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Urban River Basin Enhancement Methods
New techniques for urban river rehabilitation
Methodology
Work Package 8
LNEC João Rocha Elsa Alves EVK-CT-2002-00082
June 2005
Deliverable 8.1
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Methodology i
Research Contractor Contact Details Laboratório Nacional de
Engenharia Civil Av. Brasil, 101 1700-066 Lisboa, Portugal Tel/fax
+351 218443435/+351 218443016 web site www.lnec.pt © 2005 All
methodologies, ideas and proposals in this document are the
copyright of the URBEM project participants. These methodologies,
ideas and proposals may not be used to change or improve the
specification of any project to which this project relates, to
modify an existing project or to initiate a new project, without
first obtaining written approval from those of the URBEM
participants who own the particular methodologies, ideas and
proposals involved. This report is a contribution to research
generally and it would be impudent for third parties to rely on it
in specific application without first checking its suitability. The
URBEM partner organisations accept no liability for loss or damage
suffered by the client or third parties as a result of errors or
inaccuracies in such third party data. Dissemination Status Public
Report Authors João Soromenho Rocha, Laboratório Nacional de
Engenharia Civil (LNEC), Lisbon, Portugal [email protected] Elsa
Alves, Laboratório Nacional de Engenharia Civil (LNEC), Lisbon,
Portugal [email protected]
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Summary In this deliverable it is presented the methodology for
the application of techniques on rehabilitation of urban rivers,
taking into account the information available from other Work
Packages and the research on river engineering. Contributions to
this document represent findings on experience gained in the
analysis of case studies and on the experience of the river
engineering practice on the countries of the URBEM partners. The
rehabilitation of urban rivers includes the knowledge of adequate
techniques, and its relations with all needed type of
interventions, both before and after the implementation of
techniques. The technical interventions are divided in two main
groups: interventions to be practised in the drainage basin
(controlling the hydrological processes) and interventions to
protect maintain and improve the hydromorphological conditions in
stream channels (controlling the hydraulic processes in bed and
banks). The other associated deliverable 8.2 consists on a set of
documents, namely, recommendations, specifications and guidelines.
In the description of methodology there are remissions do that
deliverable and also other deliverables of URBEM project, guiding
the application of techniques to other aspects of the urban river
rehabilitation.
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Contents 1.
Introduction..........................................................................................................
1 2. Initiative for urban river
rehabilitation...................................................................
5
2.1 Initiative in case studies
...............................................................................
5 2.2 Methodology for the initiative in urban river
rehabilitation............................. 6
3. Site definition in urban river
rehabilitation............................................................
9 3.1 Site definition in case studies
.......................................................................
9 3.2 Methodology for site definition in urban river
rehabilitation......................... 10
3.2.1 Two ways for site definition
.................................................................
10 3.2.2 Site definition for urban river rehabilitation
.......................................... 11 3.2.3 Site definition
for urban rehabilitation including its associate river ......
13
4. Formulation of river rehabilitation
......................................................................
15 4.1 Introduction
................................................................................................
15 4.2 Assess baseline condition in urban river rehabilitation
............................... 16 4.3 Set
objectives.............................................................................................
17 4.4 Set boundaries
...........................................................................................
19 4.5 Identify controlling
factors...........................................................................
23
5. Development of
options.....................................................................................
31 5.1 Introduction
................................................................................................
31 5.2 Identify options
...........................................................................................
31 5.3 Describe the consequences of
options....................................................... 37
5.4 Score and choose
options..........................................................................
40
6. Monitoring of rehabilitated urban river
............................................................... 41
6.1 Introduction
................................................................................................
41 6.2 Decide what to
monitor...............................................................................
41 6.3 Design monitoring programme
...................................................................
44 6.4 Implement option and monitoring
............................................................... 48
6.5 Review monitoring results
..........................................................................
48
References
...............................................................................................................
50 ANNEX 1
..................................................................................................................
51
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1. Introduction One of the specific technical and scientific
objectives of the URBEM research project is "to develop innovative
urban watercourse rehabilitation techniques for use in future
schemes". This objective is covered by Work Package 8 - New
techniques for urban river rehabilitation (WP8). The deliverable
8.1 presents the methodology to adopt sound techniques for urban
river rehabilitation. The techniques for urban river rehabilitation
may be applied to the drainage basin (controlling the hydrological
processes) and to protect, maintain and improve the
hydromorphological conditions in stream channels (controlling the
hydraulic processes in bed and banks). There are different types of
techniques in both groups. However, the application of techniques
shall be done in a harmonized procedure where beside the technique
implementation; other aspects of river rehabilitation are taken
into consideration. Consequently, the proposed methodology
considers the tool developed to assess the potential for urban
watercourse rehabilitation (Work Package 5), the implementation and
review of the assessment tool (Work Package 6), the decision
support methodologies (Work Package 9) and finally the development
of indicators of success (Work Package 10). A great importance was
done to the result of the work done for the Work Package 2,
existing case studies, providing a base for the choice of the
techniques and for the understanding of relative success of
different techniques. The reflexions on the behaviour of different
techniques and the conceptual research developed in the project had
done the opportunity to define the proposed methodology. In a minor
way it is also incorporate the work developed in the study-site
monitoring (Work Package 3) and aesthetic evaluation (Work Package
4). The deliverable 8.2 complement the present deliverable. The
deliverable 8.2 is a set of recommendations, specifications and
guidelines. The recommendations on how to naturalise flow regimes
is the first work document prepared in WP8. Information from Work
Package 2 - Existing Case Studies, was used to define current
methods for re-naturalising watercourse flow. The recommendations
are divided into 5 chapters, namely, Characterisation of flow
regimes, Modifications of flow regimes in urban areas, Water
Framework Directive and flow regimes, Procedures for
re-naturalising flow regimes and Recommendations on how to
re-naturalise flow regimes. The procedures for re-naturalising flow
regimes in urban rivers are divided in two main groups: measures to
be practised in the drainage basin (controlling the hydrological
processes) and measures to protect, maintain and improve the
hydromorphological conditions in stream channels (controlling the
hydraulic processes in bed and banks). The two groups are divided
in six types of measures.
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All types of measures may be applied in each case, depending on
the modifications the urbanisation has imposed. Only measures for
river basin are to be used when the river channel did not suffer
significant modifications. Rarer is the case where there are no
modifications in the river basin; this may happen when an urban
area is situated near a large river, where only the interventions
on river channel are done, and the urban area is a small percentage
of the entire river basin area. In this case only measures on river
channel and banks are needed. The general situation is to apply
both types of measures. The recommendations to re-naturalise the
flow regimes in urban rivers include the assessment of the present
situation and of the previous situation of the flow regime, before
the intervention on river basin/channel; the comparison of both
situations in order to obtain the synthesis of the modifications
imposed by the presence of urban areas in the river basin; the
choice of the measures to be designed for the river basin or/and
river channels and banks; the Implementation of measures and the
definition of a monitoring plan if considered necessary for the
follow-up of the re-naturalisation. The recommendation on
incorporation of wetlands, floodplains and sustainable drainage
methods into urban schemes is the second work document prepared in
WP8. The recommendations are divided into 5 chapters, namely,
Wetlands in rivers, Characterisation of floodplains in rivers,
Influence of urban drainage systems on rivers, Procedures to define
urban schemes near rivers and Recommendations on incorporation of
wetlands, floodplains and sustainable drainage methods into urban
schemes. Presently, wetlands in urban areas may serve for flood
control, for water quality issues and for recreation and wildlife
purposes. Within the river rehabilitation concept, retention
facilities close to residential and commercial areas are used as
parks, playgrounds and artificial wetlands. One important
percentage of wetlands is generally associated with floodplains.
