacity of soils and water ......................................................141 Table 7-3: Total solar radiation per month (KNMI, 2005) ..........................................................146 Table 7-4: Input values in the heat balance equation ..................................................................148 Table 7-5: Results of the heat balance calculation ......................................................................148



Introduction Current situation The current state of the urban water system and urban water supply is the result of ages of measures, which have resulted from societal demands of the past. Urban water management support a wide range of functions and needs, as will be discussed in the next chapters. As a result, various interests such as ecology, public health, safety and economy should be balanced in the design of an urban water system. As different opinions exist about the importance of needs and functions of these systems, there is no agreement about what the ideal urban water system should look like. However, there is agreement about the fact that until recently, most water systems has been focused on mainly technical measures and that other aspects such as ecology and living quality are now regarded as being more important than they used to be. Consequently, a new balance should be found between demands on water systems. For this purpose knowledge is required about which concepts can be realized and which cannot be realized. Therefore, in this report research will be conducted to find out if it is possible to make use of the following opportunities.

�� Available water may be used more efficiently, while the water system still contributes to public health, environmental and ecological quality and the living environment. An example is the use of runoff for useful purposes such as groundwater and surface water storage. In particular at places where urban water supply leads to groundwater depletion in surrounding areas, it would be an advantage if local water resources were used more efficiently.

�� Use of materials, energy and space may be decreased if local water resources are used more efficiently, for instance, the required dimensions of sewer systems become smaller if rainwater is no longer transported by the sewer system. Moreover, less dilution of wastewater takes place.

�� A better balance between rainfall, storage and water shortage may be achieved by retaining and storing water within the city borders, for instance by infiltration facilities.

�� Groundwater and surface water levels may be adapted to prevent rotting of pile foundations, flooding of cellars and balance water surplus and water shortage.

Figure 0-1: Flooding in Delft in 2002 (Min van V&W, 2003)



Developments The following relevant developments can be distinguished, which should be taking into account if a new water system is designed:

�� Climate change The climate of the Netherlands, will probably face dramatic changes in the coming decades. These changes will result in wetter winters, drier summers, higher intensity rainfall and a rising sea level. (WB21, 2000) �� Land subsidence The Netherlands has been shaped by the battle against water. Building dikes and polders have protected the low-lying parts against flooding from rivers and sea. However, the continuing pumping, drainage and cultivation of these areas has resulted in an ongoing process of subsidence. This process combined with the sea level rise has already led to the fact that a large part of the country is situated below the sea level, protected by dikes against rivers, canals and the sea, which are situated higher. In the future land-subsidence will continue if the management remains unchanged. �� Changing needs from society

Urban water is no longer considered as a single purpose element, which supports water quantity functions only. The main function of urban surface water was to store rainwater. However, today urban surface water also has to support ecology and recreation and urban surface water plays a role in the urban design as well. The demands of the urban surface water and groundwater have changed in terms of quality, quantity and the need for space.

Classification of the water management problem The water management problem, which is indicated above, is a so-called persistent problem. (Rotmans et al, 2003) Persistent problems are types of societal problems that have the following characteristics:

�� Significant complexity �� Structural uncertainty �� High stakes for a diversity of stakeholders involved �� Deeply rooted in our societal structures and institutions

It can be concluded that urban water management issues satisfy the description of a persistent problem; because of the many functions and forms of urban water (groundwater, surface water and drinking water), the uncertainty of: future needs, technologies and developments, climate change, knowledge of the water system and the diversity of stakeholders (waterboards, municipalities, other institutions and water users). Furthermore, these institutions make large investments in the urban infrastructure. Transition process In case of persistent problems, there is no agreement about the problem or the solution. Moreover, these problems are characterized by a variety of interests, which may conflict with each other. Consequently, technical optimisation only, does not lead to the desired objective. In such a situation another approach is required, the transition approach is an example of such an approach. A transition is a structural change in the way a societal system operates. A transition is a long-term process (25-50 years) which is characterized by four phases and three levels. (See Rotmans



et al, 2003). Figure 0-2 and Figure 0-3 show the concept of transitions. Such a transition process in water management is already taking place and is focused on more sustainable and integrated water management. This transition process can be recognized by new approaches such as, ‘Room for rivers’, ‘Water as guiding principle’ and the retain-store-discharge principle. The transition process in water management is currently in the take off phase. (Van der Brugge, Loorbach and Rotmans, 2003) Figure 0-2: Four phases in the transition process (Rotmans et al, 2002)

Figure 0-3: Interaction between different scale-levels (Geels and Kemp, 2000).

Time

System indicators

Stabilisation

Acceleration

Take-off Pre-development

Macro-level (landscape)

Meso-level (regimes)

Micro-level (niches)



Function of this thesis in the transition process In order to shape the transition process, objectives and ideas for a future sustainable water system are needed. In this thesis technically feasible future urban water systems are described, which can play a role in developing transition paths. Objectives for a future urban water system What should a future urban water system look like? The following objectives, which are related to sustainable development, are desirable for a future urban water system:

�� Socially sustainable for future generations, which means that we should use space, energy materials and water in a sustainable way.

�� Socially sustainable for present generation. For the present generation, a reliable, clean and healthy water supply is important; moreover, also a system to collect and transport wastewater should be present. Besides, the frequency of water nuisance should be limited to an acceptable frequency and the quality of the living environment should be high.

�� Economic sustainable. The future water system should be economic feasible (costs, opportunities for companies and jobs).

�� Ecologically sustainable. A system is ecologically sustainable if the water is clean, the morphology of the water system has a lot of variations, the system is self-supporting and there are connections with other ecosystems.

Problem statement

�� Can urban water systems in the future be a feasible and more sustainable alternative for the present urban water systems?

�� Are future urban water systems (1) technically feasible (2) socially feasible and (3) preferable above current urban water systems?

General objective The development of technologically feasible and inspiring concepts of future sustainable urban water systems. Reading guide In this report concepts for future urban water systems are developed. For this purpose, in chapter 1 analysis is made of the needs and demands of urban water systems. In chapter 2 the many functions of surface water, groundwater, drinking water and rainwater are summarized. Subsequently, problems, threats and opportunities are studied in chapter 3 and the system lay out is analysed in chapter 4. Moreover, this chapter contains an analysis of the regime, to indicate actors and importance of actors. In chapter 5 a vision has been extracted from the most important policy documents, technology developments, autonomous trends and needs. The feasibility of two future water systems, the Closed City and the Two Layer City is studied in chapter 6 and chapter 7. Chapter 8 presents the implications of these systems for organisations. At last, obstacles for realization of future water systems are outlined in chapter 9. The busy reader, who wants to read more than the summary only, is recommended to read the introduction, take a quick glance at chapter 3, read chapter 5 and the concluding paragraphs of chapter 6 and 7 as well as the conclusions and recommendations chapter.



Structure of the report

Phase in research Results

1. Demands on urban water systems Needs and demands of watersystems

2. Function analysis Overview of functions of urban water 3. Problem analysis Problems and objectives

4. System analysis Overview of natural, socio-economic and administative system

5. A vision on future urban watersystems Development of a vision

6&7. Future water systems Ideas and feasibility for future urban water systems

8. Implications of future watersystems Implications for organisations and inhabitants

9. Evaluation of future water systems General feasibility

10. Conclusions and recommendations Concluding remarks and suggestions for further research

Figure 0-4: Structure and results of the report



1 Demands on urban water systems Purpose and scope of this chapter As a starting point for this study on sustainable urban water management first is evaluated why water is important and which needs should be fulfilled by an urban water system. Finally, water management policy will be elaborated.

1.1 The importance of water The importance of water is very obvious and yet often so obvious that it is forgotten or that important aspects of the importance of water are overlooked. The first reason why water is important is that humans consists for about two thirds of water and that life without water is –as far as we know- impossible. Explorations to Mars are always focused on finding water or traces of water from the past, because a sign of water perhaps means a sign of life. Water has also a strong cultural value, ancient cultures such as the Egyptian and Roman culture all started near rivers. Moreover, rivers often play a major role in a national identity and also in religion and literature, songs and paintings. Water attracts people and even today a great percentage of the world population is situated near rivers and coasts. Just over half the world's population - around 3.2 billion people - occupy a coastal strip 200 kilometers wide, representing only 10 per cent of the earth's land surface. (peopleandplanet, 2004) In her anthropological study ‘the meaning of water’ Veronica Strang reflects on how deep water is anchored in human conscience and how it stands for wealth, power and connections with others. As will be evaluated in the next chapter, water support an enormous range of functions; households, industry, transport, recreation, ecology, food production, waste water discharge etc. It is for all these reasons that water is important and in the next paragraph, management of this resource will be treated

1.2 Overall aim of water management The overall aim of water management according to the 4th National Policy Document on Watermanagement is:

‘To have and maintain a safe and habitable country and to develop and maintain healthy and resilient water systems which will continue to guarantee sustainable use.’

It is clear that both the needs of people (Safe and habitable country) and the ecosystem (Healthy and resilient water systems) are given attention in the general objective, although a healthy and resilient water system certainly also benefits the needs of people. A safe and habitable country with regard to urban areas means: no water nuisance from groundwater, surface water and rainfall. The different between nuisance and flooding is made because a wrongly designed or managed urban water system can result in nuisance (water in cellars and crawlspaces) but not in flooding, because flooding is caused by the collapse of river dikes or sea dikes. Sustainability is an important element in the overall aim of water management therefore, first will be evaluated what sustainability is.

1.3 Needs for sustainability Since the publication of the UN report ‘Our common future’ of the Brundtland commission in 1987, sustainability as attracted massive attention from researchers from around the world. The central idea of sustainability is considered primarily in terms of continuing to improve human



well being, whilst not undermining the natural resource base on which future generations will have to depend. Sustainability can be used in various ways and there are several definitions of sustainability all with their differences and similarities. There is no common agreement on the exact definition of sustainability. Four key-elements can be extracted from the most common definitions. (Rijsberman, 1999)

�� To cover the needs of the present generation �� To cover the needs of the future generations �� To preserve the elements of the system �� To preserve system integrity

The future needs are hard to determine, yet these needs shape the possible future functions, which are required in order to know which measures are promising. The systems and sub-systems of the urban environment should have sufficient quality and quantity to fulfil their function in the future as well. However, it is very difficult to estimate what ‘sufficient’ is. For some functions this is easier than for others, what is for instance sufficient water quality for recreation? And is sufficient good enough or should we strive for the best possible water quality we can achieve? System integrity should be preserved because system elements and the relation between these elements determine the achievements of a system. It does not necessarily mean that the system should stay the same; as a result of a transition, functions can also be realized in another way or perhaps disappear. The importance of system integrity lies in the fact that all the parts of a system may function well, but the system as a whole does not. Therefore, it is essential to take the relations between system elements into account. Sustainability implies often the conservation of resources; the use of renewable resources may not be higher than the speed of regeneration. Non-renewable resources may not be depleted before alternatives have been found. (Mostert, 1998) The definition of sustainability also means that a deterioration of water quality that threats the functions of urban water is not acceptable. Rotmans et al. (2001) give the following integrative approach towards sustainability.

1. Consider the dynamic development on a timescale of 25-50 years 2. Consider the spatial development on at least two scales: micro and macro scale 3. Make a distinction in sustainable social, economic and ecological development,

and try to analyse the coherence This approach can be expressed in triangle model, which has been developed by ICIS and symbolizes three domains of sustainability and their mutual relations. The three domains are the social, economic and ecological capital. Water related examples of social capital are: flooding safety and public health; economic capital is for instance: water, which can be used for economic production, such as agriculture, energy supply etc. Ecological capital can be expressed in biodiversity and quality living environment. In a sustainable approach there should be a balance between the three domains and development of one domain should not harm the other domains. For instance, economic development should not have adverse effects on the ecological and social capital. In practice, however, this is often the case. In the figure the social capital is the top of the triangle, at the left corner is the ecological capital, whereas the economic capital is at the right corner.



Figure 1-1: ICIS triangle with three domains of sustainability (Rotmans, 1998) How does sustainability relate to the general objective of water management? People and ecosystems make various demands on the urban water system. These needs lead to a range of water related functions that will be investigated later in the report. As we will see, these functions and needs can conflict with each other.

1.4 Safe and habitable country Besides sustainable use, one of the main components of the aim of water management is to develop and maintain a safe and habitable country. To make the country habitable automatically means human interference in the natural water system, at least in large parts of the Netherlands. Dikes protect more than half of the country against flooding and water management is needed for any form of development in these areas. Therefore, water systems in the Netherlands are mostly artificial systems. However, also within these artificial systems one can maximize the opportunities for ecosystems and also within these artificial systems, natural processes can be used to obtain a more sustainable water system. The fact that people do not want water nuisance in their living area, makes demands on the drainage and storage functions of the water system. If these are designed properly no frequent nuisance will occur. However, the buildings can be adjusted to fluctuating water levels to limit water related damage as well. For economic reasons a low frequency of nuisance is accepted, because it is very expensive to prevent nuisance completely. Therefore a certain return period of water nuisance is selected and the design of the drainage and storage is based upon this return period.

Figure 1-2: Houses for handling fluctuating water levels in Maasbommel (Min van V&W, 2000)



1.5 Needs for public health The needs of society with regard to the water chain are mainly related to health and comfort. The water chain consists of: drinking water treatment-distribution-water use-sewerage-wastewater treatment and discharge. In the figure below, the position of the water chain in the hydrological cycle has been indicated. A clean and reliable water supply is essential for public health. Besides, safe transport of wastewater out of the direct living environment is provided by the sewer system. These two elements of the water chain, water supply and sewage system make high living conditions in urban areas possible. Clean water is used for drinking, cooking and washing; these are all activities with a beneficial influence on health. Besides, water supply also makes comfort in houses possible as it is used for showering and bathing. The standards for drinking water quality can be found in the drinking water law (waterleidingbesluit).

Figure 1-3: The waterchain in the hydrological cycle (DWI, 2004)

1.6 A high quality living environment Preventing water nuisance is not the only goal of the general aim of water management in the Netherlands. After all, absence of water nuisance does not automatically mean that there is a high quality living environment for housing, working and recreation. To fulfil this need, good water quality without stench, algae bloom and turbidity is essential. Besides, the urban water should be visually attractive, well designed, and accessible for inhabitants, it has to fit well in the urban landscape and contribute to the quality of the urban landscape and to the cultural value of a city.

1.7 A healthy ecosystem In the general aim of water management one of the main objectives is the maintenance and development of healthy and resilient water systems. This part is especially relevant for ecosystems. In urban areas a healthy water system means a water system, which is clean, for instance a water system that has a water quality that complies with the standards that have been stated in The 4th Water Policy Document. Resilient means that the water system has a high self-cleaning capacity and is as much self-supporting as possible. Human interference to maintain the



quality of the water system should be as low as possible. With regard to water quantity, a resilient system also means a self-supporting system, which retains and stores water as much as possible. Consequently, fewer water supplies from the surrounding area are needed and water nuisance is reduced by the storage capacity. The ecological quality of urban water systems should be as good as possible, it means that a large variety of species have opportunities to sustain and develop in the urban environment. This requires the following features for urban water systems: good water quality, a varied morphology of the water system that offers living possibilities for several species and the connection to other systems to offer species possibilities for migration.

1.8 Balancing needs A good ecological quality can benefit the living environment and therefore ecological and human functions can have mutual benefits. However, also the opposite is possible, for instance because ecological functions of an area can lead to restrictions for recreational use of that area. A water system should also be economic feasible, a ecologically very healthy water system can not be realized if the costs are extraordinary high; again it is about the balance between three domains of sustainability (economic, ecological and social). This balance is dynamic, which means that the qualities and quantities of the sustainability components may change. Which balance is sustainable depends on the context of the situation and to which extent the demands on the water system are fulfilled.

1.9 Water management policy There is both national and European policy with regard to water management. These two forms of water management will be further elaborated.

1.9.1 National policy Next to the 4th Policy Document On Watermanagement, which has been mentioned before in this chapter, there is also another relevant policy document of the national government. In the policy document “A different approach to water, water management policy in the 21th century” the government vision on water management has been outlined. The following elements are most important:

�� Anticipating instead of reacting on water �� More space for water in addition to technological measures �� Not passing on of responsibilities and problems

In the policy document a tool is described, namely, the water test. This tool has to ensure that water is taken into account in spatial plans. Moreover, space, which is needed for flood and prevention of water-related problems, may not be lost by use of other functions. A principle in the policy document is the retain-store-discharge principle, which has to prevent the passing on of problems. Areas themselves are responsible to accommodate water and may not cause water problems for their neighbours by discharging it to the surrounding areas.

1.9.2 European policy Next to national policy, there is European policy as well. The most important example is the European Water Framework Directive. The Framework directive has the following objectives:

�� To prevent deterioration and improve the status of aquatic ecosystems and dependent terrestrial ecosystems

�� To promote sustainable use of water



�� To decrease the disposal of priority substances and to stop the disposal of priority hazardous substances

�� To prevent further contamination of groundwater Source: (Mostert (2004) translation by author of this report) Surface water The Framework Directive demands a good status for all waters by 2015, for surface water there are two components "good ecological status" and "good chemical status". Good ecological status is defined in terms of the quality of the biological community, the hydrological characteristics and the chemical characteristics. Good chemical status is defined in terms of compliance with all the quality standards established for chemical substances at European level (EU, 2004). Groundwater The case of groundwater is somewhat different, for groundwater quality it comprises a prohibition on direct discharges to groundwater, and a requirement to monitor groundwater bodies so as to detect changes in chemical composition, and to reverse any antropogenically induced upward pollution trend. Taken together, these should ensure the protection of groundwater from all contamination, according to the principle of minimum anthropogenic impact (EU, 2004). The quantitative status is important as well. There is only a certain amount of recharge into a groundwater each year, and of this recharge, some is needed to support connected ecosystems. For good management, only that portion of the overall recharge, which is not needed by the ecosystem can be abstracted (EU, 2004). Type of water bodies The general description and goals, which were outlined in the former paragraphs, should be applied to various water bodies. It must first be determined whether a water system is ‘in a natural state’ or has been ‘dramatically changed’. In theory, the most ambitious ecological targets apply to ‘natural’ water systems. For water systems that have been ‘dramatically changed’, less ambitious targets can be established. However, governments are accountable to the European Commission for this and must explain their reasons for lowering the targets (e.g. public feasibility and disproportionately high costs. (Water in Beeld, 2004) Measures and the river basin management plan To reach ‘a good status for all waters by 2015’ for each river basin a so-called river basin management plan must be made to coordinate measures in that particulate river basin. This plan must be updated every six years. The hydrological unit, the river basin, is the starting point for the planning of measures, instead of an administrative or regional unit. In the Netherlands there are four international river basins, namely: the Rhine, Meuse, Scheldt and Ems. Public participation and water pricing Two other important elements of the Framework directive are public participation and water pricing. Public participation is important because an integrative approach requires balancing of interests and the Framework directive desires a transparent decision making process. For public participation, in the Netherlands, regional response groups have been established. Adequate water pricing acts as an incentive for the sustainable use of water resources and thus helps to achieve the environmental objectives under the Directive. Member States will be required to ensure that the price charged to water consumers - such as for the abstraction and distribution of fresh water and the collection and treatment of waste water - reflects the true costs. (EU, 2004)



2 Function Analysis Purpose and scope of this chapter In the former chapter the importance of water and a sustainable approach were evaluated. In this chapter attention an overview will be presented of the many functions of urban water. The results are required to be able to accomplish an integrative approach, which takes into account all relevant aspects. The place and function of this chapter are indicated in the following figure.










Figure 2-1: Phase and results of chapter 2 In urban areas water appears in a number of forms, for instance surface water, groundwater, rainwater, wastewater and drinking water. These forms of water support several functions within the urban area and these functions make demands on the urban water in terms of quantity, quality and requirement of space. In this chapter the functions of the urban water will be examined.



2.1 Surface water The urban surface water supports the following functions (Van de Ven, 2004): Table 2-1: Functions of the urban surface water

Water quantity functions

Water quality functions

Social functions Fysical functions

Nature

Discharge Degradation of pollutants

Recreation Separation Ecology

Storage Transport of pollutants

Culture Residence

Water supply during dry periods

Retain pollutants Landscape

2.1.1 Water quantity functions Three water quantity functions can be distinguished within the urban water system:

�� Storage �� Discharge �� Water supply

In most cases water quantity functions have been combined in water systems in the Netherlands. Especially in the lower parts in the west of the country this is case, because there is no sufficient difference in terrain height to have separate water supply and drainage systems. In the typically Dutch polder system one will find all three functions: supply, discharge and storage combined in the belt channel of the polder. The importance of discharge and storage is to prevent water nuisance and damage. These effects can result from high water levels, high ground water levels or the lack of capacity to discharge runoff. To prevent damage and nuisance, the capacity of storage and discharge has to be sufficient. The general goal is to limit certain water levels to acceptable frequencies and therefore to limit societal damage. The importance of water supply to the urban area is mainly related to other functions such as nature and social functions. However, it is related to groundwater functions as well; these functions will be discussed later in this chapter. In temperate areas in which the precipitation exceeds evaporation, water discharge has generally more importance than the water supply. However, in dry periods water supply to the urban surface water can be necessary to avoid low groundwater tables and ecological damage. Besides, water quality can make water supply necessary.

2.1.2 Water quality functions Besides water quantity functions the urban surface water also supports water quality functions. These functions are:

�� Degradation of pollutants



�� Transport of pollutants �� Retaining of pollutants.

Degradation of pollutants is important, due to the fact that there are many pollution sources in cities. Improvement of the degradation capacity of urban surface water, for example by water circulation or reed beds, has a positive impact on the water quality and therefore is favourable for lots of other functions. Pollution in urban areas either has to be broken down or transported out of the area. Therefore, transport of pollutants out of the urban area is a function of the surface water as well. Finally, the settling of pollutants has a beneficial effect on water quality. Settling of pollutants can take place in settling ponds and reed bed filters. In these facilities pollution can be broken down further or the pollution can be removed by maintenance of these facilities.

2.1.3 Nature functions To support nature, surface water is of great importance. This is the case for vegetation as well as for nature, in both aquatic and terrestrial ecosystems. The demands that ecology imposes on the water system are related to water quality, water regime (level fluctuations) and the morphology of the water system. In general the ecological quality of the water will be higher if the oxygen content is high, the amount of pollutants is low and there is variation in the water system, which offers various species possibilities. Banks with low gradient and level fluctuations are positive for ecological quality. Finally, connections with other ecosystems are essential to give wildlife the possibility to migrate to other areas.

2.1.4 Social functions Water has an important social function for recreation, culture and landscape. Recreation possibilities increase the quality of the urban living environment. The cultural function of water is important as well; the Netherlands is famous worldwide as water country; the windmills and canals attract many tourists each year. The battle against water shaped the country and water plays a key role in the urban landscape. Therefore, to maintain the cultural function of surface water it is necessary to conserve historical elements in the city which are related to water. Furthermore, it is important to minimize water nuisance such as inundations and stench. In new areas, water can also play a cultural role if it is integrated in the urban planning and people have access to surface water.

2.1.5 Other functions Other functions of urban surface water are separation and housing. To separate districts in cities, surface water can be used. A canal is able to separate parts functionally and visually. Houseboats can be found in many places as well as floating houses. The demands of this function for the urban surface water are sufficient water quality and visual quality. Also accessibility is important.



2.2 Groundwater Groundwater has the following functions (Van de Ven, 2004): Table 2-2: Functions of the urban groundwater water

Water quantity functions

Water quality functions

Foundation Nature

Discharge Degradation of pollutants

Prevention of oxidation

Support ecosystem

Storage Transport of pollutants

Reduction of subsidence

Water supply Retain pollutants Reduction of weight

Groundwater supports a lot of functions in urban areas and at the same time the urban area has a large influence on groundwater. Moreover, groundwater in the unsaturated zone is essential for vegetation, because it is the water source for plants. Urbanisation leads to the construction of paved areas, which increases storm water flow and reduces evaporation. At the same time drinking water is pumped to the urban area and leakages occur. If the groundwater level is lower than the sewer level, leakages occur from the sewer system. If the groundwater level is higher than the sewer level, groundwater enters the sewer pipe, especially if the sewer system is old. The leakage of wastewater and various human activities cause pollution of the groundwater. The influence of the city on the groundwater is illustrated in figure 2.2.

Figure 2-2: The influence of the city on groundwater (Lerner, 2004, Barett et al. 1999)

2.2.1 Water quantity functions Groundwater has roughly the same water quantity functions as surface water, namely discharge, storage and supply. Also the objective of these functions is similar, namely to reach an acceptable risk level which is determined by a certain groundwater level combined with certain frequencies.



The main difference between groundwater and surface water is the medium of flow; which is the reason for groundwater flow to be much slower than surface water flow. Groundwater has a storage function that can be useful, especially to cope with high precipitation intensities. In case of a phreatic water table, storage results in a climbing water table. In case of a confined aquifer it results in a higher piezometric head. Storage of peak rainfall in groundwater is quite effective because it slows down the runoff peak to a large extent and transforms high velocity stormwater flow to low velocity baseflow. By using infiltration, the runoff process gets closer to the process as it works before urbanisation takes place. However, infiltration of water is only possible if there are pervious surfaces or infiltration facilities and if a rise in groundwater level is allowable Excess of water can be discharged through canals and surface water but also through the groundwater. Eventually, groundwater ends up in surface water like canals, rivers or the sea. This can be done by natural processes or by means of drainage facilities which are constructed to maintain the groundwater table between certain limits. Drainage facilities can consist of drainage pipes, soil improvement or infiltration facilities with a draining function such as wadi systems. Various functions demand various groundwater tables; this can result in complications for multifunctional use of the urban space, because groundwater cannot easily be varied within a limited area. The optimal groundwater level is therefore the result of balancing of interests. A table that is too high can result in moist problems in cellars and crawl spaces, a groundwater table that is too low can result in land subsidence. Groundwater can be used to supply water during dry periods. Besides, groundwater plays a role in water supply through the process of seepage. This is especially the case in low level polders where the seepage flow can be very large. Another destination of groundwater supply is for industrial pumping stations. Industrial companies extract groundwater to use for cooling and cleaning purposes. However, sometimes industrial extraction is even needed to maintain a current groundwater table, for instance in Delft (DSM) and Eindhoven (Philips). In these situations, equilibrium has been reached by extraction; as a result, extraction has to be continued to prevent damage.



Table 2-3: Demands on drainage depth and discharge for various functions (Van de Ven, 2004)

Activity/destination Steady drainage-computation

Drainage depth Design discharge

(m below ground level) (mm/24hrs) I. during the construction phase �� construction of structures 0.60- 0.70 �� laying of telephone-cables 0.50- 0.60

Low voltage cables 0.60 Gas lines 0.65- 1.00 High voltage cables 0.90 Sewer pipes 1.00- 3.50

�� construction of primary roads 1.00 secondary roads 0.70 squares, parking lots 0.40

�� accessibility 0.50-0.70 Summary: during the construction phase 0.70- 0.80 10 II. the habitation phase �� structures 0.70 �� cables and pipelines 0.60- 1.00 �� primary roads 1.00 �� secondary roads 0.70 �� industrial areas, centre areas 0.70 Summary: the habitation phase 0.70 5 Gardens, public gardens, parks 0.50 7 Camping areas 0.50 10 Graveyards 0.30 below underside coffin 10 Sport fields 0.50 15 Non-steady drainage computation 0.70 Drainage depth with frequency of

exceeding of 1 event per year

2.2.2 Water quality functions The water quality functions of groundwater are important, because groundwater can influence the surface water quality through seepage and affect drinking water wells. Moreover, groundwater can have an effect on public health as well if it causes moisture in houses. Human activities are a cause of groundwater pollution and because of the generally long residence time of groundwater, it can take years before effects are noticed. Pollution transport by groundwater takes place by advection and dispersion processes. Groundwater quality processes are mostly autonomous processes, which are hard to influence and, in case of dispersion, are irreversible. Therefore prevention of pollution is the best solution, also because soil cleaning is very costly. On the other hand, groundwater degradation processes can be used to purify water. A good example of this is artificial infiltration for drinking water production.

2.2.3 Foundation Groundwater has a large impact on the foundation of buildings. There are three foundation related functions of groundwater namely: Prevention of oxidation, reduction of subsidence and reduction of weight.



Peat soils are very sensitive for oxidation; as soon as the peat is exposed to oxygen the oxidation process starts. This process can result in an enormous lowering of the terrain level. In many parts of the Netherlands this has taken place and the terrain level is meters lower than it used to be. Peat oxidation is practically irreversible as the formation of new peat layers takes hundreds of years. The oxidation of wooden piles is to be prevented as well, because piles that are exposed to oxygen will start rotting and rehabilitation of a foundation is very costly. Peat and pile oxidation can be prevented if the water level is kept close to the terrain level. However, other functions often ask for a lower groundwater table. Another problem that is related to groundwater is land subsidence, lowering of the groundwater table results in a higher grain stress, which result in land subsidence, this process is irreversible as well. A high water table decreases or prevents subsidence. Moreover, groundwater absorbs a part of the weight of structures; this property of groundwater is used in designing floating roads that make use of the bearing capacity of groundwater, also for this purpose, a high groundwater table is required.

2.2.4 Nature Vegetation in gardens in park depends on the subsoil moisture content, which is determined by the groundwater level and the soil type. In cities, green areas often have both an ecological and a recreational function. For these green areas, sometimes additional supply of water is needed and sometimes drainage is needed. Various ecosystems demand various groundwater tables; the type of ecosystem determines the desired groundwater regime. However, other functions have to be taken into account during this process. The method of determination of groundwater regimes based upon (ecological) functions as been described extensively in the method of the ‘project Waternood’ (see for instance: Runhaar, 2002). Ecosystems demand a certain water quality as well, which is determined by the type of ecosystem which has to be supported.

