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Coastal Protection and Sea Level Rise

Final Report

Wadden Sea Ecosystem No. 13 - 2001 2

Colophon

Publisher Common Wadden Sea Secretariat (CWSS), Wilhelmshaven, Germany

Authors Trilateral Working Group on Coastal Protection and Sea Level Rise (CPSL)

Cover photo Jacobus Hofstede

Lay-out CWSS

Print Druckerei Plakativ, Kirchhatten, +49(0)4482-97440

Paper Cyclus – 100% Recycling Paper

Number of copies 500

Published 2001

ISSN 0946-896X

This publication should be cited as: CPSL 2001. Final Report of the Trilateral Working Group on Coastal Protection and Sea Level Rise. Wad- den Sea Ecosystem No. 13. Common Wadden Sea Secretariat, Wilhelmshaven, Germany.

Wadden Sea Ecosystem No. 13 - 2001 2

WADDEN SEA ECOSYSTEM No. 13

Coastal Protection and Sea Level Rise

Final Report of the Trilateral Working Group on Coastal Protection and Sea Level Rise

2001 Common Wadden Sea Secretariat

Wadden Sea Ecosystem No. 13 - 2001 4

Contents

Executive Summary ______7

1. Introduction ______9

2. National Administrative Structures ______10 2.1 Denmark ______10 2.1.1 Coastal defense ______10 2.1.2 Nature protection ______10 2.1.3 Future policy principles ______11 2.2 Schleswig-Holstein ______11 2.2.1 Coastal defense ______11 2.2.2 Nature conservation ______11 2.2.3 Future policy principles ______12 2.3 Niedersachsen ______12 2.3.1 Coastal defense ______12 2.3.2 Nature conservation ______13 2.3.3 Future policy principles ______13 2.4 The Netherlands ______13 2.4.1 Coastal defense ______13 2.4.2 Nature protection ______14 2.4.3 Future policy principles ______14 3. Common Knowledge Basis ______15 3.1 Wadden Sea morphology and sedimentology ______15 3.1.1 Introduction ______15 3.1.2 Morphological elements ______15 3.1.3 Sand-sharing system ______17 3.2 Effects of changes in tidal drainage area ______17 3.2.1 Dimensions and orientation of the various parts of the system ______17 3.2.2 Sedimentary characteristics of the system ______18 3.3 Effects of fixing of parts of the islands and the mainland coast ______19 3.4 The relevance of salt marshes and summer dikes ______22 3.4.1 Introduction ______22 3.4.2 Salt marshes ______22 3.4.3 Summer dikes ______24 3.4.4 Conclusions ______25 3.5 The relevance of biota for sedimentation- and erosion processes ______25 3.5.1 Introduction ______25 3.5.2 Intertidal area ______25 3.5.3 Salt marshes ______27 3.5.4 Dunes ______27 4. Analysis of Changes: Basic Assumptions and Methodology_____ 28 4.1 Introduction ______28 4.2 Past ______28 4.3 Future ______29 4.4 Methodology ______30

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5. Impact of Changes in Sea Level and Storminess ______31 5.1 Introduction ______31 5.2 Physical consequences ______31 5.2.1 Flooding time intertidal ______31 5.2.2 Surface area intertidal ______31 5.2.3 Tidal channel cross-section ______31 5.2.4 Salt marsh accretion ______33 5.2.5 Salt marsh cliff erosion ______33 5.2.6 Barrier retreat______33 5.3 Biological consequences ______34 5.3.1 Benthic biomass ______34 5.3.2 Birds ______34 5.3.3 Fish______34 5.3.4 Seals ______35 5.3.5 Seagrass ______35 5.3.6 Salt marsh vegetation ______35 5.4 Socioeconomic consequences ______35 5.4.1 Safety ______35 5.4.2 Fresh water run-off, harbors/shipping, tourism, agriculture and salinity ______37 6. Best Environmental Practice Options ______39 6.1 Introduction ______39 6.2 Evaluation ______41 6.2.1 Sandy barrier coast ______41 6.2.2 Tidal basins ______41 6.2.3 Salt marshes ______42 6.2.4 Dikes ______43 6.2.5 Mainland ______43 6.3 Conclusions ______45 6.3.1 Sandy barrier coast ______45 6.3.2 Tidal basins______45 6.3.3 Salt marshes ______45 6.3.4 Dikes ______45 6.3.5 Mainland ______45 7. Conclusions and Recommendations ______47 7.1 Introduction ______47 7.2 Conclusions ______47 7.2.1 General conclusions ______47 7.2.2 The tidal area ______47 7.2.3 The barrier islands ______48 7.2.4 Socioeconomic impacts ______48 7.2.5 Best Environmental Practice ______48 7.3 Recommendations ______49 Annexes______51 Annex 1: CPSL Terms of Reference ______51 Annex 2: CPSL Members ______52 Annex 3: Technical Terms ______53 Annex 4: Relevant Running Projects ______56 Annex 5: Literature ______59

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Wadden Sea Ecosystem No. 13 - 2001 7

Executive Summary

At the 8th Trilateral Governmental Wadden Sea islands, the tidal inlets, the ebb-tidal deltas, the Conference (Stade, Germany), it was decided to tidal channels, the tidal flats and the salt marsh- investigate the possible effects of enhanced sea es and that there are strong interactions between level rise and, on the basis of such an investiga- these elements. The main driving forces are the tion, develop proposals for future integrated coast- tides, the waves and the wind and the main link- al defense and nature protection policies. In 1998 ing factor is the sediment transport. All parts of a trilateral expert group, the Coastal Protection this sediment- or sand-sharing system are cou- and Sea Level Rise group (CPSL) was installed with pled and can be, or strive towards, dynamic equi- this remit. The members of the group represent librium with the hydrodynamic conditions. Chang- coastal protection and nature protection authori- es in any part of the system will cause a sediment ties in the three Wadden Sea countries. The re- transport to or from other parts of the system, sults of the work of the CPSL, carried out in the leading to a new dynamic equilibrium. Therefore, period 1 January 1999 till 30 June 2001, are in a moderate sea level rise in the Wadden Sea, re- this Report. sulting from both natural and man-induced pro- The remit of the CPSL can be divided into two cesses, will be compensated by the import of sed- main phases. In the first phase a so-called “com- iment which, in the long term, derives from the mon knowledge basis” was elaborated providing tidal channels, shoreface and the beaches and the starting point for the second phase of the dunes of the barrier islands. project in which an analysis was carried out of In addition to these hydrodynamical and mor- expected future developments. phological processes the group underlined the Common agreement about basic facts was importance of biotic processes for sedimentation reached regarding Wadden Sea morphology and and erosion. In this respect the relevance of sea- sedimentology, effects of changes in tidal drain- grass and mussel beds for biodeposition and re- age area, effects of fixing parts of the islands and duction of erosion and the role of vegetation in mainland coast, the relevance of salt marshes for the formation of dunes were emphasized. coastal and nature protection and the relevance In the second phase of the project the CPSL of biota for sedimentation and erosion processes. made an assessment of the possible impacts of The group acknowledged that the main ele- sea level rise and increase in storminess for three ments of the Wadden sea system are the barrier different scenarios, the latter based upon the lat-

Wadden Sea Ecosystem No. 13 - 2001 8 Executive Summary

est IPCC model calculations. Scenario 1 assumes The main socioeconomic consequence envis- a sea level rise of 10 cm in the coming 50 years. aged is an increase in costs for coastal defense. Scenario 2, the intermediate and most realistic Under the most realistic scenario (25 cm per 50 scenario, takes as a starting point a sea level rise years) an increase of costs for dike maintenance of 25 cm per 50 years. Scenario 3 is the “worst- and strengthening of at least 5 to 15% is expect- case” scenario, under which a sea level rise of 50 ed. Under the worst-case scenario costs to main- cm per 50 years is considered. For all three sce- tain dike safety may increase by 75% in Germany narios the additional impact of increase in storm- and even more in The Netherlands and Denmark. iness was evaluated. Also the costs for other coastal defense measures, For all three scenarios the impact upon selected such as sand nourishment and salt marsh works physical, biological, and socioeconomic parame- will increase considerably. ters was investigated. Another important consequence of increased It was concluded that, generally, changes sea level is that possibilities for discharging fresh caused by sea level rise will not easily be distin- water from the mainland into the sea will become guishable from changes resulting from the high less and that additional sluicing, pumping and/or natural variability, which is a specific feature of fresh water storage capacity is needed. the Wadden Sea system. Moreover, there will be The CPSL has, furthermore, evaluated a large large differences in changes occurring in the dif- number of coastal defense techniques and strat- ferent tidal basins. egies with the aim of selecting such which may, Because the Wadden Sea has a high resilience in the long-term, help maintaining the existing to changes it was considered plausible that the safety standards and alleviate the expected im- system will be able to adapt to a sea level rise up pacts of sea level rise and increase in storminess to some 25 cm per 50 years (the most realistic and which will be beneficial or, at least not nega- scenario), without substantial changes. tive, for natural assets, such as natural dynamics Beyond such levels probably a breakpoint will and habitat quality. occur because the capacity of the system to bal- This evaluation resulted in a list of so-called ance the changes will become exhausted. When Best Environmental Practice measures. These mea- such a breakpoint, which will differ for different sures should be further investigated for feasibility tidal basins, has been passed, substantial chang- in terms of cost-benefit, public perception and es in morphological and, consequently, biological legal aspects. parameters are expected. The CPSL finally formulated several recommen- One of the major changes will be a reduction dations for policy, management and research. of the size of the intertidal area. The group esti- The main message regarding policies is that, mates that, under the worst case scenario (50 cm/ as far as such is not already the case, integrated 50 years), the size of the tidal flats could decrease policies should be developed for coastal defense, by 15% (720 km2), the tidal basins becoming more nature protection and economic development in the character of tidal lagoons. An increase in the coastal zone, anticipating impacts of increased storminess would further enhance this develop- sea level and storminess. Such policies should also ment. The reduction of tidal flats will have im- address strategies for communication with the portant consequences for biological parameters, general public about the expected impacts and most notably bird species depending on the in- the introduction of additional and new coastal tertidal for foraging. A reduction in the popula- defense measures and strategies. tions of such species can be expected, not only With regard to the knowledge basis it is rec- because the potential feeding area will be less ommended to start a research project in which than today but also, and probably more impor- detailed sediment budget studies for the Wadden tant, because the feeding time will be less. For Sea are carried out, encompassing all man-induced the worst-case scenario, the CPSL also expects and natural factors, as well as, a research project changes in other morphological and biological in which the interactions between hydrological, parameters. It concerns, amongst others, an in- geomorphological and biological changes are in- crease of erosion on the barrier islands, a signif- vestigated. icant erosion of the salt mash cliffs, a decrease in benthic biomass, a decrease in seagrass and an increase in typical salt marsh vegetation.

