Medicating the Broad Coast

//////////////////////////////// THEBROAD COAST

f`rom single coastline towards a coastal landscape zone of size

Master Thesis in Landscape Architecture

November 2008

Jo H. J. GrovenIan L. Officer

Supervised byProf. Dr. Jusuck Koh

MEDICATING

PrefaceMedicating the broad coast

The Dutch coast is a fascinating delta coast. This is il-lustrated in a new perspective on the coast.

From single coastline towards a coastal landscape zone of size

The Dutch coast is a fascinating delta coast that has been historically and culturally highly entangled with our Dutch spirit, mutually influencing each other. But this mutual interest changed over the last century. The Dutch coastal landscape now expresses a successful, human-controlled battle against natural constraints, where fear is translated into will-to-control and nature has been subdued. After centuries of man-to-nature interventions, the Netherlands are commonly considered to be safer than ever, but the coastal ecosystem has become paralyzed. It became unhealthy and unable to withstand short-term shocks, restricted and unable to adapt to future changes. A medication is needed

In this Landscape Architecture Master Thesis, an ecologically approached medication is given that builds towards a sustainable and secure future landscape panorama of the Dutch coast.

Cure to secure: An adaptive environment will be constructed, an impelling image to what ecosystem processes and coastal dynamics can contribute to the current quick-fix methods of the present Dutch coast. The future coast is not to be a coastline but instead a broad coast; a healthy and dynamic living buffer landscape of size that generates security. Here, the natural system determines the language, form and use. This implies a stop to solely technical, short-term and rigid solutions.The construction of the broad coast will be directed by man but generated by natures generating processes. Seawalls are reopened to get the best out of this natural system; a resilient coastal landscape zone.

This thesis does not attempt to invent new ideas, it only binds the right existing ones together in a visible way. It does not aim to design form and place, but instead we design a reliable basis where process and time can take over to generate a landscape of new opportunities. Our goal is a paradigm change, a new perspective on the coast: from single coastline towards a coastal landscape zone of size.

Jo Groven & Ian Officer

November 2008,Chair group Landscape Architecture,Wageningen University

SupervisorProf. Dr. Jusuck Koh

Experts The following persons have helped and inspired us by sharing their expertise:Ir. Rudi van Etteger (Landscape architecture chair group at Wageningen University)Ir. Harro de Jong (Buro Harro)Ir. Hein van Bohemen (Technical University of Delft)Jan de Graaf (Co-author of Naar Zee!)John de Ronde (Rijkswaterstaat)Pieter Slim (Wageningen University)Frans Rip (Geodesk Wageningen)

J. Groven, I. Officer & Wageningen University chairgroup LAR2008

Jo H.J. GrovenKersendaelstraat 53724 [email protected]

Ian L. OfficerGeneraal Foulkesweg 136703 BJ WageningenThe [email protected]

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of either the authors or the Wageningen University LAR chairgroup.

This publication is written as a final master thesis report in landscape architecture by order of the chairgroup of landscape architecture at Wageningen University

Chair Group landscape architecture phone: +31 317 484 056 fax: +31 317 482 166 E-mail: [email protected] www.lar.wur.nl Postal address Postbus 47 6700 AA, Wageningen The Netherlands Visiting address Gaia (building no.101) Droevendaalsesteeg 3 6708 BP, Wageningen The Netherlands

Printed in the Netherlands by ABT Repro, VelpABT Repro BVArnhemsestraatweg 358VelpPostbus 826800 AB ArnhemPhone: +31 26 368 32 11www.abtrepro.nl


AbstractCure to secure: medicating the broad coast

This thesis deals with two aspects of the Dutch coast; its natural system and its defense system. It aims to come up with a solution that both cures ecological problems and secures the coastal zone for the future by eco-engineering the coastline into a broad coast, a coastal landscape zone of size.

The Dutch coast is a three-sides and varied coast, influenced by the processes of the coasts natural system such as tide and erosion. Over many centuries the Dutch attitude moved from being sea-focused towards land-focused, resulting in coastline shortening and land reclamations. This was the cause of problems within the natural system of the Dutch coast. All partial problems are highly interrelated , but overall it can be said that the main problem is loss of the gradual transition area that is under influence of both land and sea. The loss of this transition area is highly valued since it provides many ecosystem products and services and it represents great natural and economical value.At the same time, the Dutch coastal defense needs an update due to global climate change. Sea levels rise and waves become stronger, demanding an improved coastal defense that can adapt to future challenges. This update provides the motive for action, both solving the local ecological problems and securing the coast for the future

Many ideas have been developed over the years, but only a few are able to work on both the ecological problems as well as the coastal safety challenges. The most feasible ideas are soft plans that plug into the natural system and benefit from its inherent processes. The presented solution is a natural-system solution; the natural system works best in her own way and this implies thinking within natural processes and dynamics, not working against them. This demands a paradigm change; from closed breakline towards a permeable flexible zone, from single coastline defense towards a broad coastal landscape zone of size. In this thesis is stated that 1) A broad coast (contradictory to a coastline) can contribute in both solving present ecological problems and securing the coastal zone against long-term climate challenges and 2) This broad coast can be designed.Three minimal interventions are necessary to start of this development, afterwards natural processes can take over the construction process. These are 1) providing sediment, 2) allowing and guiding dynamics and exchange and 3) providing space (between a dual defense system). These minimal interventions are capable of solving the problems and long-term challenges. When the coast is developed into a broad coast, it becomes

- A flexible defense system able to dim waves, stabilize the dike base and grow along with sea level rise.

- A resilient & regulating living machine with self-cleaning abilities that can cope with short-term shocks and regulates nutrients, water mixture etc.

- A landscape of (bio)diversity, allowing nutrients to convert to biomass hereby increasing species numbers. New brackish habitats are created and functions such as saline agriculture, recreation and flood-proof housing can be added over time

A typology is developed that shows what solution-types are to be applied along the Dutch coast, either broadening landwards or seawards. The typology is applied in three examples, one of them is further detailed in a catalyzing pilot project. This design for a broad coast pilot along the Westerschelde near Terneuzen shows in a visual way how the concept is applied to reality. The site with its secondary dikes is opened for regulated tides, while nutrient-rich agricultural water is discharged in the zone. Fresh-saline transitions are created and the zone becomes an area under influence of both land and sea. Over time it transforms to a living landscape that defends, regulates and provides diversity and multifunctional use.

The conclusion is that indeed the broad coast can contribute in both solving present ecological problems and securing the coastal zone against long-term climate challenges and that it is designable. Costs of a dual defense system are comparable to traditional dike raising and the zone itself allows multifunctional use, thereby increasing land value. The broad coast concept has the potential of being applied on coastal deltas all over the world and further research will increase expertise that is exportable. Social acceptance can be a problem where landward solutions have to be taken, but a paradigm change takes time. Still, similar projects such as Space for the River have been carried out. Further research is needed on several aspects of the broad coast concept, such as cost details and salt seepage effects.

Keywords:Landscape architecture, the Netherlands, coastal defense, coast, coastline, broad coast, ecology, ecological problems, natural system, zone defense, design

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IntroductionIntroduction to this thesis report

Thesis subject & aim This thesis deals with two aspects of the Dutch coast; its natural system and its defense system. It aims to come up with a solution that both cures ecological problems and secures the coastal zone for the future by eco-engineering the coastline into a broad coast, a coastal landscape zone of size.

Thesis statement In this thesis it stated that:1) A broad coast (contradictory to

a coastline) can contribute in both solving present ecological problems and securing the coastal zone against long-term climate challenges.

2) This broad coast can be designed!

Document structure In this thesis report three main parts can be distinguished:

PART 01 starts with an introduction to the study area; the Dutch coast and its natural system. It demarcates the study area, gives a definition of the term natural system and provides the main processes that are of influence

on the coasts natural system. What is the natural system of the coast?

PART 02 deals with the problems and challenges that face the Dutch coasts natural system. First, in part 02.1 it is explained how the Dutch moved from being sea-focused towards a land-focused attitude and how this land-focused attitude was the cause of problems in the natural system. How was the natural system of the coast handled in the past? Why did the technical engineering approach of handling the coast fail?Part 02.2 discusses the local problems of the Dutch coast in detail, focusing on ecosystem- and defense problems and building up towards a problem statement. What problems did this technical engineering approach bring forth? What main problem of the natural system of the coast can be stated?Part 02.3 explains why this is considered a problem; it discusses the functional, ecological and economical value of the coasts natural system. Why is coastal natural (eco)system

Finding a solution that both cures ecological problems and secures the coastal zone for the future

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important?Part 02.4 provides a motive for action. It shows an update of the coastal defense is needed due to the global climate challenges and down-samples these global challenges to the Dutch situation. What long-term challenges do we face regarding the coastal zone? PART 03 gives a solution for the problems regarding the Dutch coasts natural system. First, part 03.1 states the assignment. What is the assignment? In part 03.2, some projects are reviewed that have been of significance in the coastal debate. What are useful existing ideas? Part 03.3 discusses what sort of approach should be followed to solve problems and comes up with a solution. How can the local problems and long-term challenges be solved?Part 03.4 shows what minimal interventions should be taken to apply this solution and what the profits of the solution can be. What concrete measures have be taken to apply this solution?