2.3 Drinking water For drinking water the following functions can be distinguished: Table 2-4: Functions of drinking water

Household water supply Industrial water supply Other Bath and shower Cleaning Firefighting Wash basin Cooling Irrigation Toilet flush Heating Horticulture Food preparation Production Dishwashing Cloth washing Drinking Cleaning

Garden

Pipe supplied drinking water is one of the most important sources of urban water. The functions of drinking water vary from household water supply to industrial supply and other purposes such as irrigation and fire fighting. Within the scope of this study, most attention will be given to



household purposes, whereas the other functions will be mentioned shortly. The main sources of drinking water are surface water and ground water. Additionally, water from dunes and water from riverbanks provide a part of the water supply. Table 2-5: Sources of drinking water in the Netherlands (Vewin, 2004)

Ground water Dune water Riverbank groundwater

Surface water

Water extraction 2002 (mln. m3) 743 12 32 514

Total: 1,301

2.3.1 Household water supply An average daily amount of 126 litres of water is used by each citizen in the Netherlands. This water is used for various functions. The following table presents an overview for the situation in the Netherlands for the year 2001. Table 2-6: Average water use in the Netherlands in 2001 (Vewin, 2004)

Water use per time (l)

Use frequency per day

Penetration Average use per person per day

(l) %

Bathing 107.9 0.07 49% 3.7 3%

Shower 60.6 0.70 99% 42.0 33%

Wash basin 4.0 1.30 100% 5.2 4%

Toilet flush 5.8 5.99 100% 34.8 27%

Cloth washing, hand 36.0 0.05 100% 1.8 1%

Cloth washing, machine 80.0 0.29 99% 22.8 19%

Dishwashing, hand 8.0 0.45 100% 3.6 3%

Dishwashing, machine 20.0 0.24 51% 2.4 2%

Food preparation 1.6 1%

Coffee, tea en water to drink 1.5 1%

Others 6.7 5%

Total 126.2 100%

Showering makes up for the biggest water use in the average household, followed by toilet flush and the washing machine. Water for all these purposes is of very high drinking water quality, whereas less than a half of the water use purposes needs this very high quality from the point of



direct health risks. (Van Dijk, 2002) From these purposes, showering uses a large part. Water to drink and food preparation only use 2% of the total water use. For toilet flushing, washing machines and others, such as watering the garden or washing the car, water of less quality could be used.

2.3.2 Industrial water supply Although industries often have their own water supply in the form of a groundwater pumping station also drinking water is being used for industrial processes such as heating or cooling. Industrial use of drinking water accounts for 14% of the total drinking water supply. (Vewin, 2000)

2.3.3 Other functions Other functions of drinking water are fire fighting and irrigation. Fire fighting is important for safety reasons and plays an essential role in the dimensioning of drinking water distribution systems. This is because the fire fighting discharge is mostly the critical demand, which determines the diameter of the pipes. However, in new design methods the influence of fire fighting demand is smaller than it used to be and the actual drinking water demand becomes dominant. (Vreeburg, 2004) The total amount of not charged water supply (leakages and fire fighting supply) was 5% in 2000 (Vewin, 2000). Also for the irrigation of public green spaces, drinking water is used.

2.4 Rainwater Rainwater has the following functions: Table 2-7: Functions of drinking water

Recharge Household water supply Surface water recharge Toilet flush Groundwater recharge Cloth washing

Figure 2-3: Groundwater and rainwater recharge by precipitation

2.4.1 Recharge Rainfall is an important source for both groundwater and surface water recharge. After interception, runoff and evaporation losses, water is added to the groundwater storage. By direct precipitation and runoff also surface water is refilled.

2.4.2 Household water supply For some of the household purposes rainwater can be used, for instance for cloth washing and toilet flushing. For this functions water of less quality could be used. However, as will be discussed in the next chapter, rainwater collection systems unfortunately have some disadvantages as well.



3 Problem analysis Purpose and scope of this chapter The former chapter addressed the various functions of the urban water systems. This chapter on one hand investigates what the problems are in urban water management. On the other hand, the goal is to find objectives and criteria to develop future water systems and to be able to evaluate those future water systems. The following figure indicates the position and results of this chapter.










Figure 3-1: Position in the report and results of chapter 3 If one or more functions are not supported sufficiently, one speaks of a problem. In other words: a problem is the difference between the desired and existing or expected situation. However, water management is not only about solving problems, also opportunities and challenges are important. In such a case the functions of the urban water system are fulfilled but it could even be done better. According to the definition of a problem, the desired situation has to be known in order to define a problem. For this purpose, an objective tree is constructed to analyse the objective and specify criteria. Only objectives, which are related to water management and energy, are evaluated in this scheme. To construct this tree, information from the former chapter has been used. In chapter 1 the key elements of sustainability where covered. Sustainability can be regarded in three dimensions, namely social, economic and ecological sustainability. For social sustainability it is useful to make a distinction between the needs of the present and future generation. For the economy and ecology this is less useful because the needs of ecology hardly change through time and economy hardly ever focuses at all on the very long term. Often there is a conflict between the economic short-term interests and the long-term social and ecological interests. Therefore, the social needs of the future generations are explicitly taken into account in the objective scheme. In the objective tree the general goal: sustainable urban watermanagement and water supply is split in four sub goals, these are:

�� Socially sustainable: needs of future generations



�� Socially sustainable: needs of present generations �� Economic sustainable �� Ecologically sustainable

These sub goals need to be elaborated further because the sub goals are still very general. The sub goals are made more concrete by the goals on the second level. For these second level objectives, it is possible to seek criteria. These criteria are necessary to be able to make a judgment of current and future water systems. However, for some objectives it is hard to make the criteria operational, for other objectives making the second level objectives more concrete by criteria leads to neglecting a lot of relevant factors. For this reason in this chapter the second level objectives are evaluated for the current situation, threats and opportunities. Each second level objective is a separate paragraph in this chapter.

Figure 3-2: Scheme of the objective tree for sustainable water management

Sustainable urban water system and water supply

Socially sustainable for

future generations

Sustainable use of water

Socially sustainable for

presentgeneration

Sustainable use of energy

Sustainable use of space

Clean water

Varied morphology of water system

Self supporting system

Connections with other systems

Reliable, clean and healthy water supply

Reliable wastewater

collection and transport

Reduce water nuisance

High quality living environment

Water use< rate of regeneration within city

Energy efficiency

multi-functional use of space

Standards 4th policy document on water

Variation in water level and water system

dimensions

Self cleaning capacity

(Ground) water level regime

Storage capacity

# connections

Standards Waterleidingbesluit

All wastewater has to be collected and

transported

Frequency of water nuisance

Area for recreation

Water quality standards 4th policy

document

Visually attractive

% of supply from renewable sources

Water retaining capacity

Operational safety

ecologicallysustainable

Economicsustainable

Economically viable

Costs

Business Opportunities

Net present value

low costs

profitability new technologies

Main Objective First level Second level Criteria



3.1 Sustainable use of water What is sustainable use of water? Several approaches towards sustainability were presented in former chapters. Moreover, both the national as the European approach towards water management were outlined. Some elements can be extracted from this information. Sustainable water use means to prevent:

�� Depletion of groundwater or surface water; the water use may not be larger than the speed of regeneration.

�� Problems in surrounding areas as a result of water use in the city.

3.1.1 Present situation There are two problems that are related to water use in urban areas. The first problem is that water use causes water depletion in other areas, such as nature reserves. The second problem is the use of drinking water for low quality purposes. In particular if water scarcity or water depletion occurs at the same time this is a problem. Water use causes water depletion The extraction of groundwater, which forms a large part of the water supply, causes water depletion in nature reserves. Water extraction contributes for 93.000 ha to areas suffering from water depletion. (Vewin, 2004) To meet the objectives laid down in the Water Evaluation policy document: by 2010 a 40% reduction in the area of countryside suffering from water depletion as compared with the 1985 figure, must be realized (4th Policy document on water). Besides, water extraction, treatment and transport costs energy, money and requires chemicals. High quality water for low quality purposes The drinking water supply in the Netherlands is of a very high quality; this quality is reached by input of chemicals, energy and money. The high quality is not needed for a large part of the water purposes, since about 50% of the total water use of 126 litres/capita/day is used for toilet flushing and cloth washing. At the same time the internal source of clean water in the city, rainfall, is hardly used and transported through the sewer system to the wastewater treatment plant. The external water supply from drinking water pipes is approximately 300 mm a year (DHV, VNG, 1996), whereas the supply by rainfall is 750 mm a year in the Netherlands. Chapter 6.2 presents an analysis, to find out whether it is possible to design a city, which only needs the input of rainfall while no additional supply is needed.

3.1.2 Threats There are some threats, which prevent the implementation of a sustainable urban water supply. Theoretically, the use of local rainfall for low quality purposes could both decrease water supply to the urban area from the surrounding areas and the use of high quality water for low quality purposes. However, some problems arise here which relate to social needs, such as public health and operational safety. Experiments with ‘dual networks’, which supply two qualities of water, have not turned out to be a success. The main reason for this failure is the fact that they impose a health risk. Moreover, these networks need more material and energy input, which can be regarded as an environmental problem. Besides, enormous amounts of capital have been invested in the current system; this makes the change to a new system difficult. The threats can be summarized as follows:

�� The government has restricted use of ‘dual networks’ for household purposes (VROM, 2004).



�� The use of rainwater, which has not been treated properly, can impose a health risk if rainwater has become contaminated with pathogen organisms by contact with roofs. (Kiwa, 2003)

�� Large amount of capital have been invested in the current system. �� Rainwater collection systems for household are not financially feasible.

3.1.3 Opportunities

There are opportunities as well for more sustainable water use. Groundwater extraction shows a decreasing trend and water use has decreased during the last years. By using disconnection techniques, local rainfall is not transported to the sewer system but added to the groundwater. The following list presents the most important opportunities.

�� Groundwater extraction is decreasing. �� Water use is decreasing. �� Development of water saving technology. �� Decrease of water use could be realized by education and water saving campaigns. �� It could be possible to supply different qualities of water depending on the water use

purpose. �� Disconnection facilities increase groundwater recharge and can decrease groundwater

depletion.

3.2 Sustainable use of energy A sustainable energy supply is an energy supply based on renewable resources, without adverse effects like climate change and air pollution. Non-renewable resources may not be depleted before alternatives have been found. In this report on sustainable urban water management the energy supply is included because the water system offers a lot of opportunities for energy conservation.

3.2.1 Present situation The two main sources of energy to households are electricity and gas supply. The energy supply is still mainly focused at conventional energy sources, because the sources are mainly non-renewable. In a sustainable approach alternatives should be found before conventional sources have been depleted. Electricity comes mainly from non-renewable resources Energy use in cities still relies for a large part on non-renewable resources. In 2002 the percentage of electricity that was generated in a sustainable way in the Netherlands, was 13% (CBS, 2004). Conservation of energy and raising the percentage of renewable resources of the total energy supply, makes the energy supply more sustainable. For an average household in 2000 the electricity use was 3 085 KWh .One KWh has a caloric value of 3.6 *106 J. Use of gas results in CO2 emission In 2002 the average household 1595 m3 gas a year was used. (CBS, 2004) The caloric value of 1 m3 gas is about 33 *106 J. One can conclude that the average energy supply from gas is much larger than the energy supply from electricity. The use of gas leads to a higher CO2 concentration in the atmosphere, which is regarded to be one of the main causes of climate change. Of the total amount of gas a large part is used for heating of buildings. This is clearly indicated by the difference between households with central gas heating and households without heating by gas. The difference of gas use between these households is 1440 m3. This opens up opportunities



because the energy use for heating is a slowly varying energy flux, which can partly be realized by using groundwater.

3.2.2 Threats There are various threats to a sustainable energy supply. One of the most important threats is the fact that sustainable energy is often more expensive. Besides, low energy prices do not lead to investments in alternative energy sources. The privatisation of the energy companies has caused reluctance to invest in alternative energy sources as well. There are the following threats:

�� Sustainable energy is often more expensive. �� Current state of the system is focused on conventional energy sources. �� Private status of energy companies does not necessary lead to the most sustainable energy

supply because of profit maximisation, shareholder interests and investment risks.

3.2.3 Opportunities There are opportunities as well for a sustainable energy supply; energy prices are rising and consequently, alternative energy sources become more interesting from an economic point of view. A number of water related opportunities for energy conservation can be found in literature, like the use of groundwater for heating and cooling. The following list presents the main opportunities:

�� Energy prizes are rising. �� Ratification of Kyoto protocol. �� Technological development of sustainable energy sources. �� Groundwater can be used for cooling and heating of buildings. �� Sustainable energy sources are applied more and are getting cheaper, water related

sources are: the use of groundwater for cooling and heating of buildings (Delft Outlook, 3.2004), the use of wastewater to generate electricity (Water21, 08/04), The use of heat from the sewer system to supply energy to the city (H2O, 14.2004).

3.3 Sustainable use of space Space is, like water and energy, one of the most important resources for a city. Once space has been put to use for infrastructure or development, in practice the situation is often irreversible. What is sustainable use of space? If the use of space is flexible and combines multiple functions, the options for future generations are kept open as much as possible and space is used efficiently. Therefore, the multifunctional use of space is the criterion for sustainable use of space. In his research Entrop (2004) defines sustainable use of space as a three-step strategy combined with the compensation principle. The preference sequence for the use of space is as follows:

1. Build within urban area 2. Build in an area with a low ecological value 3. Build in an area with a high ecological value

If it is not possible to build within the city borders, the compensation principle should be used. Another area with the same surface should be developed to an ecologically valuable area. This approach leads to concentrations of activities in the urban area and therefore also to multi functional use of space.



3.3.1 Present situation Land we use for certain purposes cannot easily be used by next generations for other purposes, or in a more general way; our use of space restricts the possibilities for future generations. This leads to a complication because sustainable development is about fulfilling both the need of the present generation and the need of next generations. Increase of pressure on space In the coming decades more space is required for the growing population and there is a higher demand for houses because families are getting smaller. Besides, more space is needed for infrastructure and water storage. Consequently, there is a higher pressure on space, the next figure presents the ongoing urbanisation of the Netherlands.

Figure 3-3: Urbanisation of the Netherlands

3.3.2 Threats Which factors make sustainable use of space more difficult? At first, multi-functional use of space requires cooperation and balancing of interests. These requirements make the decision making process more complex. At second, multi-functional use of space leads to intensifying of land use, which can also have negative effects on the urban living quality. In brief:

�� Multi functional use of space needs a lot of cooperation and willingness to share space with other functions.

�� Intensifying the use of space can have negative impacts on the living qualities of the city.

3.3.3 Opportunities

Opportunities for sustainable use of space are mainly related to national policy, which is focused more on an integrative and participatory approach. As a result, multi-functional use of space has more chance to succeed. Another development is the large amounts of agricultural space which in the future could be used for other purposes. The opportunities can be summarized:

�� The Water test (watertoets) causes different actors such as spatial planners, urban planners and water managers to cooperate.

�� New water policy ‘ A different approach to water’ asks for a lot of space for water storage, the scarcity of space stimulates to use this space for other purposes as well.

�� Further development of floating houses offer possibilities for multi functional use of space.

�� Much rural space could possibly be used for other functions in the future.

2005 19701900



3.4 Economic sustainability In designing new water systems the economy should be taken into account. In the first chapter the ICIS triangle was presented, which symbolizes the balance between economic, social and ecologic domains. Development of social and ecological capital should not be too much at the expense of the economic capital. Examples of elements of economic capital are: costs, benefits and business opportunities.

3.4.1 Present situation To get an idea of the economic importance of the water sector and to be able to evaluate new concepts of water systems in terms of economic consequences, it is useful to present some figures of the water sector. The drinking water companies employed an equivalent of 5867 fulltime employees in 2002. This number shows a decreasing trend during the last ten years, which is mainly the result the merging of drinking water companies. The income of deliveries was 1427 million euros and the investments were 374 million euro. The level of investments shows a decreasing trend. The average price for a cubic meter of water was 1.46 euro. (Vewin, 2002) For the sewer system the total amount of costs was 1171 million euros in 2002, of which 109 million was spent on employee costs. The water boards spent 464 million euros on employee costs in 2002, divided over 10500 employees, both fulltime and part time (waterschapsfinancieën 2002-2004). The wastewater treatment costs were 139 euro per household. In 1998 the total costs of public water management was as high as 3 billion euro. (Huisman, 2001) In this sum the costs of drinking water is not included because drinking water is provided by more or less private companies, which are for a large part in public hands. Of this amount 15% was spent on dikes and dams, 20% on water quantity management and 65% on water quality management. The central government, the provinces, the water boards and municipalities made these costs. The following table specifies the costs for some services per household. (Rioned, 2002) Table 3-1: Costs per household for various services

Costs per household Year Costs Drinking water 2000 153Heating and gas 2000 568Electricity 2000 427Waste disposal 2002 227Waste water treatment 2002 139Sewer system 2002 104Water quantity management* 1998 95Flood defense* 1998 42

* Rijkswaterstaat(1998), CBS(2001) in Huisman(2001)



3.4.2 Threats The most important threat, which works against economic sustainability in water management, is the constant rise of costs. For the water chain the yearly rise of costs was 3% a year, in the period 1990-2002, corrected for inflation (COELO, 2004). The costs of water management will continue to rise because of new demands from for instance, the European Framework Directive and further disconnection of paved area. Moreover because of land subsidence, sea level rise and climate change, more investments will be required to prevent water-related problems (WB21).

3.4.3 Opportunities Opportunities for more economic sustainability are mainly the improvement of efficiency by cooperation between actors in the water chain and the implementation of a new financing structure.

�� Financing of water chain in the future possibly is organized by a water chain company, which offers possibilities for cooperation.

�� Improvement of efficiency by cooperation in the water chain could lead to less cost saving, with a maximum of 500 million euro. (COELO, 2004)

3.5 Clean water Clean water is one of the most important conditions for a healthy ecosystem. Without clean water an ecosystem which supports a wide variety of species, is impossible. Clean water is also beneficial for other objectives such as a high quality living environment. The quality of water is defined by the concentrations of substances in water. For substances in water, standards and goals can be found in the 4th national policy document on water. However, a remark must be made with respect to these standards. The standards are not automatically the desired state for an ecosystem, the MTR-values are based on a maximum allowable risk per substance and is based a theoretical pollution level at which 5% of the species experiences damage. Also a desired target value is specified at which there is no damage for humans, animals and vegetation. (Steunpunt Wateremissies, 2004)

3.5.1 Present situation During the last 50 years the ecological quality of the surface water has decreased dramatically. The number target of water related target species determines the ecological quality. The next figure shows the nature quality of the Dutch surface waters.

Figure 3-4: Nature quality of regional waters compared to 1950 level (RIVM, 2004)



Water quality will probably not be sufficient in 2015 As discussed before, the Water Framework Directive has the objective to accomplish a good ecological status in 2015. For this purpose 33 substances are specified that have priority or are dangerous. It is estimated that in 2015 for 16 of the 33 substances the concentration in the surface waters will comply with the standards, the MTR concentration. The rest will either not reach the standard, is uncertain, or has a lack of information. Among others, for nitrogen, phosphorus, copper, nickel and zinc, the concentrations do not meet the maximum permissible risk levels.

Figure 3-5: Sources of surface water pollution (Water in Focus, 2004) Pollution is caused by several sources As can be concluded from the figure, surface water pollution comes from several sources, both direct and indirect. Nitrogen and phosphorus are mainly caused by leaching from soil where manure is used for agriculture. Moreover, effluent from wastewater treatment plants is an important source as well. Heavy metals mainly originate from leaching from contaminated soil and direct pollution, for instance from roofs (zinc rooftops). Moreover, bottom sediments are a considerable problem; pollution from the past has accumulated in bottom sediments and forms a continuous pollution source for water quality, especially if they are heavily polluted. Dredging and cleaning of these soils is very expensive. Sewer overflows form a threat for water quality as well, in 2005 still 82 sewer overflows which pose a health risk for animals and humans, will not me remediated (Water in focus, 2004). Water treatment is not efficient enough The primary aim of the Urban Wastewater Treatment Directive is to remove the oxygen-depleting substances nitrogen and phosphate. The goal is for treatment plants to remove at least 75% of the nitrogen and phosphate in wastewater by 2005. In 2002, the national purification rate for nitrogen was 68%. The figures on the next page show the concentrations of a few substances (Water in Data, 2004). High levels of nitrogen and phosphorus can result in eutrophication; growth of aquatic plants and algae will increase. This leads to high oxygen level fluctuations, turbidity and eventually in a poor ecosystem, which is dominated by breams and algae. (Bolier, 2002)



Figure 3-6: Phosphorus in surface water Figure 3-7: Nitrogen in surface water Figure 3-8: Zinc in surface water Figure 3-9: Copper in surface water Figure 3-10: Nickel in surface water

Figure 3.9: Zinc in surface water Figure 3.10: Copper in surface water

Figure 3.11: Nickel in surface water

Figure 3.7: Phosphorus in surface water Figure 3.8: Nitrogen in surface water



3.5.2 Threats Numerous sources of pollution are present in the urban areas and pollution from the surrounding areas can reach the urban area as well, through dry or wet deposition and through ground water flow or surface water flow. If water from rural areas has to be supplied to the city, polluted water reaches the urban surface water. Examples of pollution sources within the city itself are sewer overflows, dry deposition, building materials, traffic, pesticides, garbage, polluted groundwater and rainwater, but also leaves from trees, dog and bird excrements and fish bait from fishermen. The threats for a clean urban water system can be summarized as follows:

�� Sewer overflows. �� Pollution of runoff by various sources. �� Inflow of polluted water from rural areas.

3.5.3 Opportunities

However, there are also opportunities for clean, for instance, the European Water Framework Directive, demands good water quality in 2015 and forces actors to draw up a plan of measures to achieve that. Furthermore, the development of better water treatment techniques proceeds. Urban water systems could play a role as well in water treatment; by designing these system in a different way, the self-purifying capacity can be increased, for example by circulation and reed bed filters. In short:

�� European Water Framework Directive forces actors to take measures to reach a good environmental status.

�� Number of sewer overflows is decreasing. �� Water supply from rural areas could be decreased if more water is stored within the

city itself. �� Efficiency of wastewater treatment plants is increasing. �� Technological development of treatment processes, such as membrane filtration and

UV purification. �� Urban water systems could be optimised and play a role in water purification.

3.6 Varied morphology of water system Next to clean water, also a varied morphology is important for the ecosystem. A condition that contributes to ecosystems is: water system variation that offers possibilities to various species (biodiversity). This will be the case if there are banks with a low gradient and if there are level fluctuations. Moreover, variation of water system dimensions can offer several species opportunities.

Figure 3-11: Surface water without many variations



3.6.1 Present situation Present urban water system; often do not show the desired variation in water system dimensions and water levels. Line elements with constant dimensions are dominant in most urban water systems. As a result, opportunities for a healthy, diverse ecosystem are missed.

3.6.2 Threats The main threat for varied morphology in urban surface water is the difficulty to implement variations in existing systems. In existing urban water systems, its sometimes not possible to realize environmentally friendly banks; for example because the required space is lacking.

3.6.3 Opportunities

Opportunities are the possibility of applying wildlife friendly banks and floatlands to increase variations:

�� Number of wildlife friendly banks is increasing. �� It is possible to offer wildlife opportunities by floating gardens (floatlands) and other

variations in dimensions.

Figure 3-12: Varied morphology in floatlands Figure 3-13: Development number of wildlife friendly banks (RIVM, 2004)

3.7 Self supporting system As discussed in the first chapter, the general goal of water management is to create resilient and healthy water systems. This is the case if a system is self-supporting. For instance, a water system with a high self-cleaning capacity needs less human interference to artificially clean water or to flush the urban water system. Designing a water system that has the ability to retain and store water can fulfil that objective; the system needs less external water supplies during dry periods. With regard to groundwater this aspect is important as well. In order to be self-supporting, the groundwater regime should meet the demands of the ecosystem. If groundwater tables are to low, damage to ecosystems can occur.

3.7.1 Current situation Urban water system often need external water supply in summer. The external water supply comes from rural areas and can have adverse effects on the water quality in the urban area. In that case an urban water system cannot be considered self-supporting. Besides, stagnant water occurs, which is not beneficial for the self-cleaning capacity.



3.7.2 Threats In cities the space, which is needed to accommodate water storage, is scarce and expensive. Furthermore, storing water could lead to water nuisance in some cases; high groundwater tables can be beneficial for ecosystems but can have adverse effects on buildings. The following threats can be listed:

�� Storing water costs a lot of space, which is often scarce and expensive. �� It can be difficult to change existing water systems. �� High ground water tables to support ecosystems can cause water nuisance elsewhere. �� Climate change increases the frequency of dry periods and periods with excess of

water.

3.7.3 Opportunities As was discusses in the former chapter, the government policy aims to achieve to store water at the place where it falls. Besides, disconnection results in more groundwater recharge and consequently more water is retained within the urban area. The following opportunities could result in a more self-supporting water system:

�� General government policy focuses on retaining and storing rather than on discharge.

�� Disconnection techniques are applied more and more.

�� Reed bed filters can be used to increase self-cleaning capacity of the system.

�� By designing surface waters differently, the self-purifying capacity of surface waters can be increased.

Figure 3-14: Disconnection of paved area in Barneveld by a ‘Wadi’( Broks-Messelaar,2004)

3.8 Connections with other systems Water also plays a role in connecting urban ecosystems and connecting these systems with nature reserves outside the city, offering species possibilities for migration.

3.8.1 Present situation High population density and high mobility demand many roads, railroads and cities as the next figure shows. This leads to fragmentation of the landscape. As a result, nature reserves are scattered over the country and are often not connected, this makes it difficult for some species to migrate.

3.8.2 Threats The most important threat for the connection of ecosystem is the ever-increasing demand for space and mobility. Consequently, more infrastructure will be build which is an obstacle for migration of wildlife.

3.8.3 Opportunities On two scale levels cities can play a role in connecting ecosystems. Within the city itself, green areas or water bodies can connect ecosystems. An example is the ‘Ecolint’ in Amsterdam, which



is connects many green areas with each other, both by surface water and by green areas. On a larger scale cities can be a point in green blue networks. An example is the ‘groen-blauwe slinger’ in the Randstad, which connects nature in rural areas with cities.

Figure 3-15: Fragmentation of the landscape (RIVM, 2004)

3.9 Reliable, clean and healthy water supply Water supply is essential for life in cities. If water supply is absent, the city is inhabitable and unliveable. A clean, reliable and healthy water supply promotes public health immensely. The criteria for water supply are formulated in the water supply law (Waterleidingbesluit)

3.9.1 Present situation The current state of the water supply is reliable and clean, in the Netherlands nearly all houses have been connected to the drinking water systems, which supply healthy and clean water 24 hours a day. By laws and inspections the government supervises the water quality.

3.9.2 Threats The water supply is mainly threatened by the ongoing dispersion of pollutants in groundwater. This process proceeds very slowly; it can take years before effects are noticed. Therefore, it is still uncertain what the effects of pollution on future water supply will be. Besides, the amount of chemical substances, which are found in the environment, is very large and effects are still unknown in many cases. Another problem is the legionella bacteria that is found in drinking water pipes. The following threats can be listed:

�� Dispersion of pollutants in groundwater, which can affect groundwater wells. �� More and more different chemical substances are found in the environment; as a

result the demands for water treatment are increasing. �� Legionella bacteria are found in water pipes and can cause health risks. �� Organic contaminants are found in drinking water (very low concentrations)



3.9.3 Opportunities The most important opportunity to secure drinking water quality in the future is further development of water treatment techniques, which are getting cheaper and better. More knowledge will be developed about the effects of various chemical substances. Prevention of pollution could prevent further groundwater deterioration.

3.10 System to collect and transport wastewater Like a clean and reliable water supply, also a system to collect and transport wastewater is required to make living in cities possible. Without facilities to realize that, the present public health level and present standard of living in the Netherlands is impossible.

3.10.1 Present situation At this moment the sewer system in the Netherlands works reasonably well, however as mentioned earlier, water quality problems occur because of sewer overflows. The following figure provides figures about the several types of sewer systems in the Netherlands. (Rioned, 2002) Table 3-2: Types and percentages of sewer systems Inhabitants per sewer types Number % Not connected 263786 1.65Combined sewer 12161763 76.07Separated system 1483142 9.28Improved separated system 2078310 13.00Total 15987001 100 The table shows that the main part of the sewer system is of the combined type. A number of problems arise from this system, which combines urban runoff transport and wastewater transport. To prevent over dimensioning, overflows have been constructed in these systems. From these overflows wastewater is discharged to the surface waters if the sewer discharge exceeds the sewer capacity. To prevent negative impacts of the combined system, the separated system has been developed. In this system runoff is separated from wastewater and discharged to the surface water. However, wrong connections occur, which lead to wastewater discharge to the surface water as well. To cope with this problem, the improved separated system transports a part of the polluted rainwater as well to the wastewater treatment plant.

3.10.2 Threats The most important threat is the fact that sewer systems are often old and rehabilitation causes a lot of nuisance and is expensive.

3.10.3 Opportunities

Opportunities to maintain effective collection and transport of wastewater are: �� Disconnection of paved surfaces decreases the load on the sewer system.



�� Probably the financing of disconnection from sewer taxes becomes possible. (‘Verbreding rioolrecht’)

�� Benchmarking could lead to more effective sewer systems. (Tweede Kamer 28 966, 2004, Rioned, 2004)

�� Decentralized treatment is possible. (IBA’s)

3.11 Reduce water nuisance An acceptable frequency of water nuisance is one of the societal water system demands. The acceptable frequency of inundations for urban areas is an average frequency of once in 100 years. (IPO, 2004) High groundwater levels, surface water levels or high intensity rainfall can cause water nuisance in urban areas. This can have two causes, the city is not adjusted to occurring water levels or water levels are not controlled sufficiently to prevent nuisance. Finally, also the perception of inhabitants should be mentioned, because water nuisance is only a problem if inhabitants perceive it as a problem. The acceptance and awareness of inhabitants for the water system can be changed. Adjust city to occurring water levels To adjust a city to occurring water levels can be done by building in such a way that damage is prevented or is kept as small as possible. For example, a floating house does not experience problems if the surface water level fluctuates. A house experiences less problems with fluctuating water levels if it is build without crawlspaces. Another example is a city, which is adjusted by terrain level differences. Such a city deliberately locates water nuisance at a certain area, limiting damage and nuisance in areas where nuisance is not desired. Figure 3-16: Simplified structure of water nuisance problems and possible intervention points

Occuring waterlevel

Nuisance & damage Water nuisance problem

Perception of inhabitants

Adjust water levels to the city

Adjust city to occurring water

levels

Change acceptance



Adjust water levels to city If the city is not adjusted to occurring water levels, a system to control groundwater levels, surface water levels and collect rainwater is required. Groundwater can be controlled by a drainage system of pipes or ditches. In the function analysis the quantity functions were already mentioned. The desired state of the groundwater differs from the actual state in a lot of cities.

