MEDICATING //////////////////////////////// THE
BROAD COAST
Master Thesis in Landscape Architecture November 2008 Jo H. J. Groven Ian L. Officer Supervised by Prof. Dr. Jusuck Koh
`from single coastline towards a coastal landscape zone of size´
Preface Medicating the broad coast
The Dutch coast is a fascinating delta coast. This is illustrated 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 nature’s 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 Supervisor Prof. 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)
Š J. Groven, I. Officer & Wageningen University chairgroup LAR 2008 Jo H.J. Groven Kersendaelstraat 5 3724 Kortessem Belgium Jo_groven@hotmail.com Ian L. Officer Generaal Foulkesweg 13 6703 BJ Wageningen The Netherlands Ian.l.officer@gmail.com
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:Â +31 317 482 166 E-mail: office.lar@wur.nl 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
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From single coastline towards a coastal landscape zone of size
Abstract Cure 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 coast’s 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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Š Gregory Officer (www.gregoryofficer.exto.nl)
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Introduction Introduction to this thesis report
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 coast’s natural system. What is the natural system of the coast? PART 02 deals with the problems and challenges that face the Dutch coast’s 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 coast’s natural system. Why is coastal natural (eco)system
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Finding a solution that both cures ecological problems and secures the coastal zone for the future
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’.
From single coastline towards a coastal landscape zone of size
PART 03 gives a solution for the problems regarding the Dutch coast’s 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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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 ‘downsamples’ these global challenges to the Dutch situation. What long-term challenges do we face regarding the coastal zone?
The three-sided coast study area & demarcation Grenen
Denmark DK Baltic Sea
North Sea
Germany DE
Netherlands NL
Cap Blanc Nez
Belgium BE
France FR
Area demarcation The borders of the study area are shown in figure 01.3. The precise geographic demarcation of the study area is as follows:
Northeast and Southwest: the international border with Germany respectively Belgium. Seaward: the NAP -20 m depth contour (isobath). This contour officially marks the ‘coastal base’; the deeper coastal zone that is maintained as a foundation 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 officially part of the primary coastline, the former Southwestern tidal 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 still has a marine character. They include the Haringvliet, Hollandsch Diep, Grevelingen, Volkerak-Zoommeer, Veersemeer, Oosterschelde, Binnenschelde and Markiezaatmeer. The Westerschelde, still 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 subdivided in three different parts; the Wadden area, the Holland coast and the Soutwestern Delta.
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The Dutch coast; a large area along our primary defense line with both an aquatic and a terrestrial side.
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 aquatic side, a zone along the edge of the North Sea’s 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 flats, isles and sea. Behind the primary defense line the zone often 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 time restrictions they will not be taken into account in this study.
From single coastline towards a coastal landscape zone of size
North Sea
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IJssel(meer) 555 m3/sec
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The three-sided coast study 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 Holland to the Belgian border. Tidal inlets and Deltaworks
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 EastWest 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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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
From single coastline towards a coastal landscape zone of size
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Figure 01.3 [above]. The three sided coast with its different characteristics. Demarcation as described in text.
The natural coastal system introduction to the coastal processes
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The natural system of the Dutch coast This chapter gives an introduction to the natural system of the Dutch coast. The coastal area is highly dynamic, making it a landscape of constant change. In order to better understand the functioning of the coast, it is important to know something about the main processes that characterize and influence its natural system. First some definitions will be given. Second, some coastal terminology will be explained with the help of a figure. This is followed by a description 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 tides & currents, a part on erosion & accretion and a part on succession. Definitions As stated by Odum (1969), the interacting complex of processes forms a system. A second definition of a system is a set of interacting or interdependent entities, real or abstract, forming an integrated whole (Wikipedia, 2008). For example, the Earth and its atmosphere defines 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)(figure 01.05). The geologic processes are those by which rocks are formed, differentiated, eroded and deposited to be reformed again into rocks. They include tectonic and erosional forces. Biologic processes are interactions between natural living elements and the physical environment, holistically combined in ecosystems. An ecosystem is a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment (Christopherson, 1996). Ecosystems vary greatly in size and the elements that make them up, but each is a functioning 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
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 distinct ecosystem within this natural system.
Figure 01.4 [above]. Coastal terminology
Figure 01.5 [right]. The natural system of the Dutch coast includes both geologic and biologic processes.
Coastal terminology The coast consists of several zones and lines, situated around the coastline (fig. 01.4). A coastline is officially defined as the edge of the land at the limit of normal high spring tides, meaning it is submerged only in exceptional circumstances (e.g. during storm surges). Since the Dutch coastal defense consists partly of dikes and dams, this coastline often overlaps the primary defense line. A shoreline is the water’s edge, moving to and fro as the tides rise and fall, making a lowtide shoreline, a mid-tide shoreline and a high-tide shoreline. The shore is the zone between the water’s edge at low tide and the upper limit of wave action; the coastline. It
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From single coastline towards a coastal landscape zone of size
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The natural coastal system coastal processes; coastline genesis
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 seaward 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, foreshore 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 processes, 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
3850 B.C.
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. Originally 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 Amsterdam. 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.
2750 B.C.
- 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
Figure 01.6 [above and right]. Development of the Dutch coastline between 5500 B.C. and A.D.800. (Based on: RACM & TNO. Developed for the Nationale Onderzoeksagenda Archeologie, www.noaa.nl) Figure 01.7 [right, middle]. 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 formations, backed up by peat and clay formations. Coastline first transgressed and later regressed while depositing sediments.
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From single coastline towards a coastal landscape zone of size
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 threesided 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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Legend 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 covered with peat)
rivers
(not
River dunes (‘donken’) Open water (Sea, lagoons, rivers) Pleistocene landscape (> -6 m NAP) 30 A.D.
Pleistocene landscape (-6 m - 0 m) Pleistocene landscape (0 m - 10 m) Pleistocene landscape (10 m - 20 m)
1600 A.D.
Pleistocene landscape (20 m - 50 m)
3000 B.C.
Pleistocene landscape (50 m - 100 m) 2008 A.D.
Pleistocene landscape (100 m - 200 m)
clay formation of Duinkerke peat formation Hollandveen
young dunes old dunes
clay/sand formation of Calais
beach levees peat formation Basisveen
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The natural coastal system waterlevel (cm)
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Tides in the North Sea The tide is the daily rising and falling motion of the sea. This motion is primarily caused by the gravitational pull off the moon and sun acting on the oceans. The period between high and low tide is called ebb and the period between low and high tide is called flood. The moment of high and low tide differs from place to place along the North Sea shores. Tide wave The tides in the North Sea are caused by the tide wave from the North Atlantic Ocean, since the North Sea is too small and shallow to have its own tides. When seen from the air, the tidal wave in the North Sea spins in a whirl around several central points in a counter-clockwise direction (fig. 01.11). These whirls are caused by the rotation of the earth (the Coriolis effect). The center of such a whirl (called the amphidrome) is a fixed point with barely any vertical (tidal)
movement, the tidal range is next to zero. The North Sea is influenced 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 affects the tides in the Wadden Sea the most, while the southern amphidrome most effects the western and southwestern Dutch coast. Tidal range The tidal range is the vertical difference between the highest high tide and the lowest low tide (fig. 01.10). There are approximately two high and two low tides per day in the North Sea, with a mean difference of about 2.5 m along the Dutch coast. In the Netherlands, the tidal wave arrives first in the southwest (near Vlissingen) and moves up north arriving at the isle of Schiermonnikoog nearly eight hours later (fig. 01.9). The height of the tide is related to the distance from an amphidrome, causing tidal range fluctuations along the Dutch coast; tidal difference increases the further any given coast lies from the amphidromic point. In shallow water areas, the real tidal range is strongly
influenced by other factors, such as the position of the coast and the wind at any given moment or the action of storms. In river estuaries, high water levels can considerably amplify the effect of high tide. Twice a month a spring tide occurs when sun and moon are in the same line (after new and full moon), causing the highest tidal range (up to ±4.5 m in Vlissingen). In the same way, twice a month a neap tide occurs when sun and moon are in a 90 degree angle, causing the lowest tidal height difference (up to ±2.0 m in Vlissingen). (De Vleet, 2008) Sea currents A sea current is a directed, continues movement of sea water. On the open ocean, surface currents are generally driven by wind, while deeper currents are often driven by density and temperature gradients. In smaller seas, currents are often related to the main ocean currents. The North Sea is fed with water from the Atlantic Ocean and the rivers. There is hardly any exchange of water with the Baltic Sea. Atlantic Ocean water enters the North Sea from two different openings: via the English Channel from the south and along the Scottish coast from the
tidal range
Figure 01.9 [above, large]. Tides at different locations 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 different hours in different locations. The further the coast lays from an amphidromic point, the greater the tidal range. (Source: www.kustatlas.be)
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COASTAL PROCESSES Here, the main coastal processes that are of importance to the Dutch coastal situation will be explained. It is based on information provided by the digital encyclopedia ‘de Vleet’ by Ecomare (2008) and the Belgian Coastal Atlas (CCICZM, 2008).
From single coastline towards a coastal landscape zone of size
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The natural coastal system coastal processes; tides & currents
North Sea Germany DE
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‘forward’ flood current ‘backward’ ebb current
Belgium BE
Tidal currents As said, the tide wave is mainly responsible for the currents in the North Sea. There are three types of tidal flows at sea; the ‘forward’ flood current, the ‘backward’ ebb current and the residual current. Throughout the North Sea the flood current is greater in force than the ebb current, creating a residual current in the flood current’s direction (fig. 01.13). Along the Dutch coast, the flood current is northeastwards and the ebb current southwestwards, creating a residual tidal current along the Dutch shoreline that flows from the southwest towards the northeast (fig. 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 conditions. The main sea current, tidal currents, local wind and water depth as well as river discharge and geographical conditions determine the current at a local site. North Sea water supply The North Sea is supplied with water via several different sources. Every year, 5000 cubic kilometers of water from the Atlantic Ocean flows 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 Baltic 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. Precipitation and evaporation keep each other in balance: 500
millimeter per year evaporates and approximately the same amount is precipitated. Different water masses circulate in the North Sea, which sometimes mix poorly with each other showing clear boundaries. These boundaries are called fronts (fig. 01.13). Fronts originate because the salinity and the temperature of the water can vary as they come from different regions. The strong current in the North Sea also hinders mixture. The result is that polluting materials remain floating for a long time along the coast.
Figure 01.12 [above]. Currents along the Dutch coastline. A forward flood current that is stronger than the backward ebb current, resulting in a forward residual current. Figure 01.13 [right page]. Surface currents and under currents of the North Sea. Colliding currents and river discharge create water fronts that mix poorly.
Coastal river One of these fronts can be found along the Dutch coastline (fig. 01.13). Fresh water discharged by the Dutch rivers can ‘float’ on the heavier salt water along the coastal zone for a good length of time due to the difference in relative density. This stratified flow of fresh, nutrientrich water, called the ‘coastal river’, stretches from the shoreline to around 15-30 km offshore and is being taken northeastwards with the tidal residual current. Although it can maintain the characteristics of river water for a long
north (fig. 01.13). Because the North Seawater enters via the northwest and south, it can only exit via the northeast. This water flows along the Norwegian coast back into the Atlantic Ocean. These currents are primarily determined by the tide wave coming from the Atlantic Ocean. In turn, the currents in the Wadden Sea are primarily determined by those in the North Sea.
national borders of Exclusive Economic Zone (EEZ)
From single coastline towards a coastal landscape zone of size
surface current under current front
national borders of Exclusive Economic Zone (EEZ)
The natural coastal system coastal processes; erosion & accretion
North Sea
Ameland/25
Germany DE
11.21 mln m3 Terschelling/26 2.00 mln m3 Vlieland/14.5 2.99 mln m3 Texel/30 27.97 mln m3
Noord-Holland/55 29.33 mln m3
Rijnland/41
15.45 mln m3
Delfland/21
18.09 mln m3
Netherlands NL
Maasvlakte/2 10.47 mln m3 Voorne 0.85 mln m3 Goeree/18,5 3.18 mln m3 Schouwen/17 6.24 mln m3 Noord-Beveland/2.5 1.93 mln m3 Walcheren/30
over 0,5 million m3/yr
0 - 0,5 million m3/yr area/km coastline
15.36 mln m3 Zeeuwsch-Vlaanderen/14.5 3.76 mln m3
amount of sand nourishment (mln m3)
Increase of sand quantity
Decrease of sand quantity
over 0,5 million m3/yr
0 - 0,5 million m3/yr
soft sandy coastline
0 - 0,5 million m3/yr
over 0,5 million m3/yr
hard macadamized coastline
Belgium BE
Erosion/accretion The actual shoreline itself, where land and water meet, is naturally continuously 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 accretion. Direct causes are the influences of the currents, tides, 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 continually being moved about by sea currents in the direction of the residual tidal flow. Directly parallel along the coast, there is a net movement of sand in a northeasterly direction of values between 0,6 and 5 ton/m/day, called the sediment drift. The sand moves towards the ebb deltas of the tidal 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. Littoral drift Littoral drift is the term used for the net transport of noncohesive sediments, i.e. mainly sand, along the shoreline due to breaking waves and the longshore current (this is the tidal residual current, fig.
01.17 and 01.18). The littoral drift is also called the longshore transport or the littoral transport. Since littoral 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 effect of this is determined by factors such as the direction 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 particles (typically sand or shingle) up the beach at this angle, while the backwash brings them, solely under the influence of gravity, directly down the beach. As a result the sediment particles are gradually moved downdrift of its origin by the effects of swash and backwash; sand is transported in one direction. Erosion on the beach works concurrently with longshore drift to straighten the overall shape of the beach; by making it conform to the action 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 devided in hard (macadamized) and soft (sand) coast Figure 01.16 [below]. Dunes under storm surge conditions
Figure 01.17 [below]. Littorial drift caused by swash and backwash
Figure 01.18 [below]. Littorial drift causes erosion and accretion near obstacles
time, the fresh coastal river water will finally 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 (fig. 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 mentioned littoral drift. Scheldt water is often mixed in an earlier stage due to the Westerschelde tidal inlet. Here the tide creates strong currents and turbulence, mixing the fresh Scheldt river water with the salt North Sea water quite rapidly in an early stage preventing the stratification to take place. Before the construction of the Deltaworks, the former tidal inlets of Oosterschelde, Grevelingen and Haringvliet had the same water-mixing abilities for Rhine and Meuse river water.
From single coastline towards a coastal landscape zone of size
1816 Texel ‘De Horst’
‘Onrust’ 1863 1840 1896
Marsdiep erosion due to storm surge 1933
‘Razende Bol’
1896
1863 Den Helder 1840 wandering sandbanks near Texel
sand nourishments and dune protection
sediment drift
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.
Figure 01.19 [below]. Photo impressions of the Dutch sandy coast
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,
25
dune breach
The natural coastal system coastal processes; succession
pioneer stage - foredunes yellow (white) dune stage dune building
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
Marram grass can survive a sand deposition rate of up to 1 meter per year. Its root systems are very efficient at binding the sand
decalcination
Figure 01.20 [above]. Dune succession proces Figure 01.21 [right]. Salt marsh succession proces
decalcination The first species ease these conditions The eelgrass slows down the current, by providing plant material for a top allowing more bottom particles to soil, retain water etc. In general, settle. The sandbank continues to communities in early succession will rise and the water level above the be dominated by few fast-growing, bank decreases. Salicorn (also called well-dispersed species with many glasswort) can germinate if the bank individual plants per species. The is regularly run dry. Eelgrass needs eased of conditions provide the more water depth than salicorn. conditions for new species to take Since the sandbank is rising, the Succession Succession isdecalcination the process root, whereby the one vegetation competitiveness for salicorn in relation of more-or-less predictable and gradually changes. As succession to eelgrass is continually improving; orderly changes in the composition or proceeds, these pioneer species one makes room for another. structure of an ecosystem over time. will tend to be replaced by more Glasswort also catches bottom Succession may be initiated either competitive species in a more complex particles. The bank becomes even by formation of new, unoccupied ecosystem. The succession will end in higher and therefore is a more suitable habitat (e.g., a tidal mud flat or a a stable end-stage called the climax environment for sea meadow grass. strip of beach) or by some form stage, with a vegetation that does This succession of species continues of disturbance (e.g. fire, severe not alter any further. But in reality, while the bank gains elevation. The windthrow, large flood) of an existing most natural ecosystems experience environmental situations become less community. Succession that begins disturbance at a rate that makes a extreme with fewer dynamics. Since in areas where no soil is initially “climax� community unattainable. the circumstances are becoming more present is called primary succession, Often this happens due to climate constant, the species composition whereas succession that begins in change or the introduction of exotic is also changing more slowly. When areas where soil is already present is species. finally the salt marsh only floods a called secondary succession. Primary few times per year, a relatively stable succession is of great influence on Salt marsh succession An example vegetation establishes containing saltsedimentation and therefore an of succession is the vegetation tolerant plants, such as sea lavender, important land-generating process in growth of a salt marsh (fig. 01.21). sea wormwood, sea purslane, sea the coastal zone. In undisturbed situations, a new aster and salt sandspurry. A primary succession series starts sandbank can develop somewhere with an environment with extreme due to the dynamics of the tides. Dune succession (fig. 01.20) The conditions. Only few species are When this sandbank gains enough origination, morphology and the adapted to these harsh conditions. elevation, eelgrass will start grow. dynamics of coastal dunes are to the Dutch coastline would continue to move further inlands. To fight coastal erosion, the coast is artificially maintained; threatened coastal zones are supplied with yearly sand nourishments by the Dutch Ministry of Transport, Public works and Water Management.
From single coastline towards a coastal landscape zone of size
grey dune stage (calcareus or acidic)
conifer plantation stage
decalcination
These dunes are grey from the lichens colonizing them and the addition of some organic matter to the sand. Where pulvurised sea shells are a compontent of the sand, limeloving plants will colonize
dune scrub stage
decalcination Eventually, woodland will develop. It might be helped along by the planting of conifers
decalcination
The sand is now stable and has been enriched enough to allow the growth of shrubs
Where there are no shelly components or nutrients have been washed out, acidic communities will develop
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 fixated and the number of different plants increases, consisting of shrubs, grasslands and dune woodland. When the dunes are older, leaching and decalcifying occurs, and interesting differences between the north and south slope of the dune appear.
a large extent connected with the (wind) climate along the coast, the orientation of the coastline, the vegetation and the presence of wide sand beaches. The coastal dunes are constructed by the supply of sand from the beach. The dominant wind direction is parallel to the shore or slightly onshore (southwesterly winds), blowing the sand towards the dunes. The supplied sand piles up along the flood mark. Here, small embryonic dunes can originate, where salt-tolerant (halophile) vegetation can develop. Many plants cannot live in a salty environment with such dynamic circumstances. For this reason, the number of different 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 fixate 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 vegetation makes place for a salt-evading vegetation that can develop due to the presence of fresh groundwater, with species like sedge-, marram- and lyme grass. Marram grass is the dominating plant
28
Š Gregory Officer (www.gregoryofficer.exto.nl)
From single coastline towards a coastal landscape zone of size
28___ 30___
34___
48___
29
53___
Technical engineering failed
Sea-focussed early inhabitants
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.
30
Dynamic coastal playground for land and water has turned into a fixed, rigid single coastline
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 delta’s 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.
Chronological scheme of the Deltaworks construction Storm surge barrier Hollandse IJssel
Veersemeer (Veersegatdam and Zandkreekdam)
Cure to secure: Medicating the broad coast
Grevelingendam
Volkerakdam
Haringvlietdam
Brouwersdam Oosterschelde (storm surge barrier, Oesterdam and Philipsdam) 1953
1960
1970
1965
1975
1985
1980
land reclamation per century in km2
Land reclamation per century in km2
1200-1300
350
1300-1400
350
1400-1500
425
1500-1600
710
1600-1700
1120
1700-1800
500
1800-1900
1170
1900-1985
1900
250
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,
500
750
1000
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 landfocused thinking In a later stadium though, the lowlander changed her field of vision, she became landfocused. 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
1250
1500
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
1750
2000 km2
Figure 02.2 [above]. Land reclamation per century in km2. The development of the windmill and later (steam)engine dramatically increased reclamation efforts.Based on I.D.G., Compact Geography of the Netherlands, Ministry of Foreign Affairs, Utrecht, The Hague, 1985.