Part 03.5 shows a typology for applying the solution, including some examples. What are the different solution-types and where to apply each one?Part 03.6 details the solution by designing a pilot project. What would the solution look like in reality?Finally, in part 03.7 the final conclusions are drawn and recommendations are made for further research.

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Study area The area that is the subject of this thesis study is the Dutch coast with its natural system and its defense system. It consists of a large landscape with both a terrestrial and an aquati c side, a zone along the edge of the North Seas salt water and the Dutch mainland territory. Mainly it is made up of a zone on both sides our primary coastal defense line, whether it is a dike, dam or dune. In front of the primary defense line it is made up of beaches, mud fl ats, isles and sea. Behind the primary defense line the zone oft en consists of either dune reserve or agricultural land, but also ports and build seafronts.Explicitly it is said that this study does not take into account the Dutch rivers and their problems, nor that of the IJsselmeer and its Afsluitdijk. These areas are subject to other complex problems and require their own study. Due to ti me restricti ons they will not be taken into account in this study.

Area demarcati on The borders of the study area are shown in fi gure 01.3. The precise geographic demarcati on of the study area is as follows:

Northeast and Southwest: the internati onal border with Germany respecti vely Belgium.Seaward: the NAP -20 m depth contour (isobath). This contour offi cially marks the coastal base; the deeper coastal zone that is maintained as a foundati on for the beach- and dune area.Landwards: a zone of 5 km from the primary coastal defense line. This distance is taken because it includes both the vast majority of the dune areas and the secondary sea dikes behind the primary sea barrier. Although not offi cially part of the primary coastline, the former Southwestern ti dal inlets are included in this study, since part of the coastal problems are formed by the closure of these inlets and most of this area sti ll has a marine character. They include the Haringvliet, Hollandsch Diep, Grevelingen, Volkerak-Zoommeer, Veersemeer, Oosterschelde, Binnenschelde and Markiezaatmeer. The Westerschelde, sti ll part of the primary coastal defense line, is included as well.

Figure 01.1 [above]. The Dutch coast as part of a larger stretch of sandy coastline between Cap Blanc Nez (FR) and the North cape of Grenen (DK).

Figure 01.2 [right]. The Dutch delta is a low lying coast laying partly below sea level (purple areas) where several rivers mouth into the North Sea. The coastal area can be sub-divided in three different parts; the Wadden area, the Holland coast and the Sout-western Delta.

The three-sided coaststudy area & demarcation

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The Dutch coast; a large area along our primary defense line with both an aquati c and a terrestrial side.

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The three-sided coaststudy area & demarcation

Wadden coast: from the German border to Den Helder. Dikes and Wadden Isles

Holland coast: from Den Helder to Hoek van Holland. Dunes and beaches

Southwestern delta: from Hoek van Hol-land to the Belgian border. Tidal in-lets and Deltaworks

The 3-Sided Coast The Dutch coast as a whole is part of the sandy North Sea coast that stretches from Cap Blanc Nez in France to the head of Northern Jutland in Denmark (Luiten, 2004)(Figure 01.1). But this stretch of sand, as well as its Dutch part, is a varied coast. It is a diverse and dynamic landscape that non-stop alters its face, consisting of river mouths, tidal inlets, islands and peninsulas, lakes, shallow sea, marshlands, beaches, dune ridges and tidal flats. The Dutch coastline itself includes several parts with distinct characteristics and can be parted in three: the Wadden area, the Holland coast and the Southwestern Delta. Within these three parts, the large river systems of the Rhine, Meuse, Scheldt and Ems mouth into the North Sea (Figure 01.2).In the North, the Wadden coast is made up of the diked mainland of the provinces of Friesland and Groningen

and by the Wadden isles with their dunes on the North Sea side and dikes on the Wadden Sea side. Along the Southwestern Delta in the South, the coast consists of dunes directly along the western seaside, dikes along the tidal inlets and the dams of the Deltaworks. The East-West direction is dominant, since some of the large rivers mouth into sea at this point and tidal forces are strong. Between the Southwestern Delta and the Northern Wadden area lays the sandy Holland coast, made up by a wide strip of dunes and beaches and only few sea dikes.

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Figure 01.3 [above]. The three sided coast with its different characteristics. Demarcation as described in text.

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The natural system of the Dutch coast This chapter gives an introducti on to the natural system of the Dutch coast. The coastal area is highly dynamic, making it a landscape of constant change. In order to bett er understand the functi oning of the coast, it is important to know something about the main processes that characterize and infl uence its natural system. First some defi niti ons will be given. Second, some coastal terminology will be explained with the help of a fi gure. This is followed by a descripti on of the genesis of the present coastline, a geologic process. Finally, the most common system processes of the North Sea and Dutch coast will be given, divided in a part on ti des & currents, a part on erosion & accreti on and a part on succession.

De niti ons As stated by Odum (1969), the interacti ng complex of processes forms a system. A second defi niti on of a system is a set of interacti ng or interdependent enti ti es, real or abstract, forming an integrated whole (Wikipedia, 2008). For example, the Earth and its atmosphere defi nes the Earth system. A system can range from more natural to more man-made.

A natural system includes both geologic and biologic processes (Motloch, 2001)(fi gure 01.05). The geologic processes are those by which rocks are formed, diff erenti ated, eroded and deposited to be reformed again into rocks. They include tectonic and erosional forces. Biologic processes are interacti ons between natural living elements and the physical environment, holisti cally combined in ecosystems.An ecosystem is a natural unit consisti ng of all plants, animals and micro-organisms (bioti c factors) in an area functi oning together with all of the non-living physical (abioti c) factors of the environment (Christopherson, 1996). Ecosystems vary greatly in size and the elements that make them up, but each is a functi oning unit of nature. Everything that lives in an ecosystem is dependent on the other species and elements that are also part of that ecological community. If one part of an ecosystem is damaged or disappears, it has an impact on everything else. Ecosystems mostly have vague borders and can include or overlap with other ecosystems. When an ecosystem is healthy, it is sustainable. This means that all the elements live in balance and are

The natural coastal systemintroduction to the coastal processes

capable of reproducing themselves. There is usually biodiversity, meaning that there are a wide variety of living organisms and species in that environment. Since this thesis study deals with both geologic and biologic (ecosystem) processes, the term natural system is used to indicate the Dutch coast as a whole (including geologic and biologic processes), while the term ecosystem is used to indicate a disti nct ecosystem within this natural system.

Coastal terminology The coast consists of several zones and lines, situated around the coastline (fi g. 01.4). A coastline is offi cially defi ned as the edge of the land at the limit of normal high spring ti des, meaning it is submerged only in excepti onal circumstances (e.g. during storm surges). Since the Dutch coastal defense consists partly of dikes and dams, this coastline oft en overlaps the primary defense line. A shoreline is the waters edge, moving to and fro as the ti des rise and fall, making a low-ti de shoreline, a mid-ti de shoreline and a high-ti de shoreline.The shore is the zone between the waters edge at low ti de and the upper limit of wave acti on; the coastline. It

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Figure 01.4 [above]. Coas-tal terminology

Figure 01.5 [right]. The natural system of the Dutch coast includes both geolo-gic and biologic processes.

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Sea birds (Common Tern, Herring Gull...)

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The natural coastal systemcoastal processes; coastline genesis

5500 B.C. 3850 B.C. 2750 B.C.

includes the foreshore or intertidal zone, which is exposed at low tide, but submerged at high tide and the backshore, which is only inundated under extreme conditions.The nearshore zone, comprising the surf zone (with breaking waves) and swash zone (covered as each wave runs up the foreshore), also migrates to and fro as the tides rise and fall. The nearshore zone is bordered sea-ward by the offshore zone, extending to an arbitrary limit in deep water. The terms offshore, onshore and longshore are also used to describe directions of flows of wind, water or sediment.The coast is a zone with varying width, including at least the nearshore, fore-shore and backshore and extending inland to the limit of penetration of marine influences; it is the zone where land, sea and air meet and interact. The coast is subject to a series of pro-cesses, including tectonic movements (downward along the Dutch coast), erosion and sedimentation processes, changes in sea level (rising along the Dutch coast), the effects of tides, waves and currents and atmospheric

variations.Sea level is measured in meters above or below NAP. Normaal Amsterdams Peil (NAP) or Amsterdam Ordnance Datum is a vertical datum in use in large parts of Western Europe. Origi-nally the zero level of NAP was the average summer flood water level (not mean sea level) in the IJ in the centre of Amsterdam, then still connected with the open sea, in 1684. At present it is physically realized by a bench mark in brass in the centre of Amster-dam. Currently NAP is close to mean sea level at the Dutch coast.