3.11.1 Present situation In new Vinex districts the urban drainage system is insufficient and groundwater nuisance occurs; inhabitants complain about wet cellars and crawlspaces. Drainage capacity and level difference have decreased The level difference between surface level and terrain level has decreased from an average 1.8 meter for old districts to 1.2 meters in new districts. (Land+Water 4.2004) For this reason a high intensity rainfall event can lead to nuisance, while in the old situation it would not have caused a problem. At the same time the discharge standard is lower than it used to be. Moreover, many inhabitants are not aware that they themselves are responsible for the drainage of their own terrain and that the municipality ought to make drainage from the private terrain possible. Maintenance of drainage pipes is not sufficient Drainage systems are often not maintained very well. Therefore, a drainage system which works reasonably well in the beginning, can cause problems later. Cities like Delft and Eindhoven experience problems with groundwater. On the other hand there are also problems with rotting pile foundations caused by a low groundwater level. In Gouda and Dordrecht this leads to foundation problems that are very expensive to solve. Many possible causes of water nuisance from surface water Nuisance from high surface water levels is not desired either. High intensity rainfall events combined with a rapid runoff process can result in high surface water levels. An example is the water nuisance, which occurred in the centre of Delft a few years ago. Various causes can lead to nuisance, such as an insufficient pumping capacity, insufficient storage or a runoff process that takes place too rapidly. In areas where there is a combined sewer system, an insufficient sewer capacity can lead to water nuisance. In that case the water nuisance stems directly from rainfall, in the summer of 2004 this occurred several times in Eindhoven.

Figure 3-17: Disconnection of paved surfaces from the sewer system can reduce water nuisance



Problems are site-specific Problems of water nuisance can be connected in a complex way. For instance, groundwater problems can influence or cause problems with surface water and rainfall. If the drainage depth is too small, there is a small infiltration and storage capacity for runoff, as a result, runoff processes will occur more quickly. A high water level leads to limited storage capacity, both in surface water and in groundwater. Sewer capacity usually cannot be increased because the capacity of the wastewater treatment plant is not sufficient. Water nuisance problems are therefore highly site-specific and there is no blueprint of causes and solutions.

3.11.2 Threats Important threats to water nuisance reduction are developments such as: land subsidence, sea level rise and climate change. These developments make the water system more vulnerable, whereas the load on the water system increases with the rainfall intensity. At the same time water nuisance problems occur because attention for drainage and maintenance of drainage systems is lacking. Moreover, the fact that by disconnection more water will be transported by surface water instead of by sewer systems is not yet taken into account in the drainage standards (Land+Water 4.2004). The next list presents a summary of threats:

�� Land subsidence. �� Sea level rise. �� Climate change will probably increase the peak rainfall events, both in intensity and

frequency. �� Prevention of land subsidence restricts the use of groundwater for storage purposes. �� Maintenance of drainage systems hardly takes place. �� Drainage does not get enough attention in newly build areas. �� In discharge standards, the fact that more water will be transported by surface water

system instead of the sewer system, are not yet taken into account. �� Large amount of paved area in urban areas leads to high volume of runoff.

3.11.3 Opportunities

Opportunities to achieve an acceptable frequency of water nuisance are: the adjustment of the water system and buildings to fluctuating water levels and the possible delay of runoff processes. In brief:

�� Disconnection, green rooftops and more storage volume can slow down peak events. �� New building techniques such as building houses without a crawlspace offers more

possibilities to manage groundwater more flexibly. �� Adjustment of building technology can reduce damage in case of water nuisance.

(Land+Water (1/.2.2004) �� Permeable bricks can increase infiltration. �� Variations in terrain level can differ inundation frequencies according to the function,

for example the level of the terrain of a park can be lower than the terrain level of houses.

�� Active groundwater management by monitoring and modelling offers possibilities to reduce foundation damage. (Land+Water, 5.2004)

�� Peak and seasonal storage could be realized in aquifers. (H2O, 19.2004) �� Perception of inhabitants of water nuisance could be changed.



Figure 3-18: Delaying run-off process to reduce water nuisance: a nice example of a green rooftop

3.12 High quality living environment One of the things inhabitants demand is a high quality living environment. This need is very hard to quantify and hard to relate to criteria. In this report only the factors that relate more or less to the water system are taken into consideration. The quality of the living environment is improved if there are a lot of possibilities for different forms of recreation, if it is visually attractive and well designed by landscape architects and if the water in the city is clean. Others factors are green areas in the city and absence of noise.

3.12.1 Present situation In general surface water in urban areas is only used for a limited amount of recreation functions. Recreation near water, like fishing and walking take place frequently, whereas swimming hardly takes place, because water quality in urban areas in generally not sufficient for this purpose. Besides, the lay out of urban surface water does not enable swimming and inhabitants are not used to it. For swimming water quality, the effects and concentration of pathogenic micro-organisms is important. The concentrations of various substances may not exceed certain limits ("Directive 76/160/EEC'). However, a new European swimming water directive is about to be implemented that requires only two parameters to be monitored, as both are regarded as excellent indicators of faecal contamination (Intestinal Enterococci and Escherischia Coli). (EU, 2004) The ability of water to increase the experience value have not always been recognized in the past. However, this occurs more and more, for example in case of the developments of waterfronts (Bouwfonds, 2004).

3.12.2 Threats Further urbanisation and intensifying of land use could decrease the area available for recreation. At the same time a demographic shift towards an older population will increase demand for recreation possibilities.

3.12.3 Opportunities On the other hand there are opportunities as well, because space which is needed for water storage anyway, can also be used for recreation and more water in the city offers possibilities to increase the experience value.



Figure 3-19: The use of surface water to improve living quality as well as water storage in Dordrecht (Min. V&W, 2003)



4 System Analysis Purpose and scope of this chapter In the previous chapter the objectives for the urban water system and water supply were listed and evaluated. With these objectives, problems in the urban water management were investigated and it became clear what is desirable and useful in new urban water systems by an inventory of opportunities and threats. In this chapter the urban water system will be analysed: the natural resource system (flows and storage elements), the socio-economic system (actors) and the administrative and institutional system (government, legislation)










Figure 4-1: Position in the report and results of chapter 4

4.1 Natural Resource system The current urban water system is characterized by a very strict organisational separation between water chain (water extraction, treatment, distribution, water use, sewerage, treatment and discharge) and water system (urban surface water bodies, groundwater and connections.) Although this separation is strict with regard to organisation and responsibilities, exchange between the water system and water chain takes place by the groundwater and sewer system, for instance as a result of leakages and sewer systems overflows. These processes result in groundwater and surface water problems, which were discussed in the previous chapter.

4.1.1 Combined system Furthermore, a distinction should be made between a sewer system, which transports both wastewater and stormwater (combined system) or a system, which has separate pipes for wastewater and stormwater (separated system). In the next figure the urban water system with a combined sewer system is schematised.



Figure 4-2: Schematisation of the urban water system with a combined sewer system In figure 4.2 the distinction between water chain and water system has been indicated as well. Moreover, various storage elements are indicated as well as their relations (flows). Besides, a distinction is made between the urban and rural area.

4.1.2 Separated system For the separate system the situation is different, as figure 4.3 shows. The main difference is the presence of two sewer systems. From both sewer systems leakages occur and both can function as a drain as well, depending if the sewer pipe is above or below groundwater level. However, for the wastewater sewer in figure 4.3 these arrows are removed, to keep the picture clear.

4.1.3 Disconnected system Paved surfaces can be disconnected from the sewer system; which means that stormwater runoff is no longer transported by the sewer system. Instead, runoff discharges directly to the urban surface water or infiltrates in the subsurface by for example, a wadi system. By infiltration the groundwater volume is replenished. A disconnected system has as advantage that clean stormwater runoff is used for useful purposes, instead of being converted to wastewater. Besides, the load on both the sewer system and to the wastewater treatment plant decreases. For these reasons the general policy is to disconnect more than 60% of paved surfaces from the sewer system in new residential districts. However, there are some disadvantages as well, the pumping capacity of the surface water system should be larger, as more water is being transported by this system. Moreover, not all paved surfaces are suitable for disconnection; for instance, runoff from heavy traffic roads will contain many pollutants. Figure 4.4 shows the schematisation of a disconnected system.

Groundwater

Surface water rural area

Drinking

water

Atmosphere

Households

IndustryCombined

Sewer system

Treatment

Urban surface water

Paved area

Unpaved area

Groundwater unsaturated

zone

Groundwater saturated zone

Urban Area Rural AreaSource

P

P

E

I

E

P

ET

IN

IN

L

D

IRL

G

R

R= RunoffS=Supply

C =Capillar flowD =Drainage

E =EvaporationET=Evapotranspiration

G =GroundwaterflowI = Interception

IN =InfiltrationIR= Irrigation

P = PrecipitationPE =Percolation

L =LeakageO=Overflow

Waterchain

Watersystem

O

S

PEC

D



Figure 4-3: Schematisation of the urban water system with a separate sewer system

Figure 4-4: Schematisation of the urban water system with disconnected paved surface

Groundwater


Drinking

water

Atmosphere

Households

Industry

Sewer system Treatment

Urban surface water

Paved area

Unpaved area


zone



P

P

E

I

E

P

ET

IN

IN

L

D

IRL

G

R

R= RunoffS=Supply







Waterchain

Watersystem

S

PEC

D

Infiltration facility

R

Groundwater


Drinking

water

Atmosphere

Households

Industry

Wastewater sewer Treatment

Urban surface water

Paved area

Unpaved area

Stormwater sewer

Groundwater unsaturated zone



P

S

P

E

I

E

P

ET

IN

IN

PE

C

IR L

D

G

R

S=SupplyW=Wrong connections





PE =PercolationR= Runoff

L =LeakageP = Precipitation

Waterchain

Watersystem

W

D

L



4.2 Social Economic system Many actors play a role in urban water management; in the function analysis and problem analysis it became clear that water in urban areas serves a wide range of functions and appears in many forms. Consequently, urban water management cannot be seen separately from the inhabitants, planners and government institutions. Often innovation is technologically feasible but does not take place because of social, economical or institutional obstacles. Taking these aspects into account and involving a broad spectrum of actors can increase both the quality of the innovation as well as the chance that an innovation is implemented successfully. The next two paragraphs aim to investigate relevant actors in urban watermanagement and to get an idea of their general attitude towards innovations in watermanagement. For this purpose, the following private organisations can be distinguished in urban water management. Because there are some water-related opportunities for energy conservation, energy companies are included as well.

4.2.1 Private organisations The following private organisation con be considered as important in urban water management:

�� Drinking water companies �� Project developers �� Contractors �� Research institutes �� Tourist organisation �� Energy companies

Drinking water companies An amount of 13 drinking water companies produce drinking water in the Netherlands, most of them are private companies. However, municipalities own the stocks. As mentioned before, the drinking water law secures the water quality with regard to physical, chemical and biological parameters and with regard to reliability. The standards are roughly the same as the standards in the European drinking water law; in some cases the Dutch drinking water law is even stricter. Furthermore, monitoring of water quality takes place by the drinking water companies themselves; the Ministry of Environmental Affairs supervises the drinking water quality. In designing and realizing new concepts of water supply, involving drinking water companies is important, because their way of working might change considerably if new concepts of water supply are implemented. Project developers Project developers play an important role in the development of new residential districts, they purchase the construction site from the municipality to construct houses. The spatial plan of the municipality and the urban design determine the way a new district is constructed. During the last years, the role of project developers is becoming more important and they are nowadays involved in the building process earlier. In some cases the project developers are responsible for the preparation of the construction site, including aspects as: terrain level and drainage depth. Project developers will probably object to new concepts of urban water supply if the financial feasibility of projects is at risk. Contractors Contractors should build houses according to the construction drawings and building permission of the municipality. Mostly, contractors work under supervision of the project developer. An important law is the building and construction law (Bouwbesluit) in which construction standards can be found. In designing innovative urban water systems, attention should be paid to the fact



that contractors may not be accustomed to new building techniques. This may be an obstacle in realizing innovations. Research Institutes Research institutes such as universities and research organisations play a role in the urban water system by conducting research on innovations in urban water management. These institutes have knowledge available, which is required for designing new urban water systems. Tourist organisations As mentioned before in this report, water can be important for tourism. In particular the historical and cultural aspects of water attract tourists. At the same time tourism has economic importance for example for restaurants and hotels in cities. For new residential districts tourism might seem less important, however an innovative and well-designed urban water system perhaps could attract tourists as well. Energy companies Since the privatisation of the energy market, energy is no longer supplied by government organisations but by private parties. An important aspect is the separation of energy companies in grid administrators and energy supply companies; the separation has been implemented to give new energy supply companies, free access to the energy market. Moreover it enables consumers to choose their own energy supply company. In developing new residential districts, energy companies play an important role. For the construction of new energy infrastructure a public tender procedure can be followed. Subsequently, the municipality gives the construction rights to the company that submits the best offer. Next to costs, also reliability, sustainability and efficiency are aspects which should be taken into account in the selection process. After completion of construction the municipality appoints a grid administrator, this decision should be approved as well by the Ministry of Economic Affairs. In general energy companies are interested in new forms of energy supply, for instance the application of heat pumps. However, the uncertainty of the free market and the investment risks of new technologies can make energy companies reluctant to switch to new technologies.

4.2.2 Social organisations The following social organisations can be distinguished in urban water management.

�� Inhabitants �� Fishing organisations �� Other recreational organisations �� Environmental organisations

Inhabitants Inhabitants are the final users of the urban infrastructure and space. Therefore, a clear picture of the needs of inhabitants in the city should be available. Moreover, good public information about innovations in urban watermanagement should be present, in particular if a change in behaviour is required. For instance, if paved area are disconnected from the sewer system and water is infiltrated in the soil, car washing should be restricted to certain areas. Besides, inhabitants should be informed about their responsibilities with regard to drainage. According to current legislation, inhabitants themselves are responsible for the drainage of their plot. In general inhabitants are enthusiastic about innovations, for instance infiltration facilities and green rooftops. However,



this may change quickly if the performance of these innovations is insufficient and they experience inconvenience and discomfort. Fishing organisations Fishing is an important form of recreation that takes place frequently in urban surface water. The economic importance of freshwater fishing in terms of expenditures on fishing is 600 million euros per years. Fishing generates a total employment of 800 man-years. Half of the day trips take place within the city of residence of the fisherman. (LEI, 2004) Knowledge of fishing organisations can be used to optimise the design of urban surface water. Moreover, these organisations play a role in maintaining and managing the fish population. Fishing organisations will support innovations, which improve water quality and the amount of surface water in urban areas. However, they could object to restrictions on fish feeding and their perception of a healthy fish population is not necessarily the same as an ecologically healthy fish population. An example of this is the bream, a fish which is popular among fishermen. However, this fish is also regarded as a cause of turbidity and plays a role in eutrophication. Other recreational organisations Besides fishing, there are other forms of recreation as well that play a role in urban surface water. However, most of these forms of recreation tend to be more focused on the area outside the city. The economic importance of these forms of recreation is considerable. Table 4-1: Economic importance of water recreation (Hiswa,2005)

Participation Average frequency

Expenditure per daytrip (euros)

Total amount of daytrips per year

Sun bathing 24% 7.62 10.21 23,490,000 Swimming 19% 6.82 5.90 16,640,000 Boating 7% 5.48 12.93 4,927,000 Sailing 4% 6.02 17.70 3,100,000 Rowing 3% 5.05 11.34 1,946,000 Canoeing 3% 2.77 14.97 1,065,000

The table indicates that by involving recreational organisations and making urban surface water suitable for water recreation, economic opportunities can be opened. Environmental organisations Environmental organisations will generally support innovative and sustainable building technologies. Also green areas and nature are considered to be very important by these organisations as well as water quality. Environmental organisation can have an advising role in the design of urban water system and will probably support innovations for a more sustainable water system.

4.3 Administrative and Institutional system Next to private and social organisations, there are government institutions as well. These institutions play an important role in urban watermanagement. Moreover, legal aspects such as laws and acts should be taken into account.



4.3.1 Government organisations The following government organisations play a role in urban water management.

�� European government �� National government �� Province government �� Water boards �� Municipalities

European Government The European Government (Commission, Counsel and Parliament) is important for urban watermanagement; they influence watermanagement by issuing water related directives that are binding for lower governments. The European Water Framework Directive is an example which has been treated already in chapter 1. However there are other directives as well, for instance:

�� Fishing water directive (78/659/EC) �� Water for drinking water production directive (75/440/EC) �� Bathing water (79/923/EC) �� Hazardous substances directive (76/464/EC) �� Groundwater directive (80/68/EC) �� Urban wastewater directive (91/271/EC) �� Pesticides directive (91/414/EC) �� Nitrate directive (91/676/EC) �� Integrated pollution prevention and control (96/61/EC) �� Drinking water directive (98/83/EC) �� Habitats directive (92/43/EC) �� Others

These directives should be implemented in national legislation as well; therefore, mostly fulfilling national requirements will be sufficient. However, for some directives this will not be the case because the implementation phase is not finished yet, for instance in case of the Nitrates directive and the Framework directive. Therefore, one should be alert on the consequences of these directives for urban water management plans. The European government aims to achieve ‘ecologically healthy ecosystems’ and ‘sustainable use’ and will therefore be positive about innovations for a more sustainable watersystem. National government The national government makes several plans that are relevant for urban water management. The national water policy document has been treated in chapter 1 already. However, other national plans, namely the spatial-planning document (Nota Ruimte) and the national environmental plan (Nationaal Milieu Beleidsplan) contain water policy as well. Plans that are made on a lower level, for instance on province or municipality level should be adjusted to the national policy. The national government wants to ‘develop and maintain healthy and resilient water systems’ and will therefore probably support more sustainable concepts of water management and water supply. Province government The province is responsible for regulation of groundwater extraction by granting permission for groundwater extraction and supervising the effects of groundwater extraction. Another responsibility of the province is supervision of the water boards. Finally, the province draws up a watermanagement plan and a spatial plan as well: the provincial watermanagement plan (Provinciaal Waterhuishoudingsplan) and the district plan (Streekplan). Provincial watermanagement plans are focused on sustainable water systems and have the same starting



points as the national watermanagement plan. Consequently, provinces will probably be positive about transitions to more sustainable water systems. Water boards Water boards are responsible for water quantity management of surface water and operation and maintenance of flood protection facilities. Water boards often have a water quality task as well, for instance treatment of wastewater. Water boards have a democratically elected board and the authority to levy taxes. Furthermore, they have the authority to grant permission for surface water extraction or discharge. Water boards are positive about measures that improve water quality but could be reluctant to support innovations that lead to higher costs or more responsibilities. Municipality Collection and transport of wastewater is the responsibility of the municipality. Other responsibilities of the municipality are: to enable transport of drainage discharge from building plots and to prepare building sites. The zoning plan (bestemmingsplan) is binding for citizens and is formulated by the municipality as well. Some municipalities are very enthusiastic about innovations and will try to realize new concepts of water management. A good example is the municipality of Heerhugowaard, which made a structure plan for a new residential district with innovative concepts of watermanagement.

4.3.2 Relation between watermanagement and spatial planning Water is getting more and more attention in spatial planning. As mentioned before in this report, the water assessment (Watertoets) forces actors to take water into account in an early stage of spatial planning and the water board to be involved in spatial plans. On the other hand, the water board has the obligation to participate in the spatial planning process. Another important document with regard to the relation between watermanagement and spatial planning is the urban water plan. Water boards and municipalities started to cooperate in making urban water management plans. As a result, water boards and the municipalities develop a joint vision on urban water management.

4.3.3 Legal aspects The following laws and acts are relevant for Dutch urban water management. In this report only a list of these acts is given. For a total overview and explanation, see Mostert (2004) or Huisman (2004).

�� Water administration act (1900) �� Water board act (1992) �� Water management act (1989) �� Groundwater act (1981) �� Pollution of surface water act (1970) �� Drinking water supply act (1957) �� Soil protection act (1987) �� Spatial planning act (1962) �� Environment protection act (1979)



4.4 Regime analysis The relations between actors and the dominant practices in watermanagement are situated in the regime (meso-level) in the transition approach. In this paragraph the relations and dependencies in the regime will be elaborated as well as a historical perspective within this regime. The following picture shows the regime level within the framework of the multi level approach in transitions research. The macro level consists of long-term trends that influence the other levels. The micro level consists of individuals and organisations. These organisations are part of networks and work together in ‘dominant practices’; these networks, dominant practices and legislation form the meso level.

Figure 4-5: Multilevel approach in transitions (Geels and Kemp, 2000). Often changes will be stimulated by the macro-level, for instance by national policy or by autonomous trends such as world economy, climate change or energy prices. Also the micro-level often has a positive influence on societal changes, for instance through development of innovations. The meso-level however, is often the obstacle in realizing changes. Institutions, legislation and dominant practices, often hinder the implementation of changes. The organisations that were described before in this chapter determine the functioning of the regime to a high extent. Therefore, in this paragraph the relations within the regime and their power in that regime will be evaluated.

4.4.1 Critical actors Not all actors that were described earlier are equally important; to successfully implement innovations, it is important to know which are the critical actors and which actors possess obstruction power. Moreover, the replaceability of these actors should be taken into account. Based on these factors a level of involvement can be proposed. Table 4.2 shows that all government institutions are critical actors. However, the higher government institutions do not necessarily have to be a part of the transition arena. If an innovation satisfies demands from national and European legislation and policy, these government institutions will generally be satisfied and in that case the innovation will be supported. Therefore, consulting these institutions about the legislation and policy will be sufficient

Macro-level (landscape)

Meso-level (regimes)

Micro-level (niches)



Table 4-2: Importance and proposed level of involvement of government organisations Actors Important means

or objection power

Replace-ability

Depen-dency

Critical actor

Attitude toward innovation

Level of involvement

European government

Issuing binding directives, changing legislation

None High Yes Positive, as long as it fits within legislation

Consult, inform

National government

Authority on the field of legislation, water policy and spatial planning, changing legislation

None High Yes Positive, as long as it fits within legislation

Consult, inform

Province government

Authority on spatial planning, groundwater extraction and district plans

None High Yes Positive, if region plans are taken into account

Co-operate

Water boards Authority, knowledge, information, money

None High Yes Positive, as long as costs are kept under control

Co-decide

Municipality Authority, knowledge, information, money

None High Yes Positive, if costs are reasonable and inhabitants are satisfied

Co-decide

The province government does not necessarily have to co-decide about innovation either. Probably, both the municipality and the water board will take the interests of the province into account, because of the authority of this government institution. Therefore, co-operating with the province government will be the most appropriate thing to do. Both the municipality and the water board have authority to decide about urban water management and the implementations of innovations. Inhabitants play an important role when it comes to realizing innovations. Probably a change of behaviour is needed for innovations to be successful, for instance with regard to water use. For example: car washing, maintenance of private area, use of chemicals and use of runoff for garden irrigation may all have influence on a new water system. For these reasons, it is important that inhabitants have knowledge about the operation of the water system and their role and responsibility in this water system. Moreover, ideas of inhabitants can have a beneficial influence on the design of the water system. Fishing organisations can be involved as well because of their responsibility for managing and maintaining the fish population. Other organisations could be consulted in the design and decision making process, because of their economic importance, knowledge or influence on public opinion. Of the private organisations the drinking water companies and energy companies are most important. If new concepts and innovations are implemented, their co-operation is necessary. Although another energy/water supplier might replace them, the group as a whole cannot be replaced. Finally, also the actor table of private organisations can be made



Table 4-3: Importance and proposed level of involvement of social organisations Actors Important means

or objection power

Replace-ability

Depen-dency

Critical actor

Attitude towards innovation


Inhabitants - Influence public opinion - Start legal procedures

None Moderate Yes Positive, as long as social needs are satisfied

Co-operate

Fishing organisations

- Influence public opinion - Start legal procedures - Knowledge - Responsibility for fishing population

Moderate Moderate No Positive, if there interests are taken into account

Consult, inform

Other recreational organisations

Economic importance

Moderate Low No Positive, if there interests are taken into account

Consult, inform

Environ-mental organisations

-Influence public opinion - Start legal procedures - Knowledge

Moderate Moderate No Generally positive Consult, inform

Table 4-4: Importance and proposed level of involvement of private organisations

Actors Important means

or objection power

Replace-ability

Depen-dency

Critical actor

Attitude towards innovation


Drinking water companies

Knowledge, money

None High Yes Positive, if operational safety, public health and costs are sufficient

Co-operate

Project developer

Money High Moderate No Undefined, profitability is most important

Co-operate

Contractors Knowledge

High Low No Innovation should not hinder way of working

Consult, inform

Research institutes

Knowledge, supplier of innovations

Low Moderate No Positive Co-operate

Tourist organisation

Economic importance

High Low No Undefined, tourist attraction is most important

Consult, inform

Energy Companies

Knowledge, money

None High Yes Undefined, profitability of company is most important

Co-operate



4.4.2 Structural characteristics of the regime The listing of actors and their importance is not sufficient to successfully realize an innovation. Also the relations between these actors should be described. The two deciding actors, the municipality and water board should cooperate together, costs and responsibilities should be distributed in a correct way to avoid conflicts. Important other actors are the project developer who wants to run a profitable project and the energy and drinking water company who want to construct reliable facilities against reasonable costs. Figure 4.6 indicates the relations between the critical actors. Furthermore, to successfully realize an innovation, the authority of higher governments and the influence of inhabitants and interest groups should be taken into account by consulting and informing these groups or even co-operating with them.

Figure 4-6: Interactions in the regime between critical actors when realizing an innovation

Payment, information,instructionsPayment,

information, instructions

Regional plan Supervision

Regional plan, supervision

Influence public opinion, voting public campaigns

Influence public opinion, voting public campaigns

Information

Realisation of project and instructions

Information, instructions, supervising

Distribution of costs and responsibilities

Waterboard

Project developer

Purchase terrain and construction site preparation

Energy company

Realisation of project and instructions

Drinking water company

Inhabitants Province government

DECISION CIRCLE

Municipality

COOPERATION CIRCLE

Research institutes

information,advice, innovations



4.4.3 Development of the regime During the last years important developments in the water management have taken place. Almost all actors faced changes in scale and role. An example of an important development is the scale increase as a result of merging municipalities, water boards, energy companies and drinking water companies. These organisations now mostly have a regional scale as a result of merging organisations. Moreover, energy companies and drinking water companies have become more private organisations instead of government organisations. In the financing of watermanagement changes will probably take place. Currently, there is a discussion about ‘water chain companies’ which would include the whole water chain. Drinking water companies, sewerage and wastewater treatment would be integrated in such a company. Cost reduction and water use reduction by receiving one water bill, are advantages which are claimed by those who support the formation of these companies. The government, for instance, aims to achieve the formation of water chain companies and wants to accomplish a separate financing system between water chain and water system. However, the cost of the water chain are mainly capital based and therefore most costs are fixed; as a result a decrease of water use would lead to a higher price per unit. Municipalities object to the separate financing structure because in urban areas they experience a strong relation between water chain and water system in their cities. Examples are: sewer overflows, disconnection of stormwater and groundwater management. Another example of a trend in watermanagement is the development towards a more integrative and participatory approach that leads to more involved organisations and inhabitants. Moreover, water quality and water quantity are no longer regarded as strictly separate issues. Especially urban watermanagement is a multi issue subject which leads to a transition arena with many participants. Urban water management problems are characterized by significant complexity; therefore cooperation between actors is needed to cope with these problems. In these problems social interests are important in addition to technical issues. Also in spatial planning water is taken more and more into account and water is regarded as a guiding principle. The following trends in urban watermanagement on regime level can be summarized:

�� Increase of scale �� More commercial approach as a result of more private status �� More participatory and integrative approach �� Single issue to multi issue �� Change of financing structure

Al these trends could stimulate or hold back a transition to a more sustainable urban water system. Increase of scale The increase of scale of most actors in urban watermanagement, for instance water boards, municipalities, drinking water companies and energy companies lead to larger organisations. How does scale increase influence the breakthrough of innovations? On one hand, larger organisations have more investment capacity and more generally more knowledge available to do research. If a large organisation switches to new innovations the transition process goes faster because the effect of a large organisation is larger. On the other hand, because there are only a few organisations there is also little variation of methods and common practices, moreover standardisation of methods take place. Therefore, no clear answer can be given if scale increase is beneficial for the water management transition to take place.



More commercial approach as a result of private status A more commercial approach by actors in urban watermanagement is generally not advantageous. Because commercial organisations are reluctant to invest in new and more expensive innovations, it can hold back the transition process. However, if new techniques become cheaper the private status can become an advantage. Besides, a private status can also result in organisations that are more focused on creating opportunities and look for new possibilities and change. More participatory and integrative approach As mentioned before in this report, the general approach in watermanagement has changed from a technical oriented approach towards a more integrative, participatory approach. This new approach can be regarded as favourable for innovations. If innovations are focused on aspects as living quality and ecological quality, there is more chance of succeeding in the new approach than in the old approach. Also solutions that aim to involve stakeholders in the decision making process have a better chance to succeed. On the other hand, more involved actors may be negative about innovations because the current system is working well. Single issue to multi-issue Urban water is no longer regarded as a single purpose element. On the contrary, next to water quantity also water quality, landscape quality, environmental aspects and recreation. Innovations in watermanagement that aim to support more issues rather than one issue, will be promoted by the new approach in watermanagement. Change of financing structure At this moment the discussion about the financing of the water chain is still proceeding and it is not yet entirely clear what the financing structure will look like in the future. However, a financing structure that is focused on the water chain only, not taking into account relations between water chain and water system, will not support innovations that aim on the integration of water chain and water system. In chapter 8 will be evaluated which further changes could take place if future water systems are implemented.



5 A vision on future urban water systems Scope and purpose of this chapter In chapter 3 the problems in urban watermanagement were listed as well as the main threats and opportunities. The objective tree from chapter 3 helped to find objectives for future urban water systems. Chapter 4 showed the structure of current urban water systems. The question is then: how can we restructure those systems to fulfil the objectives from chapter 3? This chapter aims to extract a vision on future urban water systems from threats, opportunities and objectives.











5.1 The city system approach A city can be regarded as a system that is the centre of flows of water, goods, energy and waste, see figure 5.2. There are both artificial and natural flows to the city. Also the flow of people could be considered, however people are not so much part of the physical processes in the city. If a city is considered as such a system, sustainability could imply that reducing those flows is sustainable with respect to the environmental domain of sustainability. After all, less flows to and from the city means less extraction of resources and less production of waste. This idea can be applied to water flows but also to other flows from and to the city, such as energy, goods and waste. While minimizing the flows, attention should be paid to the other domains of sustainability, namely the social and economic domain. Measures should not be extraordinary expensive or have adverse effects on public health. Reducing flows by overexploiting the city itself is not a sustainable solution either. Completely cancelling flows to the city is not a strict objective. The starting point is reducing negative impacts of flows; this means if there is no negative impact, flows do not necessarily have to be reduced. This principle also fits in the policy of the Dutch Government with respect to water that is: never shift problems in area or time (WB21: a different approach to water).