31
0
Technical engineering failed
Coastline shortening and land-focussed thinking
Chronological scheme of of the theDeltaworks Deltaworksconstruction construction Chronological scheme Storm surge barrier Hollandse IJssel
Veersemeer (Veersegatdam and Zandkreekdam)
Grevelingendam
Volkerakdam
Haringvlietdam
Brouwersdam Oosterschelde (storm surge barrier, Oesterdam and Philipsdam) 1953
1960
1965
1970
1975
1980
1985
Land reclamation per century in km2
1300-1400
1400-1500
32 km long dike (Afsluitdijk) in 1932, the Zuiderzee1500-1600 ceased to exist and lake IJsselmeer was born. Shortening 1600-1700 the Dutch coastline with nearly 300 km, this also implicated that along these 300 km1700-1800 coastal towns lost their relation to the sea; a whole region converted from being sea-focused 1800-1900 fishing communities to land- focused agricultural communities. It gave the 1900-1985 conditions to reclaim over 150.000 ha of polder land, as a result of which some claim our famous0 Dutch light 250 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
350
350
425
brought us cheaper maintenance and improvement of coastal defense. By 710 dramatically shortening the coastline with the use of dams, the length of dikes to maintain and raise to Delta height became shorter. There were 500 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 fresh500 water basins (Haringvliet, 750 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). Technical1120 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. 1170 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 level 1000 1250 due to sea 1500 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
Figure 02.3 [above]. Chronological 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 construction of the Afsluitdijk and Deltaworks. Figure 02.5 [far right, above]. Decrease of fresh1900 saline transitions over the last 50-80 years in hectares in the river basins 2000 km2 of1750 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.
32
1200-1300
Cure to secure: Medicating the broad coast
North Sea saline
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
rivers (e.g. IJssel, Rhine)
Schelde
brackish brackish
fresh
Rijn
North Sea
Fresh water basins, e.g. rivers (e.g. IJsselmeer, Southwestern IJssel, Rhine) inlets
fresh saline
in its design, but already makes the dams outdated even within their technical lifespan. The construction 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 transitions as a result. Years of dam construction have restricted the dynamics and compartmented the ecosystem (fig. 02.4 and 02.5). Only the Oosterschelde has maintained some of its former dynamics but still lost its fresh-saline transition. Due to these losses the coastal regions became safer, but also more vulnerable in many ways. Our coastline has become rigid and inflexible, 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 better allow the natural dynamics and processes that are coastal inherent
fresh
Eems
ha 60.000
ha 120.000
ha 60.000
30.000
50.000
100.000
50.000
40.000
80.000
40.000
30.000
60.000
30.000
20.000
40.000
20.000
10.000
20.000
10.000
20.000 15.000 10.000
saline
Maas-Rijn
ha 35.000
25.000
Wadden Sea or salt water basins
tidal waters intertidal area tidal marshlands
5.000
1930/ 1950
2000
(MVW, 1990). It aims to stop the coastal erosion of foreshores and dunes, while still 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 mitigation solution. 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
1930/ 1950
2000
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 effect on the area that will have to be dealt with sooner or later, but the sooner the better. Chapter 02.4 will deal with these challenges.
1930/ 1950
1930/ 1950
2000
2000
coastline shortening: afsluitdijk (1932): - 300 km deltaworks (1953-1997): - 720 km at present 376 km coastline left; nearly 75% of our coastline lost within 50 years!
sorting by sand grain size is made impossible, what the effects are is not known as of yet. The change in policy has not solved the problems related to the coastline shortening. Dutch coast’s 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
33
Wadden Sea & Southern Sea or Southwestern inlets & Voordelta
The ailing sea system
What are the local problems?
Wadden area
Wadden islands Wadden Sea Frisian/Groningen coast
Holland coast
Holland coast Voordelta Haringvliet/Hollands Diep Volkerak-Zoommeer Grevelingen Oosterschelde Veersemeer
Southwestern Delta
Markiezaat/Binnenschelde Westerschelde
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):
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 challenges.
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
34
Loss of coastal grounds that are under influence of both land and sea; gradual transition areas.
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.
Cure to secure: Medicating the broad coast
4500 ha 4000 3500 3000
+
2500
24% of primairy water barriers does not meet set standards
Grevel ingen Ooster scheld e
2000 1500 1000
+
500
+
0 1970 1975
Sea grass de Greveling cline in Oostersch e en betwe en 1970 a lde and nd 2000 1980
1985
+
1990
1995
Sea level rise demand s substantial measures
22 augustus 2008 18: 10 Door onze redacteur Arje n Schreuder Rotterdam, If the sea level rises ove r 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.
swim Prohibited to n in Krammer e to Volkerak due ae blu22e-0a8-lg 2008 Date: Holland Province Zuid-
t id-Holland heef De provincie Zu het in ld ste ge in od een zwemverb t ude Tonge en he Krammer bij O Dit in . at la sp en tg ol Volkerak bij O
tuesday 14 october
+
2000
2008
Nature in Oostersc helde suffers from unsa turatable sand hunger Voor
de zandhonger in de Oosterschelde bestaat geen oplossing. Het betekent dat lan gzaam maar zeker schorr en, slikken en platen in de geulen van de zee arm verdwijnen. Het verlies aan natuurwaarde n is heel groot
steepening of coastal base
After the main problems for every distinct ecosystem have been stated, they will be summed up, generalized and placed into a scheme.
THE WADDEN SEA The 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 19101990 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
35
- Westerschelde
The ailing sea system
Local problems of the Wadden area
The last decades more sand has been absorbed by the Wadden Sea than is flowing 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 effect as sea level rise. Extra sand hunger takes place, more sand is transported from the coast into the Wadden Sea and the tidal shoals are again adapted to the current sea level. Unfortunately there is a limit to this transporting capacity. Compensation 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 differently to the sand hunger than the shoals. The channels preserve an equilibrium that’s harmonized with the movements of the tides. The shoals will subside and due to the water movements more sand and water will flow over the shoals. If there is enough sand available, the
shoals will grow and again reach an equilibrium. When shoal subsidence occurs, the channels will transport more tidal volume. It s only after 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 fields covered more than 6.000 ha of the Dutch Wadden Sea (MNC, 2008). Since 1930 the grounds disappeared due to the wasting disease and the construction of the Afsluitdijk. The eelgrass habitat became more turbid because of the changing tides and currents. After 1990 the water clarity enhanced, but in the western part of the Wadden Sea the eelgrass never recovered. At the moment the salt fluctuations 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 populating 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
Figure 02.10 [above]. The Wadden area.
36
The Dutch Wadden Sea The equilibrium condition of the tidal basins of the Dutch Wadden Sea have been subjected to numerous, large and medium scale human intervention such as closure of basins, land reclamation, coastal defense structures, sand nourishments etc. The by far largest intervention which affected the morphology of the Dutch Wadden Sea, is the closure of the south part of the basin, the Zuiderzee in 1932. Since the construction of the Afsluitdijk (1932), the Wadden Sea is still searching for a new balance. The old channels are mostly silted up. Especially the tidal inlet Marsdiep, between Den Helder and Texel, was affected to a large extent. The Marsdiep inlet imports a large volume of sediment from the adjacent coast and ebb tidal 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 extraction and sand- and shell extraction.
Cure to secure: Medicating the broad coast
! !
sand erosion sand hunger (demand) shoreline erosion stratification N,P N,P
over-fertilization nutrient shortage species & habitat decline constant dredging exchange barrier
!
weak defense spot (built area) coastal defense insufficient
! !
!
Friesland & Groningen Coastline The Zuiderzee, the Wadden Sea and the Eems-Dollard estuary together, used to form a shallow tidal area where gradual transitions occurred from fresh, through brackish, to saline water. Salt marshes are suchlike transition 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 N,P
N,P
N,P
be flooded. 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 flow velocities 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 rejuvenating and not broadening up. Therefore, these dynamic zones are growing old and too high, roughening up and losing their habitat qualities. 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 different transitions from low to high with on each zone a characteristic vegetation. In this way
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 swiftly crosses over from mudflat to dry land, without a wide area of these valuable transitions. 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 suffers from salt seepage in the agricultural land and fish migration is next to impossible. Main points: - salt marshes cannot fully develop to a wide area with buffering capacity - resilience has disappeared due to the fixed coastline, dikes and sluices. Almost no interaction between Wadden Sea and mainland. - fresh-salt transitions disappear. Brackish water areas have largely disappeared
Figure 02.11 [above]. Problems of the Wadden area
N,P
37
!
to intensive (shellfish-) fishery, mussel seed fishery and natural storms. Mussel banks,!eelgrass fields and salt marshes used to be very effective buffering systems of the Wadden area. Main points:! - sand hunger and silting up of the Wadden Sea - disappearing fish- and breeding ! due to fishery grounds ! - disappearing of habitats and with this of natural buffering capacity (mussel beds and eelgrass fields)
The ailing sea system
Local problems of the Holland coast
THE HOLLAND COAST The Holland Coast dunes The Holland coast (fig. 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 offer important (eco-)system functions, 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 reflection of this thin line. Along the Holland coast, the narrow parts in the dune strip and settlement 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 significant 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 figure 02.13 the situation of the settlements close to sea and fragile links in the coastal defense line are indicated. Along the coastline there are large differences in erosion and sedimentation processes. In the south and the north of the Holland coast
erosion occurs, causing the foreshore to steepen (fig. 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 relatively cheap coastal defense. In contrast with the dikes of the Northern and Southwestern coastline, this dune landscape is not a fixed line. The dunes are still an active dynamic landscape where the landscape formation is still in progress. The dynamics of sea, wind, salt and sun create a large alternation of dune landscapes. Still, the dynamics of the dunes are diminishing and are becoming more fixed. This happens because the natural succession of plant species has changed towards climax stages which stabilise the dunes and make dynamics with additional pioneer stages to be lost. In contrast, a stabilized end-stage vegetation settles with mainly thicket
Figure 02.12 [above]. The Holland coast. Figure 02.13 [right page]. Problems of the Holland coast. Figure 02.14 [below].Steepening of coastal base due to natural transgression demands nourishments dunes 100 years ago future
present
38
Lauwersmeer The Lauwersmeer (90 km2) originated as a tidal inlet, but was closed off from the Wadden Sea in 1969. A 13km long barrier was constructed as a retention basin for the fresh water from Friesland and Groningen. Because of the constructed barrier the water turned brackish, the existing nature altered and new fauna and flora established. Since 2003 the Lauwersmeer is designated as a national park.
!
Cure to secure: Medicating the broad coast
!
sand erosion sand hunger (demand) shoreline erosion stratification N,P N,P
over-fertilization nutrient shortage species & habitat decline constant dredging exchange barrier
!
weak defense spot (built area)
! !
coastal defense insufficient
! !
sand hunger & silting up
! ! !
ďŹ xed dune system
!
disappearing natural bu
disappearing ďŹ sh & bree N,P
N,P
N,P
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 fixed which decreased biodiversity - sand nourishment disrupts natural distribution of sand by grain size N,P
anaerobic conditions
N,P
brackish habitat nutrient overload
N,P
N ,P
ďŹ sh barriers constant dredging sluice
39
and brushwoods. This results in less difference 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 different causes. One is the extraction of drinking water in the dunes causing the dunes to gradually dry up and ! dune pools with their rare fresh water vegetation 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 different composition. The distribution 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
!
! !
The ailing sea system
!
Local problems of the Southwestern delta
! !
!
N,P N,P
N,P N,P
sand erosion sand hunger (demand) shoreline erosion
N,P
stratification N,P N,P
over-fertilization nutrient shortage species & habitat decline
!
N,P
constant dredging exchange barrier
!
weak defense spot (built area) coastal defense insufficient
The Voordelta (Fig. 02.16, 90.000 ha, salt water foreshore area, tidal range ±300 cm) The Voordelta is the shallow transition area between the North Sea and the tidal inlets of the Southwestern Delta. The construction of the large-scale Deltaworks and Maasvlakte port have been of great influence on the morphology of the Voordelta, resulting in the genesis of a young dynamic landscape of shifting sandbanks and channels, coastal accretion and degradation. With the decline of the channel width of the tidal inlets due to Deltaworks dam constructions, less sand could be transported into these
inlets. The result is that the intertidal area in the Voordelta highly increased, mainly in the mouth of the Haringvliet, while decreasing behind the dams. Still, the growth of intertidal 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 intertidal area (beaches and tidal flats) and 290 ha of salt marshes. Its water quality is determined by river discharges, mainly that of the Rhine river. Since tidal inlets are closed off, the Rhine water does not get mixed with sea water due to tidal turbidity, but is discharged at regular times into the Voordelta. The result of this poorly mixing water is the ‘coastal river’ effect, fresh water floating on heavier salt water. The Voordelta’s water quality meets the set standards, but still the nutrient concentrations 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 relatively nutrient rich and has a high productivity (Berchum & Smit, 1999). It has an important nursery function for flatfish like plaice, flounder, sole and is an important breeding-, forage-, and overwinter area for birds. The area is a wetland of international importance for seven water bird species, including the spoonbill (6.3% of the West European population). Besides this, part of the tidal flats are resting areas for seals (Berrevoets et al., 1998). Main points: - new intertidal areas not able to compensate loss due to Deltaworks - barriers for exchange of organisms with former tidal inlets (migrating fish etc.) - erosion of coastal headlands - fresh water bulk discharges that mix poorly with the sea water
Figure 02.15 [above]. Main problems of the Southwestern Delta.
The Haringvliet/Hollands Diep (Fig. 02.17, 13.700 ha, fresh water basin, tidal range 20-30 cm) With the construction of several dams in 1969-1970 the Haringvliet and
40
THE SOUTHWESTERN DELTA Current situation The following provides a short description of the current situation of the Delta waters and their distinct ecosystem (figure 02.15), based upon a Quick Scan held by the expertise centre of the Ministry of Agriculture, Nature and Food quality (Expertisecentrum LNV, 2001) and the inventory ‘Delta 2000’ held by the National Institute of Coast and Sea (RIKZ, 2000).
Cure to secure: Medicating the broad coast
bubbles’ that mix poorly with the sea water and cause many organisms to die. According to recent plans the sluices will be put ajar in December 2010. This will help the exchange of organisms and create new brackish wetlands. Still, nature is most helped by a management of the Haringvliet sluices where the sluices are only closed during storm surge, providing the most natural conditions with highest species richness and durability. The fresh water from the Haringvliet and Hollands Diep are used for agricultural water supply and to resist salt water seepage. The Haringvliet now has a tidal difference of 20 cm due to the inlet of water via the scouring sluices of the Spui. The tide of the Hollands Diep arrives though the Dordtse Kil, giving a tidal difference of 20-30 cm. Still, this tide allows 300 ha of mud flat to run dry at low water level. Main points: - silt deposits due to loss of dynamics - shoreline erosion due to loss of tide - loss of brackish marshlands
- loss of fresh-saline water transition - barrier for exchange of organisms (migrating fish)
Figure 02.16 [left]. The Voordelta system, the foreshore area of the Delta, where the North Sea meets the tidal inlets.
The Volkerak-Zoommeer (Fig. 02.18, 8.100 ha, fresh water basin, no tide) The Volkerak is connected through the Eendracht with the Zoommeer, making it one fresh water system. It originated when the Philipsdam was completed in 1987. It is the third largest fresh water basin in the Netherlands, with a water surface of 6.100 ha and about 2.000 ha of permanently run dry former mud flats and sand banks. The stagnant water level (NAP 0 m) initially led to strong bank erosion, followed by measurements to reduce erosion with a water level regime between NAP +0,15 m and NAP -0,10 m, based on rainwater fluctuation. The volkerak-Zoommeer has the same problems as several other fresh water basins; the disappearance of huge intertidal areas (about 100 km2), erosion of the banks and over-fertilized waters causing excessive algae growth and low water transparency. The aquatic ecosystem is not stable. Still, the run dry flats and
Figure 02.17 [right, above]. The Haringvliet/Hollands Diep system; A fresh water basin with little tide. Figure 02.18 [right, below]. The Volkerak-Zoommeer system; A tideless fresh water basin.
4
Hollands Diep became disconnection from the Volkerak and North Sea and turned into where fresh water basins. Of the total surface of 13.700 ha outside the dikes, now 1.850 ha is permanently run dry. The quality of nature has highly suffered from the closure. With the disconnection from the North sea most effects of the tidal current where lost, resulting in decreased flow velocity. Because of this, silt deposits (5 million m3/yr) and the area becomes more shallow. It also increased bank erosion transforming former sloping banks into steep banks, demanding foreshore protection at many sites. The Haringvliet sluices are a great barrier for the exchange of organisms between the North Sea and the large rivers. Especially migrating fish rarely survive the high flow velocities of the sluices, the limited passage and the abrupt transition of saline to fresh water. With the construction of the dams the brackish transition and accompanying brackish marshlands have completely disappeared. Discharged river water now enters the Voordelta as large ‘fresh water
The ailing sea system
Local problems of the Southwestern delta
The Grevelingen (Fig. 02.19, 13.920 ha, salt water basin, no tide) The Grevelingen became Europe’s largest salt water lake when it was dammed off from the North Sea and delta waters by the Grevelingen- and Brouwersdam (1965, 1971). With a constant water level of NAP –0.2 m, its water surface counts up to 10.800 ha and the run dry areas cover 3.120 ha. Since 2003 the sluices in the Brouwersdam are opened to continuously flush the system with
water from the Voordelta. In order to maintain the constant water level of -0.2 m the sluices are closed about 8% of the time. Water usually is clear and only moderately nutrient-rich, since most nutrient-rich agricultural water does not run into the Grevelingen. The Deltaworks changed a lot in the ecological system of the Grevelingen. Because the system is fully regulated by men, it is vulnerable to unexpected and undesired conditions. In warm summers the Grevelingen is often affected by stratification (due to differences in temperature and salinity), causing anaerobe conditions in deeper waters (Wattel, 1996). The biomass production of macrozoobenthos (multi-cellular animals inhabiting the sediments and detrital materials at the bottom of a water body) is low and dominant species change over the years, pointing out that the system is ecologically instable. The production of mussels has dropped since 1977 and cockles became nearly extinct. The amount of fish species declined. Besides that, the area of sea grass dramatically declined after closure,
since the system became more saline (see figure 02.23). Due to the constant water level and loss of current and tide, banks are eroding and deeper areas are slowly being filled up with sediment. Main points: - Ecologically instable system (Provincie Zuid-Holland, 2003) - Stratification causing anaerobic conditions - Low biomass production (lack of nutrients) - Changed seabed flora and fauna, decline or loss of many species like sea grass, mussel, cockle etc. - Bank erosion and loss of intertidal areas due to constant water level
Figure 02.19 [above, left]. The Grevelingen system; A tideless salt water basin. Figure 02.20 [above, right]. The Veersemeer system; A tideless brackish water basin.