Wadden Sea Ecosystem No. 13 - 2001 9

1. Introduction

Climate change and, in particular, its possible ef- described. Section 3.2 addresses effects of changes fects, have become a central issue in politics and in inundation area, for example through outbank- science in the 1990s. To the layman the notion ing of summer polders. In Section 3.3 the impli- climate change has almost become identical with cations of fixed coastal defense constructions un- anthropogenically induced increases in the atmo- der different sea level rise scenarios are discussed spheric concentrations of the so-called greenhouse and Section 3.4 addresses the relevance of salt gases, most notably carbon dioxide. As a result, marshes and summer dikes for coastal protection. increasing temperatures and, consequently, in- In Section 3.5 the relevance of biogenic struc- creasing water levels are predicted, caused by the tures and biostabilisation of sediment are covered. thermal expansion of the ocean water and the In Part 2, consisting of the Chapters 4, 5 and 6, melting of glaciers and polar ice caps. Also changes an assessment is given of the possible impacts of in wind climate are expected or have, according sea level rise and an increase in storminess for to some publications, already occurred. Although three different scenarios. Scenario 1 assumes a climate has always changed, the new feature of sea level rise of 10 cm in the coming 50 years. the present situation is the expected speed of the Scenario 2, the intermediate and most realistic change. This acceleration may induce significant scenario, takes as a starting point a sea level rise changes in the Wadden Sea system. of 25 cm per 50 years. Scenario 3 is the “worst- Questions regarding the consequences of ac- case” scenario, under which a sea level rise of 50 celerated sea level rise and increasing storm lev- cm per 50 years is considered. For all three sce- els and frequencies for the Wadden Sea ecosys- narios the additional impact of increase in storm- tem also entered the political agenda of the tri- iness is evaluated. In Chapter 4 a description is lateral Wadden Sea cooperation. In 1997, at the given of changes in water level and storminess 8th Trilateral Governmental Wadden Sea Confer- which have occurred in the past and which may ence (Stade, Germany), it was decided to investi- occur in the future. In this chapter also the meth- gate the possible effects of enhanced sea level odology applied by the CPSL to evaluate impacts rise and, on the basis of such an investigation, of future changes is explained. In Chapter 5 the develop proposals for future integrated coastal expected impacts of three sea level rise scenarios defense and nature protection policies. In 1998 a on physical, biological and socioeconomic param- trilateral expert group, the Coastal Protection and eters are described, under the assumption that Sea Level Rise group (CPSL) was installed with this current coastal defense practices are continued remit. The precise terms of reference of the CPSL (Business as Usual, BAU). Chapter 6 describes a are in Annex 1, the members of the group are listed large number of coastal defense techniques and in Annex 2. analyses these for the criteria suitability for coastal In this report the results of the work of the defense and compatibility with nature protection. CPSL, carried out in period January 1999 till May On the basis of the analysis a series of so-called 2001, are presented. The report consists of two Best Environmental Practice measures (BEP), parts. In Part 1, consisting of Chapters 2 and 3, which may be used as an alternative or an addition basic facts are provided. Chapter 2 addresses the to regular coastal defense practices, is identified. national administrative structures with regard to In Chapter 7, the main conclusions and the rec- coastal protection and nature protection. In Chap- ommendations of the CPSL are presented. Finally, ter 3 relevant facts regarding the main physical in chapter 8, a comprehensive summary is given. and biological aspects of the Wadden Sea eco- The report contains five annexes. In addition system, about which a common understanding to the already mentioned annexes 1 and 2, a com- was achieved within the group, are given. In the prehensive glossary of terms is in Annex 3. Annex introductory part 3.1 of this chapter the basic geo- 4 contains a list of relevant running projects. An- morphological principles of the Wadden Sea are nex 5 contains the cited literature.

Wadden Sea Ecosystem No. 13 - 2001 10

2. National Administrative Structures

2.1 Denmark very few hard defense constructions and no land reclamation measures are carried out. Most dikes The regulation of the coastal zone in Denmark is are maintained by local water boards under the covered by a number of legislative instruments supervision of the DCA and the County of Ribe or which place the responsibility on several author- the County of Southern Jutland. ities. For the most part the state authorities are responsible for the administration of the sea ter- 2.1.2 Nature Protection ritory. The ministries with the greatest responsi- The general laws in Denmark relating to nature bility for coastal defense and nature protection conservation incorporate some regulations that are the Ministry of Transport and the Ministry of directly influence the administration of the coast- Environment and Energy respectively. The admin- al zone. The National Forest and Nature Agency, istration of the land territory is mainly carried out under the Ministry of Environment and Energy, by the counties. has overall responsibility for the protection of the 2.1.1 Coastal Defense International Nature Conservation Areas (Ramsar, EU Bird Directive, and EU Habitats). The counties The national Coast Protection Act of 1988 is administer most of the regulations. They carry out the main legislation regulating all coastal defense inspections, issue permits and refusals, carry out measures. This law is mainly a procedural code, maintenance tasks, monitor, plan and dissemi- stating the procedure that the relevant authori- nate information. Some regulatory measures ties are obliged to follow when an application or worth mentioning include a ban on changes to public initiative for building or altering coastal the natural conditions in salt and freshwater defense constructions comes up. The Danish marshes, bogs and other areas, a 300 meter Coastal Authority (DCA), an organization under general protection zone along the coast and the Ministry of Transport, and the county author- conservation regulations for protected dune areas. ities, are responsible for legislation. Besides the Danish Nature Protection Law, the The overall principle is that the responsibility most significant nature protection regulation in for establishing and maintaining protection mea- the Wadden Sea Area is the Executive Order on sures lies with the persons who profit. On the other Nature Conservation and a Wildlife Reserve in the hand, landowners do not have an immediate right Wadden Sea. This executive order covers large to protect property. Each new measure has to be parts of the Danish section of the Wadden Sea considered appropriate by several authorities. The Area, and is an expression of efforts to establish main considerations within the framework of the sustainable development for the region as a na- Coast Protection Act are whether a construction tional and international nature conservation area, is necessary, can fulfil its purpose, will cause un- as well as, a way of ensuring that Denmark meets desirable side effects or conflict with nature pro- its obligations for the area including those under tection rules. The county considers project drafts the EU Bird and Habitat Directives. The Executive and decides whether the project in question is Order contains prohibitions that regulate in de- suitable to be passed on for further consideration tail aspects such as land and sea traffic, the col- or can be rejected immediately. The local munic- lection of organisms from the sea bed, hunting, ipality and other relevant authorities are always civil engineering work including coastal defense, asked to comment on projects considered suit- alteration of the terrain, canals, mineral extrac- able, and approval for all such projects has to be tion and other technical installations. The Execu- obtained from the DCA within the Ministry of tive Order falls under the jurisdiction of the Min- Transport. In general there is no public obligation istry of Environment and Energy and the National to undertake coastal defense. In particularly ex- Forest and Nature Agency. The provisions of this treme conditions the political bodies have con- order make it possible to involve other authori- sidered it a public duty to enforce or erect dikes ties, such as the Ministry of Transport and the at the Wadden Sea coast financed by public funds counties. in part or in full through the issue of special con- Finally, the Danish system of planning regula- struction laws. tions and inter-sector spatial planning is carried The most significant element of the coastal out in practice with regard to the areas that bor- defenses along the Danish Wadden Sea coast con- der the Wadden Sea. Such planning results in the sists of the existing sea dikes made of sand and definition of a framework for future development, clay. These stretch along approximately 115 kilo- which is expressed in guidelines for the adminis- meters of coastline, protecting an area of approx- trative procedures of the regional and local au- imately 600 square kilometers (Fig. 3.3). There are

Wadden Sea Ecosystem No. 13 - 2001 2. National Administrative Structures 11

thorities. The general public is always involved in marshes from erosion and, eventually, disintegra- the planning procedure. In certain situations the tion. planning act also dictates that larger construc- Coastal defense (coastal protection and coast- tion projects should be subject to an EIA (envi- al flood defense) is regulated in the Schleswig- ronmental impact assessment). Holstein State Water Act and the Master Plan 2.1.3 Future policy principles Coastal Defense (the technical and financial con- cept). In principle coastal defense devolves on the The agreements contained in the Wadden Sea Plan persons who profit. However, flood defense that are currently being incorporated into the nation- is in the interest of the public is a public obliga- al and regional plans, regulations and adminis- tion. Depending on the measures, the responsibil- trative practices. ity lies with state or municipal administration or The two Wadden Sea Counties and the DCA with local water boards. Coastal protection that are conducting a technical reassessment of the is in the interest of the public (i.e. protection of safety of the dikes in the Wadden Sea Area in the settlements against land loss) devolves on the state light of changes in sea level. This will form the administration. basis for the various water boards to make a de- The Schleswig-Holstein State Ministry for the cision as to whether to upgrade the safety level Rural Areas, Agriculture, Food and Tourism is re- of those dikes for which they are responsible. In sponsible for legislation, general planning and fi- practice this is mainly expected to take place nancing. Two regional offices for the rural areas through reinforcement of existing dikes. implement the state coastal defense programs. In general there seems to be a trend towards Public participation in state coastal defense is reg- more emphasis on the regulation of use and pro- ulated in the Schleswig-Holstein State decree on tection of the Danish coasts. For instance a spe- the implementation of public plans. Since 1998 cial 3 km broad planning zone has been imposed the integration of different uses and interests has to the land territory. A greater part of applica- been realized with the establishment of the ”In- tions for defense measures to protect uninhabit- tegrated Coastal Defense Board”. This advisory ed areas is now rejected because it is considered board is chaired by the Secretary of State for the important to protect the natural coastal process- Rural Areas and consists of representatives from es. At the same time it is considered very impor- all relevant public and private parties involved in tant to maintain and if necessary improve the pro- the different aspects of coastal defense manage- tection of the inhabitants in areas threatened by ment. flooding. The organization and administration of (pub- The protection methods in the Danish Wadden lic) coastal defense in Germany is in the responsi- Sea continue the tradition of using green dikes. bility of the respective states. However, as coastal The use of other hard constructions along the west defense has national consequences, capital mea- coast is getting rare in favor of sand nourishment. sures are co-financed by the federal government with 70% of total eligible costs (the other 30% 2.2 Schleswig-Holstein are matched by the states). The maintenance of existing state coastal defense structures, on the 2.2.1 Coastal defense other hand, is financed 100% by the state. Mu- The Wadden Sea coastline of Schleswig-Holstein nicipalities and/or local water boards that are re- measures about 553 km, 297 km of which are sponsible for coastal defense measures in their mainland, the rest island coasts (Fig.3.3). About area normally have to contribute between 5 and 425 km of the coastline are protected by State 20% to the costs. The rest is financed by state (355 km) and other dikes (70 km). In all, these sea (and federal) government. Finally, a small but in- 2 walls protect an area of 3,472 km against flood- creasing financial contribution to coastal defense ing during severe storm surges. In these coastal comes from the European Union. lowlands 253,000 people live, and economic val- In all, in Schleswig-Holstein (Wadden Sea and ues of about 31 billion EURO are concentrated. Baltic Sea coast) about 40 to 45 million EURO is Further, on the islands Sylt and Föhr, sand nourish- spent on coastal defense each year. ment is conducted to prevent coastal retreat. The third major coastal defense activity (apart from sea 2.2.2 Nature conservation walls and nourishment) in the Wadden Sea of Nature conservation is regulated in the Schles- Schleswig-Holstein are salt marsh works, nowa- wig-Holstein State Nature Conservation Act and days carried out mainly to protect existing salt the State Act for the National Park Wadden Sea of