Many cities have grown on floodplains and urban planning has to
account for potential inundations, as flooding is part of the
natural hydrological cycle. Design of flood control measures often
base on a 100-year event, but it is more and more understood that
however large the design capacity is, catastrophic events may
overwhelm this magnitude or technical measure may fail. Flood
damage reduction rather than flood protection is a more realistic
goal for urban areas. Considering the remaining risk even when
sound structural measures are present there is always necessary to
develop emergency measures and catastrophe management. The design
of sustainable urban drainage facilities is not primarily a
technical problem but more of an institutional concern, basically
the cooperation between different departments in a city’s
administration. City administration tends to follow well
established principles of clear responsibility boundaries. The
nature of urban drainage normally requires joint ownership and
operation. This often necessitates interdepartmental cooperation in
city councils in areas were often no well established
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lines of communication and assignment of responsibilities exist.
The choice of SUD measures is highly dependent on political and
public support. Other crucial factors in most installations are
land availability, types of pollutants to be removed, groundwater
levels, soil types, construction costs, maintenance costs and
desired pollutant removal. The specifications of new materials and
techniques are mainly dedicated to the interventions on the rivers
itself, namely to improve instream morphology (by classical river
engineering and by soil bio-engineering), to interventions in
drainage basin or to protect the flood in the river valleys. The
design of sustainable urban drainage facilities, and the
interventions in drainage basin, is not primarily a technical
problem but more of an institutional concern, basically the
cooperation between different departments in a city’s
administration. However, it is included in the specifications. The
specifications are prepared for three main domains related to the
rivers: the instream interventions, the river valley interventions
and drainage basin interventions. The first are also divided in two
types of interventions: the classical river engineering and the
soil-bioengineering. Considering that division of interventions
they are prepared two specifications documents, each one for one of
the types previously defined. The Specifications 8.1 deals with the
river engineering, using classical methods of intervention,
although taking into account the specific case of urban river
rehabilitation. The Specifications 8.2 deals with
soil-bioengineering instream interventions.
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2. Initiative for urban river rehabilitation 2.1 Initiative in
case studies In the Work Package 2, Existing case studies, it was
presented how the urban river rehabilitation case studies were
started. The most used initiatives are from public administrative
institutions, almost 90 % of the cases. The fact the river are, in
general, administered by public institutions shall be the major
reason to find that. In second place the initiative is coming from
civic stakeholders. It is thought a significant percentage of civic
stakeholders are in certain way in relation with public
institutions. The two major type of initiators of urban river
rehabilitations have in general a technical staff, where the
perception of the techniques to be used are known. The other two
explicit types of initiators are the interest groups and the need
to respond to legal demands. In those two types it is less probable
to find technical staff to take into consideration the technical
aspects by itself. It also important to know the reasons to
initiate urban river rehabilitation. The same Work Package shows
the major objective to the urban river rehabilitations is the
ecological improvement, almost 100% of cases. However, the term
ecological shall be considered in an extended way, as it is
explained later. The second two objectives are the
amenity/recreation and urban recreation. Both are urban driven
objectives, being the first one a river driven objective. At a
relative low distance appears flood control as an objective. In
this case there is a joint river and urban driven objective. The
last objectives to initiate urban river rehabilitations are the
public involvement, visual improvement and education. Al three are
social driven. The term ecological is, in certain way, related to
the terminology of the EU Water Framework Directive (WFD). Indeed,
all subdivisions considered in the analysis of objectives for the
ecological improvement use concepts defined in the in the WFD. The
most named objective is the stream morphology, 50 % of cases. The
second objective is the water quality. The following objectives are
related with the first one: hydrology/hydraulics, continuum and
lateral connectivity. The last two objectives are the target
species and the vegetation. Both are directly related with last of
the three components defined in the WFD, the ecology. It is
remarkable that the objectives are in very evident ranking, first
in the hydromorphology component, next the water quality and
finally, the ecology.
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2.2 Methodology for the initiative in urban river r
ehabilitation It is clear there are two main reasons to initiate a
new urban river rehabilitation process: to rehabilitate a river
that it is in a bad condition, referred to the transformations its
channel, its water or its habitats had suffer during the
urbanisation process, or to rehabilitate the urban area around the
river, referred to the historical evolution of the urban
occupation. These two types of reasons are completely different,
departing from different rationales, although there are some common
parts in the rehabilitation processes. In the proposed methodology
there is a strong emphasis in the first type of reasons, the
rehabilitation of the river itself. Of course, the rehabilitation
of the river demands an intervention on urban aspects, but they may
appear as a need, and as a consequence, and not as a point of
start. It is the rehabilitation of the river that forces the use of
the appropriate techniques to deal with river channel, river banks
and river basin, in general. On contrary, when the reason is to do
an intervention in the urban area, contemplating the river passing
in that area, the river rehabilitation is a consequence, and in
that condition, the rehabilitation in the river is only to obtain a
better urban area. Of course, the hydromorphological, water quality
and ecological aspects shall be taken into consideration, but they
tend to be considered secondary objectives, unless they are
included members in the team that deal in an adequate way the
technical considerations for the river features. It is proposed the
initiative to rehabilitate urban rivers, independently of the main
reason to do that, shall include the scope inserted in the EU Water
Framework Directive (WFD). The instream interventions to improve
the morphology of river in urban rivers, the water quality and the
ecological conditions of rivers within Europe shall comply with the
WFD. In this it is expected, but for that purposes it is also
needed, to have the appropriate hydromorphology of the river, river
bed and river banks. This is applicable either in natural rivers or
in “Heavily Modified Rivers”. The last case is present in almost
cases in the urban rivers subjected to rehabilitation. When the
initiative for river rehabilitation is done by the River Basin
Administration is natural the process considers all aspects defined
in WFD. When the initiative for river rehabilitation is done by
Urban Administrations shall be made contacts with the River Basin
Administration in order to guarantee the process also includes the
WFD scope. According to WFD one of the main objectives of the
instream interventions is to achieve good ecological conditions by
combining water resources management and city planning, hence
improving the quality of life. The interventions shall be done
with
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Methodology 7
the “best practicable technology” and the present methodology is
made to guide cities how to achieve good ecological potential in
its urban rivers. The rehabilitation of urban rivers shall result
of a planning process that may start a few years leading to the
implementation of measures involving stakeholders that define goals
and objectives and setting quantifiable targets that can be
monitored.
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3. Site definition in urban river rehabilitation 3.1 Site
definition in case studies Site definition within case studies has
displayed as well subjective approaches as methodological
approaches. In the majority of case studies, about 70 %, the sites
were defined with existing knowledge, no selection method being
applied. In remaining case studies the site definition is based in
a selection method. But these definitions have been determined by
three different specific and complementary reasons: city wide,
river network based or basin wide assessments. Again, the site
definition, as the initiative, is commanded or by city
administration or by river administration (network or basin). The
methods used to assess (potential) rehabilitation were the
following (Table 7 in deliverable of Work Package 2):
• Area wide assessments of water body state (including in
landscape planning, water body development plans, territorial
development programmes, landscape assessments);
• Impact analysis and assessments; • Ecological studies
analysing restoration potential; • Pilot projects/on-site tests; •
Site visits and assessment of the knowledge of stakeholders.
The aspects covered were the following:
• Significance of reducing water pollution; • Potential for
ecologic rehabilitation, e.g. re-colonisation; • Significance of
social/aesthetic/cultural/economic enhancement • Potential to
reduce flood damage • Site ownership and boundary lines.
It is noteworthy the aspects covered did not included explicitly
the largest type of intervention, in the river morphology, although
it may appears in the reduction of flood damage aspect. The space
and time scales are also important characteristics to be taken into
consideration in the site definition. In the case studies they were
analysed the width and length of the rehabilitated sections. The
largest ranges of width were 1-5 m (stream) and 5-25 m (small
river), both with 30% of cases; the third range was less than 1 m
width (streamlet) in 23% of cases; the range 25-100 m (large river)
had 9% of cases, and finally in 4% of cases the range was 100-300 m
(major river). In 4% of cases no information was available.