Coastline genesis The present Netherlands are part of the North Sea basin. This basin was shaped during the geological period of the Tertiary, starting nearly 65.000.000 years ago (before present; B.P.). The seabed of the at that time shallow shelf sea dropped slowly and continually, while surrounding land was rising. Large rivers deposited thick layers of mud, clay and sand in this shallow sea, coming from Baltic, Mid-European and British higher grounds.During the Quaternary (2.500.000 B.P.

Figure 01.6 [above and right]. Development of the Dutch coastline between 5500 B.C. and A.D.800. (Based on: RACM & TNO. De-veloped for the Nationale Onderzoeksagenda Archeolo-gie, www.noaa.nl)

Figure 01.7 [right, mid-dle]. Regression of the Holland coast between 3000 B.C. and 2008 A.D.

Figure 01.8 [right, below]. Geologic cross-section of the Holland coast, showing old and new dune formati-ons, backed up by peat and clay formations. Coastline first transgressed and later regressed while depositing sediments.

- present) colder glacial and warmer interglacial periods alternated. Also within these ice ages temperatures fluctuated, while the seabed kept dropping due to land subside. During the Pleistocene (the first part of the Quaternary, up to 10.000 B.P.) mainly aeolian (wind-transported) and fluvial (river-transported) sediments where deposited, which near the Dutch coast can be found at a depth of 12 to 25 meters below NAP (see chapter on terminology).The youngest interglacial period, the Holocene, started 10.000 years ago after the Pleistocene. At the beginning the sea level was nearly a 100 meters lower than at present and the North Sea coastline was located hundreds of kilometers towards the north (Backx, 2001). The Holocene is characterized by high temperatures and a rising sea due to melting glaciers and land subside. The southern part of the present North Sea slowly flooded, since it was the lowest situated land. The coastline moved southeastwards towards the present-day coastline with a speed of around 10 km per century, while the sea level rise

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Beach embankments and dunes

Intertidal area (sand flats, mud flats and salt marsh)

Peat bog and river basins (including silted-up flow channels)

Basin of the large rivers (not covered with peat)

River dunes (donken)

Open water (Sea, lagoons, rivers)

Pleistocene landscape (> -6 m NAP)

Pleistocene landscape (-6 m - 0 m)

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Legend

young dunesold dunes

beach levees

clay/sand formation of Calais

clay formation of Duinkerke

peat formation Hollandveen

peat formation Basisveen

3000 B.C.

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slowed down from over 80 cm/century to only 5 cm/century. During this time (between 10.000-6.000 B.P.) a series of sandy embankments where formed in front of the coast, that slowly moved towards the east. Sea clay was deposited behind the embankments and created an extensive tidal flat area. Most of the basins silted up after a strong reduction in the rate of sea-level rise around 6000 years before present. Due to a rising groundwater level, extensive wooded marshlands and peat bogs developed that regularly where flooded by the advancing sea (Backx, 2001). From then on the influence of the sea decreased and the coastline stabilized near the present-day location. Due to differences in tidal force and river sedimentation, the coastline developed into the present three-sided coast, as can be seen in fig. 01.5 and 01.6. Still, natural sea level rise and land subsidence caused the Dutch coastline to slowly regress over the last centuries (fig. 01.7).

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COASTAL PROCESSES Here, the main coastal processes that are of importance to the Dutch coastal situati on will be explained. It is based on informati on provided by the digital encyclopedia de Vleet by Ecomare (2008) and the Belgian Coastal Atlas (CCICZM, 2008).

Tides in the North Sea The ti de is the daily rising and falling moti on of the sea. This moti on is primarily caused by the gravitati onal pull off the moon and sun acti ng on the oceans. The period between high and low ti de is called ebb and the period between low and high ti de is called fl ood. The moment of high and low ti de diff ers from place to place along the North Sea shores.

Tide wave The ti des in the North Sea are caused by the ti de wave from the North Atlanti c Ocean, since the North Sea is too small and shallow to have its own ti des. When seen from the air, the ti dal wave in the North Sea spins in a whirl around several central points in a counter-clockwise directi on (fi g. 01.11). These whirls are caused by the rotati on of the earth (the Coriolis eff ect). The center of such a whirl (called the amphidrome) is a fi xed point with barely any verti cal (ti dal)

movement, the ti dal range is next to zero. The North Sea is infl uenced by three such whirls: one in the northeastern North Sea, one in the eastern central North Sea and one in the southern North Sea between the Dutch and English coast. The whirl in the central North Sea aff ects the ti des in the Wadden Sea the most, while the southern amphidrome most eff ects the western and southwestern Dutch coast.

Tidal range The ti dal range is the verti cal diff erence between the highest high ti de and the lowest low ti de (fi g. 01.10). There are approximately two high and two low ti des per day in the North Sea, with a mean diff erence of about 2.5 m along the Dutch coast. In the Netherlands, the ti dal wave arrives fi rst in the southwest (near Vlissingen) and moves up north arriving at the isle of Schiermonnikoog nearly eight hours later (fi g. 01.9). The height of the ti de is related to the distance from an amphidrome, causing ti dal range fl uctuati ons along the Dutch coast; ti dal diff erence increases the further any given coast lies from the amphidromic point. In shallow water areas, the real ti dal range is strongly

infl uenced by other factors, such as the positi on of the coast and the wind at any given moment or the acti on of storms. In river estuaries, high water levels can considerably amplify the eff ect of high ti de.Twice a month a spring ti de occurs when sun and moon are in the same line (aft er new and full moon), causing the highest ti dal range (up to 4.5 m in Vlissingen). In the same way, twice a month a neap ti de occurs when sun and moon are in a 90 degree angle, causing the lowest ti dal height diff erence (up to 2.0 m in Vlissingen). (De Vleet, 2008)

Sea currents A sea current is a directed, conti nues movement of sea water. On the open ocean, surface currents are generally driven by wind, while deeper currents are oft en driven by density and temperature gradients. In smaller seas, currents are oft en related to the main ocean currents.The North Sea is fed with water from the Atlanti c Ocean and the rivers. There is hardly any exchange of water with the Balti c Sea. Atlanti c Ocean water enters the North Sea from two diff erent openings: via the English Channel from the south and along the Scotti sh coast from the

Figure 01.9 [above, large]. Tides at different locati-ons along the Dutch coast, showing the difference in time of high tides and difference in tidal range. (Source: de Vleet)

Figure 01.10 [above, small]. Tidal range is the vertical difference between low and high tide.

Figure 01.11 [right]. Tidal wave (yellow line) whirling around amphidromic points, reaching high tides at dif-ferent hours in different locations. The further the coast lays from an amphi-dromic point, the greater the tidal range. (Source: www.kustatlas.be)

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The natural coastal systemcoastal processes; tides & currents

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tidal range line where tides have same tidal height difference

north (fi g. 01.13). Because the North Seawater enters via the northwest and south, it can only exit via the northeast. This water fl ows along the Norwegian coast back into the Atlanti c Ocean. These currents are primarily determined by the ti de wave coming from the Atlanti c Ocean. In turn, the currents in the Wadden Sea are primarily determined by those in the North Sea.

Tidal currents As said, the ti de wave is mainly responsible for the currents in the North Sea. There are three types of ti dal fl ows at sea; the forward fl ood current, the backward ebb current and the residual current. Throughout the North Sea the fl ood current is greater in force than the ebb current, creati ng a residual current in the fl ood currents directi on (fi g. 01.13). Along the Dutch coast, the fl ood current is northeastwards and the ebb current southwestwards, creati ng a residual ti dal current along the Dutch shoreline that fl ows from the southwest towards the northeast (fi g. 01.12). Tidal currents

along the coast and especially in the river mouths favor the exchange of water, sediments, nutrients and biota between the coast and the North Sea.

Local currents Local currents along the coast are based on the above factors and local conditi ons. The main sea current, ti dal currents, local wind and water depth as well as river discharge and geographical conditi ons determine the current at a local site.