Wadden Sea Ecosystem No. 13 - 2001 12 2. National Administrative Structures

Salt marsh works at Nordstrand (FRG). (Photo: J. Hofstede)

Schleswig-Holstein. Responsible for environmen- ment plan was established by coastal defense and tal legislation, financing and general planning in environmental authorities that aims at an eco- Schleswig-Holstein is the State Ministry for the logically sound protection and management of salt Environment, Nature and Forests. Two state envi- marshes (see also 3.4.2), salt marshes being both ronmental offices, the Schleswig-Holstein State an important (natural) coastal defense structure Office for Nature and the Environment and the and an ecologically sensitive and valuable habi- Schleswig-Holstein State Office for the National tat. Park Wadden Sea of Schleswig-Holstein (NPA) are In future, the coastal defense policy will prob- responsible for research, preparation of plans, and ably increasingly include risk analyses for single (partly) permits. Finally, several regional environ- flood units (risk being defined here as the product mental offices, as well as, the counties are re- of the probability of dike breaching and the dam- sponsible for monitoring and permits. age potential in the flood unit). Further, more at- The Wadden Sea of Schleswig-Holstein (exclu- tention will be paid to public participation and sive of the islands) is a national park, adminis- the integration of other interests in coastal de- tered by the NPA. In 1999, the national park was fense policy (integrated coastal defense manage- extended with a whale protection area in the North ment). Sea west of the island Sylt. The NPA is, amongst others, responsible for research and permits in the 2.3 Niedersachsen national park. On the Wadden Sea islands several nature reserves exist that are mainly managed by 2.3.1 Coastal defense environmental NGOs. The legal basis for coastal defense in Niedersach- 2.2.3 Future policy principles sen is the Niedersachsen Dike Act. It contains both regulations for design, maintenance, supervision The old philosophy of executing coastal defense and usage of dikes, forelands, dunes and other (building sea walls) in order to reclaim fertile land coastal defense structures and responsibilities of already ceased in the early fifties. The last sea wall the authorities and the water boards. Main ob- aiming at this purpose was constructed in jective of the Dike Act is protection of man, set- Schleswig-Holstein in 1954 (Friedrich-Wilhelm- tlements, public, industrial and infrastructure fa- Lübke-Koog). Afterwards, the policy for coastal cilities, as well as agricultural areas, against flood- defense turned into achieving the same level of ing. The overall principle is that all persons who security for all state dikes (i.e. each sea wall has profit from protection are in charge of maintain- the same probability of breaching). The sixties, ing the dikes. They are organized in water boards seventies and early eighties were characterized by which have to do the maintenance and construc- a strong belief in engineering (hard) solutions for tion works on the mainland dikes, except for some coastal defense. However, this attitude changed which are under State responsibility. The State, into trying to use more natural techniques and moreover, is responsible for all coastal protection material, e.g. sand nourishment, to combat coastal structures on the islands and the storm surge bar- retreat. In 1995 a common salt marsh manage- riers.

Wadden Sea Ecosystem No. 13 - 2001 2. National Administrative Structures 13

The Ministry of the Environment is in charge tection. The other legal regulations remain in ex- of the general guidelines and principle issues for istence. Special aspects of nature conservation are coastal defense, as well as, the master planning. assessed by the Niedersachsen State Board of Ecol- It also supervises the regional authorities, who ogy. have to fix the dimensions of the dikes in a legal 2.3.3 Future policy principles act and grant permissions for extensive coastal protection measures. The local authorities work The future coastal defense policy will be fo- on the rural district level and are supervised by cussed on the development of probabilistic de- the regional authorities. They are responsible for sign codes instead of the present deterministic all other supervision tasks including the water ones. The evaluation of the feasibility of risk anal- boards and permissions according to the Dike Act. yses for coastal protection structures will also be The technical planning of coastal protection a matter of high importance. measures and the maintenance of the state coastal On the islands a long term investigation pro- defense structures is done by the Niedersachsen gram is carried out for the evaluation of sustain- Agency for Water Management and Coastal De- able future protection concepts in areas where fense (NLWK), which is supervised by the minis- structural erosion occurs. The future management try. Special aspects of planning and applied sci- of the foreland areas will be further harmonized ence in coastal engineering are carried out by the by creating regional management plans that in- coastal research station of the Niedersachsen tegrate demands of coastal defense and nature State Board of Ecology subordinated to the conservation. ministry. The Dike Law defines the main dikes, dunes, 2.4 The Netherlands storm surge and all constructions that enhance their stability (e.g. groynes, revetments) as ele- 2.4.1. Coastal defense ments of coastal protection. These elements have The complete mainland coast of the Dutch Wad- to be maintained and, if necessary, reinforced. The den Sea, about 200 km, is defended by dikes. Also foreland (salt marsh in front of a dike) has to be the polders at the Wadden Sea site of the islands preserved in a defined width and maintained, in- are protected by dikes (Fig. 3.3). The dike length cluding all technical constructions, as a protec- on the different islands varies from a few to 30 tion element for the main dike. kilometers. Dunes form the coastal protection of the 155 km of North Sea coasts of the inhabited 2.3.2 Nature conservation islands. Since 1990 sand losses from the North The legal basis for nature conservation are the Sea coast have been compensated for with sand Federal and the Niedersachsen Nature Conserva- nourishments and this will also be the case in the tion Act, the State Act for the Wadden Sea Na- future. On Texel and Vlieland, the sandy coast re- tional Park of Niedersachsen and the legal act for ceives additional protection by breakwaters made the Nature conservation area Dollart. Except for of basalt and concrete. On the tips of parts of the the estuaries of Ems, Jade, and Weser, the whole inhabited islands natural coastal development is Niedersachsen part of the Wadden Sea has been allowed within certain limits. No or very limited designated as a national park in which the unin- maintenance is carried out on the uninhabited habited parts of the East Frisian islands are in- eastern part of Schiermonnikoog and the unin- cluded. habited islands Rottumerplaat en Rottumeroog. The general objective for the protection of the On the national level the Ministry of Transport, tidal flats and the adjacent sublittoral, the dunes, Public Works and Water Management and the and the salt marshes as valuable habitats, is to Ministry of Agriculture, Nature Management and preserve the species composition and natural pro- Fisheries are responsible for coastal defense re- cesses, including the natural morphology and dy- spectively nature protection of the Wadden area. namics of this area. The Ministry of Public Housing, Spatial Planning Under the responsibility of the Ministry of the and the Environment presents the guidelines for Environment, the National Park Administration, as local and regional plans in a national directive, a subdivision of the Weser-Ems district authority, the PKB-Waddenzee (Planological Core Decision develops general guidelines and executes the reg- Wadden Sea). ulations of the National Park Act. In addition, the The protection of the North Sea coast of the local authorities at the rural district level execute islands is executed by the Directorate-General for the regulations of nature conservation in areas Public Works and Water Management of the Min- above MHTL except those areas with highest pro- istry of Transport, Public Works and Water Man-

Wadden Sea Ecosystem No. 13 - 2001 14 2. National Administrative Structures

agement. The Provinces along the coast each have of Transport, Public Works and Water Manage- a Provincial Consultative Body for the Coast (POK). ment but also by the Ministry of Agriculture, In this body national, provincial and municipal Nature Management and Fisheries. authorities and regional water boards discuss all 2.4.2 Nature protection issues concerning coastal defense and give rec- ommendations to the Minister of Transport and Almost the entire Dutch Wadden Sea is a nature Public works. The province Groningen has no POK. conservation area by law. Exceptions are strips Here coastal affairs are discussed in a provincial along the inner parts of the islands and the main committee on water management. Only the un- shipping channels. The entire area, including the inhabited barrier islands Rottumerplaat and Rot- main parts of the islands and the coastal zone of tumeroog belong to this province. the North Sea, is part of the core and/or nature The responsibilities of the different parties are development area in the so-called “ecological main divided as follows: structure”. Most of the area has been designated as EU Habitats and Bird Directive area. The entire • the central government safeguards the posi- island of Schiermonnikoog has the status of ”Na- tion of the coastline and combats structural tional Park”. erosion; From the central government the Ministry of Agriculture, Nature Management and Fisheries is • the water boards are responsible for the de- responsible for nature conservation. Provinces and sign and maintenance of the sea defenses, ex- municipalities deal with nature protection in their cept on most of the Wadden islands, where regional and local plans. The guidelines for those the central government is responsible both for plans are given in a national directive, the PKB- coastline preservation and for the sea defens- Waddenzee (Planological Core Decision Wadden es; Sea) of the Ministry of Public Housing, Spatial • the provincial authorities are responsible for Planning and the Environment. Specific areas are owned and managed by nature conservation or- the overall coordination and for the integra- ganizations. tion with other areas of policy, such as physi- cal planning. The provincial authority also 2.4.3 Future policy principles chairs the POK. Coastal management is gradually changing from Matters which may arise in the POKs include building sea defenses and damming off coastal inlets to dynamic preservation. Coastal manage- • the position of the coastline, to be maintained ment is more and more directed at working with by sand nourishments; the natural dynamics of the coast instead of try- ing to control it. In this way, not only safety but • the annual program of nourishment works; also ecology and human use are taken into ac- • plans for alternative methods of coastal pro- count. Sand nourishments are considered a good tection; method for dynamic preservation of the coast. In the back barrier area the strict divisions between • plans for developments within the coastal dry and wet, high and low, fresh and salt are sub- zone, e.g. nature development projects. ject of discussions and projects have started aim- POKs increasingly pay attention to the links be- ing at restoring gradients. tween coastal protection, nature development, For the management of the Wadden Sea itself recreation and physical planning. Therefore, in the nature conservation laws and EU-directives be- POK for the Wadden Sea area, the central gov- come more and more important leading to con- ernment is not only represented by the Ministry flicts between nature conservation and human use.