Figure 5-2: Flows to and from the city, which have impact on the surrounding area

5.2 A vision as a result of four influence fields Four influence fields can be distinguished that influence the vision on future urban water systems. These are: society, policy, autonomous trends and technology. Autonomous trends such as climate change and increasing pressure on space make it necessary to develop visions on future water system. The current policy indicates which direction is preferred by government organisations and technology determines which visions are technologically feasible. Finally, society determines which demands are made on the urban water systems. Figure 5.3 shows the four influence fields. The four influence fields should all be taken into account, to achieve a sustainable future water system. However, attention should be paid to the fact that all influence fields can change through time. Policy might change, trends may turn out differently than expected, new technologies will be developed and promising technology may turn out not to be not successful at all. At last, societal functions and perceptions will change. Therefore, it is important to keep options open as much as possible in a vision on urban water system and be flexible for changes. Consequently, a vision should at the first place give direction to developments rather than giving a blueprint for solutions. This approach coincides with the transition approach.

CITY Water

Goods

Energy Heat

Waste

Water

Impacts

Impacts



Figure 5-3: Four influence fields on the development of a vision If the main points of the four influence fields are extracted, it can be summarized that an ideal future water system:

�� Focuses on solving problems at a local scale �� Provides good water quality �� Offers possibilities to nature �� Secures public health and living quality �� Is water and energy efficient �� Anticipates on autonomous trends �� Makes use of new technology to achieve adaptive water systems

Climate change Increasing pressure on space Subsidence Sea level rise Energy prices

Heat pumps

Living quality of urban area Water saving technology

Perception of water nuisance Membrane filtration

Costs of watermanagement Floating houses

Connection with water Sustainable energy sources

Wastewater collection Disconnection facilities

Wastewater transport Purification techniques

Reliability of water supply Green rooftops

Public health Floatlands

Recreation Reed bed filters

Visual quality of water system Permeable pavements

Building technology

No shifting of problems Space for water A different approach to water

Healthy and resilient watersystems Kyoto protocol Anticipating instead of reacting

Retain-store-discharge principle The Water test Good environmental status

Autonomous trends

Technology

Society

Policy

Vision on Future Water

Systems



5.3 Two future water systems If the ideas from the city system approach and the four influence fields are combined, it would be useful to investigate whether it is possible to design an urban water system that minimizes artificial water flow towards the city. Moreover, this water system should not have negative impacts on the surrounding area, or even better, would be entirely self-supporting, providing clean water by self-purification of the water system and would have sufficient retaining and storage capacity to handle peak events within the city borders. Furthermore this city should make use of new concepts to realize a sustainable water system. Such a city is symbolically called a Closed City and will be elaborated further in the next chapter. Next to the Closed City another future water system will be developed. Many water related opportunities for energy conservation were found in chapter 3. Therefore, after developing a water saving city, it will be investigated if the same can be done for energy conservation. A point of interest is the role of the surface water system and the groundwater system with regard to energy conservation. For this purpose heat pumps and heat storage in aquifers will be evaluated in a chapter on a second future water system, which is called the Two Layer City.



6 Future Water Systems: ’the Closed City’ Scope and purpose of this chapter This chapter deals with a future water system: ‘the Closed City’. The Closed City is a city that does not have adverse effects on its surroundings, such as water depletion or emission of pollution. This chapter aims to provide answers on the technical feasibility of a Closed City with regard to water quantity (water use), water quality and water nuisance.











6.1 Ideas for Closed City Concepts Several ways of water supply and layout of the urban surface water system can be made for the Closed City. A starting point is that precipitation is the main source of water supply for a Closed City. In case of exceptional dry conditions, water from a belt channel can be supplied to the city. To improve the inflow water quality, a reed bed filter or settling basin can be constructed. As rainfall is the main source, it is retained as much as possible in the urban area, by disconnection techniques, infiltration, storage reuse and circulation. The goal for disconnection is 100%; therefore no discharge of rainfall to the wastewater treatment plant takes place, unless it is very polluted for instance by heavy traffic. A pumping station discharges the rainfall surplus to the belt channel. Three concepts can be used to design a Closed City these are the ring, the lake and the channel. Ring concept A ring channel is constructed to circulate water through the urban area, and to make use of the natural purifying capacity of the urban surface water. The ring concept has been derived from the circulation model of the guiding principle approach (See e.g. Tjallingii, 1996). Water treatment and water supply have been added to the circulation model. At the beginning of the circulation the wastewater treatment plant is situated, at the end is the drinking water treatment plant. The



pumping station is located it a the end of the circulation ring to make use of the natural purifying capacity of the surface water and to minimize the negative impacts on the surrounding area Lake concept A central lake is constructed to supply water to the city. All effluent and rainwater is being discharged to the central lake as well. Treatment of drinking water and wastewater is centralized. The central lake opens up opportunities for multi functional use for example to combine water supply, water storage and recreation. Channel concept Circulation flow is used in the channel concept similarly as in the ring concept. The main difference between these concepts is water treatment. The channel concept has a decentralized treatment, which implies that every house has an individual treatment facility to treat surface water and wastewater. It also means that every house should be next to, or near the surface water because surface water is the source for all households. For this purpose a very long channel is constructed to connect all the houses to the water. The channel concept can improve experience value for all households and increase the connection between people and water. The following table presents the main differences of the concepts. Table 6-1: Differences of the closed city concepts

Concept Type of flow Type of treatment Ring Circulated Central Lake Mixed Central Channel Circulated Decentral

Energy input of the concepts The three concepts that have been elaborated may need energy input to function. From a sustainability point of view this would not be desirable. Therefore, circulation should be achieved as much as possible by natural processes, for instance by wind, runoff or water level differences.



The next figure elaborates the concepts: Figure 6-2: Closed city concepts

Closed city concepts

W D

Lake Central system Centralized water and waste water treatment and supply

Belt channel Closed city district

Closed city district

Channel Circulation system Decentralized (waste)water treatment and supply at household level

Belt channel

W D Drinking water treatment

Wastewater treatment

Pumping station

W D

Belt channel

Ring Circulation system centralized water and waste water treatment and supply

Closed city district



6.2 Water quantity analysis As discussed in other chapters, one of the objectives is to make a city which has no negative impact on the surrounding area. For this purpose, a water quantity analysis is needed to find out if such a Closed City would be possible. In other words: is the amount of water that is supplied through rainfall enough to compensate the water use in the city? If that is the case no external water supply is necessary.

6.2.1 Schematisation of a new housing district To make a water balance of a new district, a ‘one house city schematisation’ is made. For this purpose the area per terrain type per house is calculated and subsequently a water balance can be made. A typical value for housing density in the Netherlands is 35 houses per hectare; thus the total urban area per house is 286 m2 . This area consists of both private terrain and public terrain. The private terrain consists of house (roofs), garden and pavement. The public terrain consists of green area, surface water, paved area and public facilities, which are both buildings (roofs) and gardens. A reader on parcelling of residential areas (Hogeschool van Utrecht, 2002) provides the following guidelines. Plot area in Randstad For low building areas it ranges from 130 m2 (to rent, in a row) to 350 m2 (to buy, detached) For high rise buildings ranges from 60 m2 to 75 m2. Saleable percentage The percentage of terrain which can be sold, should be at least 50% Paved area for roads and parking lots per house Ranges from 70 m2 for a one family home to 40 m2 for high rise buildings Green area per house Ranges from 10 m2 for a detached house to 50 m2 for three level rent houses All these guidelines could lead to the following estimation of a ‘one house city schematisation’. Table 6-2: Build up of private and public area in a residential district

Private Area 140 m2

Roofs 35% Garden 32.5% Pavement 32.5% Public Area 146 m2 Green Area 30% Surface water 20% Pavement 35% Public facilities 15% (50% impervious and 50% pervious area)

Combining these figures leads to the following ‘one house city schematisation’:



Table 6-3: Area of terrain type per house

Figure 6-3: Percentage of terrain types in a city

6.2.2 Schematisation of the water system A schematisation of the water system is required to be able to calculate groundwater and surface water storage and flow. For this purpose the ‘one house city schematisation’ can be defined as a square of 16.9 x 16.9 meter, with ditches on both sides having a width of 0.86 meter and that reach to the impermeable layer. This layer is assumed to be situated at an arbitrary value, for instance 6 meters below the terrain level. The porosity is assumed to be 35%, the pore space is partly filled with water and the average storage coefficient � is assumed to be 25%. In reality the water content varies both trough the seasons and with the depth. A so-called pF curve can be made, which shows the moisture content � vs. suction pressure �. These graphs can be used to make calculations of moisture availability in the unsaturated zone and the amount of available storage given a certain porosity and moisture content. However, such curves are very much dependent of the type of soil, and for the general goal of this chapter; a rough estimation of the water availability for a closed city it is sufficient to make an estimation. Drainage depth is 0.6 m and the level difference 1.3 meters. The following picture shows the schematised water system.

Figure 6-4: Water system schematisation

Terrain type [m2] Roofs 59.9 Paved area 96.5 Green area 100.1 Surface water 29.1 Total 285.7

city schematization

21%

34%

35%

10%

RoofsPaved areaGreen areaSurface water

15.17

4.7

0.6

6

0.8 0.8



6.2.3 Water quantity model

A water quantity model can be made that is based on the schematisations of the city and the water system. A time step of one month is used to cover season variations in precipitation and evaporation. For water use such a time step is suitable, however, if we want to look at water nuisance, storm events of only a few hours can be the most important factor. Therefore, water nuisance will be covered later in another paragraph. Which flows are required to make such a water quantity model and which can be disregarded? In Chapter 4, schematisations of the urban water system where presented for both the combined and the separated sewer system. Appendix A shows the simplifications of these schematisations for a water availability calculation. These simplifications lead to the following system: Case 1: Combined Sewer System

Figure 6-5: Structure of closed city with a combined system for water quantity model Next to a lot of simplifications also an extra distinction is made between rainfall/runoff from roofs and rainfall/runoff from paved areas such as roads. The reason for this extra distinction is the fact that from paved area water infiltrates to the groundwater and from roofs no water infiltrates unless it is transported to an infiltration facility. In this new water system the distinction between water chain and water system has disappeared because the water system is now the water source for households. Also a disconnection facility has been added to store and discharge stormwater from disconnected areas.

Groundwater


At

mosphere

Households

Treatment

Urban surface water

Paved area

Unpaved area

Ground-water


P

IN

P

E

E

P

ET

D

R

D =DrainageE =Evaporation

ET=Evapotranspiration IN =Infiltration

P = PrecipitationR= Runoff

S=Supply

S

CombinedSewer system

Treatment

RoofsP

EInfiltration

facility

IN

R



The model consists of two connected reservoirs (groundwater and surface water) and 4 sources of inflow (rainfall on four terrain types). In the model all the assumptions, which were made in the former paragraphs, are used as input parameters; therefore, they can easily be changed to make calculations for other than average circumstances and to make a sensitivity analysis for mistakes in assumptions. With the model the flows and storage volumes are calculated for a monthly time step. Water which falls on roofs can either be transported by sewer pipes or, if the roofs are disconnected, infiltrated in the soil and supplied to the ground water. The disconnection percentage is an input parameter in the model, both for roofs and paved surfaces. Water that falls on parks and gardens is assumed to either infiltrate or evaporate. The water users receive the required amount of water from the surface water; after water has been used it is disposed to the sewer system. Water from the surface water can be discharged to the surrounding area if there is a water surplus. Case 2: Separated system In case of a separated sewer system similar simplifications can be made as with the combined system.These simplifications lead to the following system:

Figure 6-6: Structure of closed city with a separated system for water quantity model

6.2.4 Calculation of flows The following flows can be calculated:

�� Precipitation �� Evaporation �� Groundwater recharge �� Surface water recharge

Groundwater


At

mosphere

Households

Treatment

Urban surface water

Paved area

Unpaved area

Ground-water


P

IN

P

E

E

P

ET

D

R

D =DrainageE =Evaporation

ET=Evapotranspiration IN =Infiltration

P = PrecipitationR= Runoff

S=Supply

S

WastewaterSewer system

Treatment

RoofsP

E

Infiltration

facilityIN

R

RainwaterSewer system

RR



�� Rainfall Sewer Inflow �� Water use �� Drainage and water supply �� Total sewer discharge

Precipitation The precipitation of an average year is used as input, the average has been measured by KNMI and is the average of 5 measuring stations in the Netherlands. Table 6-4: Monthly precipitation, average of 5 measuring stations (KNMI, 2004) JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC TOTAL

PRECIPITATION

63.9

44.7 58.7 42.1 55.1 67.4 65.4 58.1 72.1

75.9

78.6 72.0 754.0 Evaporation Evaporation varies widely for various types of terrain. Moreover, evaporation varies through the seasons as well. The percentage of rainfall which becomes evaporation is a yearly average, however for making a monthly water balance the variations through the year need to be known. There are several formulae to calculate evaporation, two of them are most generally used; these are the Penman and the Makkink formulae. The Penman formula uses the open water evaporation as a starting point and is calculated with data of net radiation, wind velocity, temperature and relative velocity. The calculation of the Penman evaporation E0 is rather time consuming, as a lot of input variables are required. Fortunately, the program Cropwat (FAO, 1998) can be used to make these calculations. This gives the following results. Table 6-5: Results of Penman Eo calculation by Cropwat for average Dutch circumstances (FAO, 1998) Min Temp Max Temp Humidity Wind speed Sunshine Radiation E0 E0 oC 0C % Km/day H/day MJ/m2/day Mm/day mm/month

jan 0.4 5.1 88.0 510.0 1.7 2.7 0.57 17.7feb 0.2 5.6 86.0 467.0 2.6 5.0 0.77 21.6mrt 2.3 8.9 79.0 467.0 3.8 8.8 1.49 46.2apr 4.1 12.1 79.0 423.0 5.4 13.8 2.14 64.2Mei 7.9 16.6 77.0 389.0 7.0 18.2 3.11 96.4Jun 10.6 19.1 79.0 380.0 6.4 18.5 3.40 102.0Jul 12.9 21.3 79.0 371.0 6.7 18.4 3.62 112.2Aug 12.9 21.7 79.0 354.0 6.6 16.2 3.31 102.6Sep 10.5 18.3 83.0 380.0 4.5 10.6 2.14 64.2Okt 7.2 14.0 86.0 414.0 3.5 6.6 1.26 39.1Nov 3.8 9.0 88.0 457.0 2.0 3.3 0.70 21.0Dec 1.7 6.3 89.0 501.0 1.4 2.2 0.53 16.4Total 703.6 The Makkink formula has been used by the KNMI since 1987. In this case not the open water evaporation is used as starting point but the Reference evaporation Er of a well-watered grass. The equation of Makkink is much more simple than the Penman formula as it only requires air temperature and radiation, nevertheless, its behaviour is similar. However, in winter time the



physical base of the Makkink formula is lacking because radiation is then no longer the main driving force of evaporation. However for rough water balance calculations, the formula may be used (TNO-CHO, 1987). The KNMI presents the following figures for Makkink evaporation. Table 6-6: Average Dutch monthly evaporation Makkink (KNMI, 2004) and Penman PRECIPITATION PENMAN MAKKINK Penman/Makkink mm mm mm JAN 63.9 17.7 8.3 2.1FEB 44.7 21.6 15.7 1.4MAR 58.7 46.2 32.9 1.4APR 42.1 64.2 56.4 1.1MAY 55.1 96.4 85.1 1.1JUN 67.4 102.0 90.2 1.1JUL 65.4 112.2 95.1 1.2AUG 58.1 102.6 83.1 1.2SEPT 72.1 64.2 50.3 1.3OKT 75.9 39.1 27.8 1.4NOV 78.6 21.0 11.5 1.8DEC 72.0 16.4 6.5 2.5TOTAL 754.0 703.6 562.9 1.2 Calculation of monthly evaporation from various terrain types 1. Open water evaporation Both Makkink and Penman are not very suitable for use of real open water evaporation calculations. However, because Penman overestimates the evaporation from an open water surface; for this calculation it is acceptable to use, as the results will be on the safe side. 2. Evaporation from unpaved surfaces For evaporation from unpaved surfaces the reference evaporation according to Makkink formula can be used, to obtain the maximal actual evaporation the reference evaporation has to be multiplied by a crop factor f.

max * rE f E� Crop factors have been estimated for various crops, of all crops, grass is most similar to the public green space in cities; grass has a crop factor of 0.9 in September and 1.0 in the rest of the year. The accuracy of the crop factor approach is low. Another approach is the use of seasonal influences. In summer vegetation will evaporate less than in optimal circumstances because the vegetation is not fully watered. By Thorntwaite and Mather (1957) a method has been developed which adjusts the evaporation for the moisture content in the soil. For potential evaporation the reference evaporation of Makkink can be used or 0.8*E0; these produce similar results.

0/0

AWPL SS S e�

� with: S = Actual moisture content in root zone [mm] S0 = Moisture content at the begin of the season [mm]



AWPL = Accumulated Potential Water loss [mm] Eact = Actual Evaporation [mm] Epot = Potential Evaporation, Makkink Er or Penman 0,8*E0 [mm] Table 6-7: Thorntwaite and Mather calculation of evaporation with S0=100mm P Epot P-Ep APWL S dS Eact

mm mm mm mm mm mm mmJAN 63.9 8.3 55.6 0.0 100.0 0.0 8.30FEB 44.7 15.7 29.0 0.0 100.0 0.0 15.70MAR 58.7 32.9 25.8 0.0 100.0 0.0 32.90APR 42.1 56.4 -14.3 14.3 86.7 -13.3 43.08MAY 55.1 85.1 -30.0 44.3 64.2 -22.5 62.64JUN 67.4 90.2 -22.8 67.1 51.1 -13.1 77.11JUL 65.4 95.1 -29.7 96.8 38.0 -13.1 81.96AUG 58.1 83.1 -25.0 121.8 29.6 -8.4 74.70SEPT 72.1 50.3 21.8 0.0 51.4 21.8 50.30OKT 75.9 27.8 48.1 0.0 99.5 48.1 27.80NOV 78.6 11.5 67.1 0.0 100.0 0.5 11.50DEC 72.0 6.5 65.5 0.0 100.0 0.0 6.50TOTAL 754.0 562.9 191.1 0.0 100.0 0.0 492.48 Assumptions: P = Long year precipitation average of 5 measuring stations. Epot = Er Eact = Ep-S if (P-Ep)<0 Eact = Ep if (P-Ep)<0 3. Evaporation from paved surfaces and roofs Evaporation from paved areas in cities is poorly known, which means that values should be estimated based on observations and discharge coefficients. Evaporation from roofs and paved surfaces will be a certain fraction of the open water evaporation. The discharge coefficients that are used for the design of sewer systems give a first impression how discharge varies for several terrain types. (Clemens, 2002) Table 6-8: Discharge coefficients for various terrain types Terrain type Discharge coefficient Tile roof 0.90 Flat roof 0.5-0.7 Asphalt road 0.85-0.90 Paving stone 0.25-0.60 Gravel roads 0.15-0.30 Unpaved without vegetation 0.10-0.20 Parks and public garden 0.05-0.10



The discharge coefficient gives an impression which percentage of the rainfall results in discharge, the rest is either infiltration or evaporation. However, sewer systems are designed to handle peak events such as heavy rainstorms, when the percentage of rainfall which becomes discharge, is higher than in the average situation. However, this average situation is needed to make water balance estimation; as a result the discharge coefficient for the average situation will be somewhat lower. On roofs no infiltration takes places, and when half of the roofs are flat roofs and the other half are sloping roofs, about 70% results in discharge. For paved area the situation is different. Paved areas can be compared with parking lots; Van de Ven (1985) has studied the water balance of a parking lot. In that particular case 45% of the inflow resulted in discharge, 40% in infiltration and about 15% in evaporation. In green areas evaporation is about 450 mm of the average of 750 mm., a percentage of 60%. Therefore, under the condition that no discharge takes place from green areas, infiltration is 40%. The open water evaporation is even higher than the evaporation from vegetation and estimated at 70%; the estimations give the following picture. Table 6-9: Estimations of discharge, infiltration and evaporation at a yearly timescale Terrain type Discharge Infiltration Evaporation Total Roofs 70 0 30 100Paved area 45 40 15 100Green area 0 40 60 100Surface water 30 0 70 100 Combining the results of table 6.9 and the open water evaporation Eo, provides an estimation for evaporation from other surfaces. For instance to calculate the evaporation from paved surfaces one can multiply the monthly evaporation values by the evaporation ratio derived from table 6.4. In this case Epaved = 15/70*Eo. If this calculation is made for all the terrain types, it leads to the following table. Table 6-10: Estimation of average monthly evaporation

EVAPORATION ROOFS

EVAPORATION PAVED AREA

Ratio 30/70*Eo 15/70*Eo

mm mmJAN 3.6 1.8FEB 6.7 3.4MAR 14.1 7.1APR 24.2 12.1MAY 36.5 18.2JUN 38.7 19.3JUL 40.8 20.4AUG 35.6 17.8SEPT 21.6 10.8OKT 11.9 6.0NOV 4.9 2.5DEC 2.8 1.4TOTAL 241.2 120.6



To calculate the effective rainfall per terrain type and per month, the evaporation is subtracted from the total rainfall. The next table presents a summary of evaporation calculation in this chapter. Table 6-11: Summary of methods, as being used in this chapter

Type Method Open water evaporation, E0 Penman Unpaved area Makkink and Thorntwaite&Mather Paved area Penman, estimated percentage of E0

Roofs Penman, estimated percentage of E0

Groundwater recharge To calculate groundwater recharge, discharge and infiltration coefficients have to be calculated. For this purpose the coefficients from Table 6.9 are used. For instance, for paved surface Ci= (40/(40+45))=0.47, which means that 47% of the effective rainfall infiltrates. (1-Ci)=0.53, which means that 53% of the effective rainfall discharges to the sewer system. However, a part of the paved surface can be disconnected, in that case the disconnected fraction of the paved surface adds up to the infiltration volume. Groundwater recharge results from the following sources

1. Effective rainfall on paved surface. 2. Effective rainfall on unpaved surface. 3. Stormwater runoff on disconnected roofs.

The following formulae are used to calculated these components

,1 , , (1 )groundwater eff paved paved i eff paved paved i dQ P Area C P Area C F� � ��

,2 ,groundwater eff unpaved unpavedQ P Area� �

,3 ,groundwater eff roofs paved dQ P Area F� � � with: Fd= fraction of paved area, which has been disconnected Surface water recharge CASE 1: Combined system Surface water recharge result from effective rainfall on the surface water itself, the following formula is used to calculate the recharge.

,surfacewater eff surfacewater surfacewaterQ P Area� � CASE 2: Separated system In case of a separated system the amount of surface water recharge consists of the same component but the inflow from the rainwater system is added to the discharge.



The inflow in the rainwater system results from the following sources: 1. Effective rainfall on connected paved surface. 2. Effective rainfall on connected roofs

,1 , (1 ) (1 )sewer eff paved paved i dQ P Area C F� � ��

,2 , (1 )sewer eff roofs paved dQ P Area F� �� The surface water recharge becomes:

, ,1 ,2surfacewater eff surfacewater surfacewater sewer sewerQ P Area Q Q� � �� Rainfall sewer inflow in combined system In case of a combined system, sewer inflow results from precipitation on paved surfaces and roofs, which are not disconnected. Consequently, sewer inflow results from the following sources:

1. Effective rainfall on connected paved surface. 2. Effective rainfall on connected roofs

The following formulae are used to calculated these components

,1 , (1 ) (1 )sewer eff paved paved i dQ P Area C F� � ��

,2 , (1 )sewer eff roofs paved dQ P Area F� �� Water use The water use for an average household of 2.28 persons is 105 m3 a year. This amount can be changed in the model and monthly peak factors for water use variations are specified. Drainage and water supply If the phreatic water level is higher than the surface water level, a groundwater flow will start towards the surface water. If the phreatic waterlevel is lower the opposite occurs. The decrease or increase of the groundwater table under dynamic conditions can be described by the Glover Dumm equation: /( ) 1.16 (0) t jh t h e�

� � h(t) = Bulge halfway between drains at t=t j = Reservoir coefficient [d] At a monthly timescale the groundwater table will in most case be very near to the surface water level if no infiltration takes place. For example: for a j value of 10 days only 6% of the groundwater bulge is left after a month. If we take into account that a j factor of 10 is very high, it is reasonable to make the following assumption: the complete water volume of the groundwater bulge will drain onto the surface water in a period of a month, resulting in a new equal groundwater and surface water level. In the same month a new bulge will build up as a result of the total volume of rainfall on pervious, paved and disconnected areas. A four-step method is used to calculate the groundwater and surface water levels which consists of the following steps:



1. Drain groundwater bulge and calculate new equal groundwater and surface water level.

2. Calculate new surface water level after monthly water use and direct precipitation on surface water.

3. Adjust groundwater level to new surface water level. 4. Calculate new groundwater level resulting from groundwater recharge and

compensate for step 3. The steps of this calculation are elaborated further in Appendix B. Total discharge sewer system CASE 1: Combined system The total discharge in a combined sewer system consists of wastewater of households and inflow of rainwater. The wastewater of households is approximately 90% of the water use. The remaining 10% mainly evaporates from laundry and cooking, and a small part also in watering of the garden. In the water quantity model the assumption is made that the remaining 10% completely evaporates. CASE 2: Separated system In a separated system the discharge from households is separated from the rainwater flow; the total sewer discharge consists of those two components.

6.2.5 Water quantity assessment for several circumstances The model can be used to assess water availability for several circumstances. For this purpose one can look at the yearly water balance and water and groundwater levels. Situation 1: Average year, combined sewer system Sewer system Combined Effective rainfall: Average Water use: Average Season water use factors: None Disconnection percentage: 100%

Figure 6-7: Surface water level and groundwater level fluctuation for situation 1

Water level

3

3,5

4

4,5

5

5,5

6

T=0 JAN

FEBMAR

APRMAY

JUN

JUL

AUGSEPT

OKTNOV

DEC

Month

Wat

erle

vel(m

)

surfacewater levelgroundwater level



Table 6-12: Water balance of an ’one house city schematisation’ in situation 1 m3 % Precipitation 215.4 100Evaporation 102.4 47.5Peff 113.0 52.5 To surface water 1.5 To paved surface/roofs 111.5Use 105.0 48.8Dstorage 7.9 3.7Sewer total 94.5 Comments on the results The yearly water balance shows that for situation 1, sufficient water is available for average water use. Therefore, if one only looks at water quantity, ‘a Closed City’ is possible. For situation 1 there is even a surplus of 3.7 %. The water level fluctuations are not very large: about 30 cm for both groundwater level and water level fluctuations. Situation 2: Dry year, combined sewer system Naturally, water supply should not only be realized in an average year, but also in a dry year. To calculate the water availability it is possible to use the input for the year 2003, which is a year with an estimated return period of 1/15 per year. Furthermore, a year like 2003 could occur more frequently in the near future because of climate changes (droogtestudie.nl). In a dry year water use is generally 8% higher. Moreover, in this calculation season water use factors are specified as well. Water use in summer months is generally 10% higher than the monthly average, whereas water use in winter months, is about 8% lower. The following results appear: Sewer system: Combined Effective rainfall: Dry year (2003) Water use: Dry year (8% higher) Season water use factors: Peak factor=1.1 for summer months, 0.92 for winter months Disconnection percentage: 100% Results:

Figure 6-8: Surface water level and groundwater level fluctuation for situation 2

Water level

3

3,5

4

4,5

5

5,5

6

T=0

JAN

FEB

MAR AP

R

MAY JU

N

JUL

AUG

SEPT OK

T

NOV

DEC

Wat

erlev

el(m

)

surfacewater levelgroundwater level



Table 6-13: Waterbalance of an ’one house city schematisation’ in situation 2 m3 % Precipitation 175.1 100.0Evaporation 100.7 57.5Peff 74.4 42.5 To surface water -2.6 To paved surface/roofs 77.1 Rainwater in combined Sewer 0.0 0.0Use 114.0 65.1Dstorage -39.6 -22.6Sewer total 102.6 Comments on the results For a dry year, a water shortage occurs of about 23%; consequently no sufficient water supply is available to cover the total yearly water use. Because of water shortage, the surface water level falls 0.7 m in September, compared to the starting condition. Even at the end of the year the water level is 0.45 m lower than at the beginning of the year. If such a water level causes problems depends on local conditions, for instance the water depth, water quality, soil and foundation conditions. If it is possible to construct a water system, which can handle large fluctuations, the Closed City could work in a dry year as well. However, such a dry year should be an incident and not be structural because the shortage should be compensated in other years. Large inter annual reservoir capacity should be constructed in that case. In case of an average frequency of 1/15 /y, it is often possible to compensate dry years. Nevertheless, a possibility to supply water from outside should be present to compensate the water shortage. Also the possibility to discharge effluent from the wastewater treatment plant back to the urban water system could be a solution. In the water quality analysis will be evaluated if that would be possible. Situation 3: Average year, separated sewer system The situation for a separated system will be evaluated. In this case the disconnection percentage has no influence on the water availability. After all, for water quantity, it makes no difference if runoff reaches the surface water by the rainwater sewerage system or through infiltration facilities. Sewer system Separated Effective rainfall: Average Water use: Average Season water use factors: None Disconnection percentage: 0%



Figure 6-9: Surface water level and groundwater level fluctuation for situation 3 The water availability is the same as in situation 1, as the next table indicates. Table 6-14: Waterbalance of an ’one house city schematisation’ in situation 3 m3 % Precipitation 215.4 100.0Evaporation 102.4 47.5Peff 113.0 52.5 To surface water 1.5 To disconnection/groundwater 53.6 To rainwater sewer 57.9 Use 105.0 48.7Dstorage 8.0 3.7Wastewater sewer 94.5 check 0.0 Comments on the results The groundwater level is much lower compared with situation 1, due to the fact that there is less infiltration. On the contrary the surface water level is higher than in situation 1, which is the result from fast discharge of runoff to surface water. Situation 4: Dry year, separated system Sewer system: Separated Effective rainfall: Dry year (2003) Water use: Dry year (8% higher) Season water use factors: Peak factor=1.1 for summer months Disconnection percentage: 0%

Water levels

3

3,5

4

4,5

5

5,5

6

T=0 JAN

FEBMAR

APRMAY

JUN

JUL

AUGSEPT

OKTNOV

DEC

Month

Wat

erle

vel(m

)

Surface water levelGroundwater level



Figure 6-10: Surface water level and groundwater level fluctuation for situation 4 Table 6-15: Waterbalance of an ’one house city schematisation’ in situation 4 m3 % Precipitation 175.1 100.0Evaporation 100.7 57.5Peff 74.4 42.5 To surface water -2.6 To disconnection/groundwater 34.8 To rainwater sewer 42.2 Use 114.0 65.1Dstorage -39.6 -22.6Wastewater sewer 102.6 Comments on the results In a dry year the groundwater table falls considerably, besides, the level difference between surface and groundwater level becomes very small because the groundwater recharge is low; a large part of runoff is transported to the surface water.