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The lengths of rehabilitated sections of water courses showed
also a wide range: the largest ranges of length were 101-500 m and
1-2 km m, both with 22% of cases; the third and fourth ranges were
2-3 km and larger than 3 km, in 17% of cases; the range 0.5-1.0 km
had 9% of cases, and finally in 9% of cases the range was less 100
m. The mean length was about 2000 m. According to the authors of
the Work Package 2 deliverable, the emphasis of the survey to
primarily consider complex rehabilitation approaches with “good
practice” character, larger scheme may prevail. In fact, it can be
assumed that a much higher proportion of spatially restricted
schemes may be found in European cities. According to the
deliverable of Work Package 2, “rehabilitation projects range in
scale from incorporating an entire drainage basin down to single
interventions along very short reaches of water courses. Urban
river rehabilitation projects very often are combined with a
general upgrading of the more or less close surrounding of the
water course itself. Not seldom the schemes comprise the
landscaping of the adjacent land, the establishment of new paths or
facilities for information. For this reason the land areas affected
by rehabilitation projects also differ in size but without close
relation to the size of water course addressed”. The average
duration from initiation to implementation of a scheme took between
6 to 8 years, varying from a few months up to about two decades.
Implementation duration averaged 2.9 years, varying from a few
weeks to 15 years. Longer time periods usually were connected to
basin wide or citywide programmes, while shorter time periods
related to less complex, site related projects. 3.2 Methodology for
site definition in urban river rehabilitation 3.2.1 Two ways for
site definition The site definition is made by two different main
processes, in relation with main scope of the intervention, and by
consequence, the technical aspects of river rehabilitation. One of
the main processes is centred in the river itself, although some
urban aspects are necessarily included. In this process the driving
forces are in the River Basin Administration or equivalent
institutions. The main scope is to rehabilitate the river, situated
in an urban area, taking into consideration the target a better
river, and by consequence also a better urban in the adjacent area,
banks and flood valleys. In this case, it is natural to find an
emphasis on the river techniques. A joint work to city
administration is needed. The other main process is centred in the
urban rehabilitation near an existing bad river. Of course, the
river aspects are also necessarily included, but in a certain way
more as an urban solver. In this process the driving forces are in
the Urban
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Administration or equivalent institutions. The main scope is to
rehabilitate the city, situated near a river, taking into
consideration the target a better city, and by consequence also a
better river passing there, with its banks and flood valleys saw as
urban zones. In this case, it is natural to find an emphasis on the
urban techniques. A joint work to River Basin administration is
needed. The site definition for these two main processes is not the
same, although some aspects are necessarily present in both. 3.2.2
Site definition for urban river rehabilitation When the
rehabilitation of an urban river is initiated is needed to define
the river reach. There are not rigid rules to define the site where
the rehabilitation is to be implemented. However, using the WFD
terminology is possible to define simple criteria to define the
site where the rehabilitation is to be done. Considering the type
and intensity of efforts to be used in the rehabilitation it is
possible to divide the type of intervention, and consequently the
site definition. The first basic distinction is the
1) Instream river rehabilitation; 2) River basin rehabilitation
(including or not the instream).
The instream river rehabilitation is concentrated in the main
channel, and its lateral adjacent zones where the flood pass. The
site definition contemplates, at least, the definition of the
downstream and upstream cross sections. This is relatively
straightforward but only an expert in flow regimes can find the
appropriate cross sections to tackle with the hydraulic aspects.
The definition of the adjacent areas, equivalent to the flood prone
area, is relatively more difficult, being advisable to use a step
by step approach, unless previous data gives directly the right
definition. An accurate definition is cost and time consuming. At a
first guess a rough definition may be done with the analysis of
geomorphology and geology maps, or with the help of the inhabitants
knowing the history of past river floods, or analysing probable
flood marks. The other more accurate definitions for the flood
prone area will be done based in hydraulic modelling of present,
past or future situations. The hydraulic modelling needs good river
data to guarantee reliable results. The calibration and validation
of hydraulic modelling shall be imposed because is the only way to
be successful in the proposed river rehabilitation. For hydraulic
modelling is needed to define the contributing river basin. That
definition is only to determine the river discharge to be used in
the computation. In
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some cases the river basin is entirely outside the urban area,
in other cases the contrary may be found, all area is in the urban
area. These two limiting cases are quite different in the
implications the study may have. The last case may generate a chain
of scenarios for the reciprocal influence of river basin and
instream. The river basin definition is relatively simple on the
conceptual point of view, it is to determine the river basin
boundaries, where the river processes are generated and transported
to the river channel. Indeed, the river basin, a spatial area where
complex physical, chemical and biologic processes are generated and
transmitted downstream, may also be viewed as a network of small
streams going from the river basin boundaries downstream to the
lower cross section where the river basin is defined. The next
distinction in the site definition is related with the type of
intervention in the instream rehabilitation. Following also the WFD
terminology, and from a soft to a hard intervention they may be
defined three levels of urban river rehabilitation:
a) Biological; b) Water quality; c) Hydromorphological.
In a strictly sense they shall be viewed as a forced set of
three aspects of an unique intervention, but in practical terms,
the two first types of interventions may be used without any
physical (hydromorphological) intervention. In more complex river
rehabilitations it is necessary to have heavy hydromorphological
interventions as a base for better water quality and biological
interventions. Also, some times there is only one type of
intervention. So the consideration of the three proposed levels of
instream river rehabilitation to define the site is quite useful.
For each level the definition of the site have some particular
features. Considering again the WFD terminology, and also the
rationale considered in that Directive, the base level of
intervention is the hydromorphological, an element supporting the
biological elements. The definition of the site shall include the
three basic hydromorphological elements: the hydrological regime
(quantity and dynamics of water flow and connection to groundwater
bodies), the river continuity and the morphological conditions
(river depth and width variation, structure and substrate of the
river bed and structure of the riparian zone). Consequently for the
site definition it will be necessary to gather all pertinent data
related with the above to mentioned elements. From the beginning,
first in a very simple way, the site definition shall consider
those hydromorphological elements. For the definition of the
boundaries of the site (upstream and downstream river cross
sections) all those elements are needed. As each element has
different types of control and influence they will be found
different cross sections. Some times the hydraulic control will be
dominant, imposing larger distances for those cross sections, other
times the river bed structure are dominant, and so on. Consequently
it
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is not easy to find general and simple criteria to help find the
border cross sections for the site. This is the reason to propose
the site definition by a hydraulic expert. The same type of
considerations is valid for the chemical and physico-chemical
elements supporting the biological elements and for the biological
elements. The chemical and physico-chemical elements include a list
of parameters (general and specific pollutants) and consequently,
in order to consider different types of influence and its evolution
along the river, it may imply different cross section localisations
for the borders of the site, either in the river itself, either in
the main affluents to the river. The biological elements include
the compositions and abundance of aquatic flora, benthic
invertebrate fauna and fish fauna. The last element shall also
consider the age structure. For each of biological element we may
find different border to analyse the situation. Considering all
these elements it is straightforward to conclude the site
definition in the river must be done by a small team including at
least to basic domains: hydraulic and biology. It is very probable
that each element implies different cross section in upstream and
downstream border. It is possible to assert the site definition may
imply a variable geometry. This is not contrary to the fact in
simple case it is enough to define only two cross sections for the
border of a river reach to be subject to rehabilitation. Each of
the main cross sections used as boarders of river reach to be
rehabilitated defines a river basin. Some of the river basins are
not urban and are not included in the rehabilitation intervention.