The Veersemeer (Fig. 02.20, 3.990 ha, brackish water basin, no tide) Brackish water lake Veersemeer originated with the construction of the Zandkreekdam (1960) and the Veersedam (1961). About half of the 3.990 ha of the total surface is water, the other part consists of run dry banks and islands. The lake lacks possibilities of refreshing its water since it lost its
42
shallow areas are important natural areas. The Volkerak-Zoommeer is an important tide-free shipping lane, part of the Scheldt-Rhine connection between the port of Antwerp and the Dutch rivers/port of Rotterdam. Main points: - shoreline erosion due to loss of tide - loss of intertidal areas and marshlands - over-fertilization of water causing (blue-green) algae growth, poor ecology and malodor - loss of dynamics have lengthened the length of stay of the water
Cure to secure: Medicating the broad coast
sea lettuce, excessive algae growth and bad smell - Loss of species and instable ecosystem The Oosterschelde (Fig, 02.21, 35.080 ha, salt water tidal inlet, tidal range 325 cm at Yerseke) The Oosterschelde is a large-scale tidal landscape of 35.080 ha with a great extent of naturalness. The clean water, salt marshes and intertidal areas shape the habitat for a rich flora and fauna, with great habitat and species diversity (anonymous, 1995). The coastal inlet can be closed off from the North Sea by closing the storm surge barrier in the Pijlerdam, which happens when water levels reach NAP +3 m. In order to keep as much tidal difference as possible, compartmenting dams where constructed in the eastern part, decreasing the basin volume (Oesterand Philipsdam in 1986-1987). After the completion of the storm surge barrier the former equilibrium was disrupted; tidal range changed from 3.70 m near the town of Yerseke to 3.25 m, tidal volume was decreased
with 30% and the Oosterschelde surface declined with 22% (before compartmenting: 45.200 ha). Also, the flow velocities have decreased with 30-40%, leading to lower renewal time of the water body. Besides this, the marshes and tidal flats are severely eroding and leveling off. De mobility of channels declined, decreasing the dynamics. The tidal channels of the former equilibrium are to wide in comparison to the decreases tidal volume: 400600 million m3 of sand is needed to reach a new equilibrium. Since sand transport from the Voordelta is hindered by the Pijlerdam, it results in higher erosion than sedimentation of the tidal flats in the Oosterschelde. Due to this ‘sand hunger’ tidal flats disappear at the speed of 40 ha/yr since 1986, already causing about one third of the intertidal areas to be lost. This sand hunger will last for centuries and intertidal areas are expected to disappear completely if the situation is not handled (RIKZ, 2000). Even though the primary production has remained equal, some changes have taken place. The fresh-saline
Figure 02.21 [above]. The Oosterschelde system; A salt water tidal inlet protected by a permeable dam.
43
natural dynamics. The inlet of saline water from the Oosterschelde in spring causes salt stratification and severe anaerobe conditions. Drainage of nutrient rich polder water results in strong over-fertilization of the Veersemeer. This causes excessive growth of sea lettuce (ulva lactuca) which gives bad smell and problems for recreation. Overall it can be said that the change in oxygen content, salt content and mostly constant water level prevents the development of a stable aquatic ecosystem. Since the closure the fish fauna has severely decreased. In recent years two scouring sluices where places in the Zandkreekdam in order to refresh the Veersemeer water to a certain extent. Since 2004 between ebb and flood a total average of 40 m3 per second flows between the Oosterschelde and Veersemeer Main points: - Longer residence time of water due to loss of tide and building of dams - Stratification in summer causing anaerobe conditions in deeper water layers - Over-fertilization causing rotting
The ailing sea system
Local problems of the Southwestern delta
4500 ha 4000
+
3500
Grevelingen
Oosterschelde
3000 2500 2000 1500
+
1000
+
0
+ 1970
1975
transitions in the Oosterschelde have almost completely disappeared and with this the accompanying brackish habitats (e.g. sea grass beds) are lost. Exotic species like the Pacific Oyster, who filter large quantities of phytoplankton, by this compete with local commercial species like mussels, cockles, shrimps, etc which are also overfished. The decrease in fresh water supply has also decreased the supply of nutrients. The cockle population has declined with almost 80% between 1985-1999 (Provincie Zuid-Holland, 2003). Main points: - New equilibrium causing sand hunger: tidal flat erosion - Loss of fresh-saline transitions and accompanying brackish habitats - Food shortages for local species due presence of exotic species. - Damage on natural system due to overfishing of commercial species - Huge decline in sea grass surface (see figure 02.23) Markiezaat and Binnenschelde (Fig. 02.24, 1800ha respectively 180ha, fresh water basins, no tide)
1980
1985
1990
The Markiezaatmeer was born with the closure of the Oosterschelde by the Markizaatskade (1983) and the Oesterdam (1987), slowly transforming it from a brackish to a tideless fresh water lake with a constant level of NAP +0.60 m. Water supply and discharge are mainly by rainwater and evaporation, changing the water surface during summer and winter. The system is largely self-regulating. The valuable and rare brackish vegetation is expected to disappear between 2008 and 2013 (Röling, 1994). The quality of the water is poor, with higher nitrogen, phosphate, sulphate, chloride and zinc concentrations than national set standards. The high concentration of nutrients cause low water transparency, algae growth and strong fluctuations of oxygen content (Vugt, 1999). The Markiezaat is a wetland of international importance. Its bird species richness is high. It is used by water birds as a feeding-, resting-, and moulting area. The Binnenschelde is a relatively small,
1995
+
2000
closed off fresh water lake in the former tidal area of the Oosterschelde which originated with the constructions of the Markiezaatskade, Bergseplaat and Waterscheiding. De Binnenschelde has an instable system that has high concentrations of nutrients causing severe algae growth. The study ‘Waterbeheer Binnenschelde’ has analyzed two ways of improving the water quality. The ‘salt variant’ is concluded to be the only way of guaranteeing a stable Binnenschelde with clear waters. In the variant, the water will be flushed with salt, nutrient poor water from the Oosterschelde via a pipe system underneath the Scheldt-Rijn canal. Main points: - very severe problems with water quality - loss of brackish nature due to transformation towards fresh water lakes
high tide
erosion
low tide mud flat
channel
Figure 02.22 [above]. Sand hunger. Channels are to large for the new water flow. Due to this, the intertidal higher areas of mud flats erode and channels are filled with this sediment. Because of this process intertidal areas are dissappearing, the mud flats ‘drown’. Figure 02.23 [above, top left]. Decline in area of sea grass in the Oosterschelde and Grevelingen since 1970. Figure 02.24 [above, top right]. The Binnenschelde/ Markiezaat system.
The Westerschelde (31.900 ha, open salt water tidal inlet, full tidal range of ±4 m near Vlissingen) The Westerschelde is the only estuary
44
500
sedimentation
Cure to secure: Medicating the broad coast
The Westerschelde is one of the most polluted estuaries of Europe. The physic-chemical water quality is poor, but slowly improving. The bottom is heavily contaminated with heavy metals. Due to the port of Antwerp the Westerschelde is one of the worlds busiest shipping lanes and needs constant dredging to keep its minimum depth (14 million m3/yr). This will increase after 2008 now the channel is to be deepened for the third time to meet new standards for larger vessels. Loss in natural areas caused by the deepening have to be compensated due to EU restrictions. The shipping function has changed the tidal channel to become smaller, deeper and more fixed. As a result, the outer rims of the salt marshes erode and higher marsh areas silt up. This strong accretion causes the area to become more elevated, changing from saline to fresh water conditions and endangering the typical salt marsh flora. Main points: - constant dredging required due to sedimentation of shipping lanes
Figure 02.25 [above]. The Westerschelde system; A fully open salt water tidal inlet connecting the Scheldt river (and port of Antwerp) to the North Sea.
45
in the delta area that survived the Deltaworks because of its necessary connection of the port of Antwerp to the North Sea. Still, with the construction of the Deltaworks it was cut off from the Oosterschelde and the Veerse Gat and land reclamation accounted for the los of salt water marshlands and mud flats. It is a water system characterized by a mixture of fresh and saline water and high morphologic dynamics, caused by currents and tidal force. These factors shape rare landscapes of exceptional natural value like the brackish marshland of Saeftinge; with 2770 ha the largest brackish marshland of northwest Europe (van Eck, 1999). The Westerschelde is a breeding-, resting- and foraging area for birds, has a nursery function for young fish and is residence to seals. The strong natural water movement causes water to be turbid, resulting in limited transparency (visibility depth of 50 cm near mouth and 27 cm in the east). Since light is necessary for the primary production of phytoplankton, this turbidity causes relatively low production.
The ailing sea system
Conclusion: What are the local problems?
- many dikes not up to date - loss of foreshore protection - dike base erosion
poor coastal defense
loss of resilience
tidal flat erosion nature compensation for Westerschelde loss of brackish habitats -
- unstable ecosystems - loss of cleaning ability - unable to withstand short-term shocks
loss of habitat
‘diversity’ loss of species & species numbers
loss of dynamics
decrease in flora & fauna (e.g. seagrass) decrease in species numbers -
-
loss of water mixing ability
loss of species exchange loss of fresh-saline transitions barriers due to dikes & dams -
dunes are fixed disrupted balance Southwestern Delta fixed coastline due to dikes marshlands become fixed brushland
‘exchange’
- stratification - loss of brackish zone
loss of nutrient exchange
Loss of gradual transition area between land and sea means loss of: - diversity - dynamics/exchange - buffer/resilience
- heavily contaminated parts - need for compensation of nature due to loss by port of Antwerp and dredging Short term problem conclusion With the ecosystem compartmented, migrating fish are confronted with barriers between sea and rivers, between breeding- and feeding grounds. The subdivision also has its effects on the water quality of the several water bodies, as can be seen in the province of Zeeland. Some of these water are over-fertilized while others lack nutrients. Due to the construction of the new water barriers, the equilibrium of sand and water fluxes are shifting, resulting in sand hunger, erosion and habitat loss. Poor water quality and habitat loss are both causing decreased biodiversity and population numbers. The former estuarine system changed from a tidal aquarelle to a mosaic of fresh, brackish or saline water basins with
-
more or less constant water levels that imprisons natural life. These problems with the ecological soundness of the sea come together with new difficulties concerning our coastal defense that are related to this natural system: Erosion along the sandy coasts and loss of foreshores and mud flats that stabilize the dike base are weakening the primary coastal defense line. Slowly, this single coastline is being consumed due to the changes in the natural system.
Figure 02.26 [above]. Local problems of the Dutch coast’s natural system are all interconnected problems. The main problem here is ‘loss of gradual transition area between land and sea’. Figure 02.27 [right page]. The local problems of the Dutch coast’s natural system summed up.
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overfertilization anaerobe conditions food shortages severe algae growth
Cure to secure: Medicating the broad coast
sand erosion sand hunger (demand) shoreline erosion stratification N,P N,P
over-fertilization nutrient shortage species & habitat decline constant dredging exchange barrier
!
coastal defense insufficient
!
! !
! !
! ! !
!
N,P N,P
N,P N,P
N,P
!
N,P
47
!
weak defense spot (built area)
The Wealthy Coast
importance of the coastal ecosystem
VESSEL TRAFFIC ON THE NORTH SEA Vessel Movements in The Netherlands EEZ Average number of ships in the area (1999-2001): Routebound 174 Non-Routebound 162 Total 336 2003 Port calls in The Netherlands: Northern Seaports Noordzeekanaal Area Scheveningen Maas Approach Area Schelde Approaches Netherlands Total
3.840 8.580 1.250 31.730 6.390 51.790
Legend
Production platforms
Traffic Incidents (1986-2003)
Type Gas Oil Average number of accidents Trendline
Oil and gas
During this period, there was a slight decrease in the number of vessel movements, while the size of the vessels did increase.
Unknown Sub-sea well
Pipelines Status In use Future Abandoned NCP Shell extraction areas 2004 Licensed sand extraction area Abandoned sand extraction area Sand extraction test area Shell extraction test area
N
Published in November 2004
loss of coastal areas under influence of both sea and land is considered a problem because they are highly valued: - many functions, services & products - great natural value - great economic value
Netherlands Hydrographic Office
NOT TO BE USED FOR NAVIGATION
This chapter will discuss the importance of the natural system of the coast and its ecosystem functions and services. Importance of the sea & natural coastal system As a seafaring nation, the Dutch coast and sea have always been very important for the cultural and economical wellbeing of the Netherlands. For thousands of years the inhabitants of the Netherlands have lived with the water. Generations of lowlanders build artificial hills (terps) and dikes, dug harbors and extracted fertile land out of the sea. They traded with overseas colonies, fished coastal seas and lived on the edge of water and land. Also today the coast and sea are of enormous importance to the Dutch. The North Sea is one of the busiest and most navigated seas of the world (fig. 02.28 and 02.29). On a yearly basis, nearly 260.000 naval movements take place on the Dutch NCP alone (Bisseling et al., 2001). The port of Rotterdam ships goods from all over the world, having a throughput of 407 million tons (Port of Rotterdam,
2007). Oil and gas are extracted from natural reserves deep under our sea bed. And besides the cultural and economical importance, the natural coastal system itself also provides us with both products and services: (Micro)organisms clean the water and produce biomass. Fish trawlers supply the market with a good source of proteins and the coastal zone provides us a perfect leisure landscape.
Figure 02.28 [above, left]. Vessel traffic on the North Sea. The North Sea is one of the bussiest seas of the world. (Rijkswaterstaat) Figure 02.29 (above, right). The Dutch part of the North Sea is highly used for oil gas rigging, sand excavation, wind energy, military use etc.
Dutch coastal nature Internationally seen, our delta nature is of exceptional importance. In the North, the Dutch Wadden Sea for example, is stated by UNESCO as a World Heritage Site. It is part of the worlds largest intertidal area: the Wadden Sea area, ranging from Den Helder (Netherlands) to Esbjerg (Denmark), with a total surface of about 8.000 km2 (waddenzeewerelderfgoed.nl, 2007). This Wadden Sea area, as well as some other major Dutch wetland areas, are important nature areas for migrating birds along the East Atlantic flyway (fig. 02.30). Almost all of the Dutch dunes are part of the Natura-2000 network (the
48
Ministry of Transport, Public Works and Water Management Freight Transport
Cure to secure: Medicating the broad coast
Ecosystem products and services Within ecosystems, ecosystem
functions can be identified. Ecosystem functions are the properties of ecosystems as a functioning entity. Four groups of ecosystem functions are classified by De Groot et al. (2002). • Regulation functions include processes that lead to climate regulation or healthy fresh air, self-cleaning abilities, functions that buffer water flows and by this prevent peak discharges etc. • Habitat functions, like providing essential spawning- and nursery grounds. • Production functions, for example production and production of (raw) materials, cosmetics etc. • Information functions, including educative, scientific and recreation functions, but also aesthetic, cultural and spiritual information functions. Ecosystems provide both products and services, based on ecosystem functions (fig. 02.31). Here, ecosystem services are the conditions and processes through which natural ecosystems and the species within them sustain and fulfill human life
(Daily, 1996). The services are a form of action within an ecosystem, the ecosystem products refer to supplied matter by an ecosystem. A general overview of the ecosystem services is given by Daily (1996) and Constanza et al. (1997): • gas regulation • climate regulation • disturbance regulation • water regulation • water supply • erosion control and sedimentation retention • soil retention and formation • nutrient cycling • waste treatment • pollination and seed dispersion • biological control • refugia • food production • raw materials • genetic resources (gene pool) • medicinal resources • recreation • cultural aspects • opportunity to experience beauty • influencing the human spirit
Figure 02.30 [above]. The east-atlantic flyway. Bird migrating pattern of coastal wetland species that breed in the northern hemisphere and winter in the warmer south while resting and recovering along the way. The Wadden Sea and Dutch Delta are an important knot in this migration route. (Based on image by Waddenvereniging).
49
ecological network in EU territory), including the dunes on the Holland coast. Internationally seen these Dutch dunes are of great to very great importance (Wolff, 1989) . This is amongst other things due to the presence of ‘fixed dunes with herbaceous vegetation’ (also called ‘grey dunes’, Natura 2000 type *H2130) and of ‘humid dune slacks’ (Natura 2000 type H2190). In the south, the Scheldt estuary is the longest river delta-estuary left in WestEurope, with complete fresh-saline transitions and fresh water intertidal areas (Saeijs, 2006). Also, several habitats of the estuarine system like the Dutch salt marshes and the salt and brackish tidal areas are of very great international importance (Wolff, 1989). More than 10% of its European surface area is situated in the Netherlands and this number can be further developed. Besides this, the Netherlands also situate 1 to 10% of the total European surface of fresh water tidal areas (Wolff, 1989).
The Wealthy Coast
importance of the coastal ecosystem
Q gas regulation
P climate regulation o o water regulation
dispersion of pollen and seeds
C
%
:G SS
O
biological regulation
DLP
Resilience
=sss
S Jgene U
pool
I Y F
ECOSYSTEM SERVICES AND PRODUCTS
<
erosion/sedimentation prevention
The hidden fortune What is nature worth? Usually we do not consider the ecological significance and potentials of our ecosystems, let alone their economical value. Especially the profits of this nature are often underestimated and because of this are not being calculated and taken into account in the planning process. As Saeijs shows in his essay ‘The hidden fortune’ (2006), wet ecosystems like estuaries, rivers and seas are worth a lot of money. They represent a hidden fortune which can have very high returns. Saeijs grounds his writings upon work by a group of scientists (Constanza et al., including De Groot) that have made an worldwide estimate of the economical value of several nature products and services that are supplied by the largest ecosystems on earth (fig. 02.32). Rough estimates by Constanza et al. (1997) of the yearly profits of these worldwide nature products and services (the ‘Gross World Nature Product’) average 33.000 billion US$/year1. This enormous figure is about twice the global Gross Domestic
Product, which is estimated to be ‘only’ about 18.000 billion US$/ year. Constanza estimated the total economical value of the global coast (including coastal shelf seas as the North Sea) to be around 12.500 billion US$/year. This amount is slightly more than the economical value of the land surface. The land surface however is five times as large as the coastal sea surface. As shown, nature contributes greatly to the human wellbeing on this planet. It goes without saying that mankind should take great care for her ecosystems, after all when some of these functions are no longer handled by nature itself, they will have to be replaced by human activities that do cost money. For example, the loss of self-cleaning abilities of over-fertilized waters results in the decline of fishery products and recreation, which has to be calculated as loss of income or has to be compensated by higher water treatment costs. The Netherlands, being a delta country with a (former) estuarine character, has large surfaces of estuarine area, intertidal mudflats
food production
*
*F J water
recreation
P N
supply
cultural aspects N
nutrient cycle
and saltwater marshlands that have a high hidden fortune. The value of the nature products and services of the Oosterschelde for example, are estimated to be 0,7 billion EUR/ year (based on Saeijs, 2006). Dorp (2000) estimated the total value of the ecosystem services of the entire Wadden Sea to be 4.4 billion EUR/ year. This corresponds with a value of 1.7 billion EUR/year for the Dutch part of the Wadden Sea. The Dutch Exclusive Economic Zone (EEZ) even yields 8.5 billion EUR each year2. This is far more than the costs of the Deltaworks and even exceeds the total expenditures of the Dutch government on water tasks (water management, water defense etc), which reached 5.1 billion Euros in 2006 (MVW, 2007). In the last centuries we have reclaimed thousands of hectares of land. Figure 02.32 shows that the mean added ecosystem value of marine ecosystems compared to cropland is of an entirely different category. The ecosystem value of cropland is estimated to be less than a hundred euro/ha/year (dark grey in figure), while average yield of a
Figure 02.31 [above]. Ecosystem products and services Figure 02.32 [right page]. Deltas or estuaries are the most productive ecosystems of the world. A comparison is made with cropland, showing its ecosystem services (dark grey) and its yield (light gray).
50
W
soil formation
L
H
raw materials
waste processing
refugia
Cure to secure: Medicating the broad coast
25.000
Mean added value in €/ha/yr
€
€
a
€ €
es tu ar i
pl an es fl oo d
ri ve r
we tl an ds
sw am ps ti da l
ri ve rs
an d
la ke s
se a co
as ta l
ea n oc
€
€ € € €
in te rt id al
€€ €
€ € (i c nc ro l. pl yi and el d)
€€ € € € € €
€
€
€ €
ar ea s
€
€€€ €
€
hectare of cropland (light grey in figure) is estimated at € 3000/ha/year (Van der Meer, 2003). On the other end, the ecosystem value of intertidal area and estuarine system reach well over € 15.000/ha/year, and most reclamations where applied in former intertidal areas or estuarine systems. Shortly said, this is a devaluation of well over 500%. What the afore-mentioned implies is that in the planning process we have to deal more carefully with our wet ecosystems since they are worth a lot more than we tend to think at first sight. ) Minimum of $16-54 trillion/year (point estimate of $33 trillion/year) 2 ) In this calculation a surface of 2500 km2 is used for the Dutch Wadden Sea area and a value of the ecosystem services of €6.700/ha/yr. For the EEZ the used surface is 57.000 km2 with a ecosystem service value of €1.500/ ha/yr
51
1
20.000 15.000 10.000 5.000 0
Global challenges
Long-term challenges as a motive for action
5 oC
A1FL
4 A2
3
A1B B2 A1T 1592A B1
2
1
Coastal defense needs an update, taking into account long-term challenges.