Wadden Sea Ecosystem No. 13 - 2001 15

3. Common Knowledge Basis

3.1 Wadden Sea morphology and sedimentology 3.1.1 Introduction Tidal flats The objective of this chapter is to give an over- view of the morphology of the Wadden Sea barri-

er coast. The Wadden Sea, with a tidal range from Barrier island 1.4 to 3.5 m, fringes the Dutch, German and Dan- Tidal channels ish coasts over a distance of nearly 500 km with a maximum width of approximately 35 km. The tidal wave in the North Sea moves from the S(W) to Tidal inlet the N(E), that is from Den Helder in The Nether- lands to Esbjerg in Denmark. Towards the North Sea the Wadden Sea is bordered by some 20 large and many small barrier islands, peninsulas and sandy shoals. Behind these islands lies the largest tidal flat area in Europe. The mainland coast con- sists of dikes, some salt marshes and, especially Ebb-tidal delta towards the northern Wadden Sea, a few Pleis- tocene cliffs. Especially north of the Elbe river rem- nants of older mainland deposits form small is- lands in the tidal basins, these are the so-called “Halligen”. 3.1.2 Morphological elements The Wadden Sea is characterized by 33 adjacent Figure 3.1: tidal inlet systems, each consisting of the follow- land consists of a shoreface, beach, dunes and Morphological elements ing morphological elements: (1) barrier island, (2) overwash areas. However, some barriers, e.g. Jap- of the Wadden Sea system. tidal inlets, (3) ebb-tidal delta and inlet, (4) tidal sand, Norderoog- and Süderoogsand in Schleswig- channels, (5) tidal flats and (6) salt marshes (Fig. Holstein lack dunes. Today, on most barriers also 3.1). reclaimed salt marsh areas (polders) exist. Barrier islands Tidal inlets Barrier islands lie on the seaward side of the Wad- The barrier islands are separated from each other den Sea. They are formed and sustained by the by tidal inlets. Tidal inlets represent the transport combined action of wind, waves and tides and routes through which the tidal waters (loaded with represent a sediment sink. Normally a barrier is- sediment) enter and leave the tidal basins with

Wadden Sea Ecosystem No. 13 - 2001 16 3. Common Knowledge Basis

each tidal cycle. A dynamic equilibrium exists be- equilibrium seems to exist on tidal flats between tween the tidal currents and the cross-sectional the erosive forces of storm waves and tidal accu- area of the inlet channel (mainly controlled by mulation (mainly controlled by the time of tidal the scouring potential of the currents). inundation, Ch. 3.1.3). Ebb-tidal deltas Salt marshes The sediment that is transported by ebb-tidal cur- If sedimentation on the tidal flats exceeds ero- rents is deposited at the seaward outlet, caused sion (i.e. no dynamic equilibrium), eventually a by decreasing current velocities. In result, an ebb- supratidal salt marsh may form. Salt marshes are tidal delta develops. However, the erosive forces inter- and supratidal areas of fine sediments sta- of deep water waves coming in from the North bilized by a halophytic vegetation cover. Bound- Sea, limit the sediment volume of the deltas. A ary conditions for establishing and sustaining salt dynamic equilibrium exists between these erosive marshes are an adequate supply of fine sediments, forces and the tidal accumulation (Oost, 1995a; a low energy environment which allows for sedi- Hofstede, 1999). Because the tidal channels of the mentation (see above), regular saltwater inunda- inlet and the delta are strongly interrelated, they tion and, finally, a moderate sea level rise to bal- are normally treated as one element. ance accumulation and prohibit vegetation suc- cession. Normally (mainly controlled by the time Tidal channels of tidal inundation) tidal accumulation exceeds The same accounts for the tidal channels and the sea level rise and succession occurs. Nowadays, sub- and intertidal flats which constitute a tidal most of the mainland salt marshes in the Wadden basin. Sub- and intertidal channels function as Sea are artificial, i.e. developed by salt marsh ac- transport routes for the tidal water masses. Hence, cretion enhancement techniques (drained brush- the same dynamic equilibrium between currents wood groyne fields, Hofstede, 1996). and cross-section exists as for the tidal inlet chan- In conclusion, the elements of the tidal sys- nels. Through the channels sediment is transport- tems that constitute the Wadden Sea show strong ed towards the tidal flats with the flood currents. mutual interactions. All elements influence the Tidal flats local tidal currents and wave regime and thus the At the tidal flats this material may become set- local sediment redistribution patterns. Empirical tled as a result of decreasing current velocities, relationships document that the morphological i.e. the tidal flats act as a tidal sediment sink. Be- structure of all elements strongly depends on the cause the (energy-rich) waves from the North Sea prevailing hydrodynamic (tidal and wave) condi- are almost completely dissipated at the shoreface tions. In general, the tidal currents seem to con- and ebb-tidal deltas (Niemeyer, 1986), only local stitute a positive (accumulative) force in most el- (storm) waves limit the tidal accumulation on the ements, whereas waves are a negative (erosive) tidal flats. Similar to the ebb-tidal delta, a dynamic factor. Only at the barriers waves may act as a

Figure 3.2: Sediment transport between Wadden Sea and North Sea and along the islands. From: Louters and Gerritsen, 1994.

Watershed

Outer Delta

Tidal Basin

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 17

positive force during fair weather conditions. The coastal protection measures. A further morpho- morphology and morphodynamics of the Wadden logical result of the wave-driven littoral sand Sea are described in detail by, amongst others, transport is the long-term eastward movement Ehlers (1988) and Oost (1995a). of most of the West- and East-Frisian Islands. 3.1.3 Sand-sharing system Each tidal system can be considered to form a 3.2 Effects of changes in more or less separate (closed) sand-sharing system tidal drainage area (Dean, 1988). However, it should be taken into Sea level rise, as well as, human interventions may consideration that adjacent tidal basins may in- lead to a change in tidal drainage area. From hu- fluence each other across the tidal watersheds man interventions it is known that changes in (Fig.3.2) (Oost & Dijkema, 1993). All parts of a drainage area of a tidal inlet system may affect sand-sharing system are coupled and can be in, dimensions and orientation of the various parts or strive towards, a dynamic equilibrium with the of the system, as well as, sedimentary character- hydrodynamic conditions. Changes in any part of istics. the system will primarily be compensated by sed- iment transport to or from the other parts of the 3.2.1 Dimensions and orientation of same system. When changes are temporary and the various parts of the system limited, the old dynamic equilibrium will eventu- If changes in tidal drainage area result in changes ally be restored. For example, a moderate increase in tidal volume, the dimensions and orientation in sea level rise induces a stronger accumulation of various parts of the system may also be influ- on tidal flats and salt marshes as a result of long- enced. A decrease in size of a tidal drainage area er tidal inundation (i.e. the sediment having more will generally result in a decrease in tidal volume. time to settle). As a result, the elevation of the This decrease in tidal volume will result in a de- flats and salt marshes increases and the time of crease of the channel dimensions and the ebb- tidal inundation decreases again until the old dy- tidal delta sand volume. An enlargement of a tid- namic equilibrium is restored. If changes are more al drainage area will lead to a larger tidal volume permanent or intense, a new equilibrium will be and consequently bigger channel dimensions and established (e.g. reduction in the cross section of ebb-tidal delta sand volume. tidal channels caused by the permanent reduc- tion in tidal prism due to land reclamation). Espe- An Example of a Change in cially in the last situation sediment may be im- Tidal Volume ported from or exported to areas outside the sand- In 1969 the Lauwerszee, an embayment of the sharing system. Wadden Sea, was diked and the tidal prism of To compensate for the observed secular sea lev- the tidal inlet Zoutkamperlaag decreased from el rise (Chapter 4), each year several million m3 of 305 million m3 to 200 million m3. Before the material are deposited in the Wadden Sea. In this closure of the Lauwerszee, a dynamical equi- way the same altitude with regard to mean sea librium was maintained in the ebb-tidal delta level is maintained or, in other words, the dynam- and the backbarrier area of the Zoutkamper- ic equilibrium between hydrography and morphol- laag Inlet. The reduction of the tidal prism led ogy is maintained. In the long term most of this to the development towards new equilibrium sediment is derived from the shoreface, beaches dimensions. In the period 1970-1987 26 mil- and dunes of the barriers islands, western Jutland lion m3 of sand was transferred from the ebb- and northern Holland. As a consequence, gener- tidal delta. Also sedimentation in the inlet and ally, barrier islands tend to retreat in response to erosion of the ebb-tidal delta occurred as a re- sea level rise (Bruun, 1962). However, on the Wad- sult of reduced tidal currents. In the backbarri- den Sea barrier islands a number of factors (ex- er area the main backbarrier channel was par- cessive sediment supply by the littoral sand trans- tially filled and the eastern watershed shifted port, Pleistocene subsurface, coastal protection) as the channel east of it filled up. The changes may counteract this morphological response. For in the Zoutkamperlaag inlet system thus also example, the western coasts of Fanø and Amrum influence the adjacent, downdrift inlet system. seem to be rather stable, while Rømø is even ex- In the period 1987-1993 the inlet itself became panding seaward as a result of a strong littoral reoriented into a more downdrift orientation, sediment supply. Sylt is maintained in its position as might be expected for a decrease in tidal through regular sand nourishments and the west- prism. ern part of Norderney is kept in place by massive

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Under equilibrium conditions, the net amounts also settle in the more sheltered embayments. The of sediment which are trapped or eroded are nor- embankment of mainland areas in the past and mally small. Gradual changes in, for instance, sea resulting decrease of tidal basin dimensions has level rise or bottom subsidence, cause a slight dis- led to a decrease of the surface of those muddier traction of the dynamic equilibrium between hy- environments. As a result, muddy environments draulics and morphology. As a reaction more sed- are rare nowadays. Flemming and others showed iment will be trapped or eroded in order to re- for the Spiekeroog backbarrier area that, due to store the dynamic equilibrium situation. the embankments, the hydrodynamic energy in the After sudden changes in the size of tidal ba- remaining area increased, resulting in a decrease sins, for instance by embankments, sediment def- of the mud content in front of the dike through icits or surpluses may become so large that it takes time. decades to reach new hydraulic and morphologic In the Netherlands dikes around some summer equilibria. Those bigger changes in one basin may polders have been opened to establish new tidal also affect neighboring basins. Examples of such marshes. Because those polders are situated just sudden changes are the closures of Zuiderzee en above MHW-level, sedimentation of mud during Lauwerszee which took respectively 60 and 25 storm set-up is expected. Due to their relatively years erosion and sedimentation before more or small sizes and height above MHW level, the open- less new dynamic equilibrium states were reached ing of the summer polders has no effect on tidal (see Box). volume, height of storm-surge levels or sediment 3.2.2 Sedimentary characteristics of budget. the system Changes in grain size may have a profound in- fluence on the species composition of the sedi- As a result of the sorting processes, caused by ment (compare also 3.5) and, consequently, for- decreasing dynamics with increasing distance aging animals. from the inlet, the grain size of the sediments de- creases in this direction. The finer sediments will

Beach wall in Westerland, Sylt (FRG). (Photo: J. Hofstede)