North Sea water supply The North Sea is supplied with water via several diff erent sources. Every year, 5000 cubic kilometers of water from the Atlanti c Ocean fl ows via the English Channel between England and France into the North Sea. At least 50.000 km3 ocean water enters via the northern entrance by the Shetland Islands. The Balti c Sea delivers 500 km3 of brackish water yearly and the various rivers contribute 300 km3 of fresh water. All the water in the North Sea is refreshed once every two years. Precipitati on and evaporati on keep each other in balance: 500

millimeter per year evaporates and approximately the same amount is precipitated.Diff erent water masses circulate in the North Sea, which someti mes mix poorly with each other showing clear boundaries. These boundaries are called fronts (fi g. 01.13). Fronts originate because the salinity and the temperature of the water can vary as they come from diff erent regions. The strong current in the North Sea also hinders mixture. The result is that polluti ng materials remain fl oati ng for a long ti me along the coast.

Coastal river One of these fronts can be found along the Dutch coastline (fi g. 01.13). Fresh water discharged by the Dutch rivers can fl oat on the heavier salt water along the coastal zone for a good length of ti me due to the diff erence in relati ve density. This strati fi ed fl ow of fresh, nutrient-rich water, called the coastal river, stretches from the shoreline to around 15-30 km off shore and is being taken northeastwards with the ti dal residual current. Although it can maintain the characteristi cs of river water for a long

Figure 01.12 [above]. Currents along the Dutch coastline. A forward fl ood current that is stronger than the backward ebb cur-rent, resulting in a for-ward residual current.

Figure 01.13 [right page]. Surface currents and under currents of the North Sea. Colliding currents and ri-ver discharge create water fronts that mix poorly.

NetherlandsNL

BelgiumBE

GermanyDE

North Sea

forward fl ood current

backward ebb current

national borders of Exclusive Economic Zone (EEZ)

The natural coastal systemcoastal processes; tides & currents


surface current

under current

front

national borders of Exclusive Economic Zone (EEZ)

ti me, the fresh coastal river water will fi nally slowly mix with salt sea water.The coastal River can be made visible with remote sensing techniques because it contains higher contents of sediments and with this a higher turbidity (fi g. 01.19). This turbidity of the coastal river is not only a result of the supply of silt-rich river water, but also is caused by the dumping of dredged material at sea (taken from ports and shipping lanes) and by the above menti oned litt oral drift .Scheldt water is oft en mixed in an earlier stage due to the Westerschelde ti dal inlet. Here the ti de creates strong currents and turbulence, mixing the fresh Scheldt river water with the salt North Sea water quite rapidly in an early stage preventi ng the strati fi cati on to take place. Before the constructi on of the Deltaworks, the former ti dal inlets of Oosterschelde, Grevelingen and Haringvliet had the same water-mixing abiliti es for Rhine and Meuse river water.

Erosion/accreti on The actual shoreline itself, where land and water meet, is naturally conti nuously on the move.

The sea takes away coastal sediments at one end and drops it of at another in a constant play of coastal erosion and accreti on. Direct causes are the infl uences of the currents, ti des, waves, surf, wind and sea-level rise. Although invisible for beach strollers, the most erosion by far takes place on the fore banks. The sand dunes and ridges under the sea surface are conti nually being moved about by sea currents in the directi on of the residual ti dal fl ow. Directly parallel along the coast, there is a net movement of sand in a northeasterly directi on of values between 0,6 and 5 ton/m/day, called the sediment drift . The sand moves towards the ebb deltas of the ti dal inlets between the Wadden Islands and from here washes into the Wadden Sea. The lack of sand on the fore banks is naturally replenished from the beach.

Litt oral drift Litt oral drift is the term used for the net transport of non-cohesive sediments, i.e. mainly sand, along the shoreline due to breaking waves and the longshore current (this is the ti dal residual current, fi g.

01.17 and 01.18). The litt oral drift is also called the longshore transport or the litt oral transport. Since litt oral drift only transports non-cohesive sediments, it is a process that is found longside the sandy parts of the Dutch coastline; mainly the Holland Coast and the beaches of the Wadden Isles.The eff ect of this is determined by factors such as the directi on and fetch of the present wind and, in the long term, of the prevailing wind. Waves striking the shore at an angle as opposed to straight on will cause the wave swash to move up the beach at an angle. The swash moves the sediment parti cles (typically sand or shingle) up the beach at this angle, while the backwash brings them, solely under the infl uence of gravity, directly down the beach. As a result the sediment parti cles are gradually moved downdrift of its origin by the eff ects of swash and backwash; sand is transported in one directi on. Erosion on the beach works concurrently with longshore drift to straighten the overall shape of the beach; by making it conform to the acti on of the waves so that

Figure 01.14 [above, left]. Erosion, accretion and sand nourishments along the Dutch coastline

Figure 01.15 [above, right]. Dutch coastline de-vided in hard (macadamized) and soft (sand) coast

Figure 01.16 [below]. Dunes under storm surge condi-tions

The natural coastal systemcoastal processes; erosion & accretion

over 0,5 million m3/yr 0 - 0,5 million m3/yr0 - 0,5 million m3/yr

NetherlandsNL

BelgiumBE

GermanyDE

North Sea

Increase of sand quantity Decrease of sand quantity

0 - 0,5 million m3/yr over 0,5 million m3/yr

Figure 01.17 [below]. Lit-torial drift caused by swash and backwash

Figure 01.18 [below]. Lit-torial drift causes erosion and accretion near obsta-cles

over 0,5 million m3/yr 0 - 0,5 million m3/yr

11.21 mln m32.00 mln m3

2.99 mln m3

27.97 mln m3

29.33 mln m3

15.45 mln m3

18.09 mln m3

10.47 mln m30.85 mln m3

3.18 mln m36.24 mln m3

1.93 mln m315.36 mln m3

3.76 mln m3Zeeuwsch-Vlaanderen/14.5

Walcheren/30Noord-Beveland/2.5

Schouwen/17Goeree/18,5

Maasvlakte/2

Delfl and/21

Rijnland/41

Noord-Holland/55

Texel/30

Vlieland/14.5

Terschelling/26Ameland/25

Voorne

area/km coastlineamount of sand nourishment (mln m3)

hard macadamized coastlinesoft sandy coastline


any particles of sand that are not deposited parallel to the wave action are areas that receive the most pressure from incoming waves and wind.

Wandering islands Coastal erosion and littoral drift lead to wandering sandbanks and islands: Along the Wadden Islands, sand erodes from the western tips unless replenished with new sediments, while sand deposits at the eastern tips which become elongated. On sandbanks where no management occurs, such as the Razende Bol near Texel, this process is following its most natural course (fig. 01.19). In the past, this wandering has resulted in the loss of villages on the western side of the islands of Vlieland and Schiermonnikoog.

Wind erosion If the vegetation on the beach ridge is damaged, the wind can get a hold of the sand. A hollow is created which usually expands in a northeasterly direction and continually grows deeper. In this way, a weak spot in the beach ridge can evolve creating a dune breach. Up till recently,

damages to the beach ridge used to be repaired as quickly as possible by planting marram grass. Presently, in the framework of dynamic dune management, such hollows are accepted in the dunes as long as they are not a danger with respect to coastal defense.

Wave erosion/accretion Along the coast, sand is places in a wave pattern due to the surf, constructing sand bars close to the beach. Under good conditions more sand is transported with flood than is taken away with ebb flow. This way sand bars can slowly reach the shoreline, suddenly widening the beach. Logically, when conditions are different and ebb flow takes away more sand than the flood brings in, the coastline erodes and shifts inlands.Sand is only removed from the dune ridges during heavy storms, when there is a combination of high water levels and large waves. This dune degradation results in a quick and relatively large landwards movement of the dune front. This sand settles on the momentarily flooded beach,

which in turn slows down the action of the waves. In fact, it is more a matter of sand redistribution than one of an actual loss of sand. After a heavy storm, the beach appears raised and flatter than before. The wind blows a good part of the eroded sand back towards the dunes and the process of dune formation can start again (fig. 01.16). During calm weather, wave action does not damage the dune ridges.

Erosion along the Dutch coast Figure 01.14 shows that the erosion of the sandy coast is strongest along the coast of North Holland north of the North Sea canal up to the Slufter on Texel. Along the South Holland coast and the Southwestern inlets, there is some accretion directly along the beach, however the seaward coastal areas are also strongly eroding and therefore growing steeper. The greatest sand-catchers in the Dutch coastal system are the Westerschelde and the Wadden Sea.The dynamics along the coastline of the Netherlands can cause problems. Without any human intervention,

1816

1840

1863

1896

19331896

1863

1840

Texel

Den Helder

Onrust

Razende Bol

Marsdiep

De Horst

Figure 01.19 [below]. Photo impressions of the Dutch sandy coast

sediment driftdune breach

sand nourishments and dune protection

erosion due to storm surge

wandering sandbanks near Texel

the Dutch coastline would conti nue to move further inlands. To fi ght coastal erosion, the coast is arti fi cially maintained; threatened coastal zones are supplied with yearly sand nourishments by the Dutch Ministry of Transport, Public works and Water Management.