2050
In this chapter the global and European challenges and trends in relation to the North Sea coasts will be indicated, as well as their influence on the Dutch coastal areas. Then the challenges and possible consequences of the sea level rise for the Netherlands will be shortly stated. 02.4.1 Planet Earth With the start of the industrial revolution and the upcoming of globalization, natural resources have been exploited at a fast rate. This worldwide exploitation brought development and welfare for many, but it also left us with an short-sighted attitude of wanting to overexploit. It resulted in poor stewardship of many of the earth’s natural resources like oil & gas, timber, fresh water, fish stock, etc. To continue living on this planet with its quickly growing population, a mental and physical change is needed towards long-lasting solutions and good stewardship. An attitude change from ‘exploiting’ towards ‘harvesting the interest’ of the system. Besides that the rapid exploitation of natural reserves did much damage
2100
to natural systems and biotic populations, it also caused secondary effects. Although different climate models offer dissimilar results, it can be stated that we are dealing with an accelerated heating of our planet: the greenhouse effect (fig. 02.33). The climate is altering and sea water temperature is rising. Due to this, seas are expanding and the polar ice rapidly melts; so sea water levels rise. Because of this rise we are literally getting more sea the coming century. Besides that, sea currents may change, storms might augment and the sea’s acidity level might increase. Even if lowering the emission of the greenhouse gasses could be successful as of now, the after-effects of the emission could not be put to a halt immediately (fig. 02.34). This calls for a global challenge to adapt to the changing climate and the rising sea: Climate adaptation. The necessity for climate adaptation is quickly illustrated by the fact that thirteen of the fifteen largest world cities are situated in coastal regions, mostly deltas. Presently, more than half of the world population is living in
Figure 02.33 [above. left]. Different model estimates of the temperature rise as a result of climate change. (Based on IPCC, 2001) Figure 02.34 [above, right]. Aftereffect of the emission of greenhouse gasses. (Based on IPCC, 2001) Figure 02.35 [below, left]. Vulnerability to storm surge from sea. (Based on ESPON, 2005) Figure 02.36 [below, right]. Population density in the European coastal zone (0-10 km) in 2001. (Based on EEA, 2006)
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2000
Cure to secure: Medicating the broad coast
Required time to reach an equilibrium: Sea level rise due to the melting of the polar ice caps: several millenia
Peak CO2-emission 0 up to 100 years
extent of reaction
Sea level rise due to thermal expansion (caused by temperature increase): centuries to millenia
Temperature stabilisation: several centuries
CO2-stabilisation: 100 to 300 years
Figure 02.36 Vulnerability to storm surge from sea. coasts that are vulnerable to storm surge from sea.
100 years
1000 years
CO2-emission
Figure 02.35 Population density in the European coastal zone (0-10 km) in 2001. low density medium density high density
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Present
Global challenges
Long-term challenges as a motive for action
02.4.2 Europe and the North Sea Also within Europe there are coasts, coastal deltas and populations that are potentially threatened in the nearby future. The major part of these vulnerable coasts border the North Sea. Besides countries like Denmark, Sweden and Finland, also the Netherlands are endangered (fig. 02.35). The majority of these vulnerable coasts have a relatively low population density. The coasts of Italy, Belgium and especially the Netherlands on the other hand, have both densely populated and endangered coastal areas (fig. 02.36). Climate Change The expected climate changes have different consequences in the North of Europe in comparison to the South, while both parts eventually will have to deal with a
rise in temperature (fig. 02.37). In the North, more floods will occur because of the increase in rainfall. In the South however, the rise in temperature will lead to a substantial decrease in rainfall (fig. 02.38). Subsequently land will dehydrate, erosion will rise and productive land will go to waste in this zone. Eventually agriculture and mass tourism will decline in the southern areas. In the northern areas the rise in temperature is less intense, through which Northern- and Middle Europe will be able to compensate this decline of the South (RPB, 2007a). 02.4.3 The Netherlands Do the Netherlands have a CO2 problem? No. Crops grow faster and a higher concentration of CO2 itself will not do any harm. Is there a direct problem with the occurring change in temperature? No. Surely there will be some major biotic adaptations, but this can be handled. Do we have a problem with the sea
level rise? Not directly. Sea level rise is a common phenomenon, already going on for thousands of years along the North Sea shores and Dutch coasts. Even with the accelerated sea level rise due to global warming, the process is still gradual and at slow pace. The figures can be estimated and preparations can be made. And the sea level rise we have to deal with is not extraordinary. Twice a day the sea level rises and drops with a similar extent as the expected rise the coming 200 years. It can be overseen, butâ&#x20AC;Ś in the end our land has to keep growing with the rising sea level to save it from drowning.
Figure 02.37 [above, left]. Temperature rise untill 2030 (Florke & Alcamo, 2004). Figure 02.38 [above, right]. Change in precipitation until 2030 (Florke & Alcamo 2004).
Dike Rings and Risks The Dutch low lands are being protected against floods by dike rings. A dike ring area is an area protected by a primary water barrier, such as dams, dikes, dunes or higher situated grounds. Each dike ring has its own safety standard based on the â&#x20AC;&#x2DC;transgression chance normâ&#x20AC;&#x2122;,
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coastal areas, while in 2030 this figure will rise to 75% (Luiten, 2003).
Cure to secure: Medicating the broad coast
Source: WOZ-waarden CBS http://www.mnp.nl/images/74_overstroming_econ_schade_tcm
Safety Standard per dike-ring area
Value of immovable property per dike-ring area situation in 2004 x billion euros > 400
1/10.000 per year* 1/4.000 per year*
100-400
1/2.000 per year*
50-100
1/1.250 per year*
10-50 < 10
chance of transgression as meant in article 3, first paragraph of the ‘Wet op de waterkering’
within these dike rings will be likely to continue and because of this the consequences and damages of possible floods will increase. The Netherlands could even go bankrupt when a major flood occurs. Even though the dike rings are checked if they meet their current standard every five years, the change in effect of a flood was never taken into account. This increasing risk is a motive to rethink and possibly even raise the safety standards and to redevelop and strengthen the Dutch coastal defense. Or as Cees Veerman of the Delta Commission puts it: ‘safety is our primary necessity of life. We cannot put it at stake’ (Deltacommissie 2008). The figures urge on to reconsider.
Figure 02.39 [above, left]. Satefy standard per dikering area. (MNP, 2004) Figure 02.40 [above, right]. Value of immovable property per dike-ring area. (MNP, 2004)
Coastal safety challenge As said, the problem is not in higher CO2 concentrations nor higher temperatures. It doesn’t even directly come from sea level rise. The real
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ranging from 1/2.500 to 1/10.000 (fig. 02.39). For example, a dike ring with a safety standard of 1/4.000 means it should account for a water level of a storm flood that has a chance of happening once every 4.000 years, taking into account the wave surge. The current safety standards for each dike ring were established in the fifties and based on data from those days. The last decades the number of inhabitants of the Netherlands have increased and the economy has substantially grown. Because of this the economic value within these dike rings has risen (fig. 02.40). Since the ‘50s the Gross National Product of the Netherlands in the lower situated grounds has risen with a factor 6. (CBS, 2002) By now almost 9 million people live in these lower situated areas that are potentially threatened by flooding (Nijmeijer, 2000) and 60% of the Gross National Product is earned here. (CBS, 2007) The growth of the Dutch economy
Global challenges
Long-term challenges as a motive for action 4,5 m scenarios for sea level rise (m) excluding ground surface subsidence
4,0 m 3,5 m
Deltacommission 2008-scenario
3,0 m 2,5 m 2,0 m 1,5 m
IPCC 2001-scenario
1,0 m 0,5 m
Low estimate
Central estimate
2200
2150
2100
2050
High estimate
Temperature
+ 1°C
+ 2°C
+ 4 to 6°C
Average summer precipitation
+ 1%
+ 2%
+ 4%
Summer evaporation
+ 4%
+ 8%
+ 16%
Average winter precipitation
+ 6%
+ 12%
+ 25%
Yearly maximum of the 10-day winter precipitation sum
+ 10%
+ 20%
+ 40%
+ 20cm
+ 60cm
+ 110cm
Relative sea level rise
danger is when this is combined with quickly stacked up water. Problems and consequences of the sea level rise for the Netherlands express itself differently than in the rest of Europe and the world (fig. 02.41). This is, amongst other reasons, because it is a delta where a lot of water accumulates. As mentioned in figure 02.42, the climate change of the Netherlands will next to the sea level rise and a higher temperature also imply more rainfall. Assumingly the Dutch summers will get dryer and the winters more rainy. Rainfall will intensify and the possibility of floods will increase due to higher river peak loads. (RPB, 2007b) With the climate changing, heavier storms are expected in the North Sea that produce larger waves. A heavy northwesterly storm pushes water up against the coast of the Netherlands and Belgium. When combined with high tide, spring tide and peak discharge of the rivers, sea levels rise
even higher. And finally wave surge adds more water level. It is the wave’s force and wave run-up that really put our coastal defense under extreme pressure. By that time it is called disaster. It is understandable that this storm buildup is only becoming a problem along the coast. It is here where part of the solution lies; dimming wave surge of storms.
Figure 02.41 [far above]. Scenarios for sea level rise. The expected increase of sea level for the Dutch coast in 2050, 2100 and 2200 (effects of ground surface subsidence are not included). Figure 02.42 [above]. Climate scenarios for the Netherlands in 2100. IPCC (2001)
To sum up the above, it is shown that when the global challenges are ‘downsampled’ to the Dutch situation, the upcoming future challenges are: • Durability: long-lasting solutions and durable use of systems • Climate adaptation: growing with sea level rise • Coastal safety: dimming of larger waves
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2000
0,0 m
KNMI 2006-scenario
57
Cure to secure: Medicating the broad coast
58
Š Gregory Officer (www.gregoryofficer.exto.nl)
Cure to secure: Medicating the broad coast
58___ 60___ 62___
68___
70___
78___
88___
102___
104___
59
106___
The assignment
what is needed?
Sand erosion Sand hunger Bank erosion Stratification N,P
Over-fertilization
N,P
Nutrient shortage Species & habitat decline Constant dredging Exchange barrier
!
Weak defense spot
!
Coastal defense insufficient Growing along with sea-level rise Dimming large waves
Secure to cure: Securing the landscape for future climate challenges and by doing so ecologically curing the Dutch coast’s natural system. Cure: heal, recuperate, medicate, treat the ecological system. Make it ecologically sound, resilient. Secure: obtaining/acquiring future security/assurance/guaranty. To secure for the future , to be on the safe side. It does not solely mean coastal safety,
but also includes adaptability and sustainability.
Figure 03.1 [left]. problems faced along the coast need to cure to secure
How can the Dutch coast be secured for the coming century and, while considerable investments are made, it’s coastal system cured at the same time? Here lies the chance for an innovative Dutch coastal defense… In this chapter, first some projects will be discussed that come up with (partial) solutions for the coast. Next, the approach of handling the coast is stated, followed by the solution itself. Afterwards a concept for the whole of the Dutch coast is shown. Further details are made for three example sites, where a typology will be applied. Then, a pilot project is designed to show how the large-scale concept can work on local scale. In the last part, some concluding argumentation will be provided, as well as recommendations for further research.
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Securing the Dutch coast for future climate challenges and while doing so ecologically curing the natural system
The previous chapter shows that the Dutch coast is troubled by ecological problems in its natural system, mainly due to the loss of coastal areas that are under influence of both sea and land. And it states that the upcoming climate challenges require an update our entire coastal defense, hereby providing an excellent motive for action. Shortly said the assignment for the Dutch coast comes down to ‘securing’ and ‘curing’.
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Cure to secure: Medicating the broad coast
Current debate
view on and use of existing ideas “What has been is what will be, and what has been done is what will be done; there is nothing new under the sun” (Eccl. 1:9 RSV)
given of the most impelling projects on the basis of these two reports. First the project will be introduced after which the feasibility and the consequences of the suggested interventions will be briefly discussed. The full project list of the Quickscan by Twynstra Gudde (2007) can be found in Appendix 1.
a. Strengthening the Zwakke schakels (RWS, RIKZ, 2001) www.kustzonebeleid.nl Chance of success: Moderate/High (Twynstra Gudde, 2007) Different spots along the Dutch coast are unsafe and do not offer sufficient protection against future possible floods: The weak links (Zwakke schakels). This project searches for multifunctional solutions to minimize the chances of flooding by also improving the spatial quality of the sites. Three solution types are offered: Landward solutions, seawards solutions or strengthening and preserving the existing defence line. The first option preserves the existing coastline, while sand nourishments will be combined with building inland hard defence constructions. Seaward solutions imply a shift of the coastline seawards where only sand nourishments are preferred, but also the combination of hard constructed elements and sand nourishments
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Case studies and possible solutions
Before coming up with solutions, it is useful to first have a look at already presented ideas for the coast. The current debate brings forth many interesting ideas that can be useful as a (partial) solution to the natural system’s problems and the safety challenges. The documents ‘Quick scan alternatieve veiligheidsmaatregelen’ (Twynstra Gudde, 2007) and ‘Perspectieven voor Nederland’ (Aerts, 2008) have summarised the current water safety projects and analyzed their effectiveness and feasibility. Feasibility is determined by the costs, legal and physical aspects, its social basis and the timeframe. A final judgement is given by stating the chance of success of an alternative safety measure, divided into low/ moderate/high/very high. When for example both effectiveness and feasibility are high, the ‘alternative safety measure’ has a very high chance of success. In the following a brief overview is
Cure to secure: Medicating the broad coast
Critical review: Landward solutions offer technical solutions which diminish the risk of flooding, but do not stop the erosion of the foreshore. Besides that it has both legal complications and lacks a social base since especially where land use of the hinterland is intensive. Strengthening the present coastline and seawards solutions both reduce the risk of flooding, but the seawards solutions is most effective since it also mutes wave force. Zwakke schakels only deals with the most critical spots and solely gives local mitigating solutions, but it does not come up with an overall solution for the entire system.
b. ComCoast: zone with multifunctional use (Comcoast, 2006) www.comcoast.org Chance of success: High (Twynstra Gudde, 2007) Comcoast is a European project which develops and demonstrates innovative solutions for flood risk management in coastal areas. The project is made up of five partner countries: Denmark, United Kingdom, The Netherlands, Germany and Belgium. The implementation measures strive to be environmentally and economically sustainable and recognize the social and cultural sensitiveness. This project explores the multifunctional use of the coast by offering landward and seaward solutions that improve the coastal safety but also develop the hinterland to more wet and salty environments. Three landward (overtopping defence, managed realignment and regulated tidal exchange) and two seawards solutions (foreland protection and foreshore recharge to restore the coastline) are proposed. Critical review: The landward and seaward solutions are estimated to have very high effectiveness since they diminish the chances for floods and more control is given to the consequences of possible floods. The different options use the resilience and the natural movement of the water to maintain future safety but also give room for future economic and ecological developments. The costs are comparable to traditional dike building( 5 million euro/km), but can even be realized cost free because of the other spatial impulses. When land has to be purchased this measure gets less interesting ( 30-40.000 euro/ha). The foreshore recharge to restore the coastline will have low maintenance costs because the land behind the dike will sediment and grow up to 1,5m per century. (Twynstra Gudde, 2007) Regions will benefit from developing a more environmentally friendly coastline which will also be
more attractive for residents and visitors. For example, creating new surroundings for nature will help compensate the loss of natural coastal habitats.
c. Super dikes (RWS, 2007) Chance of success: Low (Twynstra Gudde, 2007) The goal of the super dikes is to optimally strengthen the dikes. The super dikes are to be much larger in width than the original dikes (up to 300 m) and can be combined with infrastructure and residential functions. At the moment the project is still in the conceptual phase, although these super dikes are already applied in Japan. Critical review: To prevent floods, the super dike can be very effective. But due to the large area needed for such a superdike and the long term implementation perspective, the feasibility of the project is very low. At certain points along the coast and the rivers, the super dike can be a reasonable option. When combinations of functions are made (e.g. housing construction on the dike) the costs can be reduced. Even so, the costs will be higher than the current dike building due to the large total sand mass. Also, this idea is expected to attract social resistance. Finally, this solution is merely technical and does not have any benefits to solving problems of the natural system.
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are possible (e.g. dike in dune).
Current debate
view on and use of existing ideas
Critical review: This project creates coastal safety by adding sand on a natural way so the coastal system can self-sustain and the beaches and dunes can grow. The sand will sediment on a natural way by processes of currents and littoral drift, hereby saving transportation costs and allowing natural dispersion by grain size. The current approach of dynamic maintenance by sand nourishments turned out to be very effective. Especially sand nourishment on specific locations offers large costs savings.
e. Plan Waterman (Waterman, 1981) www.ronaldwaterman.nl Chance of success: Low (Twynstra Gudde, 2007) Currents, wind, waves and sand nourishments are to transform the round Delfland coastline back into a concave coastline. The 3000 ha extra land that will be created between Hoek van Holland and Scheveningen will solve the housing shortage, the lack of nature and recreation possibilities. Sand piles of 20 million m3 will be created at specific spots in front of the coast to allow natural transportation and counter structural erosion. Critical review: At that time Plan Waterman was way ahead of its time and therefore political and financial unaccepted. At present the urge to construct this expensive project is still not high enough and a social basis lacks, while a realization will involve many procedures.
f. Bos Variant (Bos, 2001) www.bosvariant.info Chance of success: Bos Variant strives for a round shaped coastline formed by several protruding headlands along the entire coastline. The Bos Variant is a recent version of the already existing plan of Holland-Bolland. The plan focuses on the sedimentation processes on the foreshores of the headlands. The present coastline will be expanded 2km seaward with a total area of ca 55.000 ha for nature and recreation. Critical review: The natural sediment supply near the Dutch coast is facing a structural shortage, so the sand sediments needed to make the islands grow will have to be brought in artificially. Although the plan is not detailed, the idea of huge sand nourishments is a solution that suits the natural system. Extra land surface can be gained without severely increasing coastline length.
g. Blue Islands (Geuze, 2006) Chance of success: The proposed sprayed-up islands will be created 5-25km in front of the existing coastline of Belgium and the Netherlands. These dune islands, with a total area of more than 150.000ha, will break storm surge and large waves. This plan combines an agenda for safety and the necessity of new land. The economy of the islands will be based on leisure, living and nature experience. The construction of these islands can also benefit the fishing-industry. The sand winning will cause deep troughs, in which special habitats, resting areas and spawning grounds will develop. Critical review: The new islands at deep seawater levels will need large sand nourishments and heavy constructed dikes to protect the islands from eroding. The islands have no effect on the rising of the sea level. Therefore even more sand will be needed for sand nourishments to make the foreshore grow with sea level rise. The total costs for coastal maintenance will strongly increase. (Van Rijn et al, 2007) The islands do effect the waves and the tidal currents. The area between the islands and the present mainland will be cut off the tidal currents and create a more calm environment where fine sediments can deposit. An mudflat area like the Wadden Sea will arise, which has negative consequences for recreational use of the existing coastal areas. An other important effect of this seaward expansion of beach and dunes is a decrease in salt-spray that reaches the mainland. This has consequences for the existing vegetation on the dunes. This seaward expansion can also imply a growth of the fresh water buffer in the dune area, which can have negative consequences for the existing vegetation, but a positive effect on the drinking water buffer.
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d. Permanent sand nourishments: Zandmotor (RWS, 2008) www.waterinnovatiebron.nl Chance of success: Very high (Twynstra Gudde, 2007) The zandmotor (sand motor) is an experiment within the perspective of the program â&#x20AC;&#x2DC;Dynamic maintenanceâ&#x20AC;&#x2122; of the Dutch government. It focuses on permanent foreshore (underwater) sand nourishments to make the coastal system grow naturally with the sea level rise and to diminish coastal erosion. The planned proposal of the zandmotor in front of the Delfland coast imitates the natural sediment supply of the rivers. Sand is being nourished on one spot and displaced by the coastal dynamics. The coastal safety effects of the zandmotor can already show after one or two years. At the moment the zandmotor is being implemented and constructed.