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 19

3.3 Effects of fixing of still suffers from erosion and, since 1972, regular sand nourishments are carried out to compen- parts of the islands and the sate for this loss. Also the island of Norderney mainland coast has a long history of subsequent enforcements. Around 1000 AD the inhabitants of the higher dry These were carried out mainly on the western part. areas in the coastal zone started to colonize the Physically, the Wadden system forms an en- lower lying peatlands. To keep the storm tides out semble of islands, inlets, outer deltas and a series they started to surround part of the lands by dikes. of adjacent tidal basins with channels, flats and From the 13th century on, polders were created. salt marshes. They are interacting through the Windmills made it possible to change inland lakes longshore transport of sediment. The Wadden sys- into polders. In the last centuries also measures tem can be said to have a closed sand economy were taken to stabilize the sandy coast itself. In (compare 3.1.3). If part of a tidal basin in such a order to prevent erosion, groynes perpendicular system becomes deeper, for instance by relative to the coast were built. At other places the coast sea level rise, the system re-establishes equilibri- was embedded in stones. More recently sand nour- um by importing sediment and by internal sedi- ishment was introduced as a means of combating ment redistribution (from the channels to the erosion. flats). As the ebb tidal delta is in equilibrium with In The Netherlands coastal defense measures the tidal volume of the tidal basin, the ebb tidal were also undertaken at the uninhabited parts of delta cannot be a net sediment source. Conse- the islands. Starting in the 14th century sand dunes quently the sediment import of the Wadden Sea were stabilized by planting marram grass and in- will eventually lead to a net loss of sediment from dividual dunes were connected to each other in the North Sea coast. In case of an accelerated order to get an elongated uninterrupted dune ridge sea level rise more sand will be transported from all along each island. In Germany and Denmark the North Sea, mainly the coastal zone, to the coastal protection is mostly restricted to safe- Wadden Sea. If the islands are fixed by hard con- guarding the inhabited parts and infrastructure structions the question arises at what costs those of the islands. On other parts of the islands al- constructions must be safeguarded. most no protective measures were taken. One ex- Another, more recent, method of fixing the ception is the island of Sylt where the entire 38 coast are sand nourishments. With this method km long beach has been nourished at least once natural processes along sandy coasts are taken since 1984. into account and characteristic aspects of the Often the introduction of hard constructions coast are safeguarded. Compared to hard con- results in an accelerated erosion at the edges of structions it is a more flexible method because it the defended parts. Consequently, the defended can easily be replaced by other defense measures. parts need to be extended with more construc- In many locations sand nourishment offers a tions. An example of this is given by the sea de- cheap and sustainable method for coastal defense. fense along the island Vlieland in the western part Elsewhere, for instance at places with deep tidal of the Wadden Sea (Fig. 3.3). The first groynes channels, sand is rapidly carried away. In such were built in the 19th century on the western part situations hard defense elements, possibly of this island. In the course of time next to exist- combined with sand nourishments, may be more ing groynes new groynes were built in easterly suitable. direction. Nowadays the complete North Sea coast In fact, the artificial sand nourishments com- of this island is embedded in groynes. Another ex- pensate the loss of sand from the North Sea coast ample is the holiday resort Westerland at the North to the Wadden Sea. The question is whether in Sea coast of the island Sylt. Here, in the year 1907, the case of an accelerated rise in the sea level in a 70 m long wall was constructed at the upper the future there will be enough sand for the coast beach to protect a hotel. As a result of intense to maintain this method of coastal defense. At erosion at its ends, this wall had to be lengthened some places already a gradual steepening of the to about 850 m until 1954. Strong erosion due to underwater shore can be observed. In the long wave reflection at the foot of the wall was com- run, a reduction in the amount of sand available bated by revetments and, since 1960, by large tet- in the underwater landward shore zone might lead rapods. However, the beach in front of the wall to accelerated regression of the coastline.

Wadden Sea Ecosystem No. 13 - 2001 20 3. Common Knowledge Basis

Vlieland Emden

Texel

Noorderhaaks

Den Helder

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 21

Figure 3.3: Coastal defense: Main dikes, other hard constructions and sand nourishments.

Heide

Emden

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3.4 The relevance of salt Grazing marshes and summer dikes In Germany, grazing of salt marshes has long been regarded necessary for enhancing salt marsh sta- 3.4.1 Introduction bility and reducing the amounts of flotsam. This Salt marshes are tidal areas of fine sediments sta- has created a controversy with nature protection bilized by a halophytic vegetation cover (see also aims, which were directed at achieving a natural 3.1.2 and 3.5.3). They are favored in sheltered (low vegetation by abandoning grazing. Several recent energy) tidal environments with an adequate sed- investigations have made clear that, even with- iment supply and a moderate sea level rise. For out grazing, the shear strength of the salt marsh- coastal defense purposes salt marshes may be de- es suffices to prevent erosion of the surface (Erch- fined as the area between the dike-foot and the inger et al., 1994). The same authors concluded MHW-level. Summer polders are former salt that very intensive grazing may even reduce sheer marshes protected from inundation by lower storm strength. surges through lower sea walls, the summer dikes. With regard to reducing the amount of flot- Most of the salt marshes along the mainland sam there is still controversy. Most investigations coastline of the Wadden Sea are artificial, i.e. have could not demonstrate a relationship between been developed through management techniques. grazing and amounts of flotsam washed ashore Until the mid of the 20th century the main pur- (Gerlach, 1999). According to an evaluation in pose of salt marsh works was to reclaim new fer- Niedersachsen intensive grazing might significant- tile agricultural land. Later, in the 1960s and 70s, ly reduce the amounts. Investigations in the Ley- the main argument became coastal defense (Hof- bucht have shown that the amount of flotsam stede & Schirmacher, 1996). In the mid of the increased due to a reduction of grazing (Erchinger 1970s nature conservation in the Wadden Sea et al., 1996). It was concluded that, in general, became more important and, consequently, the grazing might influence the flotsam potential and nature function of salt marshes. that further investigations have to be carried out. In this section the relevance of the salt marsh- Erosion es and summer dikes for coastal protection and A more pertinent threat to salt marshes is cliff nature conservation will be discussed on the ba- erosion. Most salt marshes are nowadays situated sis of an integrated analysis of costs, benefits, risk in an exposed high-energy position as a result of of flooding, cultural-historic and natural values the former practice of artificial salt marsh cre- and public perception . ation and subsequent reclamation. Without pro- 3.4.2 Salt marshes tective measures a large part of these salt marsh- es would probably erode and in the end disinte- Coastal protection functions grate. This problem will intensify if the input of A salt marsh in front of a sea wall (also called energy by waves and tides into the Wadden Sea foreland) reduces the wave energy and transfers increases. If the height of the tidal flats does not the energy-impact of storm waves from the dikes increase enough to balance the expected sea lev- towards the edge of the salt marshes. After dike el rise, water depths in front of the salt marshes breaching, a salt marsh prevents the establish- will increase. This, in combination with an increas- ment of a scour hole within the breach and ing storminess, might enable higher waves to prevents water to flow through the breach during reach the salt marshes and induce cliff erosion. succeeding tides. Further, the salt marsh provides Intensive investigations into the stability of material (clay and salt marsh sods) for dike artificially created salt marshes under an increas- reparation and maintenance. Finally, salt marshes ing sea level rise have been carried out in the Neth- reduce the energy input and prevent damage at erlands (Dijkema et al., 1990; Dijkema, 1992). The the outer dike foot. Therefore, in Niedersachsen, results indicate that vertical accretion at the lower Schleswig Holstein and Denmark higher salt mainland salt marshes is high enough to com- marshes render the building of revetments pensate for a sea level rise of about 1 to 2 cm per superfluous. These arguments underline the year. Although at this moment the higher main- importance of salt marshes for coastal defense. land salt marshes could not balance such a sea For example, in the Niedersachsen Dike Act (2.3.1) level rise, it is expected that the higher flooding and the Schleswig-Holstein State Water Act (2.2.1) frequency will induce a stronger accumulation (see it is written that salt marsh management 3.1.3). The critical zone will be the higher mud techniques for coastal defense purposes are a flats in front of the salt marshes. Here, no signif- public affair. icant accumulation could be observed during the

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 23

Salt marsh cliff, Nord- deich (FRG). (Photo: J. Hofstede) last decade, nor can a significant increase in sed- Denmark is lower, so the salt marsh has an influ- imentation be expected as a result of higher wa- ence on the proceeding design waves. ter levels. As a consequence, the gradient between In Germany also the perception that local in- the salt marshes and the mud flats might increase. habitants have of salt marshes as an essential fac- This, in combination with an increasing wave at- tor in flood protection must be taken into account. tack, could lead to cliff formation and a horizon- For them, any reduction in salt marsh maintenance tal erosion of existing salt marshes. Dijkema et al. is a defeat in the continuous battle against the (1990) concluded that future management tech- sea and, consequently, a reduction in safety. niques to stabilize existing salt marshes should Nature protection pay most attention to the fronting mud flats. During the last decades a growing environmental Wave climate concern has led to a new appreciation of the Wad- Results of model investigations have shown that den Sea salt marshes as areas of very high eco- the effect of salt marshes on wave damping mainly logical value. depends on the water depth and the wave char- The main aim of the German National Parks is acteristics. The waves are breaking the first time that salt marsh flora and fauna be governed by on the salt marsh and the wave energy is reduced the geomorphological structure of the habitat and before the waves reach the dike. Generally, this that natural processes can take place (Stock, 1997; effect is getting smaller with increasing water level Bunje, 1997). For coastal defense this would im- (Niemeyer & Kaiser, 1999; Zimmermann et al., ply the abandonment of (most) management tech- 1999). If local water depths exceed 2.5 m, results niques. For example, for reasons of nature pro- of model investigations indicate no significant tection, generally, clay may only be taken from effect of salt marshes on waves and wave run-up salt marshes in case of emergency. In Schleswig- at the outer dike slopes (Zimmermann et al., 1999). Holstein the following compromise between the Hence, in the case of a design storm surge, no coastal defense and environmental demands was direct positive effects of salt marshes on the re- realized (Hofstede & Schirmacher, 1996): The com- duction of wave impact at the outer dike slope mon goal of both coastal defense and environ- may be expected. In the Danish part of the Wad- mental authorities is to preserve existing salt den Sea there are dikes with security levels of 30- marshes. Where no salt marshes exist in front of 50 years. Secondly, the tidal range is smaller than sea walls, they should be created. The techniques in Germany and The Netherlands. This means that used to reach this goal depend upon local circum- the design water level for these dikes is lower than stances and must be carried out as ecologically in Germany and The Netherlands. As a conse- sound as possible. If local circumstances allow quence, the water depth under design storm in such, technical measures are abandoned.