However, others of the river basins are in the urban areas. In this
case a careful definition of river basin limits shall be done,
including the main sub basins inside. 3.2.3 Site definition for
urban rehabilitation including its associate river When the
rehabilitation of an urban area is initiated including an existing
river is also needed to define the river reach. But in this case
the site definition is more intensely marked by the urban scope.
The definition of the river reach where the rehabilitation may
occur may be influenced more by the urban site definition than by
the river limit definition. Beside that, all considerations
presented in 3.2.2 are applicable. In general, in urban
rehabilitation a strong presence of river basin rehabilitation
(including or not the instream) is present. The instream river
rehabilitation, concentrated in the main channel, and its lateral
adjacent zones where the flood pass, are confined strictly with
urban area, unless an appropriate hydraulic approach leads to a
more technical based definition.
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The adjacent areas, defined as urban areas, may be quite
different the flood prone areas. Some times they are larger, other
times smaller ones. The river basin definition in an urban area may
be complex, being the sub basins difficult to find, and the
relations between surface processes and under ground networks,
generating and transporting to the river channel water and
diversified pollutants, not entirely identified for all areas. In
most cases the river basin is entirely inside the urban area. The
development of the urban areas creates pressures in river. The WFD
also imposes “the collection and maintenance of information on the
type of the significant anthropogenic pressures to which the
surface water bodies in each river basin district are liable to be
subject” (Annex II, 1.4). Among other items they are the
following:
1) Estimation and identification of significant point source
pollution, in particular by substances listed in Annex VIII, from
urban … and other installations and activities;
2) Estimation and identification of significant diffuse source
pollution, in particular by substances listed in Annex VIII, from
urban … and other installations and activities;
3) Estimation and identification of significant water
abstraction for urban …and other uses, including seasonal
variations and total annual demand, and loss of water in
distribution systems;
4) Estimation and identification of the impact of significant
water flow regulation, including water transfer and diversion, on
overall flow characteristics and water balances;
5) Identification of significant morphological alterations to
water bodies; 6) Estimation and identification of other significant
anthropogenic impacts on
the status of surface waters; 7) Estimations of land use
patterns, including identification of the main urban
… areas and, where relevant, fisheries and forests. All type of
above written items is needed to use in site definition. Indeed,
when an urban area is rehabilitated, where a river is also or not
rehabilitated, those items are needed to identify the pressure on
the river reach. This river reach may not always be inside, or in
front of, the urban area, because some actions related with water
control may be sent, or received, from adjacent or larger distances
from the urban area. The transfers to or from urban areas shall be
taken into account in the definition site of rehabilitation area,
river basin or river channel.
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4. Formulation of river rehabilitation 4.1 Introduction In the
Work Package 5 it is described the tool for assessing potential for
rehabilitation. Knowing any river rehabilitation may generate a
large number of options it was chosen the multi-attribute decision
making to select from a range of options. Like any other problem
solution in river rehabilitation the decision maker has to:
a) Set the objectives, b) Specify the criteria on which the
analysis is to be based, c) Specify how the criteria on which the
analysis is to be based, d) Specify the analysis method to be
adopted, e) Review the results of the analysis
In addition the decision maker may also be involved in:
f) Developing different options to be assessed, g) Assessing the
different options to be assessed.
The decision maker may be a single person or may be a group; it
may involve some or all of the stakeholders or their
representatives. Also the problem may only one, with a large
complexity, or it may be, in order to facilitate the decision,
disaggregated in parts, when some independency may occur. The
techniques for urban river rehabilitation, the main subject in the
Work Package 8, may be one part of the disaggregation. Being or not
disaggregated the complex of actions, in the methodology presented
they are focused the options for the techniques used in river
rehabilitation. Some remarks are made when strong links are present
for other subjects related with river rehabilitation, such as
urban, aesthetic, economic or social ones. As pointed out in Work
Package 5, the first process in the assessment of the potential for
rehabilitation is the process 1a, formulation of urban river
rehabilitation. This process is divided in four parts:
1) Assess baseline condition; 2) Set objectives; 3) Set
boundaries; 4) Identify controlling factors.
The following sections of the methodology present these four
parts of the first process applied to the techniques for urban
river rehabilitation.
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4.2 Assess baseline condition in urban river rehabi litation The
assessment of the present condition of an urban river or, saw from
a different point of view, an urban area where a river is running,
may be done with different sensibilities, different perspectives,
different interests, different institutions, shortly, is a large
spectrum question. As posed by Work Package 5, this part may be
done in two actions:
1. Review information on catchment and river, 2. Identify
stakeholders.
In the Recommendations 8.1 they are characterised the flow
regimes in urban areas, in the present situation and in the
previous conditions, in order to assess the river condition and the
potential to be rehabilitated. Considering all elements included in
that Recommendations 8.1 the following three steps are recommended
to formulate the urban river rehabilitation, or to consider the
re-naturalisation of the flow regimes in urban rivers:
1) To assess the present situation of the flow regime. The
assessment will include the river basin and the river channel and
banks elements, taking into account the information described in
chapters 2 and 3, and 6.2 of the Recommendations 8.1. This
assessment shall take into account the elements included in the
WFD, as referred to in Chapter 3 of the Methodology.
2) To assess the previous situation of the flow regime, taking
into account the
information described in chapters 2 and 3, and 6.3 of
Recommendations 8.1. The assessment may be done by two alternative
ways; i) the real previous river regime is obtained gathering data
base and historical facts and documents or ii) an ideal previous
situation is obtained by comparison of neighbour unchanged river
basins or by theoretical reasoning.
3) To compare both situations in order to obtain the synthesis
of the
modifications imposed, during all history, by the presence of
urban areas in the river basin. The list of modifications is the
basis to define the interventions to be applied for the river
rehabilitation.
From the knowledge of hydrological regime, the discharges for
different time and space situations, it is possible to characterise
the flow conditions in the river channels. The characterisation of
channel flow processes should include the characterisation of bed
and banks and the hydraulic structures. The only way to collect the
required data is to survey the site. For important structures the
design documents should be referred to, where hydraulic
computations may be included.
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The hydraulic computations using the available data may be
relatively heavy, involving skilled human resources, appropriated
models, and for good results, calibrations. It is very easy to make
large errors when calibration is not done. The results of hydraulic
computations are very sensitive to some input data, such as bed
slope, and mainly to the roughness coefficients. There is no good
method for using the right values for coefficients, unless a
calibration is done or an experienced team is involved. For the
alluvial rivers the difficulties are increased. The
characterisation of river bed sediments should be always included.
The characterisation of river flow processes should be done for the
appropriate situations, being included in most cases, at least: 1)
the flood events, where the river channels are small to convey all
water, 2) the full bank where the beginning of flood occurs, 3) an
average discharge situation, representing the more frequent
situation and 4) low flow situations. For certain rivers the
discharge decreases to zero, remaining, however, in most cases, sub
superficial flows, and small stagnant water bodies. The
computations, supported by calibrations, should deliver for the
chosen cross sections, the water flow characteristics for the cases
referred to above; water levels, velocities, singular flow
behaviour (for instance changes of flow type, sub critical or super
critical), 2D or 3D features (lateral currents, vortex). The
hydraulic characterisation may advance the sediment transport and
water quality characterisation, and also the biological
characterisation. The degree of comprehensiveness of the hydraulic
characterisation depends of the importance of the study. As the
hydraulic computations are in general heavy they should be
included, certainly, in large studies, but may be simplified
accordingly the size of the problem. If we are dealing with a
potential intervention on short reaches of small rivers it should
be enough to do simple computations with a minimum of calibration
procedures and light site surveys. The modifications encountered in
the river channels situated in urban areas may vary from
insignificant to large deviations. Similarly to the hydrological
modification analysis the knowledge of the time evolution of the
urban occupation is the basis for the characterisation of the
previous conditions, and a reference situation shall be found. It
may correspond to a situation where no urban occupation was
present, or alternatively a light occupation existed. The choice is
pure arbitrarily. It is evident the technical work shall be done
taken into consideration the experience of all, being relevant the
stakeholders, where studies may exist and personal knowledge has a
precious value. 4.3 Set objectives The knowledge of the baseline
condition of an urban river, or an urban area where an urban river
runs, is the main base to set objectives for a potential river
rehabilitation,
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or urban rehabilitation, including its river. Following the same
questions for the assessment, the setting of objectives will be
dependent of different sensibilities, different perspectives,
different interests, different institutions, having a large
spectrum scope. As posed by Work Package 5, this part may be done
in three actions:
1. Set broad objectives, 2. Consultation with stakeholders, 3.
Set specific objectives.