6.2.6 Influence of design parameters on water availability For three important design parameters in the civil engineering design, namely: disconnection percentages, surface water percentage and housing density, a water availability analysis can be made. This analysis shows how variations in these parameters influence water availability and (ground)water fluctuations during average circumstances. The results provide insight, which can be used to design urban water systems.

Water levels

3

3,5

4

4,5

5

5,5

6

T=0 JAN FEB MAR APR MAY JUN JUL AUG SEPT OKT NOV DEC

Month

Wat

erle

vel(

m)

Surface water levelGroundwater level



Disconnection percentage CASE 1: Combined sewer system The figure below presents the results, which show how the water availability in an average year varies with the disconnection percentage. The figure shows than disconnection percentage of at least 87% is required to cover the average water use of a city during an average year.

Figure 6-11: Water availability vs. disconnection percentage for a combined sewer system CASE 2: Separated sewer system As discussed before, the disconnection percentage has no influence on the water availability if the sewer system is separate. However, it has a large influence on ground and surface water levels. The next graph shows the influence on water levels, for a higher disconnection percentage more water is kept in the ground, thus groundwater levels are higher.

Figure 6-12: Water levels vs. disconnection percentage for a separated sewer system

-60,0

-50,0

-40,0

-30,0

-20,0

-10,0

0,0

10,0

20,0

0 20 40 60 80 100

disconnection percentage[%]

Wat

er s

urpl

us [m

3]

4,7

4,8

4,9

5

5,1

5,2

5,3

5,4

5,5

0 20 40 60 80 100 120

Disconnection percentage [%]

Wat

er le

vel [

m]

Average SWLAverage GWL



Surface water percentage To reduce water nuisance and increase water storage, water managers often want a high percentage of surface water in the urban area. However, for water availability it is interesting to know what the influence is of the surface water percentage on water availability. The next figure shows this relation; the availability of water decreases as open water surface increases. A high open water percentage is not beneficial for water availability because a higher evaporation takes place from surface water. However, in case of a large surface water percentage, water storage is larger and level fluctuations are lower which is desirable in dry years.

Figure 6-13: Water availability vs. surface water percentage Housing density If the housing density decreases, water availability increases because the total area per houses increases, as a result also the amount of effective precipitation. Building with lower densities increases the water availability considerably, as the next graph shows.

Figure 6-14: Water availability vs. housing density

-20

-10

0

10

20

30

40

50

60

20 25 30 35 40 45 50

Housing density (houses/ha)

Wat

er s

urpl

us[m

3]

-10

-5

0

5

10

15

0 5 10 15 20 25 30

Percentage of surfacewater [%]

Wat

er s

urpl

us [m

3]



6.2.7 Sensitivity analysis The former paragraphs described the feasibility of a Closed City with regard to water quantity. To put these results in perspective, this paragraph contains a sensitivity analysis to find out how sensitive the results are for future trends in water use and climate Climate change KNMI(2001) predicts the following scenarios based on research of the IPPC. Table 6-16: Predicted changes in Dutch climate

Low estimate Central estimate High estimate Temperature +1 +2 +4 to +6 Average Precipitation summer

+1% +2% +4%

Average Precipitation Winter

+6% +12% +25%

Summer Evaporation +4% +8% +16% For the central estimate it can be concluded that the fluctuations of the water system will increase. In summer the shortage will increase, whereas in winter the surplus will increase. As a result the maximal ground and surface water level will increase. The climate change indicators from table 6.16 can be applied on the water quantity model, this presents the following result. Table 6-17: Influence of climate change (B) on water availability compared to current situation (A) m3 m3 % A B Precipitation 215.4 228.0 100.0Evaporation 102.4 106.5 46.7Peff 113.0 121.5 53.3 To surface water 1.5 2.1 To paved surface/roofs 111.5 119.4 Use 105.0 105.0 46.1Dstorage 7.9 16.5 7.2Sewer total 94.5 94.5 Water availability increases because of climate change, resulting from more rainfall (+12%) in winter, however also the level differences between seasons increase. For instance, for surface water the level difference increases from 26 to 33 cm. Climate change will probably have no negative effect on water availability, however, this is only the case if all runoff can be stored within the city itself. Storing all runoff becomes more difficult because of season differences and will probably impose a lot of requirements on the storage capacity. In the paragraph on water nuisance the required storage capacity will be calculated.



Water use change During the last ten years the water use per capita decreased to 126 litres per day. In the future this amount could rise again a little, because more dishwashers are used and the welfare level rises. However, it could also decrease because of the presence of more water saving machines in households. Next to water use, also the population density per house is important. At this moment on average 2.28 persons live in one house. According to CBS(2004) the population density per house will decrease to 2.11 persons per house. This density would decrease water use per household with about 7.5%. Moreover, it is possible to influence water use by demand management, as will be evaluated in the next paragraph.

6.2.8 Demand management By demand management the feasibility of the Closed City for water use can be further increased. There are various ways to influence water use; firstly, it is possible to influence human behaviour by water pricing, public campaigns or installing water meters. These measures can lead to a change of behaviour, for instance less bathing and taking shorter showers. In fact, during the last years these measures have already resulted in a decrease of water use. Secondly, it is also possible for people, not to change the frequency and nature of their water use, but to switch to water saving technologies. Dubo (2004) presents the following water saving technologies:

�� Discharge restriction in water pipes (unknown saving amount) �� Water saving shower (saves 8.5 m3 phpy) �� Water saving toilet flushing reservoir (saves 6.5 m3 phpy) �� Water saving washing machine (saves 7 m3 phpy) �� Water saving dishwashing machine (saves 0.2 m3 phpy)

Consequently, even without change of water use behaviour, water use can decrease with 22 m3 from 105 m3 per household per year to 83 m3 per household per year. Implementing these measures increases the feasibility of the Closed City a lot. In that case even in a very dry year as 2003, rainfall provides a considerable part of the total water use in the Closed City, see table 6.13.

6.3 Water quality analysis Wastewater treatment techniques are getting better and cheaper, consequently effluent from wastewater treatment plants becomes more suitable for useful purposes. At this moment effluent is still discharged to the rural area; however, if it is possible to keep wastewater within the city borders, the water supply of the ’Closed City’ is certainly guaranteed. Question is: does water quality allow for this step? Therefore, in this study it is evaluated if it is possible to comply with the Maximum Allowable Risk water quality standards in case all effluent is discharged back to the urban surface water.

6.3.1 Pollution sources The main pollution source of surface water in urban areas is runoff from streets. The quality of rainfall itself plays a less important role. Contact with roofs and streets contaminates runoff, on the other hand infiltration or settling basins can improve the quality of runoff before it enters surface water. Several pollution sources can be distinguished a residential area. The picture below shows the routes pollution takes before it reaches the urban surface water. In a fully disconnected system pollution reaches the surface water after it has been infiltrated or has been purified by a settling basin. Consequently, direct runoff will be very small in that case. The effluent of the wastewater treatment is also a source of pollution, as well as pollution from the water bottom.



Figure 6-15: Routes of pollution to the urban surface water Deposition and runoff The following table presents figures for pollution level of rainwater and runoff from a residential district. Table 6-18: Water quality figures of pollution sources for urban water systems

BOD mg/l

N-Kj mg/l

P-tot mg/l

Cd �g/l

Cr �g/l

Cu �g/l

Pb �g/l

Zn �g/l

Pah-10 �g/l

Oil mg/l

Rain(1) - 1.5 0.006 0.1 0.1 2 4 13 Rain(2) 0.2 2 4.6 15 0.4 <0.1 Rain (3) 1 12 26 Dry + wet deposition(4)

0.2 1.3 26 9 68 0.7 123

Residential Distict(5)

6 2.8 0.5 0.5 13.7 50 36 144 2.2 0.1

Residential District (6)

7-13 1.5-3.6

0.22-1.5

0.5- 2.9

5-45 6-57 50-310

100-320

0.54-0.98

Residential District (7)

7-33 54-77 257-361

1.5-4.5

Rainwater sewerage (8)

15-30

Rainwater Sewerage(9)

7-22 0.2-4.6

0.03-3.1

Sources:

Urban Surface water

Dry and wet deposition

Domestic WastewaterWastewater Treatment

Infiltration

Pollution

Various sources: traffic, building

material, dogs, leaves etc.

Bottom sediment

Drainage

Soil

Runoff

Paved and Unpaved surface

Discharge

Up whirling



1. Average values national rainwater quality measurement, RIVM, 1994 in Grontmij (2001) 2. CIW, 2002 3. De Haan, 1984 (TNO) 4. Teunissen, 1998: Average values from motorways A7 and A9 and surrounding of Zwolle 5. Grontmij, 2001 6. NWRW, 1986 in Van de Ven, 2003 7. Riza, 1997 8. Van Mazijk, 2003 9. Ellis, 1985

Drainage By infiltration of runoff purifying processes take place. Wadi systems or other facilities can be used to infiltrate water in the soil. Table 6-19: Purification efficiency for various facilities

Facility COD PAH Total Suspended Solids

BOD Ntot Ptot Heavy metals

Infiltration(1) 90% 50% 50% 90% Infiltration(2) 90% Settling facility(1) 50% 25% 25% 50% Settling facility(2) 43% Reed bed filter (discharge)(3)

40% 10% 71%

Reed bed filter (storage)(3)

90% 65% 87% 89%

Reed bed filter (discharge)(4)

>80% >85%

Reed bed settling facility combination5)

91% 85% 80% 65% 94%

Sources:

1. Grontmij, 2002 2. CIW, 2002 effiency in case of road runoff 3. Kraker, de J. et al., H2O 9.2004 4. Boutin, C. and A. Liénard, Water21 4.2004 5. Wieten, M, Neerslag-magazine.nl 6.2004



Waste water treatment plant The table below shows the average treatment efficiency for wastewater treatment plant. (Van de Graaf, 2002) Table 6-20: Purification efficiency of wastewater treatments plants

Influent (mg /l) Effluent (mg/l) Efficiency (%) COD 456 51 88.82 BOD5 173 7 95.95 Ntotal 6.6 Nkjeldahl 41.8 13.5 67.70 Ptotal 6.7 1.8 73.13

Up whirling of pollution The up whirling of pollution from water bottoms is extremely hard to quantify and very site specific. A water bottom can be regarded as an internal oxygen deficit source. The amount of oxygen, which is needed for bio-degradation, depends on factors like temperature and the fact whether or not rotting leaves are present in the soil. At a temperature of 20oC, the oxygen demand ranges from 0.5 g O2/(m2/d) for sandy river bottom to 7 g O2/(m2/d) for sludge with a high content of cellulose (leaves). (Van Mazijk, 2003) Besides functioning as an internal oxygen deficit source, a water bottom also disposes BOD to the water. These are substances that will be degraded in the water while oxygen is being used. Usually a certain factor such as 0.25 times the oxygen demand is used to calculate the BOD disposal to the water.

6.3.2 Oxygen management The Maximum Allowable Risk level for oxygen concentration is 5 g/m3, the concentration may not be lower than this standard. This chapter investigates whether it is possible to discharge effluent back to the surface water while the oxygen standard is reached. For this purpose the effect of pollution on the oxygen content is calculated. The critical time for oxygen depletion is usually during summer because degradation processes are going faster and more oxygen is being used. Therefore, the water temperature is assumed to be 20o C. Schematisation of district. A district of a thousand houses has a surface of 28.6 ha. Dimensions are 535 by 535 meters. The total water surface is 10% of that area, which is 2.86 ha, consisting out of four canals with a length of 401 and a width of 17.8 meters. The canal has a depth of 1,5 meters. Water circulation takes place by a pumping station with a velocity of 0.2 meters. Estimation of pollution sources 1. Waste water treatment plant A point pollution source is the effluent from the wastewater treatment plant. The concentration of BOD is the same as in table 6.20. By future technologies the BOD level will probably be decreased. About 90% of residential water use becomes wastewater, so the total production is 1000*105*0,9=94,5*103 m3.



Concentration BOD= 7 mg/l Discharge= 94500 m3/year W=94500*7/365/24/3600=0.021 g/s 2. Discharge from infiltration facilities Another point pollution source is the discharge from infiltration facilities. The total yearly volume, which infiltrates is 111.5 m3 in average circumstances and if 100% of the paved area has been disconnected, see table 6.12. From table 6.18 an estimation of the average content of BOD in runoff from a residential district can be made, a suitable estimation is 8 mg/l Q= 111.5 m3/year/ house*1000/365/24/3600=0.00353 m3/s Concentration BOD = 8 mg/l W*=8*0.00353=0.0283 g/s Of this amount about 80% is being removed by an infiltration facility or a reed bed filter (estimation based on table 6.19.) So the total point pollution from infiltration facilities is: W= 0,00566 g/s Total Point pollution source The total point pollution is the sum of the point pollution from the infiltration facilities and the wastewater treatment. A cautious estimate of the total point pollution is the following: Wtotal=Wwastewater+Winfiltration=0.03 g/s 3. Diffuse pollution from water bottom The following estimates can be made:

�� Internal oxygen deficit source: SI,D =2g O2/(m2/d) with a temperature of 20oC

�� BOD source: SI,B=0.2*SI,D=0.4 g O2/(m2*d)

4. Biogene oxygen use and oxygen production Vegetation both uses and produces oxygen. Production typically ranges from 0.3 to 9g O2/(m2*d). Oxygen use ranges from 0.5 to 5g O2/(m2*d). A cautious estimate for the net oxygen production is 1.5 g O2/(m2/d. 5. Physical re-aeration Oxygen reaches the water through the water surface; this process is called physical re-aeration. For water of 20 oC with a low velocity the re-aeratation coefficient ranges between 0.25 and 0.35 d-1. A suitable estimate is 0,3 d-1. Calculation of oxygen concentration In a system where there are both diffuse and point pollution sources a so-called connected model can be used, combining both BOD concentration and oxygen concentration. These concentrations are connected because lowering of BOD concentration leads to a lower oxygen concentration. The following 1 dimensional continuity equation for the BOD concentration can be used. This equation is based on the assumption of a constant concentration throughout the intersection. (No variations in the y and z direction)

21 1 1

1 12 0xu K kt x x

��

� � ��



with: 1� = BOD concentration

xK = Dispersion coefficient in x direction k 1 = Degradation coefficient BOD

The oxygen content is usually expressed as oxygen deficit D.

2 2( )sD � ��

2

2 12 12 0xD D Du K k D kt x x

� � ��

� � ��

with: D = Oxygen deficit

xK = Dispersion coefficient in x direction k2 = Reaeration coefficient k12 = Connection coefficient

2� = Oxygen concentration

2( )s� = Oxygen saturation concentration The solution under assumption of plug-flow (Kx=0) of the connected equations is (Van Mazijk, 2003)

,1 ,2 ,10* 12 12 120 2 1 2 2 0 1 2

2 1 1 2 2 1 2 1

*exp *(exp exp ) ( * )(1 exp ) ( ) (exp exp )I I IS S Sk k kD Dk k k k k k k k�

��

� �

with: D0 = Oxygen deficit x=0 Expx = exp[-kx*X/U) 0� = Oxygen concentration at x=0 SI,1 = Diffuse BOD source SI,2 = Diffuse Deficit source The input values that are used to calculated the oxygen deficit are given in Appendix C Results Influence of point pollution

Point pollution Diffuse pollution



An equilibrium (horizontal line) is needed, because at the after one circulation round the pollution level should be the same again. The graph below shows that it is not possible, not even for very low pollution levels. In this case the water system does not fulfil the requirements

Oxygen content as function of point discharge

5,7955,8

5,8055,81

5,8155,82

5,8255,83

5,8355,84

5,845

0 500 1000 1500 2000

X (meters)

Oxy

gen

cont

ent(m

g O

2/l)

W=0,01 g/sW=0,02 g/sW=0,03 g/sW=0,1 g/s

Figure 6-16: Development of oxygen concentration in one circulation for various point sources Influence of diffuse pollution The graph shows that the influence of diffuse pollution is larger than the influence of point pollution. Unfortunately diffuse pollution is more difficult to reduce because no singe source can be specified. The oxygen demand of the water bottom should not be larger than 1.2 g. O2 /(m2*d) to reach the desired equilibrium.

Figure 6-17: Development of oxygen concentration in one circulation for various diffuse sources

Oxygen content vs Diffuse oxygen demand (g/(m2*d)

5,65

5,7

5,75

5,8

5,85

5,9

5,95

0 500 1000 1500 2000

distance(m)

Oxy

gen

conc

entra

tion

(g O

2/l)

O2 use water bottom= 0,5

O2 use water bottom= 1





Influence of circulation velocity Some circulation has great advantages for the natural purification and re-aeration processes. Similarly, stagnant water has a bad influence on water quality. However, the benefit of circulating faster is limited in this system. Increasing the velocity further, only increases the oxygen level a little. Moreover, more energy input is needed if the circulation velocity is higher.

Oxgen content as a function of circulation velocity

5,2

5,3

5,4

5,5

5,6

5,7

5,8

5,9

0 500 1000 1500 2000

distance(m)

O2

conc

entr

atio

n (m

g/l)

v =0.01 m/sv=0.05 m/sv =0.1 m/sv=0.5 m/s

Figure 6-18: Development of oxygen concentration in one circulation for various velocities Influence of water depth Increasing water depth has some advantage for the oxygen content but this advantage is only small. Because the water volume is larger more dilution takes place; as a result the oxygen content stays higher.

O2 content as a function of water depth

5,78

5,79

5,8

5,81

5,82

5,83

5,84

5,85

0 500 1000 1500 2000

distance(m)

O2

conc

entr

atio

n)m

g/l)

d=1d=1.5d=2

Figure 6-19: Development of oxygen concentration in one circulation for various canal depths



Optimal solution and implications for the design The influence of the factors is known and only diffuse sources such as the oxygen use of the water bottom have a major impact. The other factors have some impact, however put together they might influence the oxygen content considerably. To find out if that is the case, an optimal and feasible solution should be found which leads to equilibrium of both the connected concentrations, namely oxygen concentration and BOD concentration. The equilibrium can be found iteratively.

Factor Input Value W 0,03 g/s O2 demand water bottom 1.2g O2(m2*d) Depth 2 m Velocity 0.2 m/s Degradation coefficient k1 0.25 d-1

The input values lead to the following result, indicated in the graph below. As a result, the conclusion can be made that a self-purifying system with regard to oxygen management is possible within the ring concept of the Closed City however:

�� Self-purifying factor k1 must be increased to 0.25 1/d, which could be accomplished by the use of reed bed filters in the surface water. The morphology should be such that growth of aquatic vegetation, which increases both the contact area for degradation and oxygen production, is possible.

�� Oxygen demand of the water bottom should be decreased to 1.2 g O2(m2*d). This is a rather low value; if it is possible to accomplish this value, depends on site-specific factors like soil conditions and agricultural history.

�� In the urban planning diffuse pollution can be reduced by placing trees further away from the surface water, by maintenance (dredging) and by influencing human behaviour (fish and bird feeding and reduction of dogs excrements on harmful places like rainwater gutters)

�� Further reduction of wastewater load from stormwater is not necessary for oxygen management.

Figure 6-20: Development of oxygen concentration in one circulation in case of proposed measures

Equilibrium state of concentrations

0

1

2

3

4

5

6

7

0 500 1000 1500 2000

distance(m)

conc

entr

atio

n(m

g/l)

Oxygen contentBOD content



6.3.3 Phosphorus management

Not much is known about the self-purifying capacity of the urban water system. Required knowledge of underlying processes is not yet available. Therefore, the best available approach is to rely on empirical standards. These are unfortunately often derived in other circumstances than the problem area, which is certainly a thing to keep in mind when the results are evaluated. The following equation gives the permissible loads on surface water as a function of certain standard. (Vollenweider, 1976)

*(1 )W aqq�

� �

with:

W = Total phosphorus load [g/(m2*y) � = Concentration standard phosphorus [g/m3] a = Depth [m]

q = Hydraulic load =Qtotal/A surface [m/y] In this case is:

a = 2 m Qtotal = 113 m3/house*1000 houses= 113*103 m3/y (see table 6.12) A = 28,6*103 m2

Hydraulic load q = Q/A= 3.95 m/y � = 0.15 g/m3

for phosporus

23.95*(1 )0.15 3.95W

� �

W= 1.0 [g/(m2*y) The total phosphorus load per square meter of surface water may not be larger than 1.0 gram per year. How does this standard relate to the current state of pollution sources? About 90% of residential water use becomes wastewater, so the total production is 1000*105*0,9=94,5*103 m3. The concentration of phosphorus is 1.8 g/m3 (see table 6.20), the total load is then: W1 =94.5*103*1.8/28.6*103= 5.95 g/m2/y This amount is about 5 times higher than the permissible load, so discharging effluent back to the urban surface water is not possible if current wastewater treatment and current canals are used. Next to wastewater load there is also a load of urban runoff. Table 6.19 provides figures for an estimation of the phosphorus content of urban runoff. The estimation from these tables is 0.7 g/m3. Of this amount about 50% is removed by an infiltration facility. The total rainfall on terrain is taken, as the average urban runoff quantity in a year and is 111.5 m3/house/y. The total load per a square meter of surface water is then: W2 = 111.5*103*0.7*0.5/28.6*103= 1.36 g/m2/y



This amount alone is already a load which is too high for the urban surface water to cope with. Moreover, next to the external sources there are internal sources as well such as up-whirling from water bottoms and animals. Thus, for a closed water system to be possible a number of things should be changed. Therefore, various factors of influence should be evaluated. Influence of surface water area Often the argument is heard that a large percentage of surface water percentage leads to better water quality. This argument comes mainly from the fact that more surface water leads to more storage and as a result less water from ‘outside’ has to be supplied. However the improvement of water quality is only true if the quality of the supplied water is worse than the quality of the urban water system. Besides, more surface water also leads to a lower hydraulic load, which decreases the permissible load per square meter on the surface water. Therefore, the benefits of increasing the surface water percentage are limited as the following graph shows.

Acceptable load of phosphorus

0

0,5

1

1,5

2

2,5

3

3,5

0 10 20 30

surface water percentage

Acc

epta

ble

load

(10%

sur

face

w

ater

=1)

W totalW per m2

Figure 6-21: Acceptable load of phosphorus as a function of surface water percentage Influence of water depth If water depth increases the acceptable load also increases; the Vollenweider formula also indicates that relation. However, increasing the depth further has a negative impact on other relevant factors such as light entrance and contact area. These are important parameters for degradation of biodegradable matter.

Figure 6-22: Influence of water depth on phosphorus load

Acceptable phosphorus load vs. water depth

00,20,40,60,8

11,21,4

0 1 2 3 4

Depth (m)

Phop

horu

s lo

ad (g

/m2/

y)

W



Optimal solution and implications for design Both the surface water percentage and the water depth only have a very limited positive influence on the acceptable phosphorus load. Therefore, there are two main solutions left:

�� Reduction of internal and external waste load �� Increase of purification efficiency

For the reduction of internal and external waste load the measures are roughly the same as for BOD load namely, maintenance (dredging) and influencing human behaviour. Improvement of purification processes in the future could be realized by for instance a Membrane Bioreactor or sand filtration. The ultimate goal is to lower the effluent concentration to Max. Allowable Risk levels. Kiestra et al. researched the efficiency of sand filters and membrane bioreactor. (H2O 23.2004) The total phosphorus concentration is 0.5 g/m3 for sand filtration and 0.3 g/m3 for MBR. In the future it will possibly be 0.2 g/m3. For the calculation, the following measures are taken:

�� Increase of surface water percentage from 10 to 15% �� Improvement of effluent quality of wastewater treatment by additional purification steps

from 1.8 g/m3 total phosphorus to 0.2 g/m3 phosphorus. However, this improvement is only necessary if all effluent is discharged on the urban surface water and for water use this would not be necessary. Only a small amount is needed during dry spells; consequently less improvement of wastewater treatment purification could be sufficient as well.

�� Improvement of discharge quality from infiltration facilities, for example by additional reed bed filters and settling basins. Efficiency is 85%.

If these measures are taken, discharge of wastewater to the urban surface water system is possible, as the next calculation indicates:

The total load W1 is: W1 =94.5*103*0.2/42.9*103= 0.44 g/m2/y If the efficiency of infiltration is increased to 85% the total load W2 becomes: W2 = 111.5*103*0.7*0.15/42.9*103= 0.28 g/m2/y The total load Wtotal is Wtotal= 0.72 g/m2/y The acceptable load is: a=2 m Qtotal= 113*103 m3/y A= 42.9*103 m2

Hydraulic load q= Q/A= 2.63 m/y � = 0.15 g/m3

for phosporus

22.63*(1 )

0.15 2.63W

� �

W= 0.74 [g/(m2*y)



6.3.4 Nitrogen management For nitrogen there is the following emperical relation ( Van Mazijk, 2003, CUWVO, 1987):

0.42[( ) ]( ) 2,06*

1i N

N T�

� �

�

( )N� = Nitrogen standard 2.2 g/m3 ( )i N� = Average nitrogen concentration incoming flow T = Residence time

This formula is based on measurement and does not explicitly take into account al relevant factors, such as internal nitrogen load. Besides, leaching from soils which where used for agriculture and the condition of the water bottom can also play a role. The external total nitrogen load The total volume of runoff from the urban area is

Qtotal= 111.5 *103 m3/y (see table 6.12) The average concentration nitrogen is 3 g/m3 (Estimation based on table 6.18) Of this amount 50% is removed by infiltration

�� The total volume of wastewater discharge is

Q= 94.5*103 m3/y The average concentration of nitrogen is 13.5 g/m3

�� The total load of direct deposition by rainfall to the surface water (10%) Q= 215*103 *0,1 = 21.5*103 m3/y The average concentration is 1.5 g/m3

To estimate whether or not the estimates are realistic, they can be compared by the so-called integrative approach of Lerner (2003). For the city of Nottingham he performed a research on the nitrogen load to the city. The total load per hectare is 21 kg/ha/year due to various sources. Transfer of these results to other cities is done by reduction factors for land use and soil conditions. In this case a reduction of 25% for the absence of industry is applied. Thus, the estimate should be near 16 kg/ha/y. The total nitrogen load (minus the load from the wastewater, because in Lerner’s study there is no wastewater disposal onto the urban surface water) according to the estimates above is: W= (111.5*103 m3*3g+21.5*103 m3*1.5 g)/28.6 ha. W= 13 kg/ha/y The estimated load is in the same order of magnitude. The estimation is used to make a calculation of the water quality.



Factors of influence According to the empirical formula on the former page there are two ways to influence the resulting average concentration.

�� Increase of residence times �� Decrease of concentration of pollution

Increase of residence time is possible by increasing the surface water percentage or depth. Decrease of concentration of pollution can be accomplished by increasing the efficiency of the wastewater treatment plant by additional purification steps. The concentration of nitrogen can be reduced from 13.5g/m3 tot 3 g/m3 (Kiestra et al, 2004) The internal load is not taken into account, but plays a role as well. Attention should be paid by keeping the internal load as small as possible by measures which where discussed in paragraphs before. Optimal solution and implications for design The following measures are taken which comply with the phosphorus measures from the former paragraph:

�� Increase of surface water percentage from 10 to 15% �� Improvement of effluent quality of waste water treatment by additional purification

steps 13.5g/m3 tot 2.5 g/m3 nitrogen, the same remark which was made for phosphorus management should also be made here: this improvement is only necessary if all effluent is discharged to the urban surface water.

�� Improvement of discharge quality from infiltration facilities, for example by additional reed bed filters and settling basins. Efficiency is 85%.

The average concentration is

111.5*1.5 94.5*13.5 21.5*1.5( )

113i N��

�

( )i N� = 13 g/m3 T=V/Q=28,6*103 *2/ 113*103 =0.51 year The resulting average concentration is

0.42[13]( ) 2,06*1 0.51N� �

�

( )N� = 3.5 g/m3

This is above the standard of 2.2 g/m3, so measures should be taken.



6.3.5 Heavy metals management In contrast to nitrogen and phosphorus, for heavy metals no empirical standards are available for the acceptable load on surface water. However, by estimating both pollution loads and purifying capacities; design principles can be derived to keep the concentration of heavy metals low in urban surface water. Metal pollution can be controlled by source measures especially for building materials. Sources In paragraph 6.3.1 a table has been shown with average figures of heavy metal concentrations in urban runoff. Although, these figures give a general idea, they provide no information about the origin of pollution, which can be anything from traffic, building materials to effluents or direct deposition. On national scale these figures are known, unfortunately those figures are not specifically for urban areas. Table 6-21: Pollution sources on national scale (Water in Data, 2004)

111.5*0.45 94.5* 2.5 21.5*1.5*1.5( )113i N�

� �

�

( )N� = 2.97 g/m3 The resulting average concentration is

0.42[2.97]( ) 2,06*1 0.51*1.5N� �

�

( )N� = 1.74 g/m3 This concentration is below the MTR standard



These national figures provide an idea of the main polluters and which are less important. Based on the table distinction can be made into the following groups.

�� Direct pollution is main source �� Effluent is main source �� Leaching is main source

In the first group are arsenic, chrome and copper. Direct sources are industries, which dispose pollutants to the surface water. For these sources, the most appropriate thing to do is preventing them in the urban area. If prevention is not possible, the two networks strategy (Tjallingii, 1995) ‘from clean to dirty’ can be applied to this group of pollutants. In that case pollution sources should be located at the end of an urban watercourse; by which the main part of the urban water remains clean.