Wadden Sea Ecosystem No. 13 - 2001 24 3. Common Knowledge Basis

In Schleswig-Holstein the area with intensive mentation of the Stade Declaration. grazing of sheep has decreased from 95% in 1989 Furthermore, the Danish Nature Protection Act to 45 % in 1995. (Stock et al., 1996). Also artifi- prohibits changes in the state of salt marsh areas. cial drainage has decreased. In accordance with This prohibition includes changes in present use the Schleswig-Holstein salt marsh management (amongst which agricultural use), which leads to plan (Hofstede & Schirmacher, 1996) artificial any change in the condition/state of the area. The drainage in ungrazed salt marshes within the regulation preserves the present situation with a Schleswig-Holstein National Park has been differentiated pattern of extensive and ungrazed stopped. areas. Only few areas are grazed intensively. The Also in the Niedersachsen National Park there legislation and the limited actual demands keep has been a progressive reduction of grazing. Pres- artificial drainage and maintenance activities to ently 60% of the salt marshes are unused, 24% practically zero. In general the morphological sit- are extensively used and 16% are heavily grazed. uation in the zone between existing foreland and Also artificial drainage has been reduced consid- mudflat is in equilibrium and, consequently, coast- erably. With the aim of integrating coastal pro- al protection activities are presently at a low lev- tection and nature protection interest an ad-hoc el. It is practice (as a public task carried out by Project Group was established in 1997. With re- the Ministry of Food, Agriculture and Fishery) to gard to the management of the foreland this maintain existing salt marshes in front of dikes as group, which has in the meantime finalized its a couple of hundred meters broad foreland. This work, recommended that only in specific cases is done mainly with brushwood groynes. grazing and mowing would be possible with the 3.4.3 Summer Dikes aim of reducing flotsam (Striegnitz, 1999). Most salt marshes in The Netherlands have a Coastal protection nature protection ”function”. On the minority Summer dikes only exist in the Dutch and Nieder- (mainly privately owned) salt marsh areas agri- sachsen parts of the Wadden Sea. In The Nether- culture is the main use. The policy for the salt lands they have no coastal protection function. marshes is to establish a differentiated pattern of The present summer dikes in Niedersachsen grazing (no grazing to intermediate grazing pres- have a function in the collection of flotsam. They sure) and to stop heavy grazing with the aim of also avoid penetration of water in the dike foot enhancing the diversity of flora and fauna. To this up to medium storm surges and decrease the wave end also drainage has been reduced considerably: energy input on the main dike. Up to medium The amount of clay from digging activities in the storm surges flotsam accumulates at the summer Dutch mainland salt marshes has decreased from dike and is collected here. Should summer dikes 500,000 m3 to 150,000 m3 in the past ten years. be removed, a berm and a road would have to be This reduction is mainly due to the reduction of constructed at the foot of the main dike for the the size of ditches and of the maintenance fre- same purpose. Moreover, the construction of the quency. The reduction of artificial drainage will outer slope of the main dike in Niedersachsen dif- be further continued, both by the cessation of fers from the situation in The Netherlands. In The drainage and the introduction of better tech- Netherlands the outer slope and the foot of the niques, such as the reduction of the number of main dike are well protected with a hard con- ditches. Reduction of drainage could lead to less struction whereas in Niedersachsen there is only sedimentation. Therefore, artificial drainage is re- a clay layer. Also here adaptations would be duced to such an extent that no unacceptable ero- necessary in case summer dikes are removed. sion occurs. In Denmark there is no hard construction on In the Danish Wadden Sea there is, so far, no the outer slope or the foot of the main dike and explicit nature protection policy for the salt there are no summer dikes. Instead, the salt marsh/ marches which has been implemented in a man- foreland is maintained in areas where erosion is agement plan. observed. The policies laid down in the Stade Declaration Wave climate are considered as management guidelines. The Wadden Sea Nature Conservation and Wildlife In The Netherlands summer dikes are not regard- Reserve Executive Order aims to promote sustain- ed relevant for the design of the main dike. Sum- able management, as far as the natural dynamics mer dikes in Niedersachsen are part of the fore- in the evolution of the landscape is not influenced land which is mentioned in the dike law. There is, unnecessarily. This can be regarded as an imple- however, discussion about the possible safety function of summer dikes and its relevance for

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 25

the design of the main dike. This discussion is rel- sam or that only intensive grazing would have a evant for the option of opening or removing sum- significant effect on flotsam amounts. mer dikes for nature conservation purposes (see Summer dikes, which only exist in Niedersach- further below). On the basis of model calculations sen and The Netherlands, have a coastal protec- and hydraulic model tests Niemeyer and Kaiser tion function in Niedersachsen. Their removal (1999) concluded that, at design water level, sum- would imply adaptations to the foot of the main mer dikes have only a small wave damping effect. dike, i.e. the construction of a berm and a road Mai et al. (1998) found in physical and numerical for removal of flotsam and strengthening of the model tests a reduction in wave of more than 20% outer slope. in case the water depth over the crest of the sum- Summer dikes have only a limited function in mer dike was lower than the relative wave height. flood defense, although there is still controversy These authors concluded that, due to the reduc- about the question to what extent summer dikes tion of wave height and, to some extent on the are relevant for the design of the main dike. In wave period, the wave load on the main dike is this discussion also the perception of the local significantly reduced. For very high water levels inhabitants plays an important role. (water level above crest more than 2.4 times wave height) the influence of summer dikes is negligi- 3.5 The relevance of biota ble. for sedimentation- and Nature protection It is the Dutch policy to outbank summer polders erosion processes by opening summer dikes so as to increase the 3.5.1 Introduction total salt mars area. The background is that in the The influence of biota on marine sedimentation past large areas of salt marsh have been embanked and erosion processes is usually ignored. This is for agricultural purposes. It is not intended to re- certainly not justified for the Wadden Sea where move the whole summer dike. Only several open- innumerable individuals of plants and animals in- ings are made. fluence the muddy and sandy intertidal flats. De- In Niedersachsen the option of outbanking pending on abundance and species composition summer polders was discussed in the framework this biota influences transport, sedimentation and of compensatory measures for the construction erosion of the sediments. Moreover, the vegeta- of the Europipe. The discussion mainly focussed tion in salt marshes and dunes is the most impor- on the role of summer dikes for coastal and flood tant factor for the retention of mud respectively defense (see above) and has, as yet, not been fi- the formation of dunes and their protection nalized. against wind erosion. 3.4.4 Conclusions 3.5.2 Intertidal area From the above it is concluded that existing salt marshes have important functions in coastal pro- Biogenic sedimentation tection and that maintaining existing salt marsh- Changes in the sedimentation and erosion pro- es has several advantages compared to dikes with- cesses and in the sediment composition caused out salt marshes. Salt marshes have a significant either by biological activities or biogenic struc- effect on wave damping up to medium storm surge tures are defined as biogenic sedimentation. De- levels but their effect at high storm surges is lim- pending on the local conditions biogenic sedimen- ited. In the public opinion, however, salt marshes tation can prevail physical sedimentation as re- are still considered an important safety element. ported from the tidal basin of List (Sylt) (Bayerl et Also from the nature protection point of view al., 1998) or the Meldorfer Bucht (Gast et al.,1984) maintaining salt marshes is the preferred option. and can contribute to the raising of tidal flats There have, however, been differing positions as (Thiel et al.,1984). regards salt marsh maintenance, i.e. the intensity Wadden Sea organisms living on or in the sed- of grazing and drainage. With regard to grazing, iment actively contribute to sedimentation by there is broad consensus about the fact that this deposition (biodeposition) or by stabilization (bio- is not necessary for the stability of salt marshes. stabilisation) of the sediment. More passive There is still discussion about the relevance of epibenthic biogenic structures, such as mussel grazing for reducing the amounts of flotsam. In- beds, affect the local hydrodynamic conditions, vestigations have shown that either there are no enhance sedimentation or prevent erosion. On the causal links between grazing and amounts of flot- other hand biota is also able to increase the erod-

Wadden Sea Ecosystem No. 13 - 2001 26 3. Common Knowledge Basis

ibility of the sediment or to destruct the surface tions of these organisms have a cohesive effect by bioturbation, burrowing activities and resus- on the sediment particles and decease the rough- pension of particles. ness of the sediment surface (Asmus et al., 1994; Biodeposition Paterson et al., 1994) which results in an increased critical velocity for erosion processes. Field experi- Biodeposites are fecal pellets (feces and pseud- ments in an intertidal area of the Oosterschelde ofeces) being deposited at the sea floor (Haven & (SW Netherlands) have shown that in higher en- Morales-Alamo, 1972). Biodeposition influences ergy parts of the intertidal flats strong erosion may the sediment composition and, subsequently, the occur in places where the algae cover is chemically habitat and community structure of the intertidal destroyed (De Boer, 1981). Laboratory experiments ecosystem. Austen (1997) found that up to 80% have revealed that a diatom population that was of the sediment volume of mudflats of the Königs- allowed to re-establish itself for 24 hours after hafen (Sylt) was formed by fecal pellet.; On flats stirring, increased the critical velocity by several with mixed sediment the rate was 1 – 50% and tens of percents, as compared to freshly stirred on sand flats 1 – 13%. Biodeposites change the and redeposited sand. Stabilization by diatoms can sediment composition by agglomerating fine par- therefore be an important factor in the stability ticles (e.g. clay, silt, organic debris) to pellets with of sediment in intertidal and shallow subtidal ar- the size of sand grains. Because these pellets show eas. In addition the cellular network of filamen- the same sedimentation behavior as sand, fine tous blue-green algae causes a mechanical con- material is deposited at locations where, under solidation of the sediment (Stal, 1994). Anoxic normal physical conditions, only sand may be ex- sediment surfaces like the black spots in the Nied- pected. The fine material can be worked into the ersachsen Wadden Sea, which have very low abun- sediment by bioturbation. Biodeposites, moreover, dance of microphytobenthos, show a decrease of do not take part in the current induced transport the critical threshold velocity and can easier be processes of their original particle size (Thiel et eroded (Austen & Witte, 1997). al., 1984). Pellets can mainly be found in the sed- iment layers near the surface, whereas in deeper Biogenic structures layers they are normally converted into homoge- Biogenic structures also have effects on the sed- neous mud (Bayerl et al., 1998; Austen, 1997). imentation processes. By decreasing current ve- Maximum deposit rates of 10.5 mm/month were locities or water turbulence these structures act calculated for cockles, 0.1 mm/month for the Bal- as sediment traps for fine grained material. Mus- tic tellin and 0.04 mm/month for the soft clam sel colonies form a semi-rigid framework which (Thiel et al., 1984). tends to bind the sediment, thereby protecting it Very high biodeposition rates are common in from erosion. In seagrass meadows the propor- mussel beds. For the period 1975 to 1978, when tion of fine particles is higher than in the sur- mussel beds covered about 41.5 km2 of the Dutch rounding flats and the meadows are slightly ele- Wadden Sea, Oost (1995b) calculated an amount vated (Asmus & Asmus, 1998). The loss of sublit- of 7.7 million tons of sediment bound in the eu- toral seagrass in the 1930s increased the erosion littoral mussel beds and 9.8 million tons in sublit- in the areas where the losses occurred (Reise, toral beds. To a certain degree biodeposites will 1998). A high abundance of tube building poly- be exported from mussel beds so that mixed sed- chaete worms can change the small scale topog- iment can be found in the vicinity (Oost, 1995b). raphy of the flats by forming a layer of mud on The substantial loss of mussel beds in the Dutch the former sandy sediment surface or by develop- and Lower Saxonian Wadden Sea during the 1980s ing a distinct structure of consolidated embossed and 1990s caused a decrease of areas with mixed patterns and erosive troughs (Heuers et al., 1998). sediment (Obert, 1995; Oost, 1995b). It is con- Bioturbation cluded that mussel beds have an important influ- ence on the amount of fine material and the sed- One effect of bioturbation is the transport of fine- iment balance of the Wadden Sea. grained material, e.g. biodeposits, from the sur- face into deeper, less erodable sediment layers. Biostabilisation But bioturbation can also enhance the erodibility: Biostabilisation is defined as the stabilization of (1) by increasing the bottom roughness; (2) by ac- sediment by organisms (Thiel et al., 1984) e.g. the tively bringing grains in suspension; (3) by sorting mucous coating of upper sediment layers by of sediment. The increase in erodibility enhances benthic diatoms, filamentous networks of blue- the sediment transport. Some forms of bioturba- green algae or microbial mats. The mucous excre- tion tend to destroy small-scale structures on the