In the Recommendations 8.1 they are presented, in chapter 5, the
procedures for re-naturalising flow regimes in urban rivers and
urban river rehabilitation. They are divided in two main groups,
measures to be practised in the drainage basin (controlling the
hydrological processes) and to protect, maintain and improve the
hydromorphological conditions in stream channels (controlling the
hydraulic processes in bed and banks). The two groups are divided
in six types of measures. Both types of measures may be applied in
each case, depending on the modifications the urbanisation has
imposed. Only measures for river basin are to be used when the
river channel did not suffer significant modifications. Rarer is
the case where there are no modifications in the river basin; this
may happen when an urban area is situated near a large river, where
only the interventions on river channel are done, and the river
basin with urban areas is a small percentage of the entire river
basin area. In these cases only measures on river channel and banks
are needed. The general situation is to apply both types of
measures. These recommendations are complemented by the
Recommendations 8.2 where wetlands, floodplains and urban drainage
methods are incorporated into urban schemes. It is known the
urbanisation has been narrowing the watercourses to the minimum
space possible. Due to urbanisation pressure and narrowing of
watercourses within a very limited space, safety fencing and
supporting walls have been built, as well as other buildings that
strongly reduce the hydromorphological state and influence the
physical state and biological state of the river. Consequently, a
broad objective in river rehabilitation shall include measures to
create basic conditions for widening of the stream and management
of river banks. The basic problems are issues in terms of ownership
rights and water-related rights linked with the buildings. Besides
providing additional space for the improvement of the
hydromorphological state, by widening the channel and the banks the
channel flow is enhanced and the water level locally reduced. The
extended channel enables meandering, formation of pools and rapids,
dunes and wetland riparian areas. Also, the channel provides for a
better flow of flood waters. The influence is favourable for the
ecological state of the water body in its entirety.
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The extensions can be done in several variants, i.e. widening of
the river bed only, or widening of banks with different approaches
and modern consolidations made of natural materials. The
rehabilitation may also include the reconstruction of bridges and
enhancement of their scale. The improvement of instream morphology
using river engineering shall be based in well sound application of
river hydraulic knowledge. It is a specialised scientific domain,
and when this is neglected the success of the intervention is low.
If the above referred to broad technical objectives are worked by
the expert in river hydraulics, a following round of stakeholders
consultation is needed to refine the setting of objectives, taking
into consideration not only the technical expertise, but also the
diffuse knowledge of the river problems, coming from other
disciplines, and the constraints imposed by the existence of urban
areas. The main broad objective for the WFD is to achieve the “good
ecological potential” of urban streams. Consequently, the setting
of specific objectives in river rehabilitation shall also follow a
more natural approach, in relation with simpler hard technical
approach. In the past, many rivers were stabilised and hardened
with concrete and steel in order to accommodate navigation and to
protect urban uses from flooding and erosion. River shorelines were
typically designed for a single purpose. Today should be followed a
growing support for ecology and multiple uses as well as an
interest in using “soft engineering” of shorelines at appropriate
locations. Such an approach incorporates flood conveyance concerns,
aquatic habitat, riparian habitat, water quality, recreation and
aesthetics. The setting of specific objectives shall take into
account all these aspects. 4.4 Set boundaries Following the
knowledge of the baseline condition of an urban river, or an urban
area where an urban river runs, and the setting of specific
objectives for a potential river rehabilitation, or urban
rehabilitation, including its river it is needed to set boundaries.
As posed by Work Package 5, this part may be done in four
actions:
1. Define spatial extent of assessment, 2. Define time-scale for
assessment of plan or project, 3. Determine resources for
assessment, 4. Define success indicators and acceptability criteria
(initial review to
be refined during assessment. The chapter 3 of the Methodology
presents the first steps to set boundaries, i.e. the site
definition. In the Recommendations 8.1 they are presented, in
chapter 2 and 3, respectively about characterisation of flow
regimes and modification of flow regimes in urban areas, the main
definitions of physical processes in rivers to help the definition
of spatial and time-scale boundaries. Also the content of two
chapters in
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Recommendations 8.2 helps to define those boundaries. The
chapter 3, about characterisation of flood plains in rivers, is
related to the definition of lateral boundaries. The chapter 4,
about influence of urban drainage systems on rivers, has
information on the urban systems that, in a certain way, are
boundaries for the river system. The definition of spatial
extension of the assessment shall take into account the relative
spatial scale of the river and urban areas. In Work Package 4,
Deliverable 4.2, Methodology of classification of the aesthetic
value of the selected urban rivers it is recognized that “river
width is a geometric parameter that has a strong influence on the
interrelationships between the river and the city. It influences
the scale of the river corridor and the waterfront and its uses,
the accessibility network, the transponibility, traffic and many
other factors in the urban/watercourse environment”. Indeed, the
scale and size of an urban watercourse within the urban morphology
is a very important relationship. The river width has been chosen
in the methodology of classification of the aesthetic values as one
of the starting items for selecting the case study, due to its
relevance in the urban context.
The width of a river is a good measure of the importance of a
river, and is strongly correlated with many aspects of river system
and river basin upstream feeding water, sediments, and other water
constituents. In Recommendations 8.1, section 2.2.2 it is presented
an available quantification of the river characteristics based in
the order of the rivers. It was find out that order of the major
part of the rivers to be rehabilitated are between fourth (IV) and
ninth (IX) orders. That means with river basin areas and river
lengths between about 2 km2 to 300 km2 and 2 km to 50 km. According
to Recommendations 8.1 the modifications in the river net are very
dependent on the space scale of the two areas, the river basin area
and the urban area. Different cases can occur, and for each case
different spatial extent of assessment is necessary. Case 1 – Urban
area much smaller than the river basin
The consequences for river modification, during past times, are
minor except on the part of catchment area where the urban area is
settled. In this case, only a part of the river may be changed
during the past. Definition of spatial extent is relatively simple,
being necessary to separate the parts of rivers basin, respectively
included in the urban area and outside.
Case 2 – Urban area covering the major part of the river basin
The consequences the river may be more or less important depending
where the urban area is located in the catchment. If the urban area
is in the upstream part of catchment, it may significantly alter
the river network in the whole catchment, not only in the urban
area, but also in the downstream part. If the urban area is in the
downstream part of the river network the consequences to downstream
are not felt, and the urban area receives a natural river network
in
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the upstream border. The definition of spatial extension shall
include all types of river basins accordingly with the relative
importance.
Case 3 – Urban area covering the entire river basin In this case
usually the river net is turned completely artificial. Indeed, the
large towns may occupy more than one river basin. The spatial
extension of the river basin is practically superimposed to the
urban area.