Succession Succession is the process of more-or-less predictable and orderly changes in the compositi on or structure of an ecosystem over ti me. Succession may be initi ated either by formati on of new, unoccupied habitat (e.g., a ti dal mud fl at or a strip of beach) or by some form of disturbance (e.g. fi re, severe windthrow, large fl ood) of an existi ng community. Succession that begins in areas where no soil is initi ally present is called primary succession, whereas succession that begins in areas where soil is already present is called secondary succession. Primary succession is of great infl uence on sedimentati on and therefore an important land-generati ng process in the coastal zone. A primary succession series starts with an environment with extreme conditi ons. Only few species are adapted to these harsh conditi ons.

The fi rst species ease these conditi ons by providing plant material for a top soil, retain water etc. In general, communiti es in early succession will be dominated by few fast-growing, well-dispersed species with many individual plants per species. The eased of conditi ons provide the conditi ons for new species to take root, whereby the one vegetati on gradually changes. As succession proceeds, these pioneer species will tend to be replaced by more competi ti ve species in a more complex ecosystem. The succession will end in a stable end-stage called the climax stage, with a vegetati on that does not alter any further. But in reality, most natural ecosystems experience disturbance at a rate that makes a climax community unatt ainable. Oft en this happens due to climate change or the introducti on of exoti c species.

Salt marsh succession An example of succession is the vegetati on growth of a salt marsh (fi g. 01.21). In undisturbed situati ons, a new sandbank can develop somewhere due to the dynamics of the ti des. When this sandbank gains enough elevati on, eelgrass will start grow.

The eelgrass slows down the current, allowing more bott om parti cles to sett le. The sandbank conti nues to rise and the water level above the bank decreases. Salicorn (also called glasswort) can germinate if the bank is regularly run dry. Eelgrass needs more water depth than salicorn. Since the sandbank is rising, the competi ti veness for salicorn in relati on to eelgrass is conti nually improving; one makes room for another. Glasswort also catches bott om parti cles. The bank becomes even higher and therefore is a more suitable environment for sea meadow grass. This succession of species conti nues while the bank gains elevati on. The environmental situati ons become less extreme with fewer dynamics. Since the circumstances are becoming more constant, the species compositi on is also changing more slowly. When fi nally the salt marsh only fl oods a few ti mes per year, a relati vely stable vegetati on establishes containing salt-tolerant plants, such as sea lavender, sea wormwood, sea purslane, sea aster and salt sandspurry.

Dune succession (fi g. 01.20) The originati on, morphology and the dynamics of coastal dunes are to

decalcination

The natural coastal systemcoastal processes; succession

winds over 15 km/hr and a supply of dry sand are needed to begin to build dunes

pioneer species such as Sand Couch-grass will begin to colonize and bind the shifting sands

pioneer stage - foredunes

dune building

Marram grass can survive a sand deposition rate of up to 1 meter per year. Its root sy-stems are very effi cient at binding the sand

yellow (white) dune stage

decalcination

decalcination

Figure 01.20 [above]. Dune succession proces

Figure 01.21 [right]. Salt marsh succession proces


a large extent connected with the (wind) climate along the coast, the orientati on of the coastline, the vegetati on and the presence of wide sand beaches. The coastal dunes are constructed by the supply of sand from the beach. The dominant wind directi on is parallel to the shore or slightly onshore (southwesterly winds), blowing the sand towards the dunes. The supplied sand piles up along the fl ood mark. Here, small embryonic dunes can originate, where salt-tolerant (halophile) vegetati on can develop. Many plants cannot live in a salty environment with such dynamic circumstances. For this reason, the number of diff erent plants close to the sea is limited. The series begins with sea rocket and sand couch, both of which can germinate on small piles of sand. The plants catch sand while their roots fi xate the sand pile, thereby forming the beginning of a dune. Due to the constant supply of sand the dunes keep growing and gradually loose their saline character. The salt-tolerant vegetati on makes place for a salt-evading vegetati on that can develop due to the presence of fresh groundwater, with species like sedge-, marram- and lyme grass. Marram grass is the dominati ng plant

These dunes are grey from the lichens colo-nizing them and the addition of some organic matter to the sand. Where pulvurised sea shells are a compontent of the sand, lime-loving plants will colonize

The sand is now stable and has been enriched enough to allow the growth of shrubs

Eventually, woodland will develop. It might be helped along by the planting of conifers

grey dune stage (calcareus or acidic)

dune scrub stage

conifer plantation stage

Where there are no shelly components or nutrients have been washed out, acidic com-munities will develop

decalcination

decalcination

decalcination

decalcination

conifer plantation stage

on the sea side of the dune ridge, producing a dense mat of roots that stabilize the dune, while its leaves entrap more sand. Further inlands the dunes are more fi xated and the number of diff erent plants increases, consisti ng of shrubs, grasslands and dune woodland. When the dunes are older, leaching and decalcifying occurs, and interesti ng diff erences between the north and south slope of the dune appear.

8

Gregory Officer (www.gregoryofficer.exto.nl)


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0___

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30

Technical engineering failedSea-focussed early inhabitants

Sea-focused early inhabitants For thousands of years the generations of inhabitants of the present Netherlands lived with the water. The earliest coastal inhabitants of the lowlands housed on the higher dunes, on bay bars and natural levees and on the higher northern sea clay. The oldest coastal settlements date from 2600 B.C. and are found in the Northwest of the present Netherlands. Initially, these sea shore residents lived on coastal fishing and on that what the sea leaves behind (halobioses). During the first century before Christ the clay soils between Amsterdam and the mouth of the Eems river were permanently inhabited. During Roman times (A.D. 0-400) the first local ring dikes were raised around farms and farmland to protect the land against the water. Fertile lands could be farmed while there already was brisk trade on the water due to the deltas strategic position. After the collapse of the West-Roman Empire in A.D. 476 the coastal areas depopulated. Order was lost during these Early Middle Ages, it was the migration period of the Barbarian Invasions (roughly A.D.

300-700). Germanic tribes entered the lowlands, plundering while on the move. Around A.D. 800 large areas of the present Netherlands were a few meters above sea level and the coastline was several kilometers more seawards. Behind the higher dunes lay extensive peat lands.Throughout the High Middle Ages population rapidly increasing again and first attempts where made to drain the Western peat in order to provide agricultural land and fuel. During these years the sea had shifted more inlands and large areas of land became water. The Zuiderzee (Southern Sea, present IJssellake) was shaped, just as the tidal inlets of the southern delta. Despite this, the presence of men in the coastal areas increased, as also his cultivation of the land. The southern delta started a vast development around A.D. 900, when embankments and the damming of channels enabled the regulation of the natural drainage. From the 11th century on people in the coastal zone started to protect themselves against the sea by building sand walls, terps (artificial

Figure 02.1 [above]. The Dutch coastal area with the coastline of the year A.D. 50 projected in a red line.

Dynamic coastal play-ground for land and water has turned into a fixed, rigid single coast-line

3

Cure to secure: Medicating the broad coast

flow hills) and dikes (Backx, 2001). Neighborhood communities started to work together in order to surround their settlements and land with dikes. The construction of more dikes enabled the construction of new towns and villages. In the North the saltines were poldered in, slowly shifting the coastline northwards. Also in the Southwest dikes were put up in the 11th and 12th century to reclaim the salt flats from the sea. Land was reclaimed and cultivated, population boomed and overseas trade richly flourished, partly due to the start of the Hanseatic League.Towards the Late Middle Ages most of the land behind the coastal dunes and on the sea clay was cultivated. The great storm surges, such as the Saint Elizabeth Floods (1404, 1421 and 1424), pointed out the necessity for enhanced water control. Water boards were entrusted with the tasks of dike strengthening and land reclamation. In the West the dikes around the peat lands where combined with drainage techniques, creating the first large polders. In the next centuries land reclamation,

Storm surge barrier Hollandse

IJsselVeersemeer

(Veersegatdam and Zandkreekdam)

Grevelingendam

Volkerakdam

Haringvlietdam

Brouwersdam

Oosterschelde (storm surge barrier, Oesterdam and

Philipsdam)

1953 1960 1965 1970 1975 1980 1985

Chronological scheme of the Deltaworks construction

1200-1300

1300-1400

1400-1500

1500-1600

1600-1700

1700-1800

1800-1900

0 500 1000 1500 2000 km2

Land reclamation per century in km2

1900-1985

750 1250 1750250

350

350

425

710

1120

500

1170

1900

Figure 02.2 [above]. Land reclamation per century in km2. The development of the windmill and later (steam)engine dramatically increased reclamation ef-forts.Based on I.D.G., Compact Geography of the Netherlands, Ministry of Foreign Affairs, Utrecht, The Hague, 1985.

land reclamation per century in km2

fishing industry and trade further developed. From the end of the 16th until the 18th century the economy flourished. The lowlander was sea focused; the sea provided food, trade as well as the picturesque Dutch Light that made our painters famous. The Dutch East- and West India Trading Companies brought wealth to cities like Amsterdam, Hoorn and Delft and the fishing industry was so lucrative that from its profits entire trading- and war fleets where built (Luiten, 2004). The seas provided rich catchments of herring, anchovies and codfish, while the rivers where full of salmon and sturgeon.