Cure to secure: Medicating the broad coast
h. Artificial reefs (Royal Haskoning, WINN) www.waterinnovatiebron.nl Chance of success: Low/moderate (Twynstra Gudde, 2007) A decrease of the wave period and the wave height are the main goals of the artificial reef. The height and the width of the last hundred meters of the foreshore determine the wave height of the seawater. The reef is constructed at deep waters using hard rocky material. The coastal view will not be affected because the reef will stay a few meters below the surface of the water. Tests show that the artificial reef actually do decrease long waves. The reef can also serve as fish habitat and diving areas. Critical review: The artificial reefs are constructed using hard material so they will not be damaged by heavy wave action, which implies low maintenance costs. The long waves are responsible for coastal erosion. It is still unclear how the waves develop once passed the reef and what still the potential damage to the coastline can be. Also it is unclear what effects will be on coastal processes as littoral drift and sedimentation.
i. Haakse zeedijk (Haak en Stokman, 2007) www.haaksezeedijk.nl Chance of success: Low (Twynstra Gudde, 2007) The ‘Haakse zeedijk ‘ presents a secondary coastline shaped by a connecting strip of linear islands 20km parallel to the present coastline. At Hoek van Holland and Ijmuiden shipping lanes and channels interrupt the strip of islands. The islands will function as a rigid dike and ought to decrease the wave force, regulate the river discharges and reduce salt intrusion. These islands create three large basins that can be regulated by sluices. Within these large basins the rivers can discharge. Hydro power pump stations regulate the water level of the three large basins between the present coastline and the new sea dike. During high river discharges the water level of the basins can be lowered when needed to enable large river discharges. In each basin large recreational water areas arise and offer room for a new airport and expansion of the Maasvlakte. New land is created for 1,5 million people to work and live. The heavy constructed dike will not be visible from the coastline and refreshment of the sea water in the basins will be maintained. The construction time is estimated to be 34 years.
to longshore coastal processes, since the plan suggests to turn the concave Dutch coast into a convex coast. This naturally stimulates severe erosion.
Critical review: According to the Quickscan the project has a very low feasibility due to the low social acceptance and the complexity of the project. Besides that the ‘Haakse Zeedijk’ offers a strong buffer and can be adjusted to future climate changes. Certain technical interventions like the closing of the tidal rivers will have negative effects on water management and the ecological water quality. The total costs of the project are a large disadvantage and will vary around 34 billion euro. But money will also be generated by selling land for industrial use and housing construction. It is very uncertain what will happen
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(Slim,2007) Van Rijn et al. calculated that one island( 20km long, 5km wide and 30m high) would need about 5 billion m3 of sand. The construction of one island with defensive structures and infrastructure would cost nearly 50 billion euro. The total plan for the Dutch part will cost 150200 billion euro.
Current debate
view on and use of existing ideas
Critical review: The islands shape should indeed be seen as a metaphor, since in reality it is very cost inefficient to make an island in the shape of a tulip; it would require an enormous amount of coastline defence for a relatively small amount of new land. But when studied as a metaphor, it could result in innovative knowledge that can be exported worldwide.
k. Room for the rivers www.ruimtevoorderivier.nl Chance of success: Moderate (Twynstra Gudde, 2007) The project ‘Room for the rivers’ strives to slow down and to enlarge the river discharge capacity by creating more room for the rivers to flow. By reserving extra room, the project tries to regulate and slow down the peak river discharges to prevent possible floods. This can be done for example by lowering the river floodplains, creating water retention areas or dike shifting. The extra room offers possibilities for nature development and recreation. This project can be implemented within ten years. Critical review: According to the Quickscan these interventions will largely improve the spatial- and ecological quality of the river landscape. Effectiveness is high, but social basis can be low when residential housing has to be shifted. At the moment 2,2 billion euro is already invested by the Dutch government to implement the project. The project is interesting because it creates surplus value. Not only the river safety problems are tackled, but at the same time possibilities are created for nature, recreation and improved spatial quality.
Conclusion On the basis of two documents which tested the current ideas on their effectiveness and feasibility it became clear that many ideas have feasible solutions for the coast. Most of the plans have solutions for coastal defense in combination with reclaiming land, but only a few of these come up with solutions that also can solve ecological problems of the natural system. It seems that ‘soft’ solutions or plans that plug into the natural system and use processes that are inherent to this natural system, are most feasible (Zandmotor, Comcoast). Very radical projects like Haakse Zeedijk, Blue islands and the tulip seize the opportunity to make the Netherlands more safe, and at the same time mainly create extra land, but their feasibility is low since the projects are very hard to realize. Besides that they fail to work along with the natural system. Overall it can be said that ‘soft’ projects that allow space for coastal processes are more feasible than ‘hard projects’ that block these processes.
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j. Tulip island( Innovatieplatform, 2008) www.innovatieplatform.nl Chance of success: low The statement of the Dutch research innovation platform (innovatieplatform) is that by creating 100.000 ha of land in the North Sea 10 billion euro can be gained. Researching possibilities for creating extra land in front of the coast is supported by the Dutch government. Therefore the plan of a tulip island is suggested to test the feasibility. The tulip shape itself can be seen as a metaphor. Land prices will be higher than on the mainland but the costs of sand nourishments are lowering. Furthermore the goal of this project is to research combinations of water safety and innovative energy solutions.
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Cure to secure: Medicating the broad coast
The solution within
A paradigm change: from single coastline towards a broad coastal zone
The Dutch coast used to be a transition zone from water to land, saline to fresh and low to high
Land reclamation and diking converted the coast to a coastline, herby ignoring this zone. Useful functions of the coastal zone were lost, while underneath its surface the coast still wants to acts as a zone
By recognizing that the coast is a zone, the transition area can be brought back, including its useful functions
P N
P
Paradigm change: From single coastline defense towards a broad coastal landscape zone of size
APPROACH Mitigating towards generating First of all, the solution needs to be a solution that looks ahead of time. Not mitigate, but generate. Not solely solving problem with a small-scale solution to its former situation, but a solution of size that not only solves problems but also generates new opportunities and results in a more interesting landscape. A surplus value. Mutual benefits Secondly, it needs to be said that tackling these problems at the same time can have mutual benefits. Since for example foreshores strengthen the dike base, it is mutually beneficial when these foreshores do not erode any further, but instead grow larger. The same can be said for outer-dike marshlands. When high enough, these salt marshes can dim waves, hereby muting the force that pounds on the primary dike. These mutual benefits imply that a solution has to be found that not separates the two (natural system and defense system), but integrates them. As said by Kees Veerman, chairman of the recently developed ‘Delta
Commission 2200’: ‘You should not think about a solid coast, but about a secure sea. How do we get a secure sea? By taming and steering it, not by closing- and blocking it down everywhere’ (Antonisse, 2007).
Figure 03.2 [above]. Thinking in a natural system solution implies the recognition that the coast is a zone, not a line.
THE SOLUTION WITHIN A solution for the updated Dutch coastal defense should not be restricted by ground-bound thinking, but instead think of the advantages of the unrestricted sea. The natural system works best in her own way; a dynamic system. A healthy, dynamic natural coastal system is resilient; it is able to cope with internal and external shocks like sea level rise and over-fertilization. Because of the dynamic processes of erosion and sedimentation, land can grow with the rise of the sea. A natural system with foreshores functions as a buffer zone; it dims waves and strengthens the basis of defense works and in this way makes its contribution to coastal safety. Furthermore, biodiversity forms the base of the ‘products and services’ that the coastal system provides and
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N
Cure to secure: Medicating the broad coast
A paradigm change: Long, thin line Power defense Break line Rigid Hard structure Closed Stiff Impermeable Single duty Technical Spatial solution Macadamized line Brutal order
towards towards towards towards towards towards towards towards towards towards towards towards towards
landscape zone of size smart, creative defense bending zone resilient soft structure open flexible permeable multi duty ecological space process solution living system sensitive chaos
From single coastline defense towards a broad coastal landscape zone of size!
And thus this system needs a solution that suits; a solution within, at the roots of the problems. As Ian McHarg already wrote down in 1969: ‘If one accepts the simple proposition that nature is the arena of life and that a modicum of knowledge of her processes is indispensable for survival and rather more for existence, health and delight, it is amazing how many apparently difficult problems present ready solutions’ (McHarg, 1969). A natural-system solution, not solely a technical solution. This means thinking within natural processes and dynamics, not working against them. A solution of processes, time and change. Directing, steering and allowing movement.
The sea should not be stopped, but merely directed and tempered, muted. Therefore there is a need of flexible solutions; flexible constructions. Already at present dunes, stabilized with grasses, provide a great flexibility, accepting the waves along the beach but reducing their velocity and absorbing their muted forces. From line to zone Thinking in a natural-system solution implies that it is recognized that coast is a zone, not a line. As explained before, the actual shoreline (the edge of land and water) naturally moves to and fro during ebb and flood. Due to this tidal range, it is always a zone, an area under influence of both land and sea. And since the Netherlands are nearly flat, it is naturally a broad zone. Even in ‘unnatural’ conditions, when the coastline consists of a dike, a zone can be recognized. Underneath its skin, a zone is found of saline influences, resulting in brackish seepage at the surface. This transition between saline and fresh water is exactly why the coast needs to be considered a zone, it is by ignoring it that many of
the problems in the natural system where caused. The coast is a zone: a transition area between sea and land, saline and fresh, low and high. ‘Zone’ implies ‘space’. A zone can only exist when space is provided. Space for land and water to overlap. Space for transitions from fresh to saline and from high to low. Space for nature’s generating processes. Space for dynamics and diversity, space as a buffer to dim wave force but also a buffer to cope with short-term shocks within the natural system.
Figure 03.3 [above]. Solving problems demands a paradigm change; from single coastline defense towards a broad coastal landscape zone of size
Paradigm change The solution is found in acknowledging that the coast is not a coastline, but a broad coastal zone. This means a changeover in handling the coast and its coastal defense. Future coastal defense has to allow the coast to be what it is, a zone. Single coastline thinking has to change coastal zone thinking and with this, defense will not be treated as single coastline defense, but as a securing broad coastal landscape zone. This asks for a paradigm change.
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that are of great importance to the wellbeing of men. The natural system is a living machine, a bioreactor digesting pollution, breathing out oxygen while taking up carbon dioxide, converting nutrients to harvestable biomass. At its heart is the tidal force, rhythmically pulsating water through its veins. It is a living system of processes, time and change.
Building a broad coast
Concept for a broad landscape zone of size
Minimal interventions
Three minimal interventions; - providing sediment, - allowing and guiding dynamics and exchange, - andspace between a dual defense system
allowing and guiding dynamics and exchange by making the single defense line permeable
Thesis statement Applying the concept of a broad coast means providing space for the mutual benefits that are discussed before. We state that 1: a broad coastal defense (contradictory to a coastline) can contribute in both curing local ecological problems and securing against long-term climate challenges And 2: This broad coast can be designed. Minimal interventions To allow the single coastline to become a broad coastal zone, several measures have to be taken: Providing sediment. The growth towards a zone demands sufficient amounts of sediment. Since the broad coast is to be a generating and not a mitigating solution, a different use of structural sand nourishments is needed. Large quantities of sediment can not only put a halt to coastal erosion of foreshores, but make the coastline grow seaward, hereby providing a buffer. Allowing and guiding dynamics and exchange by opening up the rigid
defense line, making it permeable. Dynamics, powered by tidal force, are the basis for sediment transport and hereby land-generating processes that allow our coast to grow along with sea level rise. Exchange is essential, especially in the Southwestern delta, for creating biodiversity, brackish habitats and species migration. Besides this, dynamicâ&#x20AC;&#x2122;s turbulence mixes water, hereby preventing stratification and over-fertilization. Providing space between a dual defense system. This space is a coastal playground where the wave force is muted and absorbed. In or along this space processes can be guided by use of double dikes, wave breakers, overflow dikes, reed matting, helm grass etc. Along the former single coastline either or both foreshore and hinterland are to be development; It is where new habitats can arise that provide us with products and services of the coast. Here, nutrients are converted to biomass and opportunities arise for multifunctional use; the zone provides a foundation for added functions like valuable nature, recreation, (experimenting
providing space between a dual defense system or by seaward broadening
Figure 03.2 [above]. Three minimal large-scale interventions are needed in order to transform the coastline towards a broad coast Figure 03.2 [right page]. Concept for the broad coast on a national scale
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providing sediment by large scale sand nourishments
Cure to secure: Medicating the broad coast
from single coastline to a broad coast; a landscape of size -20m
grow along with sea-level rise and land subsidence large quantities of sand are nourished on tactical spots along the coast the sandy coastline can grow seawards, intertidal areas can grow along with sea-level rise sand excavation locations are linked to commercial exploitation of construction sand the single coastline is developed into a broad coastal zone the single coastline is developed into a broad coastal zone exchange and dynamics are promoted
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-20m
Building a broad coast
Concept for a broad landscape zone of size
Sand erosion
providing sediment
Bank erosion Stratification
providing sediment
providing exchange & dynamics
N,P N,P
Nutrient shortage
providing exchange & dynamics
Over-fertilization
providing exchange & dynamics, providing space
providing exchange & dynamics
Species & habitat decline Constant dredging Exchange barrier
! !
providing exchange & dynamics, providing space, providing sediment
need of a site-specific solutions
providing exchange & dynamics
Weak defense spot
providing sediment, providing space
Coastal defense insufficient
providing sediment, providing space
Growing along with sea-level rise Dimming large waves
providing exchange & dynamics, providing space, providing sediment
providing exchange & dynamics, providing space, providing sediment
loss: transition area under influence of both land and sea
with) saline agriculture or aquaculture and creative residential functions. After these measures have been taken, a situation is created in which the natural processes can take over the ‘construction’ of the broad coast. Tides and currents, sedimentation and ecological succession now become the generating motor of this living landscape machine. The broad coast becomes self-regulating, growing and transforming over time and space into a stable and resilient ‘saltscape’. This saltscape will not be a fixed and predefined end result, but an ever-changing adaptable landscape. Its system will evolve and optimize her own composition in space and time by selecting the combination of plants, microbes and animals that are best adapted to the locally created circumstances. The more the selforganization of coastal ecosystems is taken into account, the less energy is needed for its maintenance and the lower the maintenance costs will be. Problem solving These minimal interventions are capable of solving
gain: transition area under influence of both land and sea
the problems and long-term challenges that are stated in the previous chapter (fig. 03.6). • Sand erosion providing sediment • Sand hunger providing sediment • Bank erosion providing exchange & dynamics • Stratification providing exchange & dynamics • Over-fertilization providing exchange & dynamics, providing space • Nutrient shortage providing exchange & dynamics • Species & habitat decline providing exchange & dynamics, providing space, providing sediment • Constant dredging need of a site-specific solutions • Exchange barrier providing exchange & dynamics • Weak defense spot providing sediment, providing space • Coastal defense insufficient providing sediment, providing space • Growing along with sea-level rise providing exchange & dynamics, providing space, providing sediment • Dimming large waves providing
exchange & dynamics, providing space, providing sediment Profits This broad coastal defense, a mutual playground for land and sea can provide flexible safety, regulation & resiliency and diversity (fig. 03.7). 1.The broad coast as a flexible defense system. A flexible and safe natural buffer landscape zone where the growth of foreshores, dunes, intertidal areas, salt marshes, shoals and mudflats is stimulated. A zonal defense system that allows overtopping or penetration of the former coastline, using this open situation to its advantage. A landscape of size that can cope with sea level rise, stabilizes the dike base and that dims and absorbs the forces of the sea. 2.The broad coast as a resilient regulating machine. Providing space for processes and dynamics, hereby enabling the coastal zone to grow along with sea-level rise and withstand short-term shocks. The broad coastal zone has a self-cleaning capacity; it regulates the mixing of fresh and saline water and converts nutrients
Figure 03.6 [above]. Problem solving; by applying the minimal interventions, natural processes are allowed that solve the coastal problems and bring back transition area under influence of both land and sea Figure 03.7 [right page]. Profits of the broad coast are flexible defense, resilience & regulation and (bio)diversity
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Sand hunger
Cure to secure: Medicating the broad coast
the broad coast as a flexible defense system
muting and absorbing wave force, strengthening the dike base and growing along with sea level rise
N P
the broad coast as a resilient & regulating living machine
a self-cleaning machine with the ability to grow with sea level rise and able to withstand short-term shocks, with tides as landscape motor
the broad coast as a landscape of (bio)diversity
an ever-changing zone with increased productivity, species numbers and species richness due to new transition habitats. new opportunities for multifunctional use
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into biomass. It binds sediments, therefore decreasing turbidity and increasing biomass growth. 3.The broad coast as a landscape of (bio)diversity . The productivity of the system can increase, since more nutrients are fully converted to biomass, especially to higher trophic levels. Brackish habitats will arise, as well as more intertidal nature, new spawning grounds and increased biodiversity and species numbers. Besides the increase in biodiversity, the coastal zone can become more diverse in function; opportunities arise for multi duty use such as added recreational, agricultural and/or residential functions.
Building a broad coast
Concept for a broad landscape zone of size
140 120 100 80 TNO/Deltaris min
60
TNO/Deltaris max
40
DeltaCommission
20
incl 1km growth/100jr Maasvlakte2 as reference
0
Als
Providing sediment At present, sand nourishments are at the basis of the soft coastline defense and are preferred above hard measures, because they provide the possibility to grow along with sea-level rise. Supplements are nearly 100% effective, since almost all of the sediment remains in the shallow coastal zone after being nourished (van der Spek, 2007). In order to maintain the coastline of 1990 during years of sea level rise, more sediment needs to be nourished than at present. The exact amount depends on the sea-level rise that is to be accounted for (figure 03.8). But when this nourishment quantity is increased, the coast can expand to create a sand buffer for unforeseen
changes. This buffer can grow into a landscape of size when sufficient amounts of sand are nourished at a yearly base, hereby creating a broad coast. When an extra 40 mln m3/year is nourished, the sandy coastline can grow outwards an extra kilometer within a 100 years (Deltacommissie, 2008), hereby already creating around 12.000 ha of space for nature and recreation along the Holland coast alone. Figure 03..8 shows how this extra sand supplement of 40 million cubic meters relates to present and future nourishment quantities and to the amount needed to build the Maasvlakte2 (MV2), the extension of the Maasvlakte1 and Europoort harbor. As can be seen, the yearly amounts needed for growing 1 km seaward are realizable with present day equipment, since the Maasvlakte2 requires quantities of the same scale. Costs of allowing the coastline to keep up with a sea-level rise depend on the velocity of this rise. Growing along with a rise of 20cm/century will cost around 60 mln euro/year, while these costs can increase up to 340 mln euro/
year with a rise of 130cm/century. The extra costs for growing seaward 1 km over a hundred years are estimated to be 160 mln/year. This implies that the total costs of both keeping up with the sea-level rise plus growing seaward range between 0.22 â&#x20AC;&#x201C; 0.5 billion euro/year (20-130 cm/century, based on Deltacommissie, 2008). So, when spending 380 million a year, the Dutch coast can keep up with a sea-level rise of 85 cm/century (which is already a high estimate by KNMI, 2007) and increase with 35.000 ha of new broad coast. (Deltacommissie, 2008). This is only 7% of what is spend on Dutch water management on a yearly basis (namely 5.1 billion euro in 2006. MVW, 2007). Besides this, nourishment techniques can develop over the coming 100 years to make supplements cheaper. The use of larger ships and better excavation techniques can severely decrease costs over the coming decades. Sand extraction can be combined with extraction of commercial construction sand that is used for concrete. Concrete-sand is found in deeper layers of the Dutch seabed and
Figure 03.8 [above]. Necessary sand nourishment quantities compared to present sediment suppletions and Maasvlakte2 construction
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Building a broad coast How to manage this transition towards a broad coast? The three minimal interventions (providing sediment, allowing and guiding dynamics and exchange, providing space between a dual defense system ) are provided with further details in order to show their feasibility.