As referred to above the order of major part of the rivers to be
rehabilitated is between (IV) and (IX), and these orders are
associated to river basin between 2 km2
to 300 km2, which are at same order of magnitude compatible with
the size of urban areas. For smaller river orders the area of river
basin is approaching a limit where they may be hardly identified as
urban areas. For larger river orders the size of the river basin is
high compared with the area of larger towns. This does not mean
that urban areas are not present around larger rivers. But in this
case we can hardly assert an intervention in the river as a result
of the influence of the urban area, except in the case of the
banks. In this case, the bank is a border, or an interface, between
the urban area and a large water body. The river network may be
extremely disturbed in orders I and II of the stream as a
consequence of urbanisation has been destroying the natural river
network. Artificial channels for mixed sewage system and storm
water system are built and they quickly drain water from
non-permeable urban areas. Many streams have a very limited water
flow. Since artificial piping systems and culverted streams have a
smaller permeability, during some flood events the roads may change
into temporary streams. In consequence the definition of
boundaries, either in river network either in river basin areas, is
not straightforward in urban areas heavily occupied. The careful
analysis of detailed maps and field survey are needed for a good
setting of boundaries for river rehabilitation in urban areas. In
the river environment the time scale is associated to the river
size. As referred to in Recommendations 8.1, chapter 2, the
hydrologic processes in a river have times depending in river basin
size. For very small river basins the significant times are of
order of minutes to few hours. It means the rain events and
associate flow discharges are running in times of order of rain
event time and its multiples. For small river basins the hydraulic
events have generally times less than one day. The peaks of river
discharges are sharp in a time-discharge graphic and the water
level variations along time are fast. Same processes in larger
river basins have a similar variation type but now considering time
values increasing from hours to days as the river basin size
increases. However, the presence of two extreme seasonal
conditions, the wet period with large amount of rain, and dry
period with absence or small amount of rain, causes the
consideration of a second time scale for the analysis of the
hydrologic and hydraulic
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processes, the seasonal variation, and also the monthly
variation of hydrologic and hydraulic parameters. The hydrologic
and hydraulic processes vary also year from year. That variation
shall analysed in long term time series, with monthly or daily
discrimination. The river alluvial beds are moved by the successive
river regimes along the years. For that particular analysis may be
necessary to consider even large time scales, being possible to
arrive to centuries as base for the definition of river bed trends
in the past, and also for the future. The conclusion is the need to
include multiple times scales to set the time boundaries of river
rehabilitation. The time scales in river processes are accompanied
by equivalent time scales in urban activities: from short time
activities as emergency actions during dangerous flood events, to
daily action in day life of a city, like garbage collection,
cleaning of streets and of river banks, to seasonal actions like
flora activities, to yearly action like planning, building
activities and finally to average and long term activities like
urban plans or trends in society. Consequently, the definition of
time scales of plans and of detailed projects for river
rehabilitation may be different. In comprehensive river
rehabilitation projects all time scales shall be included, in order
to do not forget any important subject. In small river
rehabilitation projects, with some few details in river and urban
parts, only one time scale may be used, as for instance in a small
intervention in a cross section of a river, where is enough only
instantaneous flood discharge for the project. But for the same
example, if a alluvial river bed is present, it should be advisable
to consider the time scale for long period analysis, such as few
decades trend. If beside a physical intervention, in the
hydromorphological features of a urban river, there are
interventions in water quality and ecological elements of the urban
river, it is needed to include year time scales, covering the daily
river discharge variations along the year, or years, because both
river processes are very sensitive to river discharge variations
and also to the variation of climate parameters (temperature,
radiation) along the year. After the definition of spatial and tome
boundaries it is possible determine the resources for the
assessment and formulation of river rehabilitation. For smaller
space scale and longer time scales the needed resources shall be
larger. It may be noted that for different time scales are, in
general, associated different expertises in the analysis of river
problems, multi disciplinary teams shall be used. In the proposed
methodology the definition of success indicators and acceptability
criteria (initial review to be refined during assessment) shall be
included in the next part of the formulation of river
rehabilitation.
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4.5 Identify controlling factors Following the previous parts,
assess baseline condition, set objectives and set boundaries, there
is a last part in the formulation of river rehabilitation, of an
urban river, or an urban area where an urban river runs, identify
controlling factors. As posed by Work Package 5, this part may be
done in five actions:
1. Check legislative requirements, 2. Determine financial
limits, 3. Check relevant strategies and plans (including flooding,
land use
planning, environmental, etc.), 4. Identify stakeholder
requirements (including public), 5. Identify physical
constraints.
As already referred to in the proposed methodology it is
included an action coming from the previous part:
6. Definition of success indicators and acceptability criteria
(initial review to be refined during assessment).
The actions 1, 2 and 4 are not directly related to the
techniques for the river rehabilitation. However, all three have an
indirect link with the techniques, mainly the second, imposing cost
limits imposes also limits to the type of solutions. The
stakeholder requirements may also impose some limits to the type of
solutions. The actions 3, 5 and 6 are associated to the technical
formulation of river rehabilitation in urban areas. For the point
of view of technical intervention in river rehabilitation the
kernel questions are in the action 3, to provide the relevant
strategies. Side by side the technical team and other discipline
teams shall raise the potential strategies, taking into
consideration the legislative requirements, the financial limits
and the stakeholder requirements. In the Recommendations 8.1 they
are presented, in chapter 5, procedures for re-naturalising flow
regimes, the planning procedures and the measures to be practised
throughout the river basin and for urban stream rehabilitation in
channel bed and banks. Also the content of chapter 5, in
Recommendations 8.2, procedures to design urban schemes near
rivers, is a base to encounter the relevant strategy or the best
plan of river rehabilitation. The main technical strategies for the
urban river rehabilitation, or for urban rehabilitation including a
river, are, as already presented in 3.2.2 and 3.2.3, the
intervention in one or more than one level, considering the
rationale of the WFD:
a) Hydromorphological, b) Water quality; c) Biological.
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Also the intervention may be done in one or more of the
following situation: 1) Instream river rehabilitation; 2) River
basin rehabilitation 3) Urban area rehabilitation with some or all
components of passing rivers.
The strategies to be checked shall including the appropriate
isolated or combined types of intervention to rehabilitate river
and urban areas together. The next fundamental question is about
the target for the river rehabilitation. There is the intention to
renaturalise just as the river was before the urbanisation? In
Europe this means there is the intention to recover centuries of
history. Only in rare cases this is an attainable target. The most
common case is to restore some aspects of the previous river
environment. The main scope of the strategies of river
rehabilitation shall be to obtain good combinations of
interventions to restore as much as possible the “natural”
conditions of the river. The “natural” conditions are very
difficult to define. A relative broad set of conditions are
possible, turning this fuzzy concept. Consequently, even in a team
of river experts there will raise different targets, and by this
reason it is easily found different parallel strategies. The
combination of strategies for the river itself and other strategies
of urban rehabilitation, when that exists, leads to a great number
of set of interventions. In Work Package 5 the Process 1b, defining
method of assessment, helps to tackle this problem. It is important
to remark it is possible to consider an extension of the target
“natural” conditions, in the sense of identical to the original
conditions; to the target “natural” conditions with the sense of
conditions where the natural forces and processes are used to
“create” a river environment like natural, but where the
controlling of processes is not identical as the original one. We
call this river rehabilitation more as “river creation”. When this
process is not scientifically sound there will be problems to solve
in the future, because they will be needed additional interventions
to maintain the design “created” river. The problems may arise
easily in the morphological interventions and in the ecological
interventions. The corrections for the first one tend to be costly,
compared to the second one. Relatively the interventions in the
water quality are easily done and with lesser doubts in the
results, although they can have higher costs compared with other
two. The physical constraints shall be identified. There are
different types of physical constraints, some associated to the
river channel (like minimum or maximum permissible hydraulic
parameters, singularities on the river bed, water quality standards
compliance, ecological maintenance, etc.) or river basin
(permission on or not of water transfers, maintenance or not of
some land cover, etc.) other with urban features (historical
buildings or infra-structures, administrative subjects, social
status, etc.). Some of the constraints are self evident, but others
are only known by expertise. This leads to discussion because they
do not seem constraints for some in opposition to others. Again the
identification of constraints is a multi disciplinary work,
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and the final list of constraint is not a straightforward task,
but an iterative task, implying some consultation outside the
teams. Finally, there is the last action of the Process part 1a –
Identifying Controlling Factors, to define (success) indicators and
acceptability criteria. It is admitted it is iterative action, with
an initial review to be refined during assessment. In Work Packages
3, 4, 5, and 10, they are proposed parameters to, in a
complementary way, identify controlling factors. The four lists
have similar characteristics, but they are also different in the
way of presentation, and in different amount. The lists are
presented in the Annex 1. All except the Work Package 4 are based,
in a certain way, in the WFD, for the case of the ecological
parameters. The terminology for parameters is different. The term
parameter is used in WP5 and WP8, the term data is used in WP3, the
term indicator is used in WP4 and WP10 and The terms objective and
attribute are used in WP5. The amount of parameters are also quite
different, from 38 to 99, compared to 15 for the WFD, although
these are incomplete for the purpose of URBEM, being also needed
for social and economy identification beside the ecological one.