Coastline shortening and land-focused thinking In a later stadium though, the lowlander changed her field of vision, she became land-focused. From 1800 to the second half of the 20th century the Netherlands where struck by floods on a regular basis. As a reaction, dikes where heightened and widened, artificial foreshore protection was placed while still the land reclamation continued. Industrial revolution changed

everything. With the invention of the steam engine, transport routes changed from sea based to land based routes, connecting islands with the mainland. Due to the industrialization the agriculture and fishing industry where mechanized, farming was specialized and became more and more fresh water dependent. Management optimized in order to provide sufficient amounts of agricultural fresh water and the fishing industry changed to fossil fuel. People started to loose their relation both to nature and the sea, while industry, technology and traffic problems grew rapidly causing a disturbance of the environment. The landscape was neglected with disastrous results, such as pollution, waste dumping, dike bursts and coastal erosion. Appreciation of the natural environment had changed.Modern times where arising, with high belief in the makability of society. In the first part of the 20th century the disastrous Zuiderzee flood of 1916 was responsible for the later construction of the longest sea dam in the world. With the completion of the

32

32 km long dike (Afsluitdijk) in 1932, the Zuiderzee ceased to exist and lake IJsselmeer was born. Shortening the Dutch coastline with nearly 300 km, this also implicated that along these 300 km coastal towns lost their relation to the sea; a whole region converted from being sea-focused fishing communities to land- focused agricultural communities. It gave the conditions to reclaim over 150.000 ha of polder land, as a result of which some claim our famous Dutch light was lost. Coastline shortening became a concept, constructing dikes part of our international fame.After the storm flood of 1953, the implementation of the Deltaplan accelerated. In 1957 the Dutch parliament accepted the plan that was to protect the low parts of the Netherlands against storm surges. The construction of the Deltaworks that resulted from this engineers plan took over 40 years (figure 02.3). All the tidal inlets except the Westerschelde where to be closed off and dikes where raised to Delta height. Most of the plan was realized within the first thirty years. The Deltaworks primarily

brought us cheaper maintenance and improvement of coastal defense. By dramatically shortening the coastline with the use of dams, the length of dikes to maintain and raise to Delta height became shorter. There were more advantages: the dams were taken into the highway network making the islands accessible. This gave an impulse to the economy and allowed recreation to develop on the islands. The formation of the large fresh water basins (Haringvliet, Hollandsch Diep, Volkerak-Zoommeer) provided vast amounts of fresh water for drinking water supply and agricultural use. With the final completion of the Deltaworks in 1997, the Zeeuwse coast was reduced from 800 to 80 kilometers. Remarkably enough, the present length of the Dutch coastline is controversial. American intelligence measures 451 km of coastline (CIA, 2008) while our own Ministry for Public Works and Water Management only counts 376 km, of which 260 km consist of dunes (Rijkswaterstaat, 2001). Beyond doubt it can be said that of the once long and erratic Dutch

coastline little is left at present (fig. 02.6 and 02.7).

Technical engineering falls short Until 1970 the Dutch produced land and reduced the coastline, but never truly felt responsible for the sustainability of the coastal natural system. Maintenance was solely focused on coastal defense. But the process of raising dikes and pumping away water of sub sea level polders cannot continue forever due to sea level rise and geotectonic subsidence. In the last three to four decades a slow change has taken place; a renewed interest in the natural environment and our relation to the (salt) water. The first demonstrable example of this trend breach is the decision in the late seventies to build a permeable flood barrier for the Oosterschelde in stead of an ordinary dam (Schmidt, 2003). Also, it became known that the coastline shortening and technical engineering did not solely have positive effects. In the construction of the Deltaworks, only the technical lifespan was taken into account. The ecological lifespan was not included

Storm surge barrier Hollandse

IJsselVeersemeer

(Veersegatdam and Zandkreekdam)

Grevelingendam

Volkerakdam

Haringvlietdam

Brouwersdam

Oosterschelde (storm surge barrier, Oesterdam and Philipsdam)

1953 1960 1965 1970 1975 1980 1985


1200-1300

1300-1400

1400-1500

1500-1600

1600-1700

1700-1800

1800-1900

0 500 1000 1500 2000 km2

Land reclamation per century in km2

1900-1985

750 1250 1750250

350

350

425

710

1120

500

1170

1900

Figure 02.3 [above]. Chro-nological scheme of the Deltaworks construction up to 1986. Phillipsdam (1987) and Maeslandkering (1997) where to follow. Based on Wolters-Nooordhoff Atlas Productions, 1988.

Figure 02.4 [right, above]. Fresh-saline transition before and after the con-struction of the Afsluit-dijk and Deltaworks.

Figure 02.5 [far right, above]. Decrease of fresh-saline transitions over the last 50-80 years in hec-tares in the river basins of the Schelde, Maas-Rijn, Rijn and Eems rivers.

Figure 02.6 [far right, middle]. Former coastline. Coastline shortening has decreased our coastline with nearly 75% since 1932.

Figure 02.7 [far right, below]. Present coastline. Coastline shortening has decreased our coastline with nearly 75% since 1932.

Technical engineering failedCoastline shortening and land-focussed thinking


33


Wadden Sea & Southern Sea orSouthwestern inlets & Voordelta

North Sea

North Sea

Wadden Sea or salt water basins

Fresh water basins, e.g. IJsselmeer, Southwestern

inlets

saline fresh

rivers (e.g. IJssel, Rhine)

rivers (e.g. IJssel, Rhine)

fresh

brackish

saline

freshsaline

brackishha 120.000

100.000

80.000

60.000

40.000

1930/1950

20.000

2000

ha 35.000

25.000

20.000

15.000

10.000

1930/1950

5.000

2000

30.000

ha 60.000

50.000

40.000

30.000

20.000

1930/1950

10.000

2000

ha 60.000

50.000

40.000

30.000

20.000

1930/1950

10.000

2000

tidal watersintertidal areatidal marshlands

Decrease of fresh-saline transitions over the last 50-8- years in ha in the river basins of the Schelde, Maas-Rijn, Rijn and Eems rivers

Schelde Maas-Rijn EemsRijn

in its design, but already makes the dams outdated even within their technical lifespan. The constructi on of dikes that has taken place for centuries has led to a hard division of inner- and outer-dike nature, with declined species exchange and ecological transiti ons as a result. Years of dam constructi on have restricted the dynamics and compartmented the ecosystem (fi g. 02.4 and 02.5). Only the Oosterschelde has maintained some of its former dynamics but sti ll lost its fresh-saline transiti on. Due to these losses the coastal regions became safer, but also more vulnerable in many ways. Our coastline has become rigid and infl exible, no more than a thin break line, requiring careful precision maintenance. It does not comport with the ecological system. Slowly the Dutch government has changed her policy from the macadamizing of the coastal defense towards dynamic maintenance of the coast. Since 1990 the policy of dynamic maintenance is put to a start in order to bett er allow the natural dynamics and processes that are coastal inherent

coastline shortening:afsluitdijk (1932): - 300 kmdeltaworks (1953-1997): - 720 kmat present 376 km coastline left; nearly 75% of our coastline lost within 50 years!

(MVW, 1990). It aims to stop the coastal erosion of foreshores and dunes, while sti ll allowing natural processes. Nowadays the coastline is preserved as determined in 1990; sand nourishments compensate the sediment loss in the shallow coastal zone (up to -6 or -8 m) and deeper coastal zone (up to -20 m) that is caused by erosion and sea-level rise. Maintaining the coastline of 1990 is a miti gati on soluti on. When the line is crossed due to erosion, precision maintenance is required to bring the coastline back towards its former state. Due to these on-spot nourishments, natural sediment sorti ng by sand grain size is made impossible, what the eff ects are is not known as of yet.The change in policy has not solved the problems related to the coastline shortening. Dutch coasts problems are two-parted. On one hand there are the (local) problems at present (2008), problems within the natural system. Old technical issues concerning coastal defense have been traded in for these current problems of ecological (and

geomorphologic) nature. This group of problems is more visible and more urgent, they are to be dealt with on the short-term. The next chapter (02.2) will address these problems.On the other hand there are future (global) challenges concerning climate change that have eff ect on the area that will have to be dealt with sooner or later, but the sooner the bett er. Chapter 02.4 will deal with these challenges.

34

The ailing sea systemWhat are the local problems?