Cure to secure: Medicating the broad coast
Present situation: Fresh water stock in dunes counter salt intrusion of the hinterland to a certain extent
coastal nature. The wide buffer allows seawater to breach the dunes during storms, creating washovers and restarting pioneer processes. Gradual transitions between saline and fresh water can exist, while new space is provided for recreation and waterdurable residential construction. The growth of new dunes will create larger fresh water stock, hereby countering salt intrusion of the hinterland and providing more drinking water for the west of the Netherlands. Applying large sand nourishments along the sandy coastline does also have positive effects for the Wadden Sea. Since sand is naturally transported northwards due to littoral transport, the nourishments can help the Wadden Sea to receive sufficient amounts of sediment to keep growing along with sea-level rise. Allowing and guiding dynamics and exchange Many of the problems regarding water quality along the coast can be improved by reconnecting water basins. This is especially true for the Southwestern Delta, where dams and dikes form
barriers for water and species exchange. When dams are made permeable with the use of pipes and sluices, the several water basins can be rejoined, hereby allowing species exchange and water mixing, but still retain their defense constructions. This improves water quality, nutrient distribution and creates possibilities for new brackish habitats. Several plans have been drawn up to reintroduce salt tidal water in the Southwestern Delta (Provincie ZuidHolland, 2003). Main conclusions are that the best way to counter ecological problems is to reconnect basins and to (partially) reintroduces tidal seawater. Fresh river water is to be let into the Haringvliet, Volkerak-Zoommeer and possibly Binnenschelde/Markiezaat coming from the rivers through the Hollands Diep. Salt water will be let into the Haringvliet, Volkerak-Zoommeer and Binnenschelde/Markiezaat coming from the Oosterschelde, Grevelingen and Voordelta. Also, the Westerschelde is to be connected to the Oosterschelde. This will allow more water to flow
Figure 03.9 [above]. Broader dunes will increase the fresh-water stock, hereby countering salt intrusion of the hinterland
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is only accessible when the topsoil of commercially uninteresting sand is removed. For every cubic meter of concrete-sand, a tenfold of non concrete-sand has to be shifted in order to reach that cubic meter. At present this is not feasible, but when this tenfold can be used for coastal nourishments, it can become so. Deeper sandpits can be excavated that after being exploited create new aerobe habitats for fish and other sea life due to differences in light climate and currents. At present only the top two meters of sand exploitation grounds are being, hereby affecting large surfaces of organism â&#x20AC;&#x201C;rich topsoil. From an ecological point of view deeper sand excavation pits are preferred above current toplayer excavation, since less organism-rich topsoil is affected for exploiting same quantities of sand. The coastal expansion will grow gradually over the years, giving time to natural processes to sort sand by grain size, generate new beaches and dunes and start ecological succession. This brings possibilities for nature that is more dynamic than our present
Broad coast situation: Fresh water stock in dunes counter has increased, hereby countering salt intrusion of the hinterland to a larger extent
Building a broad coast
Concept for a broad landscape zone of size
and providing gradual fresh-saline transitions. This will cause blue algae to disappear in the current fresh water basins, stratification is countered due to tidal movement and water exchange and bank erosion is stopped because of the tidal range. In return new species (such as sea grass) and brackish habitats can be expected, as well as increased species numbers due to the optimal use of nutrients. Fish can migrate between rivers and sea, having effects that reach deep into the European continent. More biomass means more consumable
species, an advantage for the fishing and aquaculture industry. Part of these interventions have already taken place in recent years or are planned to take place in the near future. As stated in the analysis of chapter 02.2, the Veersemeer system has in recent years been partially opened up and connected to both the Oosterschelde and Voordelta with the use of inlet sluices. Similarly, plans are to open the sluices of the Haringvliet year-round, allowing tides and dynamics in its system. These recent interventions follow this line of
O2 O2O2 N
P
P
P
exploited deep sand pits can become new aerobe habitats potential landward and seaward broad coastal zone existing dunes large-scale sand nourishments on tactical spots are redistributed by coastal processes port exchange by reopening barriers permeable dams
-13,1m
fairway to port of Antwerp primary defense line
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into the Westerschelde, increasing water depth during normal circumstances. During extremely high tides the connection can be used to store Westerschelde water in the Oosterschelde, hereby lowering water levels at the eastern side of the Westerschelde and increasing safety. Also, the Oosterschelde, Grevelingen and Volkerak-Zoommeer together can be used for temporary storage of river water during peak discharges combined with very high tides. All basins are (partially) reopened, hereby restoring tidal dynamics
Cure to secure: Medicating the broad coast
Providing space between a dual defense system In order to design a broad coastal zone, space needs to be provided. This can be done either land- or seaward of the existing primary coastal defense line. While along the soft dune coast (Holland coast and the outer parts of the North and Southwest) the zone will literally ‘grow’ seaward over time and by this provide the extra space needed for buffer, exchange and diversity, the Northern and especially Southwestern diked coastlines are a different story. Along the dikes of the mainland expansion from coastline towards a zone can also be either land- or seawards. The suitability of extending landward or seaward depends on factors like secondary dikes, seaward distance to shipping lanes or deep channels etc. This is further explained in chapter 03.5. Since at certain locations seaward extension is made difficult due to these factors, space will need to be provided by ‘depoldering’; giving (reclaimed) land back to the influences of the sea. Depoldering land is controversial in the Netherlands, especially within older generations that been grown up with land reclamations as the idea of progress; (partially) allowing the influences of the sea might seem like throwing away a good piece of agricultural land, hereby throwing money down the drain. But this financial aspect deserves a better look. In the Quickscan held by Twynstra Gudde (2007), it is stated that the costs of constructing a broad or double defense line are comparable to the costs of traditional dike raising, videlicet 5 million euro/km. This means that the only costs left are those of land purchase. In the essay ‘Ontpolderen zo gek nog niet’ (Saeijs, 2006), an effort has been made to show that depoldering can have financial benefits. The essay has its focus on the Westerschelde, explaining how the Port of Antwerp is in constant need of dredging due to the increased depth of its fairway.
This fairway will soon be deepened even more, allowing larger ships to enter the port. In the meantime, international regulations state that the valuable Westerschelde environment should not be damaged, but improved. Saeijs shows how in the Westerschelde system the tidal volume (the mean amount of water that flows in and out of the estuary every six hours; an estimated 1 billion m3) dominates river discharges during that same time (an estimated 2.5 million m3). Therefore, especially changes in the tidal volume determine whether erosion or accretion processes will set in. Changes in tidal volume can be caused by both natural and human factors. Accretion by river- and sea sediments, but also land reclamations, cause the tidal volume to decrease and subsequently the channels to adapt to a smaller tidal volume; channels become smaller as well. On the contrary, floods increase the tidal volume, leading to larger channels. Dredging and regulating of fairways lead to larger channels, without the same proportional change in tidal volume. This leads to accretion of nearby areas as a result of which the tidal volume decrease. Causing more dredge work… The solution to this dredging problem is depoldering upstream of where channels are too shallow. By allowing water to enter a zone behind the present dikes, more tidal volume is once again allowed. More tidal volume deepens the channels and this saves dredge work. Quick calculations by Saeijs show that 2000 ha of depoldered land upstream can save ca. 5 million euro/year in maintenance costs. This while costs of land purchase and development will coast near 60 million euro. Within 12 years the benefits have exceeded the costs, while the planned fairway deepening can vastly increase financial benefits (Saeijs, 2006). Besides these financial advantages, the extra (inter)tidal areas will have positive effects on lowering turbidity and increasing system productivity. More natural area is created with possibilities for nursery functions for sea life, but also for functions like recreation and fishery. As was
shown in chapter 01.4, when land is depoldered and hereby becomes part of the estuarine system, the yearly profits for of ecosystem products and services alone reach up to nearly 20.000 euro/ha/year. The depoldered areas provide excellent conditions for the origination of rare and highly valued salt and brackish habitats, home to endangered bird species and plants. The space provided for constructing a broad coastal zone can be privately owned or put on a leasehold. This allows private investors to add functions such as recreation, saline agriculture and flood-proof housing hereby severely increase the profits of the broad coastal zone. The new multifunctional use replaces former monofunctional use, hereby increasing the value of the land.
Figure 03.10 [left page]. The broad coast concept applied on the complicated Southwestern delta, showing sediment provision, exchange between compartments and provided space
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reopening the several compartments to tide and salt water, hereby allowing both tidal dynamics and water- and species exchange.
Broad coast typology
Applying the BroadCoast concept along the 3-parted coast
From single coastline to broad coast by seaward extension along the sandy coastline
a broad defense system with either landward or seaward solutions
From single coastline to broad coast by landward extension along the macadamized coastline
In this chapter the translating has been made between the broad coast concept on a Dutch scale towards the application along the three distinct parts of the Dutch coast. Previously it has been stated that while the â&#x20AC;&#x2DC;softâ&#x20AC;&#x2122; dune coast of mainly the Holland coast can grow seawards, the options for developing a coastal zone in the diked parts of the North and Southwest are either landward or seaward (and of course both are possible simultaneously). A typology is developed that shows the range of possibilities of dealing with the transformation from a single coastline towards a broad landscape zone of size. This is followed up by a method for deciding whether a coastline has better possibilities for developing either landwards or seawards. At the end of the chapter, three examples sites along respectively the Wadden coast, the Holland coast and the Southwestern delta show how the broad coast concept can be developed along the three parts of the coast. In chapter 03.6, the final example is detailed into the design of a catalyzing pilot project.
BROAD COAST TYPOLOGY FOR MACADAMIZED COASTLINES In order to provide site-specific solutions to transform the coastline towards a broad coast, a typology is developed. This typology is the result of a literature study and mainly based on ideas developed by the EU funded Comcoast project (ComCoast partners, 2006). The typology gives solution-types that can be divided into seaward, landward and exceptional solutions. Since the traditional dike raising solution is not a suitable solution-type for building a broad coast, it will be mentioned as an exceptional solution-type. The several types will be discussed here. Exceptional solution: E1- Dike raising (conventional method) E2 - Exceptional solution E1: Dike strengthening The conventional way of improving safety standards is by raising dike heights. New materials are placed on top and slopes of the present dike in order to gain more height and
Figure 03.11 [above]. Three ways of applying the broad coast concept along the 3parted coast
stability. The height should be enough to prevent overtopping of sea water during extreme conditions. Cure: This method does not have any ecological benefits, instead it creates a larger barrier between seaward and landward ecology. Secure: It is effective in increasing safety of the hinterland. Spatial development: The solution does not directly provide new possibilities for spatial development. E2: *Exceptional solution* In places where a landward or seaward BroadCoast solution-type is not implementable, special locationspecific solutions are needed. Since the necessary solution is exceptional and very site-specific, to accredit this solution solely means that an exceptional solution is to be found outside the typology.
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From single coastline to broad coast by seaward extension along the macadamized coastline
Cure to secure: Medicating the broad coast
Seaward solutions: Foreshore salt marsh development. S1 - S2 - Foreshore protection by a breakwater, foreland dike or embankment S3 - Foreshore sediment nourishments: artificially elevating the foreshore
Description To build a sustainable defense in front of the primary defense to provide a brackish area between the defenses for habitat or farming practices. This area can be flooded up to 10x/year.
Required action To build brushwood dams in order to slow down water movement and catch sediments to act as a buffer for the primary defense.
Required action To build a soft embankment to act as a buffer for the primary defense.
S1: Foreshore salt marsh development This solution-type involves the placement of sediment catching structures in front of the primary sea barrier in order to develop foreshore salt marshlands. Sediment settles due to the decreased wave action and currents as a result of the structure. The area becomes a salt marshland that is periodically flooded with the potential to grow along with the sea level rise. This method has been used over decennia for land reclamations along the coast. Here, it will not be used for this purpose, but solely for creating higher laying foreshore land. This solution-type creates new freshsaline transitions and habitats for several animal and plant species. The safety of the primary defense line is improved, since the foreshore â&#x20AC;&#x201C;when high enoughâ&#x20AC;&#x201C; decreases the surge force on the primary water barrier and stabilizes the dike base. Foreshore areas should have sufficient elevation in order to be effective by braking large waves during storm surges, since studies show that naturally generated foreshore marshlands hardly effect dike stability and necessary dike height (Comcoast, 2006-2). Possibilities arise for nature, recreation (e.g. marina) and saline agriculture that are consistent with the possibility of temporal flooding.
S2: Foreshore embankment or dike The solution of foreland protection by embankment or dike consists of placing a construction seawards in front of the present primary defense line. By this the safety of the primary defense line is improved, since the construction decreases the surge force on the primary water barrier. The area between the seaward construction and the primary water barrier is a brackish zone with decreased wave action and can be permanently or periodically flooded. The area between the foreshore embankment and the primary dike has the potential to grow along with the rising sea level. Sediments settle due to the decreased wave action and the foreland strengthens the base of the primary water barrier. The created foreshore area offers possibilities for nature, recreation and saline agriculture/aquaculture and flood-proof housing as long as the functions are suitable or adaptable to frequent or permanent flooding.
Description Eroded sediments are replaced by pumping dredged materials on top of the eroded foreshore. The dredging (mud, sands, gravel) would otherwise be dumped at sea and lost. The new sediments reinforce the natural flood defense and help to restore wildlife habitats. Required action Replenishing the foreland with environmentally friendly dredge sediments.
S3: foreshore sediment recharge to restore the coastline This foreshore nourishment solution implies the seaward placement of sediments (mud, sand, gravel). These new sediments strengthen the natural foreshore defense against the water and help (re-)create habitats for several animal and plant species. Possibilities arise for nature, recreation (e.g. marina) and saline agriculture that are consistent with the possibility of temporal flooding. Foreshore areas should have sufficient elevation in order to be effective and break large waves during storm surges, since studies show that naturally generated foreshore marshlands hardly effect dike stability and necessary dike height (Comcoast, 2006-2).
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Description To build a sustainable foreshore in front of the primary defense to provide a brackish area for habitat or farming practices. This area can be flooded 10x/year up to daily, depending on height.
Broad coast typology
solution types
Landward solutions: L1 - Overtopping-enduring dike defense L2 - Overtopping-enduring dike defense with regulated tidal exchange L3 - Managed realignment: relocating the dike land-inward, leaving a foreland dike
Required action Replace the top of the defense and its inner slope with a revetment that will not wear away by severe overtopping.
L1: Managed realignment: relocating the dike land-inward, leaving a foreland dike Managed realignment involves repositioning the primary sea barrier more inlands while remaining (parts of) the former dike. A dynamic zone is generated between the former and new primary sea barrier that is permanently or periodically flooded. Wave force on the new sea dike is lower in the new situation due to the wave breaking remains of the former dike. The intermediary zone can become silted up at the same rate as the sea level rise without human intervention. This increases the dimming of waves and hereby heightens safety (Comcoast, 20062). The solution-type is suitable for nature (creating fresh-saline transitions) and recreation. Agriculture is possible to realize when conditions are dry enough. If this is not the case, aquaculture has possibilities due to the warmer waters lacking strong currents. Flood-proof housing is possible as long as the they are suitable or adaptable to frequent or permanent flooding.
Description Allow tidal water to flow onto the coastal floodplain to reduce surge tide levels. The intertidal zone may silt up keeping (more or less) pace with sea-level rise and land subsidence. Required action Partial or full realignment of the flood barrier to allow managed tidal inundation of the floodplain creating a dynamic intertidal zone with considerable natural and recreational value.
L2: Overtopping-enduring dike defense With this landward solution, the inner slope of the primary dike is strengthened with overtoppingenduring revetment. This allows overtopping of the primary sea barrier. The overtopped water has to be stored before it can be drained or pumped back towards sea. This implies including a second dike as part of the coastal defense which creates a buffer zone for the overtopped water and secures the hinterland from salt intrusion. The brackish buffer zone can have positive effects on spatial developments like nature development, recreation, saline agriculture and possibly housing construction. Present functions can have negative effects from the overtopping. Positive effects are only possible if the primary dike is low enough. With the current dike heights the overtopping will statistically only occur once every 100-500 years (Comcoast, 2006-2). The landward area will hardly become brackish and inundated, therefore not benefiting from the positive effects to the full extent. When a more brackish situation is desired behind the overtopping dike, it can be partly lowered in order to increase the chance of overtopping. This will put more strain on the secondary dike during extreme conditions.
Description Allow tidal inundation of the coastal floodplain in a controlled manner. This creates a transitional zone where the land can evolve over time into a more saline environment. The transitional zone may silt up keeping (more or less) pace with sea-level rise and land subsidence. Required action Regulation of tidal waters through a system of sluice pipes and/or pumps. Low-lying land requires a secondary line of defense.
L3: Overtopping-enduring dike defense with regulated tidal exchange Here, the same solution is used as the overtopping-enduring dike defense, but with the addition of a regulated tidal inlet. This inlet is placed in the primary sea barrier, creating a controllable transition zone. A second dike is necessary to stop the sea water at the inland side. Since the inlets are used to let water in the interlaying zone, there is no need to lower the primary sea barrier (as with the overtopping enduring dike defense). The influence of the sea in the interlaying zone raise possibilities for several new functions. The regulated zone can silt up and keep up with the sea level rise. Possible new functions are nature, recreation and saline agriculture. Residential housing is possible when buildings are adapted to the controlled inundation conditions.
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Description Making the defense resistant to wave overtopping and ensuring that any water is washed over the top can be temporarily stored and drained away.
Cure to secure: Medicating the broad coast
Southwestern Delta
Holland Coast Wadden Area
North-Holland Coast example
Westerschelde Coast example
Groningen Coast example
increases the suitability of seaward solution-types, since it makes the realization of landward solution-types more difficult. A list of questions is used to fill in score tables that apply a score for either a landward or seaward solution. Explicitly it must be said that the scores cannot be compared directly but only relatively. The full method, analysis and criteria are stated in Appendix 1. THREE EXAMPLE AREAS The BroadCoast concept will be implemented on three example sites, one in each part of the three-sided Dutch coastal zone. Site selection Sites are selected that are representative for that part of the coast. This means that the Wadden coast and Southwestern delta example sites have ‘hard’ coastlines, while the Holland coast example site has a ‘soft’ coastline. Also, it is tried to choose sites in such a way that both landward
and seaward solution-types can be applied. The sites mainly consist of rural coastlines, by this meaning unurbanised coast fronts. This, because broad coast transformation becomes nearly impossible along densely built waterfronts, hereby requiring special site-specific solutions. All three example sites give the range of what the potential borders of the Broadcoast, as well as an image of how the present coast can look like after it is developed into a broad coastal zone of size. Also, the results will be given of the site analysis that determines the suitability for either landward or seaward solution-types for the ‘hard’ coastline examples.
Figure 03.12 [above]. Three example areas for applying the broad coast typology
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Landwards or seawards extension In order to apply the solutiontypes, it is first necessary to find out whether either a landward or a seaward or solution is more suitable or whether an exceptional solution is needed. With the aid of topographical map analysis and several criteria, the extent of suitability can be determined. This method has been based on a similar method created in a Comcoast study (Comcoast, 2006-2). The suitability of a solutiontype is dependent on the spatial characteristics of the coastline. Because these characteristics differ, the example areas are first subdivided into ‘autonomous’ coastal subparts. Then both sides of the primary water barrier are analyzed for several criteria, such as their presence of channels, secondary dikes, amount of built-on lots etc. The presence of built-on lots near the coast for example,
Broad coast typology
typology example 1: North-Groningen
Figure 03.13 [left]. Location of the example area along the Dutch coast
Groningen Seawards Landwards
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Figure 03.14 [left]. Tables showing the outcome of the criteria questions and score-tables Figure 03.15 [below]. Potential broad coastal zone (green), distance lines (pink), channels (blue) and autonomous compartments (numbered)
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Presence of deep channel or shipping lane/fairway within 500 meters seaward? Presence of shallow foreshore within first 500 m seaward that runs dry at low tide? Presence of shallow foreshore within first 1000 m seaward that runs dry at low tide? Number of build on-lots within 1000 meters or dike ring (ordinal, 1-5)? Less than 20 build-on lots present? Less than 1 build-on lot present? Presence of landward secondary ‘sleeper’-dike connected to primary sea barrier? Presence of secondary ‘sleeper’-dike within 500 meters landward? Presence of secondary ‘sleeper’-dike within 1000 meters landward?