Figure 6-23: Strategy of the two networks (Tjallingii, 1995) In the second group are antimony and mercury, for this group, effluent from wastewater treatment plants are the most important sources. Possibilities for preventing heavy metals in urban surface water are: improving purification processes or applying a settling basin where heavy metals can by absorbed by organic particles or clay particles. In the third group are cadmium, zinc, nickel and lead. For these substances the main source is leaching from agricultural areas. For urban areas it means that, depending on the local situation, inflow of water should be prevented from agricultural areas with high concentrations of these metals. If inflow of water is nonetheless necessary, measures should be taken, for instance purification by a settling basin or a reed bed filter. In the city itself there are sources as well of these metals, for example traffic and zinc gutters. Naturally, pollution from these sources should be prevented as much as possible. Purification In chapter 6.3.1, it has been mentioned that by use of infiltration facilities, reed bed filters and settling basins, purification efficiencies up to 90% are possible. Therefore, if source prevention is



not possible, applying these facilities can reduce pollution to urban surface water, immensely. Maintenance of these facilities is important because metal pollution does not disappear; it accumulates in the purification facility. By TNO-MEP (2002) research has been done on accumulation of metals in infiltration facilities; risks for groundwater pollution are very limited. Only after hundreds of years, saturation of the top 30 cm takes place. Nevertheless, some maintenance by periodically scraping off the top layer is required for these facilities. Also the PH should be maintained above 7 to prevent an increased solubility of metals. Reed bed filters need maintenance as well; gathering of reed should be done every year. Settling basins should be dredged to remove pollutants and preserve their purification efficiency. The optimal solution and implications for design The following principles should be applied to reduce the levels of heavy metal pollution in the urban area.

�� Prevention of pollution by not using certain building materials, for example copper roofs and zinc gutters.

�� Prevention of pollution by not supplying polluted water from agricultural areas. �� Purification of polluted runoff by infiltration, reed bed filters or settling basins to remove

up to 90% of the total heavy metal pollution. �� Application of the strategy of the two networks if source prevention is not possible.

6.4 Water nuisance In chapter 2 the water quantity functions were discussed and it was stated that the main functions of storage and discharge are to limit certain water levels to a certain frequency. In chapter 3 water nuisance problems in urban areas were evaluated further; the simplified structure of water nuisance problems was presented with three ways to tackle water nuisance problems: to adjust water levels to the demands of the city, to adjust the city to occurring water levels and to influence the perception of inhabitants on water nuisance. The first two elements will be considered in this chapter on water nuisance. The last element will be considered in the chapter about implications of future water systems. However, at first, precipitation will be discussed.

6.4.1 Precipitation STOWA (2004) presents new statistical figures for precipitation in the Netherlands that are based on the period 1906-2003. These new figures replace the old figures, which were based on the period 1906-1977. The following table presents these figures for De Bilt. Table 6-22: Rainfall quantities for various return periods and durations.

Return period T

4 hours (mm)

8 hours (mm)

12 hours (mm)

24 hours (mm)

48 hours (mm)

96 hours (mm)

1 21 24 27 33 41 52 2 25 29 32 39 48 60 5 31 36 40 47 58 71

10 36 41 46 54 65 80 20 41 47 52 61 73 89 25 43 49 54 63 75 91 50 49 56 61 71 84 100

100 55 62 68 79 92 109 200 61 69 75 87 101 118 500 71 79 86 98 113 130

1000 78 88 95 108 123 140



These figures result from statistical operations and should not be regarded as figures which are absolutely certain. Especially for higher return periods, fewer data are available which results in more uncertainty. The next table shows the 95% confidence intervals of table 6.22. Table 6-23: The 95% confidence interval of figures from table 6.25

Return period T

(years)

4 hours (mm)

8 hours (mm)

12 hours (mm)

24 hours (mm)

48 hours (mm)

96 hours (mm)

1 19-22 23-26 26-29 31-35 39-44 50-55 2 23-27 27-31 30-35 37-42 45-51 57-64 5 28-34 33-39 37-43 44-51 54-62 67-76

10 32-40 37-46 41-50 49-59 59-71 74-86 20 36-47 41-54 46-59 54-69 65-82 80-98 25 37-50 43-57 47-62 55-72 67-85 82-102 50 40-60 46-67 51-73 60-85 71-99 87-115

100 44-71 50-80 54-86 64-99 76-114 92-131 200 46-84 53-94 58-102 68-116 80-132 96-149 500 50-106 57-117 62-126 72-143 85-160 101-175

1000 53-126 60-139 65-149 75-167 88-185 105-198 If a row from table 6.22 is plotted in a graph, the rainfall duration frequency curve appears; multiple rows give multiple curves for various return periods.

Figure 6-24: Rainfall depth duration curves for three return periods.

6.4.2 The urban water system To be able to determine which rainfall events are critical for ‘the Closed City’ more details are required. Therefore, a more detailed elaboration of ‘the Closed City’ will be given here.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50

time (hours)

Prec

ipita

tion

dept

h (m

m)

T=1 yearT=5 yearT= 50 year



Closed City water system layout The ‘Closed City’ urban water consists of two main components, the first component consists of water bodies. From the three main concepts which were presented at the beginning of the chapter, the circulation concept is elaborated further because this concept offers the best opportunities with regard to water quality. The second part of the urban water system, which has not yet been discussed, is the stormwater collection system. The following stormwater collection systems can be distinguished:

�� Sewer systems �� Street surface collection systems �� Infiltration facilities �� Drainage systems

An infiltration system, such as a wadi, offers good opportunities because the purifying capacity of these systems is favourable for water quality. However, stormwater should be transported to infiltration facilities as well, which can be done by street surface runoff collection systems, such as gutters. Street surface collection systems make water visible and restore the connection between water and the inhabitants. Moreover, such a system is usually cheaper than a stormwater sewer system. However, some gradient is required to make water transport possible, which can be a disadvantage, especially in flat Dutch polder situations. In the wadi, runoff infiltrates or is transported by surface runoff in case the wadi is saturated or the runoff intensity exceeds the infiltration capacity. A wadi system combines the advantages of infiltration systems and drainage systems and is therefore a promising technology for the Closed City. Wadis are most suitable if the permeability k=0.5m/day or higher, however from the point of water quality it is still useful to apply wadis in situation with low permeability soil types. Van de Ven (2004) presents the following guidelines on the design of wadi facilities:

�� Trench width is 4 meters on average �� Depth is about 0.4 meters �� Side slope is 1:4 �� Depth of the percolation trench below the trough is about 0.6 meters �� Width of the percolation trench is 0.6 to 1.0 meters

For the design the 1000 houses city schematisation is used, which was used earlier for the water quality analysis as well. The area of this city schematisation is 28.6 ha; which is 535*535 meters. Gutters collect rainfall at the street surface and transport runoff to the wadi, which is situated at right angles to the street. To start with, the dimensions of the wadi are determined. A percentage of 3% wadi surface leads to a total wadi area of 8600 m2, if the width is 4 meters, the total length is 2150 meters. The residential area can be subdivided further into street blocks, which consist of both public and private area, and on average have the same distribution of terrain types as the total city. The following picture shows a suitable urban water system layout that result from wadi dimensions and the subdivision in street blocks.



Figure 6-25: System layout of the closed city.

6.4.3 Demands on the urban water system To know which measures have to be taken, the demands on the urban water system should be made concrete. However, the quite rigid norm of T=100 year for inundation of urban areas, from the regional flooding standards (IPO, 2004) is not very useful for designing innovative urban water systems. After all, if such an inundation frequency is desired, depends on (1) the function of the inundated area, (2) the building technology and (3) the perception of inhabitants. For instance, if a park has been designed in such a way that it is inundated every year for a short period, probably not many people would object. Using the standard of T=100 year for the design of this park by installing pumps and additional drainage capacity, would be very costly and would also accelerate rainfall runoff processes, which is not desirable. Another example of a situation where the regional standards would not be very useful, is a residential district, which is designed to handle various water levels, for example by using floating houses. It is therefore better to design resilient systems which deliberately locate inundation to certain areas by a well designed urban landscape and urban water system. Level differences in the urban terrain can play an important role in this respect. The same can be said about sufficient storage capacity; the next paragraph will present more on storage and discharge capacity.

6.4.4 Design of storage and discharge capacity In principle, there are two ways to cope with water excess in a water system; either the water is stored or it is discharged from the water system. However, in designing closed water systems a problem occurs: one can only speak of discharge if a water system is not fully closed. If all water is kept within the urban area the only choice, which is left is where to store the water. Surface water is often used to store water, however one can think of other possibilities as well, such as:

Wadi

Pumping station

Street block

Canal

535 m



�� Subsurface storage �� Storage at flat roofs �� Storage at green roofs �� Storage at street surface and terrain depressions

Storage in the subsurface is especially suitable in areas with well permeable soil and a low phreatic groundwater table. These types of areas are found in the eastern and southern part of the Netherlands. Infiltration facilities or permeable pavements can be used to infiltrate water in the subsurface. A positive effect is the fact that the amount of surface water that is needed decreases. As a result more space can be used for other purposes. Moreover, the natural water storage is filled; water depletion is prevented, as well as high surface water levels and erosion that could occur if runoff would be transported by canals. In the lower parts of the Netherlands infiltration and storage in the subsurface can be useful as well. Although groundwater levels are generally high and the permeability of the soil is generally low, infiltration is useful for water quality purposes. For water quantity aspects, additional surface water storage is needed. Storage at flat roofs is possible as well: the initial precipitation loss is about 2 to 4 mm, even without extra provisions for storage (Van de Ven, 2004). As a result, the peak runoff discharge is delayed and tends to be lower. However, attention should be paid to the strength and stability of the construction and the maintenance of roofs to prevent accumulation and leakages. A drawback is the fact that the stored volume on flat rooftops will eventually be lost in evaporation; as a result, this amount of water cannot be used for household purposes or other purposes. Storage at green roofs can also be used in water systems. In the soil on top of the roofs an amount of water can be stored and the delay time of green roofs is considerable in case of short, high intensity events. Other advantages are in the field of energy conservation, experience value and water quality (purification capacity of green roofs). However, by evapotranspiration, green roofs use a lot of water, which is not beneficial for the feasibility of the Closed City. After all, less water is available for other purposes. Storage at street surface takes place in ponds and small depressions. In literature values are found between 0.5 and 1.5 mm (Van de Ven, 2004) By designing level differences, using a small terrain gradient and lengthen the runoff route, storage on the street surface can be increased. In the paragraph about influencing the rainfall runoff relation, more attention will be paid to this aspect. Determining the amount of required storage The method that is applied most frequently to determine the amount of required storage in relation to the discharge is the method based on rainfall duration curves. This method is not correct as it disregards initial conditions, the shape of the rainfall event and uses the total precipitation amount instead of the net precipitation amount. However, the method is suitable to obtain a general idea of the amount of storage and discharge that is needed. Moreover, in a system with a low discharge and high storage, as the Closed City is, the error which is introduced by the shape of the rainfall event, is low because eventually the main part of the rainfall volume is to be stored anyway. On the other hand, the error that is made by neglecting initial conditions does play a role. How large is discharge in the Closed City? Strictly speaking the discharge is zero but some water does leave the water system. The first outflow from the water system is evaporation; the second is water use for household purposes. The third flow is the water surplus, however this amount is very small, about 4% of the first two components and therefore not included in the graph.



However, it should be mentioned that household water use is only an outflow component if wastewater is transported out of the urban area. Both flows are mentioned in table 6.12, and both flows are in the order of magnitude of 1 mm/d. In the rainfall duration frequency graphs, the following curve appears.

Figure 6-26: Rainfall duration curve with water use and evaporation A broad perception of the Closed City If the resulting outflow discharge is placed in a rainfall duration graph, it appears that there is no point where the discharge line and the rainfall duration curve are parallel, which means that the required storage is not within the reach of the graph. For both return periods this is the case. Two methods are available to cope with this problem: either very large reservoirs can be installed or pumping capacity should be installed. The second option seems most logical, although strictly speaking one can no longer speak of a Closed City. However, this should not be seen as a problem, in a more general way, the Closed City is a city that has no adverse effects on its surroundings. If the Closed City discharges water to water to the surrounding area in exceptional circumstances, it does not necessarily lead to problems in that area. The other way around, the Closed City has by its large storage capacity, the ability to accommodate water nuisance problems from surrounding rural and urban areas as well. Especially in case of high intensity-short duration events this would be useful. By installing pumping capacity in the ‘Closed City’, adjacent water systems and the Closed City can have mutual advantage by shifting problems on purpose to a place where it causes no problems. This approach can be regarded as a real integrated approach. A feasible combination of storage and discharge Pumping capacity can be installed to discharge water from ‘the Closed City’. For instance, a small pumping capacity of 1 m3/minute (0.6 l/s/ha) leads to a required storage capacity of 73 mm for a return period T=50, as the next graph indicates. This means that this amount of storage has a probability of being exceeded of 1/50 per year. Remarkable is the fact that the critical time from the graph is 4 days, this is entirely different from most current water systems that have response times which are very short.

0

20

40

60

80

100

120

140

0 50 100 150 200

Time (hours)

Prec

ipita

tion

dept

h

Depth duration curve T=50 yDepth duration curve T=10 yWater use+ evaporation



Figure 6-27: Rainfall duration curve with water use, evaporation and additional discharge The required storage capacity can be realized in various ways, as has been stated before. Groundwater storage is to be preferred because it costs no additional space and infiltration has a beneficial effect on water quality. However, in the typical Dutch polder city subsurface storage is hardly possible during wet periods, in such a case a possible combination could be:

�� Storage on roofs and street surface: 3 mm �� Storage allowable water level rise 70 mm

(For instance: Inundation area 15%, allowable waterlevel rise 500 mm.) The inundation area consists of both surface water and area that is suitable for inundation such as parks. An important point of attention is the fact that the additional level fluctuation for a critical design situation should be taken on top of the seasonal level fluctuation that occurs every year. Therefore, 0.5 m level fluctuation should be available compared to the winter surface water level. In practice, the exceeding frequency will be lower than the precipitation event frequency that has been used in the design. After all, a design precipitation event will not always coincide with the most unfavourable starting condition. The resilience of the water system is further increased by a freeboard that results from appropriate design of parks next to the circulation channel. The total level difference is calculated as follows: Level difference= Seasonal level rise + critical level rise + freeboard In this example: Level difference= 0.1+0.5+0.3= 0.9 meters. A typical value for level difference in new residential districts is 1.2 meters, consequently, it can be concluded that this concept does not lead to extraordinary level differences. However, an essential condition is the fact that buildings and infrastructure should be adjusted to resulting higher groundwater tables that will be caused by high surface water level during critical periods.

0

20

40

60

80

100

120

140

0 50 100 150 200 250

Time (hours)

Rai

nfal

l dep

th (m

m)

Rainfall duration curveT=50 yearDischarge line

Parallel discharge line

73 mm



Figure 6-28: Realisation of storage capacity by alternative water system design

6.4.5 Design of gutters and wadi The fact that sufficient storage and discharge capacity has been installed in the urban water system does not mean that water nuisance will not occur. For instance, if the stormwater collection system has not been designed adequately, inundation can occur because runoff is not transported to the storage channel. An important process in this respect is the rainfall runoff process; in an urban area precipitation is converted to runoff. This process is influenced by several factors which include soil conditions, terrain slope and lay out of the runoff collection system. Design situation In urban areas many processes play a role with widely varying timescales. For each of these processes, there are different design situations. For stormwater sewer systems, for instance high intensity precipitation events are critical, whereas for surface water systems, typically the total volume in a longer period is most important. Also for the design of culverts, the short duration events can be critical. To be able to design the runoff collection system of ‘the Closed City’ water system, it is important to know which events and which processes are determining. Time of concentration An important parameter that is related to the rainfall runoff process is the time of concentration. The time of concentration indicates the time, which is needed for the whole water system to contribute to discharge at the system boundary. If the time of concentration is larger, the probability decreases that during this whole period a high intensity of precipitation occurs. To illustrate this, figure 6.26 is represented in another familiar way: the intensity duration frequency curve.

Winter season water level

Critical water level

Additional freeboard

Circulation channel Park Park



0

2

4

6

8

10

12

14

4 8 12 24 48

Time (hours)

Inte

nsity

(mm

/h)

T=1 yearT= 5 yearT= 50 year

Figure 6-29: The intensity duration frequency curve From the figure can concluded that for longer precipitation events the intensity is much lower. This corresponds with what is expected; very intense rainfall events mostly have a short duration. It is beneficial if the characteristics of the urban water system result in slow processes, because in that case the time of concentration is larger and therefore also the design intensity for runoff collection systems is lower. The time of concentration for urban water system components can be very low, for instance in the order of minutes. This results a water system, which is very sensitive for short duration- high intensity events. Time of concentration of ‘the Closed City’ components What is the time of concentration of the Closed City components? Several formulae are available to calculate the tc, however all of them are very empirical, with coefficients that are by no means dimensionless. For instance, in many formulae the time of concentration goes to infinity as the terrain gradient goes to zero, which is not realistic. Transferring these formulae to an entirely different, not yet existing water system means that the results should be interpreted with some reservations. For example, the U.S. Federal Aviation Agency (FAA) assumes for paved surfaces:

1/ 2

1/3

3.260(1.1 )c

Lts

��

�

with tc = “time of concentration”(minutes) S = gradient [%] L = length of the longest flow path � = average runoff coefficient over the drainage stretch With this formula the tc of a street block (as defined in figure 6.25) can be estimated. The FAA formula has been derived for the rainfall runoff relation of airports but is used frequently for urban areas. The figures on terrain types of table 6.3 and discharge factors from table 6.8 can be used, because the calculation of tc is about a design situation. If the dimensions of a street block are 40*130 meters the following table shows the total runoff coefficient.



Table 6-24: Runoff coefficient of a street block

The average discharge coefficient of a street block is 0.41. Thus, for a peak event about 41% of the total precipitation volume results in runoff. The longest overland flow path, is the point which is the furthest from the wadi inlet point, in this case L=40+130=170 m. With street slope 1%, the time of concentration tc= 29 min. After this period, the whole street block contributes to runoff at the wadi inlet point. Design of gutters At the street surface, a gutter is constructed to transport water to the wadi. The time of concentration can be used to calculate design discharge and derive the dimensions of the gutter. The characteristic rainfall cumulative rainfall volume for half an hour with a return period T=25 year, is 28 mm, according to the old rainfall duration curves of Bouwknegt en Gelok (1988). these curves are used because the new standards do not provide data for short duration events. The resulting intensity i=28/29/60/1000=1.609*10-5 m/s. The expected discharge can be calculated by the rational formula:

i Q C A� � � with: Q = Discharge [m3/s] C = Runoff coefficient [-] i = Intensity [m/s] A = Contributing area [m2] The runoff coefficient of the contributing area is C=0.41, the total contributing area is 5200 m2, for both see table 6.26. Usually only the contributing paved area and the runoff coefficient of the paved area is taken into account. However, also non-paved area contributes to runoff, especially during critical events. Therefore, in this calculation all terrain types are taken into account. The resulting discharge is:

-5

3

0.41 1.609*10 52000.034 /

QQ m s�

�

� �

Terrain type [m2] C Weighted Average C

Roofs 1219 0.8 0.185 Paved area 1950 0.5 0.185 Green area 2031 0.1 0.040 Total 5200 0.41



Figure 6-30: Street surface runoff collection system One gutter with a width of 0.3 and a height of 0.2 meters is designed to transport runoff to the wadi, the total discharge capacity can be computed by the Strickler formula.

2/3 1/ 2Q k A R s� � � � with: Q = Discharge [m3/s] k = Strickler roughness [m1/3/s] A = Cross section [m2] R = Hydraulic radius [m] s = Slope of energy line [-] The Strickler roughness of the gutter is estimated to be 45 m1/3/s, the cross section is 0.06 m2, the hydraulic radius is 0.06 m and the slope is 0.01 in case of uniform flow. The resulting design capacity of the gutter is then:

2/3 1/ 2

3

45 0.06 0.06 0.010.041 m /

QQ s�

�

� � �

The dimensions of the gutter are sufficient, because the full capacity of the gutter is larger than the design discharge that can be expected if T=25 year. Design of wadi In the former paragraph the design discharge of the contributing gutters was calculated. To get a general idea of the design discharge of the wadi, the total design discharge of the wadi is calculated. Figure 6.25 shows that a maximum of 5 street blocks contribute to the wadi discharge, making the maximal wadi discharge, the rainfall on the wadi itself is neglected, because the wadi is only 3% of the contributing area. The design discharge of the wadi Q=5*0.038=0.2 m3/s. Guidelines for the design of wadis were already given; these guidelines could lead to the following dimensions: Length = 200 meter Through depth = 0.4 meter K = 30 m1/3/s Bed width B = 1 meter Side slope v:h = 1:4 Total width = 4.2 meters Bottom Slope = 0.3 %

0.2

0.3

Street surfaceGutter



Figure 6-31: Wadi dimensions During a critical event the storage capacity of the trench will be full, consequently water flow will be mainly in the through. The program Profile can be used to calculate the resulting water depth by the Strickler formula. FILENAME : DATE : 02-10-2005 ________________________________________________________________________ Q h ks=(1/n) b m s n v T E m^3/s m m^1/3/s m (v:mh) 10^ -3 (b/h) m/s N/m^2 W/m^3 ________________________________________________________________________ 0.20 0.23 30.00 1.00 4.00 3.00 4.35 0.45 6.76 13.35 ________________________________________________________________________ The results give h=0.23 m and v=0.45 m/s. This is below the wadi depth of 0.4 meters, thus the dimensions of the wadi are sufficient.

6.4.6 Influence rainfall runoff process The rainfall runoff process can be influenced by the urban design. By doing this, the time concentration can be increased, which results in lower design intensities and consequently smaller gutters and wadis. An important remark in this context is the fact that changing the rainfall runoff process has not much influence on the discharge and storage capacity of the total water system. For those aspects the total volume of runoff is most important, as stated before. Consequently, advantages of a higher time of concentration in the Closed City are limited to smaller wadi and gutter dimensions or a lower exceeding frequency of wadis and gutters. Naturally, in existing urban water system the situation is entirely different; in such a situation increasing the time of concentration can decrease the load on the sewer system and reduce sewer overflows. To change the rainfall runoff process, two methods are available: changing the runoff route or changing the rainfall runoff transformation by using other terrain types.

0.3

1.0 1.6 1.6

0.4

0.4

Trough

Trench



Changing the runoff route The time of concentration can be increased if the runoff route is increased by the lay out of the water collection system, for instance by making another street layout. The following figure indicates the influence of lengthening the flow path on the time of concentration.

Figure 6-32: Influence of overland flow length on time of concentration Changing the rainfall runoff transformation Runoff coefficients are used frequently to calculate the percentage of precipitation, which is converted to runoff. Because of the following reasons not the complete volume of precipitation will be converted to runoff.

�� Interception losses �� Infiltration �� Storage at the terrain surface �� Evaporation

Runoff coefficients describe the percentage of precipitation that is lost as a result of these processes. In case of runoff coefficient, the loss percentage is assumed to be constant, which is a wrong assumption. Starting conditions influence the runoff coefficient, for instance it is very important if the storage capacity is empty or full at the beginning of a rainfall event. Moreover, the size and shape of the rainfall event influences the runoff coefficient as well. However, for comparing measures the runoff coefficient is useful, because the goal is not to describe the process as accurately as possible but to compare situations and calculate the effect of measures on the rainfall runoff relation. Use of rainfall coefficient provides insight in these effects. Runoff coefficient can be influenced in various ways, table 6.26 in the former paragraph showed that the runoff coefficient of the street block is 0.41. About 41% of a critical rainfall event ends up as runoff at the wadi inlet point, the rest in lost as a result of processes that were mentioned at the beginning of this paragraph. The following measures can be used to decrease the runoff coefficients:

�� Application of green rooftops and flat roofs �� Use of permeable pavement

05

101520253035404550

0 100 200 300 400 500

Overland flow length (m)

Tim

e of

con

cent

ratio

n (m

in)



Green rooftops and flat roofs In chapter 3, green rooftops were mentioned as an opportunity to slow down runoff processes and reduce peak discharges. The discharge coefficient of a conventional sloping roof is 0.9. In Germany extensive research has been done on the performance of green rooftops on the discharge coefficient. Rüngeler (1998) presents the following figures: Table 6-25: Runoff coefficient of green rooftops

Author C [-] Delay time [min]

Total thickness, roof coverage [m]

Roof Slope [ 0]

Event Duration [min]

Precipitation Intensity [mm/h]

Kolb(1987) 0.47-0.95

5 0.12 0 15 80

Diestel (1997) 0.44 15 0.05 Unknown 20 76 Diestel (1997) 0.24 30 0.12 Unknown 20 76 Kaufmann (1998)

0.72 5 0.1 2 5 90

Kaufmann (1998)

0.37 60-120 0.1 2 20 31

Liesecke (1998)

0.2 unknown 0.4 2-3% 15 120

The table shows that for short duration- high intensity events the reduction of runoff is considerable. These events are often the critical events in urban areas, if a conventional sewer system is used. However, the Closed City is not such a conventional system. Furthermore, the figure indicates the influence of the roof thickness, which is large. Besides, most cases in the table above are about a flat or almost flat roof, which influences the results as well. The German study gives runoff values for the water balance at a yearly timescale and seasonal timescale as well, (s) refers to summer half year, (w) to winter half year and (y) to the yearly average, as the next table shows. Table 6-26: Runoff coefficient on a yearly timescale of green rooftops (Rüngeler, 1998)

Author C [-] (s=summer, w=winter, y=year)

Total thickness, roof coverage [m]

Slope [ 0]

Liesecke (1998) 0.2-0.35 (s) 0.65-0.7 (w)

0.06-0.15 1.1-1.7

Lösken (1991) 0.35-0.45 (s) 0.7-0.8 (w)

0.02-0.06 Unknown

Schmidt(1992) 0.21-0.3 (y) 0.11 12

Kaufmann (1998) 0.66 0.1 2



From this table can be concluded that there is a large seasonal influence; during summer the green rooftops reduce the peak volume of runoff a lot more than in winter conditions, probably due to the fact that the average filling percentage of the storage capacity is lower in summer than in winter. Green rooftops work for both short intense rainfall events and at a yearly timescale. However, nothing can be concluded from the tables about low intensity events with a long duration; probably the storage capacity will be full and the reduction of peak volumes will be a lot lower in that case. Guidelines about discharge from green rooftops are given by DIN (1986), which present the following runoff coefficient for peak events. Table 6-27: Runoff coefficient standards for green rooftops

C Green rooftops, intensive vegetation 0.3 Green rooftops extensive vegetation, thickness>0.1m 0.3

Green rooftops, extensive vegetation, thickness<0.1 0.5

Based on the tables above, it seems realistic to assume that the runoff coefficient for roofs in table 6.26 can be reduced from 0.8 to 0.6 by applying well-designed green rooftops. Instead of sloping roofs, flat roofs can be used as well. The runoff coefficient of this kind of roofs varies between 0.5 and 0.7. Permeable pavements Permeable pavements can help to reduce peak runoff considerably. The amount of reduction depends heavily on site-specific factors like soil type and the groundwater table. In literature a variety of runoff coefficients are mentioned for permeable pavements. An American study by Clausen (2003) gives a runoff coefficient for permeable surfaces of 0.24. Another American study (EPA, 2000) on the infiltration behaviour of parking lots indicates a runoff coefficient of 0.2 if the permeable pavement is combined with grass strips between parking places. Cao et al (1998) report a runoff coefficient of 0.15 to 0.25, depending on the terrain slope. Combining these figures, it seems realistic to use a runoff coefficient of 0.25 for permeable pavements. However, a well permeable underlying fill material should be used or a drainage system should be present in case of soil types with a low permeability. Optimal solution and implications for the design With all these measures, which were mentioned on the former pages, the peak volume of runoff will decrease considerably. The same calculation of table 6.24 can be made again. By applying a combination of measures, such as green rooftops and flat rooftops the runoff coefficient from roofs will decrease to 0.6.



Table 6-28: Runoff coefficient for closed city Terrain type [m2] C Weighted

Average C Roofs 1219 0.6 0.14

Paved area 1950 0.25 0.094

Green area 2031 0.1 0.040

Total 5200 0.27 The table shows that by implementing the measures which where mentioned before, only 27% of the total precipitation volume of the peak event ends up as runoff which is a reduction of more than 30% compared to the first calculation. Concluding, applying these measures has a significant effect on peak reduction and consequently smaller gutters and wadis are needed. Moreover, beneficial effects on runoff quality also take place by settling, infiltration and absorption processes. In particular for green rooftops another benefit is energy conservation. A disadvantage is the fact that green rooftops use a lot of water, which can no longer be used for other purposes. For the feasibility of the Closed City with regard to water use this is not favourable.

6.4.7 Design of drainage No attention has been paid yet to water nuisance from groundwater. In this chapter the possibilities to prevent groundwater nuisance will be evaluated. To prevent groundwater related problems often drainage capacity should be installed in the urban area. Although discharge facilities and wadis have a draining function, in many cases additional drainage capacity will be required. The Closed City causes both groundwater and surface water to fluctuate; therefore the buildings should be adjusted to fluctuating water levels anyway, for example by making constructions without crawlspaces. However, the groundwater level should not be structurally high. Especially for vegetation this is very unfavourable, because the root zoon has no chance to develop well. Drainage depth A drainage depth that is often applied in urban areas during the habitation phase is 0.7 m in combination with a steady drainage capacity of 5 mm/day. However, in the Closed City different groundwater levels could be designed for different areas and functions. Depth of the drains Another important parameter in the design is depth positions of the drains. This position is mainly determined by other subsurface infrastructure such as electricity lines and gas pipes. Because of this, subsurface drainage pipes are preferably situated at a minimum of 1.2 meters below terrain surface level. If the drainage pipes discharge to the surface water, which is often the case, this also determines the relative level difference between surface water and terrain level. For steady state drainage computations the formula of Hooghoudt is used.

21 2

2

8 4K dh K hqL�

�

K1 = permeability below the surface water level



K2 = permeability above the surface water level d = equivalent depth from the drain to the impervious layer q = discharge h = bulging of groundwater between two drains L = distance between drains A drainage calculation can be made for the Closed City if assumptions are made for some parameters. For instance: Drainage depth = 0.7 m Depth of the drains = 1.8 m Discharge = 5mm/day K1=K2 = 0.5 m/day Pipe diameter = 0.2 m Depth impermeable layer = 8 m Substituting these values in the Hooghoudt formula gives the following result:

2 880 484L d� � By iteration and using the tables of Hooghoudt (1940) the required pipe distance can be derived. Eventually this leads to L=56 m with equivalent depth d=3.0m. Other aspects of drainage Attention should be given to other aspects of drainage as well. The wrapping material should be well chosen, to prevent washing in of soil particles that can eventually lead to a low efficiency of the drainage system. The second reason to use wrapping material is to make groundwater flow into the drain possible. The O(90) value is an important parameter for the selection of wrapping material; it indicates the characteristic soil particle diameter for which 90% of those soil particles remains on the wrapping material. The O(90) value is generally efficient if it is chosen between 0.4 mm and 1.1 mm, if the groundwater contains a lot of iron, the O(90) should be between 0.7 and 1.1 mm. (Van de Ven, 2004) Another important aspect is the maintenance of drainage. To keep the drainage system efficient, maintenance by flushing or rodding is needed. To be able to do maintenance, it is important to design the drainage pipes in such a way that they are accessible and can be found easily. In most cases, maintenance should be carried out once per five year.