For the methodology for the techniques of urban river
rehabilitation the dominant parameters are ecological, including
the hydromorphological, chemical and physico-chemical and
biological. However, a few socio and economic parameters shall be
taken into consideration. The WP3 uses the lowest number of data,
38, being divided by 9 hydromorphological, 9 chemical and
physico-chemical, 1 biological and 19 socio- economic. The WP4
increases the number of indicators to 52, being divided by 14 for
the river (5 hydromorphological, 4 biological and 2 on risks), 19
for the city (including 1 for pollution) and 19 for people (7 for
river, 4 for city and 8 personnel). The WP5 increases again the
number of parameters to 72, being divided by 32 for WFD, 32 for the
aesthetic (17 for river and 15 for city), 10 for social and 2 for
economic. The WP10 increases again the number of indicators to 99,
being divided by 43 ecological, 43 social, 8 economic and 5 site
specific. It is evident the possibility to increase as much it is
possible the number of parameters, but this is inconvenient for the
treatment of data. Indeed, the WFD only needs 15 parameters divided
by 5 hydromorphological, 7 chemical and physico-chemical, and 3
biological.
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As referred to before for the techniques for urban river
rehabilitation the dominant parameters are those related with the
WFD system. The reasons to arrive to comparative large numbers of
parameters are the redundancy (unnecessary), the disaggregation
(excessive) and needs to include specific thematic parameters.
Departing from the base, the hydromorphological parameters, it is
followed the description inserted in Table A1.2 in Annex 1, to
describe the fundamental parameters to be considered in the
techniques for urban river rehabilitation. The parameters are
designated by T (technique) and H (hydromorphological), C
(chemical) or B (biological) and by a number in sequence. The first
2 parameters TH1 to TH2 are related with the Hydrological regime
(quantity and dynamic of water flow). The main two parameters are
river discharge and river slope . They represent the two dominant
driving forces: the amount of water running in the system and the
gravitational forces moving the water. It is known to compute river
discharge is needed other parameters but they do not need to be
explicit, like rainfall, basin area, topography, concentration
time, etc. The simpler way is to use only two parameters TH1 as Q,
and TH2 as S. However, for some rehabilitation projects is
convenient to split Q in two or three Qi, for design discharge (for
instance, 100 year return period, Q100) or average discharge (Qave)
or dry season discharge (Qmin). Also, S may be splited in more than
one characteristic slope of the system. In total it may be
necessary two to six parameters, TH1A to TH1C and TH2A to TH2C. The
letters following the number designate parameters in a series of
the same kind parameters. In WP4 they are used the R1 and R2, and
in WP10 the indicators 14, 15, 33. It is also noted the parameter
for floods are mainly inserted in socio-economic subject. Although
the perception and the damages of floods are such that, it is
important do not skip the main and first step of flood analysis, to
know the flood discharge and the consequent flood depth, flood
velocity, and flooded area, before arrive to its consequences. In
WP4 there are the indicators R13 and P4, and in WP10 the indicators
34 and S20. The connection to groundwater bodies may be represented
only by one parameter TH3, subterranean discharge from or to river
Qsub. In WP10 they are used the indicators 16, 36 and 37. The river
continuity may be characterised by the presence or absence of
obstacles, like straightening, weirs, bridges, blocks, rock
formations, and so on. It is difficult to define a consistent
numerical parameter, but maybe the head loss associated to that is
a good solution. It is proposed the TH4, head loss , ∆H.
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In WP4 there is the indicator R8 and in WP10 the indicator 17
and 39 (repeated?). The morphological conditions of the river to be
rehabilitated need to be characterised in the minimum by four
parameters: TH5, river depth (H), TH6, river width (B), structure
of river bed, TH7, median grain size of aluvionar bed (D50) and
structure of riparian zone, TH8, median grain size of aluvionar
bank (Db50). The morphological conditions are function of space and
time. Consequently the measures of the above parameters shall be
done in time series data. The time may be also separated in pre and
post intervention, as a lot of parameters described here. It is
also noted the depth is associated to a discharge, although not in
a unique way. The cross-sections shall also be known by draws, or
in a digital terrain model, that is in a 3D format. This set of
parameters, the cross sections , is designated TH9, Z(x,y). In WP4
the indicator is R3 (only width), but also R4, R6 and R7 are
morphological indicators. In WP10 there is the indicator 18, and
maybe repeated the 42 and 43. In WP3 and WP5 there are references
to the bank or bed material. An additional two parameters important
to analyse the hydromorphological conditions, and not included in
the WFD, are the TH10, sediment yield of the river basin (Ps) and
TH11, sediment transport capacity of the river (Qs). Both are
needed to determine the sediment balance in the river, and
consequently to quantify the state of aggradation or degradation of
alluvial river bed. The same analysis may be done comparing the
time evolution of the cross sections. The sediment transport shall
be also divided in two main fractions: the transport of coarser
grains are more relevant for the morphological condition of the
river than the transport of finer grains, passing the cross
sections without any interference in the river bed, unless a
siltation process occurs. So they are proposed the parameters
TH11A, bed load discharge (Qsb) and TH11B, suspended load (Qss),
wherever they are needed. Only in WP10 there is an indicator
related to the sediment transport, the 48, siltation. Also in WP10
there are two indicators aggregating the morphological conditions,
8 and 9. They are respectively the morphological quality and
hydromorphological conditions, a little bit conflicting each other.
The next set of parameters is related to the chemical and
physico-chemical water quality, indicator 7 in WP10. In the
techniques for the rehabilitation it is enough to consider the
aggregate format as it is included in the WFD. Indeed, the quality
of water depends in a large amount of physical and chemical
parameters, but for the present purpose the fine disaggregation of
parameters is not needed. They are taken only seven parameters such
as is written in WFD. They are TC1, thermal conditions (T), TC2,
oxygenation conditions (O), TC3, salinity (Sa), TC4,
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acidification status (pH) and TC5, nutrient conditions (N) for
the general pollution and TC6, pollution by priority substances
(Pps) and TC7, pollution by other significant substances (Pss). In
WP3 and WP5 they are indicated the data and parameters covering the
same set of chemical properties, relatively more disaggregated in
WP5. For instance the nutrient status shall be determined by the
presence of NH4, NO3, NO2, and PO4. In WP10 the seven main
parameters are covered by the indicators from 22 to 28. There is
also an aggregate indicator, 38, specific pollutant load. In WP4
there are only two indicators C19, pollution, and P5, pollution
also, but the first is really measured and the last is a public
perception. A particular case is the suspended sediment transport.