Cure to secure: Medicating the broad coast
Figure 03.16 [below]. Providing space between a dual defense system by seaward broadening
Figure 03.17 [right]. Effects of the seaward solution-type ‘foreshore embankment’ t=0 year
Figure 03.18 [right]. Effects of the seaward solution-type ‘foreshore embankment’ t=10 year
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Figure 03.19 [right]. Effects of the seaward solution-type ‘foreshore embankment’ t=50 year
Broad coast typology
typology example 2: North-Holland
Figure 03.20 [left]. Location of the example area along the Dutch coast
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Figure 03.21 [below]. Potential broad coastal zone (green), distance lines (pink), channels (blue) and autonomous compartments (numbered)
Cure to secure: Medicating the broad coast
Figure 03.22 [below]. Providing space by seaward broadening
Figure 03.23 [right]. Impression of the broad as a dynamic sandy coastline
Figure 03.24 [right]. Broadening of the sandy coastline by large-scale sand suppletions t=0 year
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Figure 03.25 [right]. dening of the sandy coastline by large-scale sand suppletions t=50 year
Broad coast typology
typology example 3: Southwestern delta
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Figure 03.26 [left]. Location of the example area along the Dutch coast
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Figure 03.27 [left]. Tables showing the outcome of the criteria questions and score-tables Figure 03.28 [below]. Potential broad coastal zone (green), distance lines (pink), channels (blue) and autonomous compartments (numbered)
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Presence of deep channel or shipping lane/ fairway within 500 meters seaward? Presence of shallow foreshore within first 500 m seaward that runs dry at low tide? Presence of shallow foreshore within first 1000 m seaward that runs dry at low tide? Number of build on-lots within 1000 meters or dike ring (ordinal, 1-5)? Less than 20 build-on lots present? Less than 1 build-on lot present? Presence of landward secondary ‘sleeper’dike connected to primary sea barrier? Presence of secondary ‘sleeper’-dike within 500 meters landward?
Cure to secure: Medicating the broad coast
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Figure 03.29 [left]. Providing space between a dual defense system by landward or seaward broadening
Broad coast pilot project
Site choice and analysis
in cm < -146 -146 - -100 -100- -50 -50 - 0 0 - 50 50 - 100 100 - 150 150 - 200 200 - 250 250 - 300 300. - 350 350 - 400 400 - 450 450 - 800 800 - 1100
Site choice The choice for using the Westerschelde-Terneuzen example as a pilot design has been made for several reasons. Firstly, the Southwestern Delta is the most problematic and complicated part of the three-sided coast, consisting of many different subsystems. The Holland coast is not very suitable to have a pilot project, since its design solution comes down to one intervention that affects
the whole sandy Holland coast. Between the Wadden coast and the Southwestern delta the choice is made for the delta, since it is here that often landward solutions need to be applied. Many locations can only be developed landwards due to seaward tidal channels and fairways as can be seen in the previous chapter. This allows the pilot to show how present agricultural land can develop into a saltscape; a broad coastal zone of size. In the Wadden area, implementations are easier, because more possibilities exist for developing seawards. Thus, the need for a pilot project is greater in along the Southwester delta, since here the pilot can show that developing a broad coast is also possible in more complicated areas. Within the delta, the Westerschelde is the only remaining estuary that is intact. Because of this, the initial conditions of â&#x20AC;&#x2DC;dynamics/exchangeâ&#x20AC;&#x2122; are already present, allowing the development of the pilot area towards a broad coast to be implemented at present or in the near future. Besides this, due to the dredging of the Antwerp port fairway, intertidal nature
needs to be compensated for along the Westerschelde. This can be a spinoff for the pilot project. Within the Westerschelde area, the Westerschelde-Terneuzen example site contains several secondary dikes that allow a pilot project to be implemented faster and at lower costs. Also, not to many built plots are found directly behind the dike, hereby increasing the opportunity for faster realization of a pilot project. Finally, the existence of two creeks with water discharge locations offer opportunities to create on-site freshsaline transitions.
Figure 03.30 [above, left]. Location of the pilot project site along the Westerschelde estuary Figure 03.31 [above, right]. Former creek patterns show clearly in the height map Figure 03.32 [right page]. A quick site analysis showing creeks, secondary dikes, pumps etc.
Demarcation of pilot site The pilot project site consists of the autonomous areas 2-7, as shown in the third typology example. On the northern side, the edge is made up by the Westerschelde with its fairway. On the landward side the edge is made up by the secondary dikes. In the west the pilot site is bordered by the urban area of the city of Terneuzen. Site analysis A quick site analysis
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Introduction For the final design of a pilot project, a site is chosen near the city of Terneuzen, along the Westerschelde. It is not intended to show a detailed, finalized design for this location. Instead, it is tried to show simply what the site can look like when it is a part of the broad coast. The pilot shows how this area can turn into a landscape of size. At the basis of this is the broadcoast as a flexible defense system, a resilient regulating machine, a landscape of biodiversity. This stable basis provides a landscape of opportunities for added nature, recreation, saline agriculture and/or flood-proof residential functions.
Cure to secure: Medicating the broad coast
reveals that two creeks run into the Westerschelde on or very near to the site. Pumps are used to discharge the brackish and nutrient-rich creek water into the Westerschelde. A small part of the site is affected by salt intrusion. A glance on the height map shows former creek patterns in the reclaimed agricultural land. It also shows clearly that the outer-dike salt marsh is more elevated than the hinterland due to sedimentation processes that allow the marsh to grow along with sea level rise.
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shipping fairway creek with direction of flow primary dikes pump draining creek water in Westerschelde brackish land due to salt intrusion secondary dikes
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Broad coast pilot project
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Design for the broad coast near Terneuzen
Cure to secure: Medicating the broad coast
broad c o ast pilot proje ct West
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ersch Terne elde uzen
Broad coast pilot project
Design for the broad coast near Terneuzen
shipping fairway near the primary coastline is not affected by the Broad Coast
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fresh-saline transitions are created by discharging brackish creek water into the Broad Coastal zone, herby allowing mixture and natural runoff towards the Westerschelde
pumps and inlet-sluices allow both brackish creek water and saline Westerschelde water to influence the zone
use of dams for directing the water flow, hereby lengthening its course and increasing nutrient uptake and mixture
difference in water levels and dynamics create diverse habitats like tidal marshland and saline meadowland
built-on plots within the broad coast zone are surrounded by small dikes, hereby securing safety and allowing residential functions
initial programme consists of nature and recreational functions. Extra functions such as flood-proof housing or saline agriculturecan be added over time, depending on market demand
location of cross-section
Figure 03.2 [above]. Providing space between a dual defense system or by seaward broadening
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dual defense system, consisting of primary and secondary dikes
Cure to secure: Medicating the broad coast
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Broad coast pilot project
Design for the broad coast near Terneuzen
functioning of the overtopping resistant dikes low tide
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biodiversity biomass production land level sea level
extra functions resdential function extra functions allowing exchange & dynamics providing space between a dual defense system sand nourishments
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Cure to secure: Medicating the broad coast
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2x/day 8 About twice a year the broad coast pilot site is fully flooded when storm surge pushes waves up the primary dikeâ&#x20AC;&#x2122;s slopes, causing overtopping and indundation.
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Broad coast pilot project
Design for the broad coast near Terneuzen
New intertidal areas compensate for loss in the Westerschelde due to land reclamations and dredging of the fairway. This valuable intertidal nature attrracts many endangered ‘red list’ species such as the godwit(Limosa limosa) and avocet (Recurvirostra avosetta)
Possibilities for (outdoor) recreation and ‘into the wild’ experience. Backpacking, gathering food, fishing etc. When the pilot example is followed by national application, the broad coastal zone can grow into a landscape of size making multiple-day hikes possible and providing large areas of connected nature
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Information and education functions can increase attachment to the site and increase local stewardship
Cure to secure: Medicating the broad coast
The broad coast is a landscape of movement and constant change. Large cargo ships move slowly along the horizon, while the zone is flooded twice a day. During the year the colors of this landscape of size change. Aster tripolium flowers purple in summer, while Salicornia Europaea changes from green to bright red in autumn.
salt marsh with Aster tripolium vegetation during summer
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The broad coast pilot project as a natural parkland with recreational functions such as hiking and bird watching. In autumn, Salicornia Europaea turns red-colored
Broad coast pilot project
Design for the broad coast near Terneuzen
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opportunities for saline agriculture and mariculture
Cure to secure: Medicating the broad coast
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The broad coast pilot project perfectly lends itself for (experimenting with) saline agriculture or aquaculture. Fish, mussels, salicorn (salicornia europeae), sea kale (crambe maritima) and rocket (eruca sativa) are just a few examples of eatable products that have the potential of being commercially exploitable
Broad coast pilot project
Design for the broad coast near Terneuzen
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opportunities for flood-proof housing
Cure to secure: Medicating the broad coast
101
The broad coast pilot area becomes an interesting location for (experimenting with) flood-proof residential functions
Thesis conclusion
Conclusion and further research
binds sediments, therefore decreasing turbidity and increasing biomass growth. The coast is more diverse because brackish habitats have developed as well as dynamic pioneer nature, hereby increasing biodiversity. Besides the increase in biodiversity, the coastal zone has become multifunctional, allowing added recreational, agricultural and/or residential functions. Implementation Economic profit – as is shown in chapter 03.4, the broad coast can become a profitable solution that pays back its own costs. Costs of overtopping dike are comparable to traditional dike raising (Comcoast, 2006-2). This means the only costs left is the purchase of land. As shown before, increasing of the tidal volume can save a lot of maintenance costs for the Westerschelde fairway, hereby already paying back its investments. Besides that, financial profits are to be expected in water quality regulation (less turbidity, less over-fertilization) and increased commercially exploitable biomass (more nutrients
are converted to biomass, while new nursery habitats arise). The improvement of the spatial quality of the site can give the surrounding rural area an uplift, attracting more recreational users and stimulating local tourist business. Politics – Due to global climate change the coastal safety of the Netherlands has been put high on the Dutch political agenda. The Dutch Water Board, the Delta Commission 2008, the Dutch Innovation Platform; all are currently working on ideas that can provide a solution for the Dutch coast. By further investigating the possibilities of the Broad Coast concept, the Netherlands have the possibility to maintain their reputation of having state-of-the-art coastal defense solutions. Besides this, the implementation of the pilot project itself will urge on further research for Broad Coast applications and allow experimentation. New research can provide new insights that save money and time. The Broad Coast solution as well as any further research has the potential to be exported abroad,
since many worldwide delta regions are facing similar problems in the near future. People – Social acceptance can be critical in the application of such a large-scale solution. The advantage of the Broad Coast concept is that it can be applied one piece at a time; every autonomous compartment has possibilities of developing autonomously as well. Easier parts can be developed first, hereby raising the public’s interest and making people used to the idea. Social acceptance for depoldering agricultural land can be a serious problem for applying the Broad Coast concept in the landward solutiontypes, especially in the Southwestern Delta. But this reluctance is a generation problem, especially by the older generation of farmers that where brought up with the idea of land reclamation as progress. Since the Broad Coast concept is a long-term solution, there is time. A paradigm change takes time, but new generation will probably be more open to accept the Broad Coast as a
102
Thesis conclusion In the previous pilot project design it is shown that a broad coast can contribute in both curing local ecological problems and securing against long-term climate challenges. By taking few minimal interventions, the right conditions are created for nature’s generating processes to take over. Hereby the coast can build itself towards safe, resilient and diverse landscape zone of size, with new possibilities for multifunctional use. The coast is safer because a broad buffer zone is created that allows a certain kind of penetration by the sea. This buffer zone mutes and absorbs the sea’s forces, stabilizes the dike base and can grow along with sea-level rise. It is no longer a single breakline, but now a flexible zone where possible breaches can be seen in advance. The coast is more resilient to shortterm (ecosystem) shocks and adaptive to long-term climate challenges. The broad coastal zone has become a living regulation machine that has a self-cleaning capacity; it regulates the mixing of fresh and saline water and converts nutrients into biomass. It
Cure to secure: Medicating the broad coast
Application The application of the Broad Coast is a solution for the whole of the Dutch coast. Still, it is not applicable everywhere. In the Wadden area and Southwestern delta, the solution can be implemented as long as either a landward or seaward solution-type is possible. When no landward or seaward solution-type is possible, an exceptional site-specific solution needs to be implemented, hereby not developing a Broad Coast at that location. These exceptional site-specific solutions will mainly arise
along urban coastal fronts. Therefore, the Broad Coast concept is a solution for the majority of the more rural coastlines, not so much for the highdensity urban coastlines. Recommendations for further research Since this final thesis is restricted in time as well as geographical study area, several topics are recommended for further research: • Price tag: what are the exact costs and profits of applying the Broad Coast in the Netherlands? • Time frame: monitoring of several present locations can provide more knowledge on growth rates, succession rates that can be useful for further planning and design of the Broad Coast concept. What are the possibilities for guiding this growth, especially along the sandy coastlines where urban coastal fronts require specific solutions? • Providing sediments: What are the best spots to place large quantities of sediments so that
•
•
•
natural processes can take over distribution? Can combinations be made with relocating nearshore deep channels? Brackish agriculture: fresh-saline transitions are more and more becoming a topic of interest, but there is little knowledge on the agricultural possibilities of saline and brackish landscapes. How can the development of saline agriculture positively influence the implementation of the Broad Coast and vice versa? Salt seepage: what are the effects of the Broad Coast on salt intrusion of the hinterland? What can be done to increase positive effects or counter negative effects? Inland growth with sea-level rise. The deepest polders near the Wadden sea and Southwestern coast are situated the further inlands. Can a system be introduced that allows sediment to be transported further inlands, hereby allowing these deep polders to grow along with sealevel rise?
•
•
How can dikes be made overtopping-enduring, and can this be done in a eco-technical way (e.g. with combinations of deep-rooting native shrubs)? Secondary dikes: when are secondary dikes in a sufficient condition to be used for building a broad coastal zone? When is it cheaper to develop a new secondary dike?
103
solution. Besides that, future increase in salt intrusion along the reclaimed polders will probably demand for a change of thinking as well, making saline agriculture more profitable and hereby providing excellent combinations with the development of the Broad Coast. Looking at the ‘Room for the Rivers’ project shows that social acceptance of such a project is possible. Room for the River is now widely accepted and applied along all of the large rivers in the Netherlands. The next step is ‘room for the coast’; the Broad Coast.
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Appendix 1
list of projects analysed by the Comcoast quickscan (comcoast partners, 2006) Nr.
Beoordelingscriteria Maatregel
Fase veiligheidsketen
Haalbaarheid Kansrijkheid
Effectiviteit
Financieel
Juridisch
Fysiek
Draagvlak
Tijdigheid
Preventief
Gemiddeld. Kans op overstromen wordt verkleind.
onbekend, wordt wel samen met bedrijfsleven ontwikkeld
++ weinig hobbels
+/- deels bewezen technieken en nader te ontwikkelen
++ weinig partijen nodig voor draagvlak
+ relatief snel te realiseren
groot
0,7 miljard
+/- juridische hobbels naar verwachting groter bij landinwaartse oplossingen, waar ruimtegebruik intensiever is
+ maatregelen zijn fysiek haalbaar
+ meeste draagvlak voor zeewaartse oplossing; minder draagvlak voor consolideren/landinwaarts
+ Uitvoering op termijn van enkele jaren
groot
++ weinig hobbels
++ wordt reeds toegepast
mogelijk weerstand bij ophoging
++ op korte termijn realiseerbaar + is uitgevoerd
groot
1 a
Niet-traditionele versterking waterkeringen Grondtechnieken voor dijkversterking
b
Versterking zwakke schakels in kustwaterkeringen
Preventief
Groot. Kans op overstromen wordt verkleind
c
Dijkversterking door vorm
Preventief
Gemiddeld. Kans op overstromen wordt verkleind.
d
Opblaasbare stormvloedkering (balgstuw)
Preventief
+ is uitgevoerd
++ is uitgevoerd
+ is uitgevoerd
Combikering (Den Helder)
Preventief
Groot. Kans op overstromen wordt verkleind Gemiddeld tot groot. Effect op kans op en gevolgen van overstroming, afhankelijk van variant.
+ is uitgevoerd
e
onbekend, zicht op verhouding van kosten/baten voor de varianten
huidige regelgeving als kader, aantal procedures afhankelijk van gekozen variant
+ fysiek mogelijk. Onzekerheid over functioneren drijvende golfbrekers
+/- bij dijkstad en - bij terrasstad, + bij zeestad
f
Keren in de breedte 1. Overslagdijk (ComCoast)
Preventief
Groot. Kans op overstromen wordt verkleind en de gevolgen zijn verminderd
vergelijkbaar met versterking traditionele dijk; € 5 miljoen/km
+ Past binnen huidige wet en regelgeving. Doorloopt MERprocedure
+ realiseerbaar, onder condities dat voldoende overslagwater geborgd kan worden
+/- weerstand vanuit landbouw; meer voorlichting nodig voor impact op wonen
groot
2. Dijk met Bereik
Preventief
Groot. Kans op overstromen wordt verkleind en de gevolgen zijn verminderd
vergelijkbaar met versterking traditionele dijk; € 5 miljoen/km
+ Past binnen huidige wet en regelgeving. Doorloopt MERprocedure
+ realiseerbaar, onder condities dat voldoende overslagwater geborgd kan worden
+/- weerstand vanuit landbouw; meer voorlichting nodig voor impact op wonen
groot
3. Dubbele Dijk
Preventief
Zeer groot
+
+
+/-
groot
g
Superdijk
Preventief
Groot. Kans op overstromen wordt aanzienlijk verkleind
vergelijkbaar met versterking traditionele dijk; € 5 miljoen/km - grootschalig en omvangrijk werk
- aanpassing leggers en mogelijk wetgeving
- grote Ruimtevraag
h
Begeleidingsdijk
Preventief
Niet beoordeeld
Niet beoordeeld
Niet beoordeeld
Niet beoordeeld
- veel weerstand te verwachten, maar voordelen van meervoudig ruimtegebruik Niet beoordeeld
2
Tegengaan van erosie
a
Continu suppleren (Zandmotor)
Pro-actief
Groot. Effect op veiligheid na enige tijd (1 à 2 jr) als meer zand in hoger deel van het profiel terecht komt (door natuurlijke verplaatsing)
interesse van marktpartijen om mee te financieren
++ weinig hobbels
+ goed mogelijk, enig aanvullend onderzoek nodig
b
Bioduinen
Preventief
Gemiddeld; verkleining kans op overstromen; lokale toepassing
++ toepassing zelf niet duur l
+ waarschijnlijk geen juridische kaders van toepassing
c
Ecobeach (passieve zanddrainage)
Preventief
Gemiddeld; verkleining kans op overstromen; vooral lokaal toepasbaar.
+ markt is betrokken bij ontwikkeling en toepassing
++ weinig hobbels
d
Plan Waterman
Preventief
Gemiddeld voor huidige situatie is de maatregel gunstig, bij niewbouw wel weer secundair veiligheidsvraagstuk
vanwege omvang grote kosten, die vooral via woningbouw moeten worden terugverdiend
-- veel procedures
3 a1
Verminderen golfaanval Verminderen golfaanval op waterkeringen langs meren
Preventief
Groot. Kans op overstromen wordt verkleind
Kosten / orde grootte onbekend, vergelijkbaar met kustsuppletie
a2
IJmeer zoekt verdieping, Markeroog
Preventief
Groot. Kans op overstromen wordt verkleind
+/- vanwege grootschaligheid (70 miljoen m3 zand ter ophoging)
+ weinig hobbels, lokaal mogelijk wel rekening houden met natuurwetgeving - Vogel- en Habitatrichtlijn
b
Verminderen golfaanval op waterkeringen langs kust (Holland Bolland) Verminderen golfaanval op waterkeringen langs kust (kunstriffen)
Preventief
Gering, werking is gebaseerd op andere uitgangssituatie Onvoldoende bekend, schaalproeven laten zien dat lange golven door het kunstrif substantieel afnemen
d
Haakse zeedijk
Preventief
Gemiddeld voor huidige situatie. Wel veiligheidsvraagstuk voor de nieuwe kustlijn
grote omvang kosten, ca. 34 miljard.