6.4.8 Variation of level difference and inundation frequencies In the Closed City not all areas need to have the same drainage depth and inundation frequency. Therefore, stationary drainage standards for the whole urban area, and inundation standards for the whole urban area are not very useful. By definition, surface water levels will fluctuate in the Closed City, consequently the level difference will fluctuate and thus the drainage capacity and groundwater level will fluctuate as well. This situation is entirely different, perhaps almost opposite, to current water systems, which are focused on keeping the water levels at the target level. In the Closed City water nuisance can be located deliberately located to green areas, by situating them lower or near surface water. Figure 6.28 is an example of this approach. By creating slopes near gutters, the resilience can be increased, as figure 6.33 shows. Besides, drainage capacity calculations as in the former paragraph can be varied per terrain type as well.



Therefore, varying level difference and inundation frequencies is a promising concept to realize the Closed City in practice.

6.4.9 Make use of adjusted building technology Making use of adjusted building technology is crucial for the realisation of the Closed City. To start with, building must be able to cope with fluctuating groundwater and surface water levels in the Closed City. As a result, buildings without crawlspaces and well-designed foundation structures are required. Watertight floors and preventing accumulating of moisture in walls are very important to guarantee the living quality in the Closed City. Another opportunity is the realisation of floating houses that makes combination of storage and housing possible. By applying these structures, the resilience of the Closed City can be improved further compared to figure 6.28, as the following picture shows.

Figure 6-33: Increasing storage capacity by applying adjusted building technology

6.5 Concluding remarks The purpose of this chapter was to make a design and investigate the technical feasibility of an ideal future urban water system that would not have adverse effects on its surroundings, such as water depletion or pollution emissions. Such a city is symbolically called a ‘Closed City’. The following conclusions can be made: Water use

�� Effective rainfall is enough to compensate water use in the Closed City, however there are a number of conditions.

�� The city has a separate sewer system or a very high stormwater infiltration percentage (87%).

�� The city has a low housing density: 30-35 houses/ha. �� External surface water supply must be possible for extremely dry circumstances or large

inter-annual reservoirs are required. �� Best solution seems however to lead a part of the wastewater treatment effluent back into

the urban surface water system during dry spells. �� Demand management can increase the robustness of the Closed City during dry spells.

Water quality �� The circulation concept offers good opportunities to reach water quality standards.

Floating houses

Additional storage capacity



�� It is possible to discharge back all effluent to the Closed City, under the following conditions.

�� Self-purifying factor k1 of the water system must be increased to 0.25 d-1, which could be accomplished by the use of reed bed filters in surface water. The morphology of the urban water system should be such that growth of aquatic vegetation, which increases both the contact area for degradation and oxygen production, is possible.

�� Oxygen demand of the bed sediment should preferably be decreased to 1.2 g O2 (m2*d). This is a rather low value; whether or not it is possible to accomplish this value depends on site-specific factors.

�� Further improvement of wastewater treatment processes has a negligible influence on the oxygen concentration, however for the nutrient balance, improvement of these processes remains important.

�� Improvement of discharge quality from infiltration facilities, for example by additional reed bed filters and settling basins. Efficiency of nutrients removal should be 85%.

�� Prevention of heavy metal pollution by not using certain building materials as copper roofs and zinc gutters and preventing supply of polluted water from agricultural areas

�� Application of the strategy of the two networks if source prevention is not possible. �� Purification of polluted runoff is needed for instance by infiltration, reed bed filters or

settling basins to remove up to 90% of the total heavy metal pollution. �� To guarantee the water supply of the Closed City it is not necessary to discharge back all

effluent, on the contrary, only a part is needed during dry spells.

Water nuisance �� The total amount of required storage is 73 mm, how this amount of storage should be

realized, varies from place to place. In polder areas surface water will be needed, while in cities on sandy soils subsurface storage can be used. Some pumping capacity is required to discharge water excess during long periods with a very large amount of total precipitation.

�� Runoff collection by a wadi system and street surface runoff transport combined with sufficient storage capacity, offers good opportunities to purify water and keep water within the city borders.

�� The Closed City has the ability to accommodate water nuisance problems from the surrounding area that result from short duration events.

�� Buildings and infrastructure should be adjusted to fluctuating groundwater that will be caused by high surface water level during critical periods.

�� Increasing overland flow length, using permeable pavements and green rooftops lead to a larger time of concentration and consequently to smaller dimensions of the runoff collection system. However, these measures are not useful to decrease the required amount of storage in the Closed City.

�� Flat rooftops, green rooftops, street surface storage and surface water storage increase evaporation and therefore decrease water availability for water use. Subsurface storage decreases evaporation and increases water availability.

�� Instead of maintaining target levels which is done is current water systems, the Closed City is characterized by managing fluctuations and adapting the city to fluctuations for example by variation of terrain level.



7 Future Water Systems: ’the Two Layer City’ Scope and purpose of this chapter In the former chapter ideas were presented for a city with a strongly reduced water supply compared to the current situation. This chapter investigates if the same can be done with energy supply, therefore another future water system: ‘the Two Layer City’, will be presented. The Two Layer City is a city that makes use of the watersystem to save energy.











7.1 Energy conservation In chapter 3 the use of groundwater was mentioned as an opportunity for energy conservation. Heat pumps can be used to extract heat from the groundwater for household purposes. This application has a number of benefits: first, no combustion is needed for heating houses, only the operation energy of heat pump is needed, which is lower than the conventional energy use. Second, as energy prices are rising this ‘free’ source of heat is becoming more interesting. In the Netherlands the demand for heat exceeds the demand for power by a factor 6 (Oostendorp, 1997) and exactly for supplying heat, groundwater is very suitable. Heat is lowly valued energy source, lowly valued in the sense that only a small part of the energy can be converted into work. On the contrary, electricity and gas are highly valued energy sources because a large proportion can be converted into work. The Carnot process defines the amount of energy, which can be transformed into work. Heat engines transform heat into work, however not all heat can be transformed into work; a part is left as heat as well. The efficiency is lower if the flux of heat, which remains after the transformation into work, is large. The Carnot efficiency is defined by the following formula.

1 cCarnot

h

QQ

� � �



With Qc is the heat flux to the cold side and Qh is the heat flux from the hot side. In an ideal situation there is no resulting heat flux and all the input heat flow is transformed into work; in that case the Carnot efficiency is 1. In the worst case, no heat flux is transformed into work at all and the output heat flux is as large as the input heat flux, in that case the Carnot efficiency is zero. The following picture shows the fluxes in a heat engine.

Figure 7-2: Schematisation of a heat engine From the viewpoint of efficiency, it is not sensible to use highly valued energy sources for purposes where low quality energy sources would be sufficient. Therefore, heat pumps can be regarded as a promising technology; a heat pump supplies lowly valued energy (heat from aquifers) to houses, consequently highly valued energy sources can be used for other, more useful purposes. However, a highly valued energy source, namely electricity is needed to operate the heat pump.

7.1.1 How a heat pump works A heat pump is just the opposite of the heat engine; it transforms work into heat while the heat flows from low temperature to high temperature as the following picture shows.

Figure 7-3: Schematisation of a heat pump Heat pumps are devices that transport heat from a place with a low temperature to a place with a higher temperature. By (thermodynamic) laws of nature this does not occur spontaneously; a comparison can be made with water, which does not flow from a low pressure level to a high pressure level in itself. To transport water from a low pressure level to high pressure level a water pump is needed, similarly, to transport heat from a place with a low temperature to a place with a

W

Qc Qh

Th Tc

W

Qc Qh

Th Tc



higher temperature a heat pump is needed. The most widely applied heat pump is the one in the refrigerator, this heat pump transports heat from a cold place (inside of refrigerator) to a warm place (room). The same principle can be used for heating houses with groundwater; heat is transported from the groundwater (12oC) to the house (20oC). The next picture gives a further elaboration on the heat pump.

Figure 7-4: System components of a heat pump (modified after Groen-Holland, 2004) In a groundwater heat pump, the evaporator would be situated in the aquifer. By evaporating the working fluid in the heat pump, heat is extracted from the groundwater, which is equivalent to cold being delivered to the groundwater. In the compressor the pressure is increased, as a result the temperature increases as well. At this point the working fluid, which is still in the gas phase, becomes suitable for delivering heat to, for instance, the floor heating system of the house. In the condenser the working fluid becomes liquid again by the condensation process. During the condensation process heat is being released which, at this point, is being supplied to the house. In the expansion valve the pressure is decreased, which leads to a fall of the temperature. At this point the cooling fluid is suitable again to extract heat from the aquifer by its low temperature and by evaporation in the evaporator. The same process can be used for cooling a building; in that case the process works the opposite way.

7.1.2 Types of groundwater heat pump systems There are two main types of heat pumps, open system heat pumps and closed system heat pumps. An open system is a system in which groundwater is pumped from an aquifer, heat is extracted from the groundwater by a heat pump and finally low temperature groundwater is infiltrated again in the aquifer. For these systems other permissions are required because water is extracted and infiltrated. A closed system is a system, which has a closed loop of pipes in the aquifer. Through this loop a working fluid flows that extracts heat from the aquifer. The closed loop can be both vertically or horizontally orientated. In a residential area the amount of space that is required for a

Cold delivery

Heat delivery

Expansion valve

Compressor

Condensor Evaporator



horizontal system, is often lacking. Therefore, in these circumstances a vertical system is most common. Another aspect that is important is the aspect of regeneration. If the same amount of heat is supplied to the aquifer as is extracted from the aquifer, it is often easier to receive permission for these facilities. In following paragraphs in this chapter will be evaluated if heat from surface water can be used for regeneration.

Figure 7-5: A vertical closed loop system (left) and an open loop system (Geoexchange, 2005; Duurzame energie, 2002)

7.1.3 Efficiency of heat pumps Heat pumps only need a small amount of energy for compressor operation and for pumping working fluid through the system. The advantage of heat pumps is, that the amount of energy that is used by the compressor is converted into heat as well. Because of this process, a heat pump supplies more energy to the house than the extracted amount from the aquifer. Moreover, the amount of delivered heat (extracted heat +compressor heat) is larger than the amount of energy that is needed to operate the heat pump (compressor operation energy). Consequently, the efficiency of heat pumps is larger than 100%. The efficiency of heat pumps is generally known as Coefficient of performance (COP), for heating of houses the COP is mostly about 300% to 400%. The theoretical COP is given by the following formula.

0

th TCOPT T

�

�

with: T = Temperature of heat supply point [oK] T0 = Temperature of heat extraction point [oK] The formula shows that the COP increases if the temperature difference is small. For this reason groundwater is a very efficient heat source in winter as it has a constant temperature of 11oC. Air on contrary, is less efficient because outside temperature is about 3oC or even lower. The same reasoning applies to the heat supply point. Floor heating (about 35oC) is much more efficient than



radiators (between 60 to 80oC). Moreover, low temperature heating systems are more comfortable and have health benefits, as they do not spread dust through houses as ordinary radiators do. In short: a heat pump works better if the temperature difference is low. In practice the real COP will be lower than the calculated theoretical COP, because energy dissipation and heat losses occur in the heat pump.

7.1.4 Working fluids In refrigerators for a long time Chloro Fluor Carbons (CFC), where used as working fluids.CFC’s have favourable thermodynamic properties; they have very suitable condensation and evaporation points and supply and absorb heat easily. However, CFC’s play an important role in deterioration of the ozone layer and have therefore been banned. Alternatives are Hydro Fluor Carbons (HFC’s) and propane, these substances have no adverse effect on the ozone layer but do still contribute to the greenhouse effect. Also water can be used as a working fluid, however major drawbacks are the low volumetric heat capacity (kJ/m3) compared to CFC’s and the fact that water freezes at 0oC. Especially for groundwater heat pumps this is unfavourable because very low temperatures can occur at the evaporator. For this reason mostly a water/antifreeze mixture is used for groundwater heat pumps. A new working fluid that is used is CO2, this working fluid offers good opportunities as high efficiencies can be achieved.

7.1.5 Heat pumps for residential use An average Dutch household uses 1575 m3 gas a year; this is equivalent with 52 GJ. Not all of this demand is useful energy; a part is lost by inefficiencies of the heating system. The useful demand is about 35 GJ if the efficiency of the heating installation is 70%. The main part of the supplied energy is used for heating of rooms and water. For new houses Energy Performance Standards have been formulated; a new house must have an Energy Performance Coefficient (EPC) of 1.0. An EPC of 1.0 means that only 28 GJ/year may be used for heating, 20 for heating of space and 8 for heating of water. Additionally, 12 GJ/year is needed for electricity. The next table presents an overview for a well-isolated house with EPC= 1.0. Table 7-1: Residential energy use if EPC=1.0 (Duurzame-energie.nl, 2004)

Unit Heat Electricity Energy use one house

GJ/y 28 12

Peak capacity KW 6.0 4.2 Off-peak capacity KW 0.25 0.2

In a situation where heat pumps are installed in houses, ideally no gas supply would be needed at all. All heat supply should be extracted from the aquifer and the operation energy of the heat pump. If the COP is 3.5: 1/3.5*28 GJ=8 GJ energy is needed to operate the heat pump. With this amount of energy an additional amount of 20 GJ is extracted from the aquifer and no gas supply for heating is necessary. The total energy use is only 12 GJ for electricity and 8 GJ for operation of the heat pump. Consequently, the total energy use is 20 GJ instead of 40 GJ in table 7.1, provided that the heat capacity of the aquifer can supply this amount of heat. It is expected that the EPC for new houses will be decreased further to 0.8 in 2007. Heat pumps can play an important goal in reaching these targets. Heat pumps, which are available on the market, can cover the whole demand for room heating. For this purpose a heat pump with a peak capacity of 6KW is needed. For heating water for showers, the heat pump can be used as well, but



the efficiency is lower because the required temperature lift is larger. A heat pump works best in a well-isolated house, because otherwise an additional heating device should be installed which makes the solution more expensive. A combination of measures are applied in the ‘Itho energy house’ (itho, 2004): heat pumps are combined with solar energy, heat pumps in the air conditioning, heat exchange system in the shower outlet and a high efficiency extractor fan. This energy house has an EPC which is lower than 0.5. The following picture shows the concept of the energy house.

Figure 7-6: The Itho Energy house (itho, 2004)

7.1.6 Applicability of groundwater heat pumps Not all situations are equally suitable for the application of groundwater heat pumps. Old poorly isolated buildings are not suitable because an additional heating installation is necessary, which is very unfavourable. Besides, the soil type and soil configuration are important factors for the applicability of groundwater heat pumps. In general the following features can be regarded as positive factors for the application of heat pumps.

�� A high groundwater flow velocity �� A high groundwater table �� A high thermal conductivity of the soil layer �� Absence of an isolating top layer of the soil �� High natural groundwater temperature

1. Heat pump 2. Solar energy panel 3. Soil heat exchange 4. Water heating system 5. Low temperature room

heating system



�� Absence of groundwater protection areas in the direct vicinity A high groundwater flow velocity is beneficial because by groundwater flow, heat is supplied to the place where it is extracted; by groundwater flow the heat storage is filled again. A high groundwater table is beneficial because in that case deep boreholes are not necessary and the thermal conductivity increases sharply with the soil water content. A high thermal conductivity leads to a better heat transport to the heat pump. Sand has generally a high thermal conductivity whereas clay has a low thermal conductivity. The following table gives an indication of the thermal properties of soils, however, the uncertainty range is large. Table 7-2: Indication of thermal capacity of soils and water (Diao, 2004; Hukseflux, 2005; Nordic, 2005)

Soil type Thermal conductivity (W/(m*K))

Heat capacity (MJ/(K*m3))

Sand, coarse, saturated 3.5 2.6 Sand, fine, saturated 2.8 2.3 Sand, fine, dry 0.35 1.3 Fine sand, clayey, saturated 1.8 2.3 Silt, saturated 2.0 2.8 Clay, saturated 1.6 3.3 Peat, saturated 0.8 1.9 Limestone 2.5 1.3 Sandstone 4.5 3.6 Water 0.6 4.2

The presence of an isolating top layer decreases the feasibility of heat pumps because it decreases heat supply from the atmosphere to the groundwater. Examples of isolating top layers are: a sand layer with a low groundwater table or a clay layer. However if the groundwater is also used for storage of heat an isolating top layer can be an advantage. More heat can be extracted if the natural groundwater temperature is higher because heat storage in the aquifer is higher in that case. Finally, near groundwater protection areas, for instance drinking water wells, heat pumps may not be constructed. In situations that are less favourable for the application of heat pumps, heat pumps can still be applied. However, a higher heat pump capacity (up to 100% more) is necessary in those situations. (Hehenkamp, 2001)

7.1.7 System response of groundwater By continuing extraction of heat, the temperature of the aquifer will decrease until a new equilibrium is reached. In this equilibrium state, heat will be supplied from the atmosphere, by groundwater flow and from deeper lying ground layers. Although the heat capacity of an aquifer is very high, the final temperature change in the aquifer can be considerable. Several methods are available to calculate heat transfer to the aquifer. Analytical method One of the first methods to calculate the effect on groundwater layers is the Ingersoll approach (1948), which makes use of the Kelvin line theorem. In this approach the heat source is



schematized as an infinitely long heat source in a homogeneous infinite medium. The resulting equation is then:

2

( , ) ( )2 2

Where: 2

B

us s

q e qT r t T dB I Xk B k

rXt

� �

�

�

� � �

�

�

Where: T(r,t) = Soil temperature as a function of radius and time [oC] Tu = Uniform initial soil temperature [oC] r = Radial distance from heat source [m] � = Thermal conductivity of the soil [m2/s] t = Run time of the heat pump [s] q = Heat transfer rate to the ground [W/m] ks = Thermal conductivity of the soil [W/(m*K)] I(X) = Integral term B = Integration variable Application of this formula provides results as shown in following results from a calculation which has been done by IF technology.

Figure 7-7: Soil temperature as function of time and distance (IF technology,1997) Models The Ingersoll approach is not suitable for calculating the effect of multiple heat sources, which will often be the case in residential districts. Models exist for these applications such as the Earth Energy Designer (EED) or HST2D (US Geological Survey), which simulates groundwater flow and heat transports in two or three dimensions; in these models both the influence of multiple heat pumps and the heat flow from atmosphere and deeper ground layers can be taken into account. Model simulations (e.g. IF Technology, 1997) show a considerable temperature decrease for large-scale heat pump application with small mutual distances.

T [oC]

Distance from heat pump [m]

-. 0.5 year -- 1 year --- 5 years …. 10 years__

25 years



Groundwater related problems with heat pumps Extracting large amounts of heat from aquifers leads to a structural decrease of groundwater temperature, especially if many buildings within a relatively small area make use of heat pumps. A decrease of temperature of an aquifer is undesirable from an ecological point of view and because effects of such a decrease are still uncertain. In case of a Two Layer City, substantial amounts of heat will be extracted from the aquifer. Therefore, to prevent a structural large decrease of soil temperature, methods should be found to supply heat to the aquifer to reach equilibrium. Cooling houses in summer and subsequently providing it to the aquifer can supply a part of this supply; the same heat pump installation can be used to cool houses by reversing the flow direction in the heat pump. However, the cooling demand of houses is considerably smaller than the heating demand. For office buildings, on the contrary, both demands are about the same. (Delft Outlook, 2004.3) Another possible concept is cooling urban surface water in summer to load the aquifer with heat, which can be used in winter for heating of houses.

7.2 Integration with the surface water system Sources of heat are required to fill the heat storage of an aquifer; surface water offers good possibilities to realize that. If surface water can be cooled in summer by use of heat pumps, heat can be stored in an aquifer and can be extracted in winter. The following picture elaborates this concept.

Figure 7-8: Use of surface water in a lake to deliver heat to aquifer



The sun is the source of heat for the surface water, in picture 7.8 the surface water is a lake, however also the circulation concept could be used for heat extraction, see picture 7.9. A part of the heat that is stored in the surface water is extracted by the heat pump; the working fluid with a low temperature absorbs heat from the water. After this, cooled water is released again to the lake. A compressor increases both temperature and pressure and heat is transferred to the closed ground loop that in its turn supplies heat to the aquifer. The function of the system in figure 7.8 is heat transfer from the lake to the aquifer. To calculate the amount of heat, which can be extracted from surface water, the temperature of surface water in summer months should be known. The natural water temperature is generally known as the equilibrium temperature.

Figure 7-9: The use of the circulation concept to extract heat from the surface water

7.2.1 Equilibrium temperature of surface water The equilibrium temperature of surface water is mainly determined by air temperature. The average monthly temperature series for the Netherlands are provided by KNMI. However, Observations show that the temperature in an urban area is about 1.5 oC higher (Van de Ven, 2004). Gameson (1959) derived the relation between average air temperature and equilibrium surface water temperature. He derived this empirical relation for measurements in the Thames river basin. However, comparison with Dutch figures (for instance, Wemelsfelder, 1968) shows a clear resemblance. The relation between air temperature and water temperature is:

0.5 1.109e aT T� �

H

Residential District Circulation channel

Heat pump



where: Te = Equilibrium temperature of surface water [oC] Ta = Average air temperature [oC]

Figure 7-10: Temperature of air and surface water The figure shows that the water temperature in August and July is higher than 20oC. In this period often problems are experienced with algae bloom, turbidity, fish mortality and stench in urban areas. Lowering the water temperature with 2oC in these two months would be very beneficial for water quality and at the same time would offer opportunities to extract heat from surface water to store in the aquifer. Decreasing the water temperature with two degrees restores the natural water temperature in the summer months to a level that would occur in non-urbanized situation. An important question is then: how much energy can be extracted and is it enough to compensate for the extracted amount of heat from the groundwater? For this purpose a heat balance of the surface water should be made.

7.2.2 Heat balance of surface water In surface water the following sources supply or extract heat from the surface water

�� Solar radiation �� Atmospherical radiation �� Lake radiation �� Evaporation �� Heat conduction to/from atmosphere �� Heat extraction by heat pump �� Others

Solar radiation The sun provides heat to the surface water by both direct and indirect radiation. Direct radiation heats water directly, indirect radiation has been influenced by dust particles in the atmosphere. As a result the wavelength of this type of radiation is slightly different. The summation of these two sources of solar radiation is the total solar radiation [W/m2] and is measured by KNMI.

0,0

5,0

10,0

15,0

20,0

25,0

jan mrtmei jul se

p nov

Month

Tem

pera

ture

Air temperature

Air temperature city

Water temperaturecity



Table 7-3: Total solar radiation per month (KNMI, 2005)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

28 52 99 156 209 209 211 184 119 72 34 21 [W/m2]

Atmospherical radiation Clouds and vapour absorb solar radiation, after absorption clouds function as source of radiation as well, though with a longer wavelength than direct solar radiation. Atmospherical radiation depends on the cloud density, the type of clouds, height of clouds, atmospherical pressure and vapour pressure. The law of Stefan Boltzmann gives the following general relation:

4( 273) a SB aH T� �� where: Ha = Atmosperical radiation [W/m2] � = Coefficient that depends on cloud density, and vapour pressure, summer

estimation =0.83 �SB = Constant of Stefan Boltzmann (5.67*10-8 W/m2/K4) Ta = Air temperature in oC Lake radiation Lake radiation takes place to the atmosphere, this process can also be described by the law of Stefan Boltzman, the only determining factor is the water temperature and in this case �=0.97. The heat flow has a negative sign because it is a heat extracting process. The resulting heat flow is:

4( 273) l SB wH T� �� where: Hl = Lake radiation [W/m2] Tw = Water temperature in oC Evaporation By evaporation, heat is extracted from surface water and the other way around, by condensation heat can be delivered to surface water. The extracted amount of heat depends on the wind velocity, the atmospheric vapour pressure and the saturation vapour pressure. The next formula (Van Mazijk, 2003) gives the evaporation heat flow. This heat flow is positive if the atmospheric vapour pressure is larger than the saturation pressure; in that case condensation takes place and heat is supplied to the surface water. If the atmospheric vapour pressure is smaller evaporation takes place, consequently heat is extracted from the surface water.

a s(3.68 2.65 ) (p -p ) e windH v� � � � where: He = Evaporation heat extraction [W/m2] vw = Wind velocity [m/s]



pa = Atmosperic vapour pressure [millibar] ps = Saturation vapour pressure [millibar] The atmospheric vapour pressure is the pressure of vapour on its surrounding as a part of the gas mixture in atmosphere. A suitable estimate for a city situation in the summer months is pa= 16 hPa. The saturation vapour pressure above surface water is given by the following formula:

( 20)23.4 1.062 wTsp �

� � where: Tw = Temperature of surface water [oC] Heat conduction to/from atmosphere If there is a temperature difference between the atmosphere and the water, a heat flux will occur by conduction. The driving forces between this flow of heat are the temperature difference dT and the wind velocity. This leads to the following formula (Van Mazijk, 2003):

(2.02 1.46 ) ( ) c wind a wH v T T� � �� with: Ta = Air temperature Tw = Water temperature This term is positive if the air temperature is higher than the water temperature and negative if the opposite is the case. Heat extraction by heat pump Heat extraction by the heat pump Hh is the component of the heat balance that is to be calculated to find out whether or not sufficient heat can be extracted in the summer months to supply heat to the houses. Other processes These include: heat transport by precipitation, turbulence, heat conduction to and from the bed sediments and biological and chemical degradation processes. However, the contribution of these processes is sufficiently small to be neglected in this calculation. Summing all components of the heat balance gives the heat balance equation, in this equation a equilibrium surface water temperature Tw must be substitutes and according to this temperature there is a heat flow surplus that can be extracted by the heat pump. This heat flow will be larger if the chosen temperature is lower; in that case more heat can be extracted.

4 4h s SB a SB w wind a s wind a wH =H +β σ (T +273) -β σ (T +273) +(3.68+2.65 v ) (p -p )+(2.02+1.46 v ) (T -T ) � � � � � � � �



Table 7-4: Input values in the heat balance equation

July August Unit Hs 211 184 [W/m2]� 0.86 (atm) / 0.97 (lake) 0.86 (atm) / 0.97 (lake) [-] �SB 5.67*10-8 5.67*10-8 [W/m2/K4]Ta 18.6 18.7 [oC] Tw 19.0 19.0 [oC] Vwind 4.0 3.8 [m/s]pa 16 16 [hPa] ps 22.0 22.0 [hPa]

T� -0.4 -0.3 [oC] Substituting the values in the heat balance formula and applying them to a 1000 houses schematisation which was used before to make calculations on the feasibility of the Closed City, gives results as indicated in the next table. Table 7-5: Results of the heat balance calculation

July August total

Hh 62 40 W/m2

Eff. Output 1773 1130 KW

A total 28600 28600 m2

Total energy 4748 2930 GJ

Per house 4.7 2.9 7.7 GJ

Heat pump operation 1.6 1.0 2.6 GJ

Total aquifer energy supply 6.3 3.9 10.2 GJ The table shows that cooling urban surface water by heat pumps to a temperature of 19oC, delivers 7.7 GJ energy per house in case of a district with 1000 houses and 2.86 ha surface water. If this result is compared with the total heat demand for room heating for a house with EPC=1.0, the conclusion can be drawn that applying this concept can provide 39% of the total yearly energy demand for room heating. The operation energy of the heat pump is added to the aquifer as well and is approximately 2.6 GJ, if the COP value is 4. As a result the total amount of energy, which is supplied to the aquifer in these two months, accounts for 50% of the total room heating demand of houses for the whole year. Moreover, at the same time beneficial effects take place for water quality because of the lower surface water temperature.



7.2.3 Required pump capacity The effective output in July is 1364 kW, to get an idea of the required pump capacity, the following formula for effective output can be used.

pumpP s Q T�� with: P = 1364 kW (Effective output) �� = 1000 kg/m3 (Specific density) s = 4186 J/(kg*oC) (Heat capacity of water) �T = 40C (Temperature decrease of return flow) Substituting these values in the formula results in a pumping discharge of the heat pump of Q=0.08 m3/s. This is only 0.08 l/s /house which is very low. The heat pump should operate in such a way that 0.08 m3/s of water is extracted from the lake and that this water is cooled 40C, in the calculation example water with a temperature of 15oC would be discharged back into the lake. Besides, the extraction and discharge of surface water can be used to circulate water for water quality purposes as well. Pump operation energy For calculating the efficiency of the total heat extraction system, it is useful to know the energy that is required to operate the water pump. If this pump requires a large energy input, it would decrease the efficiency of the total heat pump system. The following formula can be used to calculate the required pumping energy.

1000pump

operatione

g Q HP

�

�

��

� � �

�

Poperation = Operation energy [kW] �e = Electrical efficiency of pump [-] � = Specific density of water [kg/m3] g = Gravity acceleration [m/s2] Qpump = Pump capacity [m3/s] �H = Level difference including friction and bend losses [m] Substituting some representative values, for instance: �e=0.5 and �H=3m, shows that the pump energy is only a small fraction of the energy that is extracted from the lake (3.5 %) and has therefore only a minor influence on the efficiency of the heat pump system. Moreover, a small amount of these losses are converted to heat in the heat pump system as well by friction and dissipation processes.



7.2.4 Influence of further temperature decrease It is also interesting to know how much energy could be extracted if the surface water temperature is decreased to a lower value than 19oC. The following graph shows the influence of cooling the surface water on energy extraction from the surface water.

Figure 7-11: The amount of extracted energy per house as a function of chosen surface water temperature Naturally, if the surface water temperature is 21 oC, the amount of extracted energy is zero. After all, no lowering of temperature by heat pumps has taken place and the water temperature is the same as in the ordinary situation, see figure 7.9. If the temperature of the surface water is decreased to 19oC the extracted amount of energy per house is 8.9 GJ, which is the same as in table 7.5. To cover the total room heating demand, the surface water temperature should be decreased to 16.5 oC in the months July and August. The total extracted amount of heat is 15GJ per house in that case; an amount of 5 GJ can be added to this, resulting from heat pump operation energy. However, a very low water temperature in summer could disturb ecological processes. Therefore, such a large decrease is undesirable.

7.2.5 Implications for design New housing districts are build with a Energy Performance Coefficient of 1.0, which means that on average 28 GJ per house is required for both room heating and water heating. For water heating (shower) a sun boiler can be used, however additional heating is necessary for such a system. Another alternative is the electrical boiler, however the efficiency of such an installation is low. Applying groundwater heat pumps can cover the total room heating demand. However, heat extraction lead to a considerable lowering of soil temperature. Restoring heat to the aquifer can be provided be the following sources:

�� Heat extraction from surface water, by decreasing the water temperature in July and August to 19oC compensates 50% of total extracted amount.