In the previous chapter it was pointed out that the technical engineering of the last century had many negative effects on the natural system. Largely due to this technical approach of fixating the Dutch coastline, the natural system of the Dutch coast has dramatically changed (fig. 02.9). Gradients between fresh and saline waters, wet and dry, high and low have become very rare and are hard to preserve within the current natural conditions. Drastic transitions and barriers due to the construction of dikes and dams - have resulted in loss of characteristic habitats and plants- and animal species, as well as species exchange. Compartmenting of former tidal inlets turned them into biologically instable systems. The water quality declined due to over-fertilization and stratification, resulting in booming algae growth and anaerobe conditions. Fish stocks are diminishing due to loss of spawning grounds and overfishing. The current fragmentation of the Dutch coastal system has large management costs, since systems are less stable and resilient to short-term shocks.

In this chapter the natural system of the Dutch coast will be subdivided into the distinct ecosystems. A brief overview of the system will be given, together with an analysis of the main problems of that particular system. The Ijsselmeer system will not be discussed, since it is a complex system and necessary for fresh water retention, thereby requiring specific research and eco-solutions. The following systems will be discussed (see figure 02.8):

WADDEN AREA- Wadden Sea- Wadden islands- Frisian/Groningen coast

HOLLAND COAST- Holland Coast dunes

DELTA- Voordelta- Haringvliet/Hollands Diep - Volkerak-Zoommeer- Grevelingen- Oosterschelde- Veersemeer- Markiezaatmeer & Binnenschelde

Loss of coastal grounds that are under influence of both land and sea; gradual transi-tion areas.

Figure 02.8 [above]. The several systems that are analyzed in this study.

Figure 02.9 [right page]. The natural system of the Dutch coast is subject to both local problems as well as long-term global chal-lenges.

Wadden area

Holland coast

Southwestern Delta

Wadden islands

Wadden Sea

Frisian/Groningen coast

Holland coast

Voordelta

Haringvliet/Hollands Diep

Volkerak-Zoommeer

Grevelingen

Oosterschelde

Veersemeer

Markiezaat/Binnenschelde

Westerschelde

35


- Westerschelde

After the main problems for every distinct ecosystem have been stated, they will be summed up, generalized and placed into a scheme.

24% of primairy water barriers

does not meet set standards

Prohibited to swim

in Krammer en

Volkerak due to

blue algae Date: 22-08-2008

Province Zuid-Holland

De provincie Zuid-Holland heeft

een zwemverbod ingesteld in het

Krammer bij Oude Tonge en het

Volkerak bij Ooltgensplaat. Dit in

steepening of coastal base

4500 ha

4000

3500

3000

2500

2000

1500

1000

500

01970 1975 1980 1985 1990 1995 2000

GrevelingenOosterschelde+

+

+

+

+Sea grass decline in Oosterschelde and Grevelingen between 1970 and 2000

Sea level rise demands sub-stantial measures22 augustus 2008 18:10Door onze redacteur Arjen SchreuderRotterdam, If the sea level rises over one and a half meter, the neccesary measures will be highly expensive, like the construction of a second row of dunes along the whole coast.

tuesday 14 october 2008 Nature in Oosterschelde suffers from unsaturatable sand hunger

Voor de zandhonger in de Oosterschelde besta-at geen oplossing. Het betekent dat langzaam maar zeker schorren, slikken en platen in de geulen van de zeearm verdwijnen. Het verlies aan natuurwaarden is heel groot

THE WADDEN SEAThe Dutch Wadden Area (fig. 02.10) consists of the Dutch Wadden Islands, the Dutch Wadden Sea and the mainland of Friesland and Groningen. Here, the focus will mainly be on the last two areas.

The Dutch Wadden Islands From outside to inside, the Wadden islands consist of the underwater shore, the intertidal beach, the coastal strip of dunes, followed by salt marshes and the adjacent mudflat.The dunes on the Wadden islands were mobile until the beginning of the 20th century. The dunes dispersed by wind due to intensive grazing. Later on, the dunes were fixed for coastal safety, coniferous trees where planted and the grazing stopped. From 1910-1990 artificial dunes were created and fixed with boards of willow and reed. These sand barriers captured in sand and by moving and recreating them, dunes were artificially copied. Fortunately much attention has been paid to the future development of the islands. Nowadays the Wadden Islands have gained more dynamics,

due to the dynamic maintenance or no maintenance at all. As a result the Wadden islands are adapting, developing and changing to a equilibrium including dynamics. Almost all the islands have salt marshes and they are still intact due to salt spray. Gradients between beach, dune, salt marsh and tidal flat are recovering.The main problem of the Wadden Islands lays in the future adaptation to the sea level rise. At the moment the cities on Eastern-Vlieland and Western-Terschelling are appointed as spots that are situated too close to the shoreline. Something has to be done here to suffice to the Dutch coastal safety standards. The future of the existence of the Wadden Islands depends on the speed of the sea level rise and the available sand supplies to keep up with the sea level changes.Main points:- part of the defense system does

not cope with safety standards - future development and existence

of the Wadden Islands is uncertain

36

The ailing sea systemLocal problems of the Wadden area

shoals will grow and again reach an equilibrium. When shoal subsidence occurs, the channels will transport more ti dal volume. It s only aft er the recovery of the original shoal height, that also the channels can recover to their original diameter.At the start of the 20th century, eelgrass fi elds covered more than 6.000 ha of the Dutch Wadden Sea (MNC, 2008). Since 1930 the grounds disappeared due to the wasti ng disease and the constructi on of the Afsluitdijk. The eelgrass habitat became more turbid because of the changing ti des and currents. Aft er 1990 the water clarity enhanced, but in the western part of the Wadden Sea the eelgrass never recovered. At the moment the salt fl uctuati ons in the western Wadden Sea are too large due to the discharges of fresh water coming from the IJsselmeer, for eelgrasses to get a good chance of populati ng the area. Similar to the eelgrass, the mussel banks have largely disappeared. Stable old banks used to cover 4000 ha of the Dutch Wadden Sea. In 1997 approximately 100 ha remained due

The Dutch Wadden Sea The equilibrium conditi on of the ti dal basins of the Dutch Wadden Sea have been subjected to numerous, large and medium scale human interventi on such as closure of basins, land reclamati on, coastal defense structures, sand nourishments etc. The by far largest interventi on which aff ected the morphology of the Dutch Wadden Sea, is the closure of the south part of the basin, the Zuiderzee in 1932.Since the constructi on of the Afsluitdijk (1932), the Wadden Sea is sti ll searching for a new balance. The old channels are mostly silted up. Especially the ti dal inlet Marsdiep, between Den Helder and Texel, was aff ected to a large extent. The Marsdiep inlet imports a large volume of sediment from the adjacent coast and ebb ti dal delta every year, ranging between 3-5 Mm3/year (Elias, 2002) (Waddenvereniging, 2005). The natural sand hunger of the Wadden Sea has increased due to this closure of the Zuiderzee, but also due to gas extracti on and sand- and shell extracti on.

The last decades more sand has been absorbed by the Wadden Sea than is fl owing out, at the expense of the beaches of Northern-Holland. The incoming sediment is even bigger than what is needed to keep up with the sea level rise. The eastern part of the Wadden Sea is growing at the expense of the western part.Tectonic subsidence has the same eff ect as sea level rise. Extra sand hunger takes place, more sand is transported from the coast into the Wadden Sea and the ti dal shoals are again adapted to the current sea level. Unfortunately there is a limit to this transporti ng capacity. Compensati on is only possible when tectonic subsidence and sea level rise together are smaller than 4-6mm a year (NAM, 2004). In the Wadden Sea the channels react diff erently to the sand hunger than the shoals. The channels preserve an equilibrium thats harmonized with the movements of the ti des. The shoals will subside and due to the water movements more sand and water will fl ow over the shoals. If there is enough sand available, the

Figure 02.10 [above]. The Wadden area.