4
Aanleg/versterken van secundaire / compartimenteringskeringen
Preventief
Groot. Leidt tot verkleining van de gevolgen
Afhankelijk van dijkring: 5 - 270 miljoen
Preventief
+ er zijn al ervaringen in het buitenland opgedaan, kostenschatting wordt nog gemaakt
+/- harde elementen niet conform beleid, maar ook mogelijkheden voor zachte toepassingen -- veel procedures
- diverse procedures
19
groot gering/gemiddeld
- niet op korte termijn te realiseren
gering
Niet beoordeeld
conceptueel, niet beoordeeld
+ geen hinder voor toeristen; uitbreiding van ruimte; bestuurlijke draagvlak voor idee
+ na onderzoek en bij medefinanciers vlot te realiseren
zeer groot
+/- nader onderzoek naar werking en duurzaamheid nodig
+ in situ toepassing, geen effect op omgeving
+ gezien nader onderzoek niet op korte termijn grootschalig te realiseren
gemiddeld
+ techniek beproefd in Denemarken, nog geschikt te maken voor NLsituatie ++ goed mogelijk
+ breder/hoger strand, gunstig voor recreatie
++ op korte gemiddeld/groot termijn toepasbaar
- eerdere plannen voor kustlocatie zijn gestrand door gebrek aan draagvlak (geen urgentie)
-- alleen op lange termijn realiseerbaar
gering
+ relatief eenvoudig te realiseren maatregel
+
++
groot
- lastig in beheer
+/-, momenteel veel draagvlak maar niet te voospellen of er bij concretisering meer tegenstand ontstaat
Niet voor 2015 realiseerbaar, wel kansen voor een gefaseerde realisatie
gemiddeld
++ potentie voor andere functies (duikers/visserij)
+/- op middellange termijn realiseerbaar
gemiddeld/groot
-- weinig draagvlak voor dergelijk grootschalige aanpak (geen urgentie)
-- alleen op lange termijn realiseerbaar
gering
- Het ene gebied kan wel vollopen, het andere niet. Hoe om te gaan met gelijkheidsbeginsel?
+/- Sterk afhankelijk van uitgangssituatie
Gemiddeld (sterk afhankelijk van de locatiespecifieke situatie)
+/- positieve ervaringen in Dubai. Vertaling naar NL-situatie nodig, waarbij ook knelpunten worden gezien. '+/- moet mogelijk zijn; nader onderzoek naar wijze van aanleg nodig +/- Beschikbare ruimte is beperkende factor
gering
106
c
- gezien juridische procedures op lange termijn realiseerbaar
Cure to secure: Medicating the broad coast
Nr.
Beoordelingscriteria Maatregel
5 a
Schadebeperking objecten Dry-proofing van woningen en bedrijfsgebouwen (bouwen op palen, bouwen op terpen, drijvend bouwen, bouwen met water)
b
Dry-proofing van vitale objecten en gebouwen (vb: crisiscentra, communicatiecentra, ziekenhuizen, rioolzuivering, drinkwatervoorziening) Dry-proofing van vitale infrastructuur (vb: communicatienetwerken, gasdistributie, electr. distributie, weginfra, railinfra) Verminderen overstromingsrisico nieuwe verstedelijkingslocaties door middel van ophogen of omdijken/omkaden
c d
Fase veiligheidsketen
Financieel
Juridisch
Fysiek
Draagvlak
Tijdigheid
Proactief
Lokaal gemiddeld tot groot effect. Schade aan woningen wordt beperkt of voorkomen.
afhankelijk van variant
+ of onbekend
locatie: beperkte waterstandsfluctuatie
+/- afhankelijk van gebied en schaal waarop maatregelen plaats vinden
+/- realiseerbaar op termijn van 510 jaar
gemiddeld tot groot
Proactief
Groot effect, vermindering/voorkomen van grote economische schade.
orde 1-5miljard voor heel laag-NL
Onbekend
Onbekend
vooral weerstand bij beheerders
Onbekend
gering
ophoging: zeer groot (verkleinen gevolgen); omdijking: groot (verkleinen kans)
20-50 miljoen bij nieuwbouw van 10.000 woningen
Onbekend, is afhankelijk van het draagvlak voor het nieuwbouw project
+/- 5-10 jaar tussen plan en uitvoering
gemiddeld-groot
iets duurder dan andere oplossingsrichtingen
Onbekend is namelijk onderdeel van het ruimtelijke planvormingsprocessen
juiste materialen gebruiken;
- vraagt om acceptatie van de bewoners dat huis onder water kan komen te staan
+/- realiseerbaar op termijn van 510 jaar
+/- weerstand tegen verplaatsen van woningen/bedrijven. Urgentie van vraagstuk -
+/- op termijn van 10 jaar te realiseren
gemiddeld
-
gering
Proactief/Preventief
Wet-proofing van woningen en bedrijfsgebouwen (bijv. sponswoning)
Proactief
f
Minder kwetsbaar maken van kwetsbare objecten/instellingen (gericht op veiligheid bewoners zoals bejaardenoorden). Minder kwetsbaar maken van risico-objecten (milieurisico) zoals BRZO-bedrijven
Proactief Proactief
verkleinen gevolgen (milieurisico)
Proactief
Groot.
2,2 miljard (bij uitgangspunt 16.000 m3/sec)
+/- diverse procedures te doorlopen
+
Gemiddeld
+ de reservering op zich kost weinig
+/- diverse procedures te doorlopen
- neemt veel ruimte in beslag
+/- diverse procedures te doorlopen
+/- neemt veel ruimte in beslag
6 a
Ruimte reserveren Ruimte creeert: ruimte voor de rivier
b
Ruimte reserveren: planologische reservering voor toekomstige waterkeringen en aangepast landgebruik
Proactief
c
Ruimte reserveren: Onteigening/aankoop van gebouwen in risicozones
Proactief
d
Fysieke voorbereiding op noodherstel (bijv. depots met herstelmateriaal, goede toegangswegen) Ruimte reserveren: nieuwe rivier
e
Kansrijkheid
Proactief
e
g
Haalbaarheid Effectiviteit
Preparerend
gemiddeld - groot; afhankelijk van reactietijd en mankracht
+/- weerstand bij personen die moeten verhuizen
+, geen wettelijke procedures
groot gering
Proactief
Groot
- ( 3 miljard)
-, veel procedures
- neemt veel ruimte in beslag en is ingrijpend
-- weerstand te verwachten bij veel betrokkenen
++, kleinschalige trainingen en simulaties worden in NL al toegepast +, maatregel wordt nog niet toegepast ++, risicokaarten worden al gemaakt
+
0-2 jaar
gemiddeld
+
0-2 jaar
gemiddeld
+
0-2 jaar
groot
7 a
Risicocommunicatie Verhogen bewustzijn bestuurders en professionals
Proactief
Gering
0-20 mln
+, geen wettelijke procedures
b
Verhogen bewustzijn algemeen publiek
Proactief
Gering
0-20 mln
+, geen wettelijke procedures
c
Vergroten informatie en handelingsperspectief burgers en bedrijven
Preparerend
Gemiddeld
0-20 mln
+, geen wettelijke procedures
8 a
Crisiscommunicatie Vergroten informatie en handelingsperspectief burgers en bedrijven
Repressief
Gemiddeld
0-20 mln
++
+
0-2 jaar
groot
b
Vergroten informatie en handelingsperspectief bestuurders en professionals 1. State of the art voorspel- en waarschuwingssysteem (rivieren en kust) 2. Voorspel- en waarschuwingsdienst (rivieren en kust) 3. State-of-the-art bestuurlijk/ operationeel beslissingsondersteunend systeem
+, geen wettelijke procedures. Voor cell-broadcasting is dit onbekend
Proact./ Prep.
Gemiddeld
0-20 mln
++
Gemiddeld
0-20 mln
++, kleine groep 0-2 jaar positieve betrokkenen ++, kleine groep 0-2 jaar positieve betrokkenen 0-2 jaar ++, kleine groep positieve betrokkenen
groot
Preparerend
+, geen wettelijke procedures +, geen wettelijke procedures +, geen wettelijke procedures
9
Organisatorische voorbereiding
a
Onderzoek en visievorming over organisatorische maatregelen
b
Opzetten en instandhouding crisisbestrijdingsorganisatie
c
Repressief
Gemiddeld
0-20 mln
++ ++, betreft bestaand systeem
groot groot
Proactief
Gemiddeld
0-20 mln
+, geen wettelijke procedures
++, geen noemenswaardige knelpunten
+, grote groep 0-2 jaar positieve betrokkenen
groot
Prep./ Repr.
Gemiddeld
100-500 mln
+, geen wettelijke procedures
++, ze bestaan reeds in NL
+, grote groep 0-2 positieve betrokkenen jaar
groot
Opzetten en instandhouding fysieke noodmaatregelen voor lokale, regionale en landelijke inzet
Repressief
Gemiddeld
+, geen wettelijke procedures
0, op voorhand onduidelijk
gemiddeld
d
Opstellen operationele plannen (rampen- en evacuatieplannen)
Repressief
Gemiddeld
0-20 mln
+, geen wettelijke procedures
+, er is behoorlijke capaciteit nodig voor uitvoering ++, ze worden reeds gemaakt
10
Hulpverlening na overstroming (psychosociaal)
Nazorg
Onbekend
Onbekend
+, geen wettelijke procedures
++
11
Vergoeden van overstromingsschade bij burgers en bedrijven
Nazorg
groot
++
+/-, wellicht zijn aanpassingen van wet- en regelgeving nodig
++
2-5 jaar in verband met aanschaf middelen 0-2 jaar voor individueel plan
+, grote groep overwegend positieve betrokkenen +, grote groep 2-5 jaar positieve betrokkenen
(waarschijnlijk) groot
0-2 jaar, mogelijk langer
107
+, grote groep betrokkenen die gemengd tegenover maatregel staan
20
groot
gemiddeld
Appendix 2
application of seaward or landward solution-types APPENDIX 2: Application of seaward or landward solution-types Introduction In order to apply the solution-types, it is first necessary to find out whether either a landward or a seaward or solution is more suitable or whether an exceptional solution is needed. With the aid of topographical map analysis and several criteria, the extent of suitability can be determined. This method has been based on a similar method created by Comcoast partners (2006-2). The suitability of a solution-type is dependent on the spatial characteristics of the coastline. Because these characteristics differ, the example areas are first subdivided into ‘autonomous’ coastal subparts. Then both sides of the primary water barrier are analyzed for several criteria, such as their presence of channels, secondary dikes, amount of built-on lots etc. The presence of built-on lots near the coast for example, increases the suitability of seaward solution-types, since it makes the realization of landward solution-types more difficult. A list of questions is used to fill in score tables that apply a score for either a landward or seaward solution. Explicitly it must be said that the scores cannot be compared directly but only relatively. The full method, analysis and criteria are stated in this Appendix. Autonomous coastal subparts The suitability of a solution-type is dependent on the spatial characteristics of the coastline. Because these characteristics differ, the example areas are subdivided into ‘autonomous’ coastal subparts. An autonomous coastal subpart is a part along the primary coastline that can be seen as an entity on its own. Subparts are primarily made up of adjacent polders, since these can be seen as autonomous parts and have clear borders (the polder dikes). When adjacent polders with secondary dikes are absent, other borders are to be used, such as roads and ditches. Both sides of the primary water barrier are analyzed. When landward secondary dikes are found, these make up the inland limit for the subparts. When secondary dikes are absent, the inland limit is placed on an offset of 1000 m from the primary water barrier. Seaward, the same 1000 m offset is used. Here, an offset of a 1000 m is chosen because the construction of new secondary dikes (regulated tidal exchange, dike overtopping) and new primary dikes (managed realignment) can all be placed within this offset. Besides that, most of the existing secondary dikes fall within this offset area. The outer seaward limit of a 1000 m is used because the vast majority of the northern salt marshes fall within this offset. The differences in spatial characteristics of each autonomous coastal subpart determine whether a traditional, landward- or seaward solution-type should be used and which solution-type within these three options suits best. The presence of residential housing near the coast for example, increases the suitability of seaward solution-types, but makes the realization of landward solution-types difficult. De presence of a secondary sea barrier (e.g. ‘sleeper’ dike) increases the suitability of a landward solution, while its absence increases the suitability for a seaward solution-type (Note: only when secondary dikes are in good state. When considered to be in poor state, the construction of a completely new dike can result in the same costs as upgrading the former secondary dike). The presence or absence of a seaward fairway or deep tidal channel near the coast also influences the suitability. Here, the seaward solutions become less suitable, while the landward solutions suit better. Finally, the opportunity to develop new functions in the newly developed Broad Coast also determines the suitability of a solution-type in a distinct coastal subpart. Criteria With the aid of the Comcoast literature (ComCoast partners, 2006-2), criteria are formulated that indicate the usability for a seaward or landward solution-type: Spatial characteristics for seaward solution-types: Positive characteristics Absence of deep tidal channel/fairway Presence of shallow foreshore Presence of permanent buildings Absence of secondary defense line Immeasurable data Need to realize new functions/spatial development
Criteria No deep tidal channel/fairway within 500 m seaward of the primary sea barrier First 500 m of foreshore run dry at low tide Landward are 0, 1-5, 6-10, 11-20, or over 20 build-on lots No secondary defense line within 500 m, 1000m or more landward of the primary sea barrier Criteria No measurable data, depends on site-specific characteristics
Spatial characteristics for landward solution-types: Positive characteristics Absence of permanent buildings
Criteria Landward are 0, 1-5, 6-10, 11-20, or over 20 build-on lots
Presence of secondary defense line
No secondary defense line within 500 m, 1000m or more landward of the primary sea barrier Deep tidal channel/fairway within 500 m seaward of the primary sea barrier First 500 m of foreshore do not run dry at low tide criteria No measurable data, depends on site-specific characteristics No data, expert analysis required
Presence of deep tidal channel/fairway Absence of shallow foreshore Immeasurable data Need to realize new functions/spatial development Qualitative state of secondary defense barrier
108
The criteria determine the suitability. A list of questions is used to fill in score tables for applying either a landward or seaward
Cure to secure: Medicating the broad coast
solution. These score tables are based on the answers of the following questions: Seaward situation: 1. Presence of deep channel or shipping lane/fairway within 500 meters seawards? 2. Presence of shallow foreshore within first 500 m seaward that runs dry at low tide? Landward situation: 3. Number of built-on lots within 1000 m or dike ring (ordinal, 1-5)? 4. Less than 1 built-on lot present? 5. Less than 20 built-on lots present? 6. Presence of landward secondary ‘sleeper’-dike connected to primary sea barrier? 7. Presence of landward secondary ‘sleeper’-dike within 1000 m? 8. Presence of landward secondary ‘sleeper’-dike within 500 m? Ordinal scale: 1 = 0 lots 2 =1-5 lots 3 = 6-10 lots 4 = 11-20 lots 5 = >20 lots Score tables See next page
Site selection Sites are selected that are representative for that part of the coast. This means that the Wadden coast and Southwestern delta example sites have ‘hard’ coastlines, while the Holland coast example site has a ‘soft’ coastline. Also, it is tried to choose sites in such a way that both landward and seaward solution-types can be applied. The sites mainly consist of rural coastlines, by this meaning unurbanised coast fronts. This, because broad coast transformation becomes nearly impossible along densely built waterfronts, hereby requiring special site-specific solutions.
Wadden coast example location: Eastern shoreline of Groningen mainland Autonomous coastal subparts and their numbers are shown in the figures. Presence of deep channel or shipping lane/fairway within 500 meters seaward? Presence of shallow foreshore within first 500 m seaward that runs dry at low tide? Presence of shallow foreshore within first 1000 m seaward that runs dry at low tide? Number of built-on lots within 1000 meters or dike ring (ordinal, 1-5)? Less than 20 build-on lots present? Less than 1 build-on lot present? Presence of landward secondary ‘sleeper’-dike connected to primary sea barrier? Presence of secondary ‘sleeper’-dike within 500 meters landward? Presence of secondary ‘sleeper’-dike within 1000 meters landward?
Seawards or landwards solutions Groningen 1 2 3 4 Seawards 5 4 3 Landwards 2 1 1 2
5 2 3
6 -
7 2 3
8 3,5 2,5
1 Y
2 N
3 N
4 N
5 N
6 Y
7 N
8 N
9 N
10 Y
11 N
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
1
3
1
1
1
5
1
2
2
5
3
Y Y Y
Y N Y
Y Y Y
Y Y Y
Y Y Y
N N Y
Y Y Y
Y Y Y
Y N Y
N N Y
Y N Y
N N
N N
N N
N Y
Y Y
N N
Y Y
N Y
N Y
Y Y
N Y
9 3,5 2,5
10 -
11 4 2
Southwestern delta example location: Westerschelde near Terneuzen Autonomous coastal subparts and their numbers are shown in the figures. 2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
109
1
18
Appendix 2
application of seaward or landward solution-types Presence of deep channel or shipping lane/ fairway within 500 meters seaward? Presence of shallow foreshore within first 500 m seaward that runs dry at low tide? Presence of shallow foreshore within first 1000 m seaward that runs dry at low tide? Number of build on-lots within 1000 meters or dike ring (ordinal, 1-5)? Less than 20 build-on lots present? Less than 1 build-on lot present? Presence of landward secondary ‘sleeper’dike connected to primary sea barrier? Presence of secondary ‘sleeper’-dike within 500 meters landward? Presence of secondary ‘sleeper’-dike within 1000 meters landward?
Delta Seawards Landwards
1 -
2 4
3 4
4 5,5
Y
Y
Y
Y
N
N
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
N
N
N
N
N
Y
Y
Y
N
N
N
N
N
N
N
N
N
Y
Y
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Y
5
3
3
2
2
1
2
5
1
2
4
2
1
1
5
2
5
2
N N Y
Y N Y
Y N Y
Y N Y
Y N Y
Y Y Y
Y N Y
N N N
Y Y Y
Y N Y
Y N Y
Y N Y
Y Y Y
Y Y Y
N N N
Y N Y
N N Y
Y N Y
Y
N
N
N
N
N
Y
N
Y
Y
N
N
Y
Y
N
N
N
Y
Y
N
N
Y
N
N
Y
N
Y
Y
Y
Y
Y
Y
N
Y
N
Y
7 1 4,5
8 -
13 7
14 7
5 3,5 3,5
6 3,5 3
9 7
10 6,5
11 4,5
12 5,5
15 -
16 5,5
17 5 -
18 2,5 3,5
Seawards solutions Presence of deep tidal channel/ fairway within 500 m seaward of the primary sea barrier?
No? (+0) Does first 500 m of foreshore run dry at low tide? No?(+0)
Yes?(+1)
Does shallow foreshore within first 1000 m seaward runs dry at low tide?
Yes?
No?(+0) Absence of secondary defense line within 500m landward of the primary sea barrier? No?(+0) Absence of secondary defense line within 1000 m or more, landward of the primary sea barrier? No?(+0)
Yes?(+1)
Yes?(+1)
Yes?(+1)
Presence of Presence of Presence of Presence of Presence of no permanent permanent permanent permanent built-on lots? No? No? No? No? buildings over 20 buildings over 11buildings over 6-10 buildings over 1-5 (+0) (+0) (+0) (+0) built-on lots? 20 built-on lots? built-on lots? built-on lots? Yes?(+1) Yes?(+2) Yes?(+0.5) Yes?(+1,5) Yes?(+0) Count score
Count score
Count score
Count score
Count score
110
Landwards
Cure to secure: Medicating the broad coast
Landwards solutions Presence of permanent buildings over 20 built-on lots?
Yes?
No? (+0) Presence of secondary defense line within 500m landward of the primary sea barrier? No?(+0) Presence of secondary defense line within 1000 m or more, landward of the primary sea barrier? No?(+0) Presence of deep tidal channel/ fairway within 500 m seaward of the primary sea barrier? No?(+0)
Yes?(+1)
Yes?(+1)
Yes?(+1)
Absence of shallow foreshore within first 1000 m seaward that runs dry at low tide? No?(+0)
Yes?(+1)
Absence of 500 m of foreshore that runs dry at low tide? No?(+0) Absence of permanent builton lots? Yes?(+2) Count score
Yes?(+1) Presence of Presence of Presence of permanent permanent permanent No? buildings over 1-5 No? buildings over 6-10 No? buildings over 11(+0) (+0) built-on lots? (+0) built-on lots? 20 built-on lots? Yes?(+1) Yes?(+0,5) Yes?(+1,5) Count score
Count score
Count score
111
Seawards