0

2

4

6

8

10

12

14

16

15 16 17 18 19 20 21 22

Surface water temperature

Extra

cted

ene

rgy



�� Reversing flow direction of residential heat pumps for air conditioning of houses during summer months can compensate a part of the heat extraction. In a project of Ecofys about 25% of total extracted amount of heat could be supplied back to the aquifer by cooling buildings. (Ecofys, 2001)

�� Heat supply from terrain surface and deep ground layers should compensate the remaining part.

7.3 Concluding remarks In this chapter groundwater energy extraction for energy conservation has been evaluated. In the Two Layer City a considerable part of the total energy demand for residential use is supplied by the groundwater. Moreover, the integration with the surface water system has been treated as well. The following conclusions can be made about the Two Layer City: Energy conservation

�� The use of groundwater heat pumps is a promising concept for energy conservation. �� Groundwater heat is a very suitable heat source for heating rooms because it is a lowly

valued energy source and very high efficiencies can be achieved. �� For existing poorly isolated houses, heat pumps are not very feasible because an

additional heating system would still be necessary. �� Groundwater heat pumps can be applied nearly everywhere in the Netherlands, however

for certain soil types longer ground loops are required because of the smaller heat conductivity of aquifer.

�� Applying heat pumps in a new residential district can reduce energy use by 50%, compared with an ordinary house with EPC=1.0.

�� Applying heat pumps on a large scale within a district will result in a considerable decrease of groundwater temperature. Therefore, preferably the aquifer will be regenerated as well. Integration with the surface water system offers good possibilities to supply heat to the aquifer.

Integration with surface water

�� Decreasing the temperature of urban surface water with 2oC by heat pumps in July and August provides 39% of the total yearly room heating demand in a residential district with EPC=1.0.

�� This amount is increased further to 50% because the energy to operate the heat pump is supplied to the groundwater as heat as well.

�� Cooling houses in summer could supply an additional 25%.



8 Implications of future water systems Scope and purpose of this chapter If one would try to achieve one of the two discussed future water systems in practice, a number of institutional obstacles would probably emerge. Chapter 4 described the actors in urban water management and their role, importance and relations to other actors. The realization of the two water systems implies different roles of actors or even new actors. Therefore, this chapter deals with the societal implications of future water systems.







8. Implications of future watersystems

Implications for organisations and inhabitants




8.1 Implications of the Closed City The Closed City is characterized by the integration of water chain and water system; after all, the urban water system itself is the water source for the water chain. As a result, the strict separation of responsibilities of organisations is no longer useful in the Closed City. On the contrary, more intensively cooperation between organisations in urban water management is required than at this moment.

8.1.1 Implications for organisations More dependencies between actors result from the system layout of the closed city. In the Closed City drinking water supply relies on effective disconnection of paved surfaces (municipality) but also on the state of the water system (water board). If effluent is (partially) discharged back to the urban surface water, also the wastewater treatment plays a role in drinking water supply, as wastewater treatment is a source for the water system as well. The complex nature of urban water management issues should in the Closed City be reflected in the way of working of involved organisations. After all, they can no longer cope with problems on their own, but instead have to rely on, and cooperate with others Formation of a network of cooperating organisations would be necessary if the Closed City is realised in practice. For the most important organisations the



dependencies in the Closed City can be listed, for such a new situation. The current roles and responsibilities of organisations have been described in chapter 4. Water board Tasks: Operation, management and maintenance of the urban water system with regard to both water quantity and water quality. Depends on:

�� Municipality, to manage and maintain runoff collection systems, public area drainage systems, infiltration facilities and disconnection facilities to secure both water quality and water quantity of the urban water system. Besides, the maintenance of the sewer system and subsurface drainage system by the municipality influences the water system also the maintenance of the public space influences the water system.

�� Inhabitants, for support, payment, drainage of property and cooperation to maintain the quality of the water system by their behaviour.

Municipality Tasks: Collection of runoff, collection of wastewater, maintenance of public space, groundwater management public space. Depends on:

�� Water board, to treat wastewater properly, to maintain living quality of the urban area and to make a clear distribution of costs.

�� Inhabitants, for support, payment and cooperation to maintain living quality of the urban area.

�� Drinking water company, to realize a clean and reliable water supply and thus maintain public health.

Drinking water company Tasks: Realisation, operation and maintenance of a clean and reliable water supply and water sources. Depends on:

�� Water board, to secure water quantity and water quality, on which the water supply depends, in the urban water system by effective water management.

�� Municipality, to effectively manage infiltration, runoff collection and disconnection facilities on which the water quantity in the water system depends.

�� Inhabitants, to keep their water use within reasonable limits and for payment Another possibility is the formation of one water company that manages the whole urban water system and water chain could be an option. The merging of organisations to one water company has recently been proposed in Amsterdam where the water board, municipality and drinking water company will cooperate in a new water company. As a result all urban water management issues such as drinking water supply, water quality, wastewater treatment, runoff collection, sewer system and groundwater management would be handled by one organisation, In Stockholm such an organisation already exists. Summarizing, one could say that if the organisations are maintained in their present from, not much changes occur in their general tasks. However, an important change is the fact that fulfilling tasks becomes more important for others. Because all water related tasks are realized within the Closed City itself, more dependencies between actors arise. In case of the formation of one organisation, there are of course more changes because the cooperation takes place between



different departments of one organisation. However, also in that case conflicts about costs and responsibilities are likely to arise.

8.1.2 Implications for inhabitants For inhabitants, a number of things change if the Closed City is realised in practice. Inhabitants experience their drinking water supply in their own living area and influence their drinking water supply by their behaviour. By seeing and experiencing the water supply in the urban living environment, the connection between human beings and water supply is brought back to a small local scale. If this connection is combined with appropriate public campaigns and inhabitant involvement, it should result in more awareness and sensible behaviour towards the water system. Because water is organised at a local scale, more commitment to the managing organisations can be expected. This can be regarded as an improvement of the current situation where the involvement of inhabitants in municipalities and water boards is generally low. In the Closed City the importance of the water organisations is entirely clear and can be comprehended by inhabitants because of the local scale of the water supply. Additionally, the financing structure could be much more simple for inhabitants, especially if there is only one water company.

8.1.3 Obstacles and advice for realization of the Closed City To realize the Closed City in practice it is important to make an estimation of the obstacles and risks, which would hinder implementation of this future water system. Public health risks There are risks as well; giving inhabitants influence on the water supply could also result in damaging of the water system and a risk for public health and operational safety. What if people continue to wash or repair their car next to the water system that supplies water to them? Next to this simple example, there could be numerous unforeseen consequences and risks. These risks should, however, not be a reason to reject the Closed City altogether. Instead, experimenting, focusing on learning and improving the Closed City should take place by protecting innovations and controlling risks until these innovations are feasible to be implemented at a larger scale. However, this should only take place if a concept has been developed well and is ready for large-scale implementation. Psychological obstacles A characteristic of The Closed City is level fluctuation and variation of inundation frequency according to the function of an area. This means that a park may be flooded more often than a residential street. An important obstacle is the psychological acceptance of these inundations near the living environment. Good public information and involvement of inhabitants should make this possible. Another psychological obstacle is the use of a part of wastewater effluent in the urban water system during dry periods. However, this only occurs in very dry years and the current water supply also relies partly on wastewater effluent in rivers. Alternatives are demand management, construction of inter-annual reservoirs or supply from the surrounding area. Organisational obstacles An important obstacle that can be expected is about the distribution of costs and responsibilities. At this moment the municipality has no direct responsibility for the water supply, although in many cases they are shareholder of the local drinking water company. In the Closed City on the contrary, effective infiltration and disconnection is the source of the water supply. A question that arises is then: who should pay for these facilities? Should the drinking water company and the water board also pay for maintaining these facilities? After all, they certainly also benefit from



these facilities and they even depend on it. It is also important to know who is responsible that there is enough water in the water system, because most involved organizations influence the water system. If every organization is responsible, it might turn out that none of these organizations is responsible. Either cooperation between organisations or merging into one organisation seems the best solution to cope with this problem. Financial obstacles The financing of such a multi-organisation responsibility will turn out to be very complex, in particular if some of these organisations (municipality and water board) have the right to levy taxes and the other has to determine a unit price (drinking water company). The simplest solution seems to have one financing source for the entire Closed City water system. A special Closed City system tax could be introduced for this, much more simple seems however, to finance these tasks from general sources, similar as the maintenance of roads and public services. However, for demand management it is useful to have unit prices and connect costs with water use. Therefore, one financing source which (partially) depends on water use is likely to be the most appropriate solution. Other obstacles Also for other relevant aspects obstacles can be expected. Measures should fit in the BRUHO chain (Dutch acronym for Beleid, Regelgeving, Uitvoering, Handhaving en Organisatie). This means that the following aspects should be taken into account or should be changed if future water systems are implemented. These aspects are: policy, legislation, implementation, enforcement and organisation. If these aspects are disregarded and if these aspects conflict with future water systems, successful realization is doubtful.

8.2 Implications of the Two Layer City The Two Layer City is characterized by the integration of the water system with energy supply. As a result, organisations, which used to do separate tasks, will now have to cooperate. Another possibility is the introduction of new tasks for existing organisations.

8.2.1 Implications for organisations By integrating the energy supply with the water system, the water board, being the manager of the water system, gets involved in the energy supply. Heat from surface water is extracted in summer, stored in an aquifer and extracted in winter. Consequently, cooperation between the water board and the energy supplier is needed. The temperature impact on the groundwater and surface water is expected to be limited. The water board (and the province government) can control this by issuing permits for heat extraction. It is imaginable that the energy supply company will have to pay for this permit or that a public tender procedure is started for the exploitation of this ‘free’ heat source. Although, at this moment heat pumps are not competitive with conventional heat sources, this will probably change in the future if energy prices will rise and the heat pump technology will be developed further. Compared to the current situation the relation between energy company and water board changes a lot. Only the energy related factors for the Two Layer City are indicated in the following overview of dependencies. Water board Tasks: Operation, management and maintenance of the urban water system with regard to both water quantity and water quality Depends on:



�� Energy company, to effectively extract heat from the water system to increase water quality. Moreover, the energy company should keep the extraction within determined limits.

Energy company Tasks: Realisation, operation and maintenance of a reliable energy supply. Depends on:

�� Water board, to be able to extract the required amount of heat from the water system �� Inhabitants, for payment

Another possibility is a situation where the water board takes up the responsibility to supply heat to households in the city. The additional income for the water board could perhaps be used to cover the increasing costs of water management. The most important consequence of the Two Layer City is the fact that the water board gets involved in the energy supply, either by cooperating with an energy supplier, either by supplying heat. In the Two Layer, it is therefore important that the water board has knowledge about energy issues.

8.2.2 Implications for inhabitants If the Two Layer City energy supply works well, inhabitants will not experience many changes. The houses are equipped with a low temperature heating system, which is more comfortable than conventional radiators. Moreover, by simply switching the flow direction of the heat pump system, each house has a cooling installation as well. Besides, the total heat demand of the house will be supplied by heat from the water system. Therefore, if the houses are isolated adequately, a gas supply can be absent. A possible configuration of the Two Layer City is the individual heat supply, each house has its own installation in that case, and therefore no heat supply organisation would be required. Consequently, inhabitants themselves are responsible for the maintenance and operation of their heat supply system.

8.2.3 Obstacles and advice for realization of the Two Layer City One of the most important obstacles for realization of the Two Layer City is the aspect of exploitation. Currently, groundwater heat pump systems are still more expensive than conventional systems. However, this may change quickly by rising energy prices and technology development. It could be that these techniques turn out to be cheaper in the long run. In that case energy companies will be positive on implementing these innovations. Another obstacle is the fact that formerly unconnected organizations will now have to cooperate. An important advice is to involve the energy supply company in the transition process because their knowledge is important for accomplishing a reliable energy supply. If the Two Layer City is realized the water board should obtain knowledge about the energy supply as well to be able to cooperate effectively with the energy company. If the water board has enough knowledge about energy supply they might even be able to run the exploitation of the city heat supply.



9 Evaluation of future water systems Scope and purpose of this chapter In this report the technical feasibility of future water system has been treated as well as the implications for involved organizations and inhabitants. No attention has yet been paid to feasibility in a broader sense, which also includes preferability and costs. The general feasibility of a future water system is evaluated in this chapter; the evaluation consists of the following components.

�� Contribution to sustainable development �� Effectiveness �� Technical feasibility �� Desirability �� Affordability �� Preferability

If all these aspects are taken into account, one can conclude if a future water system is generally feasible.


9.1 Contribution to sustainable development One of the most important aims of future water systems is to contribute to sustainable development. In chapter 3, the objective tree has been constructed to evaluate various aspects of sustainable development. How do the concepts of future water systems contribute to sustainable development? The following most important aims can be distinguished from the objective tree:












�� Efficient use of scarce water �� Secure public health �� Low use of materials and energy �� Improve environmental quality �� Multi functional use of space �� Improve living quality of urban area

Efficient use of water is only needed if water of sufficient quality is scarce; if there is a surplus of water, water efficiency has a lower importance. Therefore, the Closed City is most appropriate for water scarce cities such as The Hague rather than for cities with a large natural water supply like Dordrecht. Public health can be secured in both future water systems by effective treatment and distribution, however no improvement compared to the current situation can be expected. Besides, the input of materials and energy should be low. Both future water systems have a positive impact on the use of materials and energy. The Closed City has a positive impact because the transportation distance of water and wastewater decreases, the Two Layer City because less energy is needed for heating of houses. The environmental quality is increased by both systems, in the Closed City water quality is improved and more possibilities for nature are available, in the Two Layer City because emissions from heating decreases. Multi functional use of space is promoted by both future water systems. Moreover, the Closed City offers possibilities to improve the living quality of the urban area by the high amount of surface water. The following summarizing table can be made for the alternatives for their contribution to sustainability, compared to the current situation. Table 9-1: Contribution of alternatives to sustainable development compared to current situation

CLOSED CITY TWO LAYER CITY Efficient use of scarce water + 0 Secure public health 0/- 0 Low use of materials and energy + ++ Improve environmental quality + +/0 Multi functional use of space + + Improve living quality of urban area + 0

In conclusion, both alternatives offer opportunities for more sustainable water systems; however, the Closed City needs a better public health risks management, in order to be realizable.

9.2 Effectiveness Effective alternatives contribute to solutions for problems of current water systems. For the Closed City can be concluded that it is effective in solving problems of current water systems, such as water quality and water nuisance problems. It only uses local rainfall and consequently and it does not lead to water depletion in other areas, thus no shifting of problems to other areas occurs. Moreover, the Closed City is even able to accommodate water nuisance problems from surrounding areas. By the large amount of surface water it offers opportunities for recreation and landscape quality.



For the Two Layer can be concluded that it is effective in contributing to energy conservation and comfort in houses. Moreover, water quality is influenced positively by this concept, especially during summer months where most problems occur.

9.3 Technical feasibility The technical feasibility of the two future water systems has been evaluated in chapter 6 and chapter 7. Both future water systems are feasible from a technical perspective under certain conditions.

9.4 Desirability Whether or not the Closed City is desirable depends on the way the Closed City can compete with current water systems on all relevant aspects. Under the effectiveness paragraph the many positive effects of the Closed City were already mentioned. However, there could also be undesirable effects, for instance the system is more vulnerable for behaviour of inhabitants. The desirability of the Closed City depends also on local circumstances; if natural water resources are scarce in a city, the Closed City is desirable. If there is a local water surplus the desirability is lower, although the water quality and water nuisance properties of the Closed City would still be very useful. The Two Layer City reduces energy consumption of a residential area considerably. Moreover, heat pumps are reliable and only require little maintenance. The lowering of temperature of surface water in summer can have positive effects on water quality.

9.5 Affordability Not much is known about the affordability of the Closed City. Consequently, more research is needed on costs and benefits. However, some remarks can be made about these aspects. Because water supply is organized locally, less extensive networks and infrastructure are needed; this can be regarded as cost saving. On the other hand, a residential district will need its own drinking water treatment, which will probably be more expensive. Another positive aspect for affordability is the fact that the urban surface water will be used for more purposes and as a result the economic value of the urban water system will increase. Heat pumps are still not competitive, however they are applied because of their higher comfort level, their lower energy use and the fact that there are subsidies available for these systems. The affordability of the Two Layer City depends on local circumstances as well, for instance on soil conditions. Probably in the future the affordability of these systems will increase with increasing energy prices.

9.6 Preferability Is the Closed City to be preferred above other imaginable water systems and current water systems? This question can only be answered if all relevant effects of the Closed City are known and all aspects of general feasibility are covered. Therefore, more research should be conducted on the Closed City and in particular experiments to gain knowledge about the effects and performance of the Closed City are required. If the Closed City concept has been developed well and the effects are known, the preferability of the Closed City above existing and other future can



be assessed. After this research, it can only be concluded that the Closed City offers opportunities to tackle some serious problems in water management. For the Two Layer City the same reasoning applies as for the Closed City. Also in this case more research is needed, for instance on the effects of temperature decrease of surface water. However, also in this case the conclusion can be made that the Two Layer City offers opportunities for energy conservation and improvement of water quality. Table 9-2: Evaluation of both future water systems

CLOSED CITY TWO LAYER CITY Contribution to sustainability + + Effectiveness + + Technical feasibility + + Desirability Depends on situation + Affordability ? - Preferability ? ?

9.7 Concluding remarks After this chapter can be concluded that both alternatives contribute to sustainable development and that both alternatives are quite effective, both in tackling some serious problems of existing urban water systems, as well as making use of opportunities. However, to make a conclusion about the preferability of these systems, more information is needed of all effects and costs of these systems.



10 Conclusions and recommendations Scope and purpose of this chapter In this report research has been conducted for the following problem statement: Can urban water systems in the future be a feasible and more sustainable alternative for the present urban water systems? In this chapter the conclusions of this report will be presented as well as recommendations for further research.


10.1 Conclusions In this report first, sustainability has been evaluated in such a way, that it can be used to develop objectives for future water systems and systematically make a problem analysis of the urban water systems. Moreover, threats and opportunities for urban water management have been listed. For this purpose sustainability has been defined as a long-term development objective, which tries to balance social, ecological and economic interests. Subsequently, the urban water system has been examined with regard to natural, technical and institutional aspects. Moreover, trends, changes and developments have been studied to identify a direction in the approach to urban water management. In chapter 5, the influence of policy, society, technology and autonomous trends were integrated in a vision on future water systems and as a result two future water systems were defined to be elaborated further. The Closed City The first future water system that has been elaborated in this report is the ’Closed City’. The Closed City is a city that does not have adverse effects on its surroundings, such as water depletion or emission of pollution. For this purpose, the technical feasibility of the ‘Closed City’ has been studied for three aspects: water quantity, water quality and water nuisance. Calculations for water quantity in this chapter have shown that it is possible to design a residential district that









10. Conclusions and recommendations

Concluding remarks and suggestions for further research



uses local rainfall as the only source of water. However, the housing density should be low, about 30-35 houses/ha, and the stormwater infiltration percentage should be high. Moreover, the feasibility of the Closed City can be improved significantly by recirculation and demand management measures. Additionally, about the water quality analysis can be concluded that (1) the urban water system can play a role in water purification and (2) the robustness of the ‘Closed City’ can be improved if effluent from the wastewater treatment is discharged back to the urban surface water, during dry spells. Calculations in chapter 6 have indicated that even discharging all effluent back to the urban surface water is possible, although under strict conditions with regard to purification efficiencies, internal load and water system dimensions. However, to increase the feasibility of the ‘Closed City’ only a small part of effluent is needed, thus less strict conditions will be sufficient. The calculations about water nuisance have shown that it is possible to accommodate water nuisance problems locally. Although a small pumping capacity will be required, the Closed City also has the ability to store water from surrounding areas and help its neighbours. Level fluctuation and operational management of these fluctuations is the key feature of the Closed City. The Two Layer City The second future water system that has been analysed is the Two Layer City. The Two Layer City is a city that makes use of the water system to save energy. For this purpose heat pumps are used for the extraction of heat from surface water and aquifers. The total house heating demand can be covered, by applying this technique in new residential districts. Applying this technique results in about 50% energy savings. However, extracting heat at a large scale from aquifers, results in a considerable temperature decrease of the groundwater. Therefore, sources of heat to load the aquifer with heat should be found. Calculations in chapter 7, have shown that extracting heat from the urban surface water during summer, is a promising concept to reload the aquifer, adding up to 50% of the total room heating demand to the aquifer. A temperature decrease of the surface water to a constant level of 19oC during July and August can already deliver this amount. Moreover, cooling houses in summer can also supply additional heat to the aquifer. Implications Institutional obstacles could hinder implementation of future water systems in practice. Roles and responsibilities of organisations will change if future water systems are realized. In case of the Closed City, integration of water system and water chain, preferably leads to integration of involved organisations as well. Integration can take place by forming a network of interdependent organisations or by forming one water company, which is responsible for all water issues and tasks. In case of the ‘Two Layer City’ energy supply and water system will be integrated which should lead to either a strong cooperation between water boards and energy companies or the exploitation of heat supply by the water board. Evaluation Both alternatives contribute significantly to sustainable development and both alternatives are quite effective in tackling some serious problems and making use of opportunities in water management. The Closed City reduces external water supply almost entirely, whereas the Two Layer City provides about 50% of the total room heating demand by extracting heat from surface water. Moreover, both future water systems are technically feasible, although under certain conditions with regard to purification efficiencies, stormwater infiltration and surface water



percentage. However, to make a conclusion about the preferability of these systems, more information is needed about all effects and costs of these systems.

10.2 Recommendations In this report an exploration has been made on future water systems and, their feasibility and the transition problems to be expected. The approach in this report has been general, due to the fact that a lot of issues had to be given attention. This is caused by the complex nature of urban water management problems; these problems require investigation of a variety of issues and aspects. Next step in the transition process… According to transition theory, a group of involved organizations should be formed (a so-called transition arena) to start a common learning process in order to start the transition process to more sustainable urban water systems. This transition arena should consist of frontrunners in innovation to develop the concepts of future water systems further. A transition will only work if all organisations cooperate and together tackle obstacles and gather required knowledge. The transition approach does not give a blueprint for a path to future water systems. Instead, it only gives a direction; the path and exact objective will be changed as insight, technology and demands change in time. The function of the future water systems as they have been described in this report is to play a role as inspirator in discussions in the ‘transition arena’. By these discussions a common objective and agreement about a direction in future urban water management can arise. This agreement could eventually lead to new urban water systems in the future. Moreover, expected obstacles such as: the required cooperation between organisations in urban water management, distribution of costs and responsibilities, responsible behaviour of inhabitants, public acceptance of new ideas and lacking knowledge about risks and costs are to be discussed and resolved. Key players in the transition arena are the municipality and the water board; other players include project developers, drinking water companies, energy companies and constructors. An innovation paragraph in the urban water plan could an important first step in the transition arena. Recommendations to improve technical aspects

�� Site-specific evaluation of future water systems. In this report average precipitation and average city layouts where used for calculations, to learn more about future water systems, application of these concepts to specific cases would be useful.

�� Distinction should be made between future urban water systems in polder situations and in other situations, for instance cities near rivers and cities on sandy soils. In this report mainly the polder situation has been given attention.

�� Future water systems in other countries, under different climatic and administrative conditions, are to be investigated.

�� Scale up the research to a whole city instead of a residential district only. �� More insight in the role of groundwater and the relation between groundwater and

surface water. �� Research on future water systems at a smaller scale. At this moment only the system

has been evaluated at town section level. Independent water supply at household level could be an inspiring example of such a smaller scale approach.

�� Research on water quality processes in urban water systems, because in this report, still very empirical rules for water quality processes were used. To be able to use the urban water system for effluent purification more knowledge about these processes is needed.

�� Further research on other heat sources to load aquifers, for instance industry, offices, electricity plants, road surfaces, etc.



Recommendations to improve societal aspects

�� More study on the economic feasibility should be performed to find out if and under which conditions future water systems are economic feasible.

�� Insight in management of public health risks in the Closed City. �� Options of financing of the future water systems. �� More information about combining the Two Layer City with the Closed City. �� Information about how transitions fit in the European Water Framework Directive. �� Experimenting with future water systems in practice to learn more. These

experiments should be conducted at a small scale in a protected environment until the concepts have been further developed and can be implemented at a larger scale.

�� Formation of a transition group with frontrunners in innovation to develop the concepts of future water systems further.

In conclusion Not all the recommendations are equally important. Essential for succeeding of the urban water management transition is site-specific evaluation of future water systems, because in that case, the formation of a specific transition group is possible and unforeseen effects and obstacles will appear, which in its turn will lead to more knowledge and adjustment of the transition path. Moreover, more knowledge about water quality processes in both groundwater and surface water is essential as well as knowledge about public health risk management and costs.



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Appendix A: Simplifications for water systems Case 1: Combined sewer system

Figure a-0-1: Simplifications of water system for calculations The following terms are cancelled: A: Drinking water cancels because a closed city is a city without external drinking water

supply. B: Industry cancels because the study is about a residential district without industry. C: Interception cancels because on monthly timescale there is no change of storage in

interception. D: Flow from paved to unpaved surface and the other way around cancels because it is

assumed that runoff on paved surface either infiltrates or is transported by the sewer system. Rainfall on unpaved surfaces is assumed to infiltrate completely.

E/F: Leakage from and drainage to the sewer system is assumed to compensate each other. Furthermore, because a calculation is about a new district there will not be many leakages. During the years this term will become more important.

G: Overflows from sewer systems cancel because in terms of water quantity they are neglectable.

H: Groundwater flow between urban and rural area, such as seepage is assumed to be zero because it is very site specific. In a typical Dutch polder situation neglecting upward

Groundwater


Drinking

water

Atmosphere

Households

Industry

Treatment

Urban surface water

Paved area

Unpaved area


zone



P

P

E

I

E

P

ET

IN

IN

L

D

IRL

G

R

R= RunoffS=Supply







Waterchain

Watersystem

O

S

PEC

D

CombinedSewer system

A

I

B

C D

G

E

F H



seepage leads to a under estimation of the available water quantity. By neglecting this term we are on the safe side with respect to water availability.

I: The distinction between the zones of groundwater is neglected and a storage coefficient is assumed as discussed before

Case 2: Separate sewer system

Figure a-0-2: Simplifications of water system for calculations A: Drinking water cancels because a Closed City is a city without external drinking water

supply. B: Industry cancels because the study is about a residential district without industry. C: Interception cancels because on monthly timescale there is no change of storage in

interception. D: Flow from paved to unpaved surface and the other way around cancels because it is

assumed that runoff on paved surface either infiltrates or is transported by the sewer system. Rainfall on unpaved surfaces is assumed to infiltrate completely.

E: Leakage from and drainage to the sewer system is assumed to compensate each other. Furthermore, because a calculation is about a new district there will not be many leakages. During the years this term will become more important.

F: Wrong connections are assumed to be zero because it is a new district and in terms of quantity this amount is low.

G: Drainage from the groundwater to the rainwater sewer is assumed to be zero and assumed to be complexly draining directly to the urban surface water.

H: Groundwater flow between urban and rural area, such as seepage is assumed to be zero because it is very site specific. In a typical Dutch polder situation neglecting seepage

Groundwater


Drinking

water

At

mosphere

Households

Industry

Sewer system Treatment

Urban surface water

Paved area

Unpaved area

Rainwater sewer

Groundwater unsaturated zone



P

S

P

E

I

E

P

ET

IN

IN

PE

C

IR L

D

G

R

S=SupplyW=Wrong connections





PE =PercolationR= Runoff

L =LeakageP = Precipitation

Waterchain

Watersystem

W

D

L

B A

F

C

I

GE

D

H



leads to a under estimation of the available water quantity. By neglecting this term we are on the safe side with respect to water availability.

I: The distinction between the zones of groundwater is neglected and a storage coefficient is assumed as discussed before



Appendix B: Elaboration of four calculation steps groundwater and surface water levels Step 1: Drain groundwater bulge and calculate new equal groundwater and surface water level

Figure b-0-1: New water level after groundwater drainage For groundwater flow continuity must hold. The total volume per meter is:

1 2 2223totalV w h w h w b� ��

The factor 2/3 in the last term comes from the surface under a parabola, which is 2/3 times width times height. After the lowering of the groundwater table this volume must be the same because of conservation of mass. The new ground and surface water level therefore becomes:

1 22total

newVh

w w��

�

Step 2: Calculate new surface water level after monthly water use and direct precipitation on surface water The surface water level increases, because of effective rainfall and decreases because of water use. These components determine the change of waterlevel.

, , 2sw new new eff swditch

Wateruseh h PA

� � �

w2

h

w1 w1

b

hnew



Figure b-0-2: New surface water level after water use and precipitation Step 3: Adjust groundwater level to new surface water level The groundwater is set on the same level as the surface water level, to prevent discontinuity in groundwater and surface water level.

,gw sw newh h� However, the amount of water we add or subtract to the system by this step must be compensated in the next step because of conservation of mass. Figure b-0-3: Groundwater level after adjustment

w2

hsw,new

w1 w1

hnew

w2

hg

w1 w1

hsw,



Step 4: Calculate new groundwater level resulting from groundwater recharge and compensate for step 3 The effective rainfall, which falls on the terrain will build up a new groundwater bulge, the volume, which has been added to the groundwater volume by step 3, has to be subtracted from this volume because of preservation of mass:

,,

( )1.5*1000

eff gw compensategw new gw

P Ph h

�

�

� �

The compensation resulting from step 3 is calculated as follows.

( )*1000compensate gw newP h h �� Figure b-0-4: New groundwater level after groundwater recharge and compensation

w2

hgw

w1 w1

hgw,n



Appendix C: Input values for oxygen deficit calculation Width canal 17.83m Depth 1.5m Velocity 0.2m/s Qdesign 5.349m3/s Oxygen saturation 20 degrees 8.84g/m3 Oxygen deficit x=0 3g/m3 BOD concentration x=0 1g/m3 k1 0.21/d k2 0.31/d k12 0.21/d Biogene O2 production 2g O2(m2*d) Biogene O2 use 0.5g O2(m2*d) Oxygen use water bottom 2g O2(m2*d) BOD from water bottom 0.4g O2(m2*d) Sources Point discharge W 0.03g/s Initial concentration 1.01g/m3 Diffuse deficit SI2 0.333333g O2(m3*d) Diffuse BOD source SI1 0.4g O2(m3*d)

Transitions to more sustainable urban water management … faculteit...Transitions to more sustainable urban water management and water supply Rutger de Graaf April, 2005 Expansion

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