Beside it be a hydromorphological parameter it is also a quality
parameter. So it is important to add the parameter TC8, turbidity
(Tu). This is also included in WP5 and in WP10, in last case as
indicator 21, transparency. Indeed, the suspended sediment may have
different sources, such inorganic grains, inert or with attached
substances, pollutant or not, and also organic and biological
matter. A final note shall be done to distinguish between the
status of water chemical quality and the causes of its status. So
important is to know how the water is than from and how much
causing factors are entering in water. Consequently, in WP3, WP5
and WP10 there are parameters dealing in a certain way with the
sources of pollutants. For instance in WP3 they are identified the
urban runoff, mining, industrial, road, agricultural and sewage
sources. In WP 10 it is included the indicator 40, “nutrient
immision”. It was not needed to specify parameters for the sources
of the pollutants in the present analysis of techniques for river
rehabilitation. This is in accordance with the adoption for the
water amount; they are not parameters for the genesis of river
discharge. The last set of ecological parameters is for the
biology. They are indicate only 3 parameters in the WFD, and they
are adopted in the present analysis, TB1, composition and abundance
of aquatic flora (CAaf), TB2, composition and abundance of benthic
invertebrate fauna (CAbif), TB3 and composition, abundance and age
structure of fish fauna (CAff). In WP3 it is adopted only the first
type of data, which results from the present situation of
implementation of WFD where only the first parameter has enough
studies to be applied in practice by all countries in a harmonized
way. In WP4 there is the indicator R9, the biological diversity,
but also more 3 indicators for riparian vegetation, R10 to R12. It
is also proposed a parameter for this in the techniques. In WP5 it
is also referred a parameter for the sediment quality and a few
parameters for bank vegetation. The WFD parameters are also adopted
in WP with indicators 11 to 13, beside the global biological
parameter 6. However they are also included more biological
indicators, from 44 to 47, dealing with biomass and densities, and
also an indicator for the width of riparian fringe, 41.
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Methodology 29
In the techniques for urban river rehabilitation it is proposed
the parameter TB4, riparian vegetation (RV), because they have also
an important structuring function in the river bank, beside the
ecological and landscape functions. To complete the physical
properties of the rivers necessary to cope with all aspects of
river rehabilitation they are added two more parameters for the
flood aspects. The proposed parameters are the TS1 (S for social),
flooded area (Fa), and TS2, flood risk (HfVf). The flooded area is
self explained, it measures the flood prone area, and it defines an
important river adjacent area where some constraints to the city
development must be taken into consideration. Internationally the
100 years return period is admitted, but in each particular case
other period may be adopted with pertinent justification. In WP4
there is the indicator R13, flood vulnerability and in WP5 the
flood risk area is referred to. The measure of flood risk is
provided by the product of the water depth and water velocity in
the flooded area. This product is internationally adopted as a
measure of personnel or infrastructure flood risk. Larger numbers
are associated a more dangerous and destructive floods. The flood
risk is adopted in WP3, in WP4 with indicator P4, perception of
flood risk, WP5, and in WP10, indicators S20, flood risk and S24,
fear of hazardous floods. Another social parameter is proposed in
the river rehabilitation techniques, the TS3, intervention
acceptation (IA). This measure the acceptability of the projected
designed or concluded rehabilitation. Inquires and public
participation are the base to determine it. Finally, the last set
of indicators is dedicated to the economic aspects. They are
proposed only 3 parameters, two last included in the WP5 and one of
them in WP10, EN4, and the first included in WP10, EN6. The
parameters are TE1, flood damage cost (FC), TE2, capital cost (CC),
and TE3, annualized maintenance cost (MC). In summary, they are
proposed a minimum of 29 parameters to deal with techniques for
river rehabilitation. They are divided in 23 related with WFD, 3
with social aspects and 3 with economic aspects. The 23 ecological
parameters are divided in 11 for hydromorphological aspects, 8 for
chemical aspects and 4 for biological aspects. The proposed
parameters are in general agreement with the parameters and
indicators proposed in WP3, WP4, WP5 and WP10.
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5. Development of options 5.1 Introduction In WP5 the second
process in the assessment of the potential for rehabilitation is
the process 2a, development of options. This process is divided in
four parts:
1) site selection; 2) identify options; 3) describe the
consequences of options; 4) score options.
The site definition, first than site selection, was presented in
chapter 3 of present methodology. The identification of options is
mainly an expertise task to be done by a multidisciplinary team
covering a large spectrum of skills. Even in the case it will be a
small in stream intervention, an enlarged overview of different
aspects shall be taken into consideration, namely the imposed
constrains by the presence of the city, and the public
participation, saw as input of data and decision help. In the
description of the consequences the maximum of technical
intervention is attached. The modelling of consequences is
dominantly a technical aspect. The scoring of options is again a
team task, to safeguard all important aspects in the development of
options. The following sections of the methodology present the
three remaining three parts of the second process applied to the
techniques for river rehabilitation. 5.2 Identify options According
to WP5 a set of realistic options need to be developed for
consideration. This part of the process may be done in three
actions:
1. Consider controlling factors 2. Consider objectives 3.
Consider likely cost.
To obtain a good set of potential options it must be obtained
professional advice in drawing up a list. The level of detail
required will depend upon the stage that the project has reached.
At feasibility stage then one may only require an outline of each
option. At this stage it is important that the options should cover
a wide range. At later stages of project
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development attention may be concentrated on a smaller range but
may need to be described in more detail. The controlling factors
were presented in section 4.5. All options shall take into
consideration all those factors, the minimum proposed, and expanded
as necessary to cover all particular aspects. The objectives for
urban river rehabilitation were presented in section 4.3. All
options shall be directed to the objectives. In the process the
broad objectives are to be focused in specific objective. For each
specific objective there in general a set of elements of the global
option. That is an option is a set of elements, each attaining a
specific objective. Within an urban context there are often
constraints that limit the potential for river rehabilitation. The
situations that can potentially arise are so diverse that it is not
possible to list all the potential constraints that have to be
considered. In WP5 they are presented four examples of
constraints:
a) the presence of contaminated soil in the banks of the river
may preclude any changes to the banks of the river channel as this
might release contamination into the river system;
b) the presence of contaminated land near the banks of the river
may preclude changes to the flow regime of the river that would
permanently raise water levels as increased water levels might lead
to mobilisation of contaminants within the groundwater system; and
it may also limit the potential for channel re-alignment if the new
channel cannot be constructed within the contaminated area;
c) the presence of drainage outlets along the river bank may
significantly affect the cost of any channel re-alignment if this
would involve modification or relocating the outfalls; and to avoid
this cost it may be necessary to constraint any changes to the
alignment of the river so that the existing outfalls can be
retained;
d) the presence of services, such as gas, electricity or water
mains may constrain the potential for changes to the bank profile
or for channel realignment if they are buried within or close to
the river bank; and the cost of moving such services may be
prohibitively expense. There may also be services running under the
bed of the river channel. This may constrain options for modifying
the bed of the channel.
It is evident by these examples only a large team including all
stakeholders can prevent the identification of options that are
from the beginning condemned. In Recommendations 8.1,
Recommendations 8.2, Specifications 8.1 and Specifications 8.2 are
presented the base for technical intervention in river
rehabilitation. The first two documents present the background and
in the specifications are presented the details for the
techniques.
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Considering all elements included in the Recommendations 8.1 the
following two steps are recommended to identify options for urban
river rehabilitation, or to consider the re-naturalisation of the
flow regimes in urban rivers:
1) To chose the measures to be designed for the river basin
or/and river channels and banks. The measures described in chapter
5 have the effect of recovery to the previous situation.