37


to intensive (shellfi sh-) fi shery, mussel seed fi shery and natural storms. Mussel banks, eelgrass fi elds and salt marshes used to be very eff ecti ve buff ering systems of the Wadden area.Main points:- sand hunger and silti ng up of the

Wadden Sea- disappearing fi sh- and breeding

grounds due to fi shery- disappearing of habitats and with

this of natural buff ering capacity (mussel beds and eelgrass fi elds)

Friesland & Groningen Coastline The Zuiderzee, the Wadden Sea and the Eems-Dollard estuary together, used to form a shallow ti dal area where gradual transiti ons occurred from fresh, through brackish, to saline water. Salt marshes are suchlike transiti on areas in this shallow coastal zone where the saltwater gradually levels up to higher land. They constantly silt up and rise up to normal sea level. The natural overgrown parts between the salty Wadden Sea and the fresh mainland, are called salt marshes. Only at high water levels the salt marshes will

be fl ooded. More than 10% of the European salt marshes, almost 9000 ha, are situated in the Dutch part of the Wadden Sea (Waddenzeebeleid Adviesgroep, 2004). The current small strip of salt marshes along the mainland of Groningen and Friesland look natural, but are in fact constructed by man to create agricultural land. Ditches were dug out for drainage and earth dikes or wicker wood dams were raised to decrease fl ow velociti es and retain the sediments. Some of the present marshes are coping with erosion, and at the moment wicker wood dams are needed to make growth of the salt marshes possible. Furthermore the salt marsh areas are not rejuvenati ng and not broadening up. Therefore, these dynamic zones are growing old and too high, roughening up and losing their habitat qualiti es. Natural, broad and dynamic salt marshes are capable to self sustain and are ideal habitats for unique fauna and birth life. The ideal salt marsh consists of diff erent transiti ons from low to high with on each zone a characteristi c vegetati on. In this way

N,P

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they contribute to coastal safety. At present the strip of salt marshes along the Friesland and Groningen coast is to small for the Waddensea system; it swift ly crosses over from mudfl at to dry land, without a wide area of these valuable transiti ons. Therefore the salt marshes cannot retain enough silt in comparison to the system, causing the Wadden Sea to be quite turbid (Waddenvereniging, 2008). As a result of the rigid defense barrier in the form of dikes there is an absence of foreshore fresh-saline land gradients, but also fresh-saline water gradients. Because of this, the mainland suff ers from salt seepage in the agricultural land and fi sh migrati on is next to impossible.Main points:- salt marshes cannot fully develop

to a wide area with buff ering capacity

- resilience has disappeared due to the fi xed coastline, dikes and sluices. Almost no interacti on between Wadden Sea and mainland.

- fresh-salt transiti ons disappear. Brackish water areas have largely disappeared

sand erosion

sand hunger (demand)shoreline erosionstratificationover-fertilizationnutrient shortagespecies & habitat declineconstant dredging

exchange barrierweak defense spot (built area)coastal defense insufficient

N,P

N,P

!

Figure 02.11 [above]. Pro-blems of the Wadden area

38

Lauwersmeer The Lauwersmeer (90 km2) originated as a ti dal inlet, but was closed off from the Wadden Sea in 1969. A 13km long barrier was constructed as a retenti on basin for the fresh water from Friesland and Groningen. Because of the constructed barrier the water turned brackish, the existi ng nature altered and new fauna and fl ora established. Since 2003 the Lauwersmeer is designated as a nati onal park.

THE HOLLAND COASTThe Holland Coast dunes The Holland coast (fi g. 02.12) is a 120 km long barrier coast and consists of closed coast dune areas, varying in width from less than 100m to several kilometers. It is home to the best known sea resorts of the country. The dunes are of major importance and off er important (eco-)system functi ons, but are unfortunately disconnected and fragmented. Increasing the safety standard of

this thin coastal strip is the one of the important challenges for future development of the Dutch coastal landscape; The major economical- and cultural value of its hinterland calls for a refl ecti on of this thin line.Along the Holland coast, the narrow parts in the dune strip and sett lement directly along the coast cause most of the defense problems. Several points in the coastline do not correspond with the set safety standards and by this are signifi cant for the solidity of total defense line of its dike ring. At certain points like Callantsoog and Ter Heijde the solidity of the dunes also lacks, this can become vulnerable when forceful waves are present. In fi gure 02.13 the situati on of the sett lements close to sea and fragile links in the coastal defense line are indicated.Along the coastline there are large diff erences in erosion and sedimentati on processes. In the south and the north of the Holland coast

erosion occurs, causing the foreshore to steepen (fi g. 02.14). The central part also used to be erosive, but stabilized and slightly accreted during the last century. The dunes along the Dutch coast have already for centuries provided us a solid and relati vely cheap coastal defense. In contrast with the dikes of the Northern and Southwestern coastline, this dune landscape is not a fi xed line. The dunes are sti ll an acti ve dynamic landscape where the landscape formati on is sti ll in progress. The dynamics of sea, wind, salt and sun create a large alternati on of dune landscapes. Sti ll, the dynamics of the dunes are diminishing and are becoming more fi xed. This happens because the natural succession of plant species has changed towards climax stages which stabilise the dunes and make dynamics with additi onal pioneer stages to be lost. In contrast, a stabilized end-stage vegetati on sett les with mainly thicket

The ailing sea systemLocal problems of the Holland coast

Figure 02.12 [above]. The Holland coast.

Figure 02.13 [right page]. Problems of the Holland coast.

Figure 02.14 [below].Stee-pening of coastal base due to natural transgression demands nourishments

dunes

100 years ago

presentfuture

39


and brushwoods. This results in less diff erence in habitats and less biodiversity. Another problem the dune landscape has to face is withering. The withering of the dune scenery has a number of diff erent causes. One is the extracti on of drinking water in the dunes causing the dunes to gradually dry up and fresh water dune pools with their rare vegetati on to be lost.Due to the erosion along the Holland coast, sand nourishments are carried out on a regular base. Here, one of the problems is the use of sand sediments of a totally diff erent compositi on. The distributi on of sand by grain size is neglected and even disrupted when nourishments are placed onshore. This can hold back the natural development of dunes and coastline. The presence of important ports and fairways along the Holland Coast is making coastal- and fairway management very expensive due to constant dredging of these shipping

sand hunger & silting up

xed dune system

disappearing natural buering capacity

disappearing sh & breeding grounds

anaerobic conditions

brackish habitat

nutrient overload

sh barriers

constant dredging

sluice

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channels.Main points:- parts of coastline do not cope with

the Dutch safety standards- erosion causes steepening of the

foreshore- dunes are disconnected, fragmented

and fi xed which decreased biodiversity

- sand nourishment disrupts natural distributi on of sand by grain size

sand erosion

sand hunger (demand)shoreline erosionstratificationover-fertilizationnutrient shortagespecies & habitat declineconstant dredging

exchange barrierweak defense spot (built area)coastal defense insufficient

N,P

N,P

!

40

THE SOUTHWESTERN DELTACurrent situati on The following provides a short descripti on of the current situati on of the Delta waters and their disti nct ecosystem (fi gure 02.15), based upon a Quick Scan held by the experti se centre of the Ministry of Agriculture, Nature and Food quality (Experti secentrum LNV, 2001) and the inventory Delta 2000 held by the Nati onal Insti tute of Coast and Sea (RIKZ, 2000).

The Voordelta (Fig. 02.16, 90.000 ha, salt water foreshore area, ti dal range 300 cm)The Voordelta is the shallow transiti on area between the North Sea and the ti dal inlets of the Southwestern Delta. The constructi on of the large-scale Deltaworks and Maasvlakte port have been of great infl uence on the morphology of the Voordelta, resulti ng in the genesis of a young dynamic landscape of shift ing sandbanks and channels, coastal accreti on and degradati on. With the decline of the channel width of the ti dal inlets due to Deltaworks dam constructi ons, less sand could be transported into these

inlets. The result is that the interti dal area in the Voordelta highly increased, mainly in the mouth of the Haringvliet, while decreasing behind the dams. Sti ll, the growth of interti dal areas in the Voordelta have not been able to compensate the loss of natural area due to the Deltaworks (RIKZ, 2000). In recent years a new equilibrium has established; the shoal height does not increase any further. The Voordelta now has a total surface of around 90.000 ha, including 3.000 ha of interti dal area (beaches and ti dal fl ats) and 290 ha of salt marshes.Its water quality is determined by river discharges, mainly that of the Rhine river. Since ti dal inlets are closed off , the Rhine water does not get mixed with sea water due to ti dal turbidity, but is discharged at regular ti mes into the Voordelta. The result of this poorly mixing water is the coastal river eff ect, fresh water fl oati ng on heavier salt water. The Voordeltas water quality meets the set standards, but sti ll the nutrient concentrati ons of phosphate and nitrogen are much higher than the goals strived for. Large parts of the Voordelta coast are

eroding, causing only 20% of the dune coast to be unprotected. The Voordelta is relati vely nutrient rich and has a high producti vity (Berchum & Smit, 1999). It has an important nursery functi on for fl atf ish like plaice, fl ounder, sole and is an important breeding-, forage-, and overwinter area for birds. The area is a wetland of internati onal importance for seven water bird species, including the spoonbill (6.3% of the West European populati on). Besides this, part of the ti dal fl ats are resti ng areas for seals (Berrevoets et al., 1998). Main points:- new interti dal areas not able to

compensate loss due to Deltaworks- barriers for exchange of organisms

with former ti dal inlets (migrati ng fi sh etc.)

- erosion of coastal headlands- fresh water bulk discharges that

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