Wadden Sea Ecosystem No. 13 - 2001 3. Common Knowledge Basis 27

surface. Intensive bioturbation can obliterate rip- this zone the upper marsh commences with nor- ples formed during one tide. mal grassland plants. On the higher parts of the tidal flats organisms Besides the deposition of fine silt and clay in have sufficient time to completely modify the orig- the middle and higher marshes during (very) high inal depositional structures. One of the most im- water, beds of sand and shells may be deposited portant bioturbators in the Wadden Sea is the lug- during storms over kilometer wide areas. More worm. The animal lives in a U-shaped burrow at substantial shell hash deposits, situated further depths of 15 to 20 cm, almost continuously in- inland, are the result of activities of birds such as gesting sand. From time to time the animal ex- eiderducks, oystercatchers, gulls and crows. cretes the ingested sand at the surface. It has been calculated that the top 30 cm of the tidal flat 3.5.4 Dunes sediments can be reworked completely by lugworms Along the Wadden Sea coast dune formation, sta- each year (Cadée, 1976). The grains that are too bilization and protection against erosion, is closely large to be swallowed are concentrated at the connected to plants which are able to settle in deepest point of the U-burrow. In this way exten- such a barren sandy environment. Dunes without sive layers of shells, especially of mud snails, are vegetation are unstable, for example small formed. barkhans (Sicheldünen) on the beaches or very large, moving ”transversal ridges” (Wanderdünen) 3.5.3 Salt marshes at the inner borders of the dune areas on some In the pioneer zone (the transition between tidal islands, which occur when the vegetation cannot flats and salt marshes) and in salt marshes, plants cope with the moving sand or after destruction of adapted to the extreme environmental conditions fixed dune systems (Doing, 1983; Ellenberg, 1982). are the principal biotic component influencing The establishment of more permanent dunes starts sedimentation. Where a tidal flat is elevated to when, under ”favorable” conditions, e.g. sufficient some decimeters below the mean high water lev- rainfall and presence of some organic matter, pi- el, the pioneer plants glasswort and common cord- oneer plants settle on sand which is piled up by grass settle, followed with increasing elevation by the wind in the lee of shells, plants or flotsam. the sea aster and the annual sea-blite (Dijkema Sand couch grass and lime grass are the halotol- et al., 1990). Glasswort does not significantly in- erant pioneers which are able to start dune suc- fluence sedimentation, but enables other plants cession on the beaches, accumulating sand to pri- to settle, while the common cord-grass is known mary dunes with maximum heights of about 2 m. to enhance sedimentation. When the elevation of The second step of dune development, the white the pioneer zone increases, the vegetation cover dunes, which can be piled up to ridges of up to 10 of pioneers becomes denser and other plants start m, is a result of the growth of sea marram which to settle. is the most effective dune forming plant. The The border between the pioneer zone and the plants are able to fix the sand with their strong lower marsh, i.e. the area around or above the vertical straws and long horizontal root systems mean high-water level is characterized by the ap- and are able to grow through the sand when they pearance of marsh grasses. By decelerating the are covered during storms. Layer by layer they flow of the current during flooding, the vegeta- climb up with the sand which is deposited due to tion of halotolerant plants enhances sedimenta- the drop of the wind speed in their presence (El- tion rates to maximum values (Dijkema et al., lenberg, 1982). More landward, where the mov- 1990). In this way large amounts of sediment are ing sand calms down and the accumulation of retained and stabilized by the root systems of the humus, decalcification, leaching of nutrients and marsh plants; the marsh accretes vertically. In ad- acidification starts soil development, gray and dition, erosion is strongly reduced. When the marsh brown dunes, densely covered with characteristic becomes even higher, sedimentation rates de- plant societies, form the next stages of dune suc- crease due to the decreasing number of floodings cession (Neuhaus & Petersen, 1999). Here, vege- and also due to the lower sediment supply of in- tation mainly prevents wind erosion. In all suc- dividual floodings. As a result of sedimentation cessional stages and in all dune areas where wind, the lower marsh zone evolves into a middle marsh waves, rainwater, animals or man damage the veg- zone with a characteristic plant community. Above etation, sand drifts may occur.

Wadden Sea Ecosystem No. 13 - 2001 28

4. Analysis of Changes

Analysis of Changes: Basic Assumptions and Methodology

4.1 Introduction 4.2 Past In the foregoing chapters an overview has been About 18,000 years ago, during the maximum of presented of current Wadden Sea nature protec- the last glacial period, global sea level stood some- tion and coastal defense polices and the common where between 120 m and 175 m lower than the knowledge basis regarding geomorphology and present (Jelgersma & Tooley, 1993). Huge volumes related biological processes and coastal defense of water were bound on land in icecaps. With in- techniques in the Wadden Sea. In this chapter an creasing temperatures, these icecaps started to overview will be given of changes in water levels melt. As a consequence of this melting, but partly and storminess which have occurred in the past also by subsidence of the North Sea basin, sea (section 4.2) and which are expected to occur in level rose by as much as 21 mm/yr (2.1 m per cen- the future (section 4.3). For the latter the scenar- tury!) over the time period 8,600 to 7,100 BP ios as elaborated by the Intergovernmental Panel (Streif, 1989). After about 6,000 BP bottom on Climate Change (IPCC) will be used. In the fi- subsidence (at a rate of 1 to 1.5 mm/yr) began to nal section 4.4 a description is given of the meth- dominate, eustatic sea level (the change in sea odology applied by the CPSL for the evaluation of level without considering changes in bottom lev- possible consequences of changes in sea level and el) now rising at a rate of only 0 to 1 mm/yr. storminess. Over the last about 100 years numerous gaug- es have registered tidal water lev- 170 els in the Wadden Sea. Long-term Figure 4.1: Yearly mean high water Mean MHW, MSL and MLW 19-year running mean analyses of changes in tidal water at gauge Cuxhaven. 150 levels show a high spatial and tem- poral variability. Some of the gaug- 130 es, especially those in the inner

Sea level (GOL + cm) parts of the estuaries, are influ-

110 enced by human activities like 1850 1875 1900 1925 1950 1975 2000 dredging. For these gauges anthro- pogenic effects may outweigh the 30 Yearly mean sea level natural long-term changes in tidal 19-year running mean water levels. However, mean trends 10 in yearly mean high water (MHW), yearly mean low water (MLW) and -10 yearly mean tidal range (MTR) in the

Sea level (GOL + cm) Wadden Sea become obvious. Over -30 the last about 100 years a mean 1850 1875 1900 1925 1950 1975 2000 MHW-rise of about 0.2 to 0.25 mm/ yr, an insignificant mean MLW-rise, -120 Yearly mean low water and a mean MTR-rise of about 0.2 19-year running mean to 0.25 mm/yr is given by most au- -140 thors (e.g. Jensen et al., 1990, 1993; Töppe, 1993). On the basis of time -160 series for the period 1890 - 1989,

Sea level (GOL + cm) Jensen et al. (1990) observed a -180 strong increase in the mean MHW- 1850 1875 1900 1925 1950 1975 2000 Years rise for 12 German gauges over the

Wadden Sea Ecosystem No. 13 - 2001 4. Analysis of Changes 29

last decades. A linear regression through the yearly vestigations, Stengel and Zielke (1994) suggested MHW-values for the time period 1890 - 1989 re- that the MTR in the Wadden Sea might increase sulted in a mean MHW-rise of 2.5 mm/yr, for the by about 30% of MSL-rise. This might result in period 1971 - 1989 this value amounted to 6.7 the following (plausible) hydrographic scenario mm/yr. This acceleration is probably the result of 2100: long-term cyclic fluctuations and human activi- MHW +0.6 m ties (see above), rather than a consequence of an MLW +0.4 m (anthropogenic) climate change (Töppe, 1993). MTR +0.2 m From 1990 to 1997 the MHW level did not change For the scenario 2xCO , von Storch (1997) cal- significantly at most German gauges. As an ex- 2 culated possible changes in storm surge heights ample MHW, MSL and MLW at gauge Cuxhaven along the North Sea coastlines. For the Wadden are given in Figure 4.1. Sea he came up with a small increase in the order Long-term changes in wind (and storm) climate, of about 0.1 to 0.2 m, i.e., well within the natural wave climate and storm surges have been inves- climatic variability. Zielke et al. (1997) predicted tigated by different authors. Based on a 1907- a small increase in maximal wind speeds (storm- 1980 time series of wind data from five lightships, iness) in the Wadden Sea for the 2xCO scenario. Hoozemans (1989) established an increase of 2 Bijl (1997) investigated the possible effects on the mean wind speeds of about 1 to 2 m/s per century storm surge heights in the southern part of the along the Dutch coasts. Using long-term obser- North Sea of two wind climate scenarios: (1) vational records of sea level, wave height and northward shift of the wind climate system and wind, Bijl (1996) could not find a sign for a (2) increase in the intensity of storms. Scenario 1 significant increase in storminess over north-west only has a small impact on the storm surge heights Europe (German Bight and south-western North in the area. Scenario 2, on the other hand, sug- Sea) over the past 100 years. However, on smaller gests a high sensitivity of storm surge heights on time-scales there is considerable natural variabil- changes in the intensity of storms. Finally, regard- ity. Schmidt (1997) investigated the geostrophic ing future storminess on a regional scale, the IPCC wind speeds in the German Bight (1876 - 1992) (1995) states: ”In the few analyses available, there to arrive at possible trends in storminess. He could is little agreement between models on changes in find no long-term trend either. Using the same storminess that might occur in a warmer world. data (geostrophic wind speeds), von Storch et al. Conclusions regarding extreme storm events are (1993) calculated monthly mean wave heights in obviously even more uncertain”. the northern North Sea. Again, no trends but high In January 2001 the Intergovernmental Panel values in the beginning and the end of this cen- on Climate Change presented new figures for cli- tury were established. Finally, Siefert (1984) and mate change and sea level rise. According to these Führböter and Dette (1992) investigated the de- new data the global average surface temperature velopment of storm surges in the German Wad- in the 20th century has increased with 0.6 ± 0.2ºC. den Sea after 1900. They observed a clear increase The increase in temperature in the 20th century in storm surge activity since about 1959/60 in this is likely to have been the largest of any century area. during the past 1000 years. Globally it is very likely In summary, although a clear increase in storm that the 1990s was the warmest decade and 1998 parameters between about 1960 and 1990 was the warmest year in the instrumental record since established by most authors, no long-term trends 1861. It is also very likely that precipitation has seem to exist if we consider the last 100 years. increased by 0.5 to 1% per decade in the 20th century over most mid and high latitudes of the 4.3 Future northern hemisphere continents and that there Based upon different socioeconomic scenarios the has been a 2-4% increase in the frequency of IPCC (1995) calculated global water levels for the heavy precipitation events over the latter half of next century. The best estimate gives an increase this century. in global eustatic MSL of about 0.5 m until 2100. Tide-gauge data show that global average sea This rise results mainly from the melting of gla- level rose between 0.1 and 0.2 meters during the ciers and thermal expansion of the upper layers 20th century. Global ocean heat content has in- of the ocean. The lowest emission scenario (IS92c) creased since the late 1950s, the period for which gives a projected eustatic sea level rise of about observations are available. 0.15 m, the highest emission scenario (IS92e) of There is new and stronger evidence that most 0.95 m until 2100. Based on numerical model in- of the warming observed over the last 50 years is

Wadden Sea Ecosystem No. 13 - 2001 30 4. Analysis of Changes

attributable to human activities. Furthermore, it As time horizon for the evaluation the year is very likely that the 20th century warming has 2050 was chosen. On the basis of the IPCC sce- contributed significantly to the observed sea lev- narios the Working Group expects average sea el rise, through thermal expansion of sea water level to increase between 4.5 and 44 cm within and widespread loss of land ice. Within present this period. In addition to the absolute sea level uncertainties, observations and models are both rise, bottom subsidence causes an increase of the consistent with a lack of significant acceleration water level. Therefore a range of 10 to 50 cm of sea level rise during the 20th century. was taken as the expected increase until 2050. Human influences will continue to change at- Within this range three scenarios were mospheric composition, temperature and sea level distinguished by the CPSL. In Scenario 1 a sea throughout the 21st century. Based on a number level rise of 10 cm/50 years is assumed, reflecting of climate models the globally averaged surface the current situation (compare 4.2). Scenario 2, temperature is projected to increase by 1.4 to the intermediate and most realistic scenario, 5.8ºC. This is much larger than the observed assumes a sea level rise of 25 cm/50 years and changes during the 20th century. Also global av- under scenario 3, the worst-case scenario, a sea erage water vapor concentration and precipita- level rise of 50 cm until 2050 is expected. The tion are projected to increase over northern mid- possible impact of increase in storminess will be to high-latitudes and Antarctica. evaluated in addition to the impact of rising water Global mean sea level is projected to rise by levels. 0.09 to 0.88 meters between 1990 and 2100 for In Chapter 5 the possible impacts of changes the full range of scenarios. This is due primarily to in sea level rise and storminess are evaluated for thermal expansion and loss of mass from glaciers all three scenarios under the assumption that to- and ice caps. The mean values of all used climate day’s safety level is maintained. This approach models for all socioeconomic scenarios vary among has been termed “Business As Usual (BAU)”. Under 0.3 and 0.4 m until 2100. These may be seen as, at the BAU approach three categories of parameters present, the most realistic outcomes. have been evaluated, namely physical, biological Global mean surface temperature increases and and socioeconomic. rising sea level from thermal expansion of the In chapter 6 several management practices and ocean are projected to continue for hundreds of technical measures are evaluated. In order to years after stabilization of greenhouse gas con- make it possible to make choices on future man- centrations, owing to the long time-scales on agement strategies for the Wadden Sea region which the deep ocean adjusts to climate change. these have been assessed for their contribution Also ice sheets will continue to react to climate to maintain safety and their impact on the envi- warming and contribute to sea level rise for thou- ronment, expressed as effects on habitats and sands of years after climate has been stabilized. interference with natural dynamics. Also an in- dication of the feasibility of the different options 4.4 Methodology from the technical, financial, legal, public opin- ion and spatial point of view is given. The options The IPCC scenarios are the basis for the method- that are positive from a coastal defense point of ology applied in the evaluation of the possible view and which have a positive or only slightly impacts of sea level rise and changes in stormi- negative impact on nature, have been selected ness. This evaluation is presented in chapters 5 as Best Environmental Practices (BEPs). and 6.

Wadden Sea Ecosystem No. 13 - 2001 31

5. Impacts of Changes

Impacts of Changes in Sea Level and Storminess

5.1 Introduction 5.2.1 Flooding time intertidal In this chapter, the possible changes in morphol- The flooding time of the intertidal flats is expect- ogy, biology, and coastal defense efforts for the ed to increase by 2.5 to 7.5% under the 25 cm hydrological scenarios under the assumption scenario, and between 5 and 15% under the 50 “Business As Usual - BAU” are described. To this cm scenario. This increase will be further aggra- end, appropriate parameters that characterize vated if storminess increases as well. However, the morphology, biology and coastal defense in the working group stresses that the changes will Wadden Sea were selected. The results represent strongly differ from one tidal basin to another (Fig. the expert opinion of the working group mem- 5.1), depending on the amount of sediment avail- bers. For most of the parameters almost no quan- able to balance sea level rise. Some tidal basins titative data and/or scientific outcomes exist, ei- already seem to suffer from a sediment deficit. ther because there is no monitoring of appropri- Hence, the flooding time in these tidal basins will ate parameters or monitoring has only started re- probably be much more affected than suggested cently. Hence, it was only possible to achieve qual- by the mean values mentioned in the table. itative estimates based on the present state of knowledge and (practical) experience. Conse- quently in Table 5.1 no absolute figures but per- centage ranges or, for biologic parameters and storminess, signs (positive, neutral or negative) indicate the expected relative changes for each scenario. The present situation has been set at 100%. Under the 10 cm scenario no or only minor changes are expected, as this scenario represents the continuation of present sea level rise. In sections 5.2 and 5.3 the expected changes in physical and biologic parameters under the three hydrological scenarios are presented. The consequences for safety, fresh water run-off and harbor/shipping and salinity for each hydrologi- cal scenario are described in Section 5.4. All results have been summarized in the over- Figure 5.1: view Table 5.1. 5.2.2 Surface area intertidal Possible changes in geomorphological and The effects of rising sea levels on the surface area biological parameters for 5.2 Physical consequences of the intertidal flats are expected to be the same individual tidal basins To characterize the possible physical consequenc- as for the flooding time. Hence, the spatial extent under sea level rise. Up to a es for the Wadden Sea under the three hydrolog- might, under the 50 cm scenario, diminish by up certain „break point“ 2 parameters react slowly ical scenarios, six parameters have been selected to 15% or 720 km compared to the present situ- and within the range of 2 by the working group: ation (4,800 km ). This will, obviously, significantly natural variability. After influence the biological parameters (Ch. 5.3). the break point, which • flooding time intertidal flats (the period with Under the “worst case” scenario the Wadden Sea differs for different tidal salt water cover); basins, reaction to SLR is might start to evolve from an ecosystem charac- evident but again different • spatial extent intertidal flats (surface area be- terized by large intertidal areas, towards a more for the individual tidal tween mean low and mean high water level); open water, lagoon-like environment. basins. • tidal channel cross-section; 5.2.3 Tidal channel cross-section A well-known parameter to characterize tidal • salt marsh accretion (changes in height of the channels is the tidal channel cross-section (Fig. salt marshes); 5.2). In general it is expected that a rise in sea • salt marsh cliff erosion (horizontal develop- level will result in a (relatively small) increase in ment of seaward salt marsh edge); the cross-sectional areas of the tidal channels. An • barrier retreat (migration of barriers). increase in storminess might, on the other hand,

Wadden Sea Ecosystem No. 13 - 2001 32

Table 5.1: Overview of expected changes in physical, biological and socio-economic parameters under three hydrological scenarios under Business as Usual (BAU) policies. *1) The change is given as either absolute, relative (Situation in 2000 = 100%), qualitative (+,-, 0) or descriptive. The range given is an average (compare figure 5.1). *2) Qualitative indication of additional effect increase (frequency/intensity). *3) Generally sea level rise will increase erosion. A sea level rise of 25 cm to 50 cm will cause an additional retreat of ca. 1.50 m per year or more. Along the western shores of Amrum, Eiderstedt barriers and Dithmarschen retreat is balanced by a strong sediment input from the longshore drift. Rise in sea level will not have a large affect on the accretion at the west coast of Rømø and Fanø, with a sea level rise of 50 cm a decrease of accretion, or even erosion, can be expected. *4) For each country the relative share of expenditure for each of these categories is given in Table 5.2.

Present situation Change 2050 compared to Storms Remarks present situation *1) *2) 10 cm/50yr 25cm/50yr 50 cm/50yr scenario scenario scenario I. PHYSICAL ASPECTS

Flooding time 0 +2.5 to +7.5% +5 to +15% + Assuming sedimentation. Large intertidal area differences between tidal basins (0 to +25%). Surface area NL 1,300 km2 0 -2.5 to -7.5% -5 to -15% - Lister Dyb tidal basin -30% intertidal flats Nds+HH 1,500 km2 (under 50cm/50yr scenario). SH 1,300 km2 DK 700 km2 Channel 0 to +5% Up to +10% 0 to + cross-section Salt marsh accretion SH +0.5 to +2.5 +0.5 to +2.5 0 to +2.5 -0.5 to +0.5 - In worst-case scenario less (in height) cm/yr cm/yr cm/yr cm/yr accretion and some drowning. Salt marsh cliff erosion 0 to 2 m/yr 0 to 2 m/yr 0 to 4 m/yr + Very large local differences. Barrier Retreat *3) *3) *3) II. BIOLOGICAL ASPECTS Benthic biomass 0 0 to - - - Depends strongly on sediment composition (and, consequently, dynamics). Birds (selected species) 0 - - - Depends on frequency of high population size floods (breeding birds) and benthic biomass Fish nursery 0 - - - Temperature, change of habitat and turbulence important factors Seal population size 0 0 0 to - - Seagrass area 0 - - - Related to decrease intertidal Dune vegetation 0 0 0 to - - Salt marsh vegetation 0 to + + + diversity III. SOCIOECONOMIC ASPECTS Efforts to maintain present safety standards Dikes 100% *4) 0 5 to 15% 15 to 75% 15% Depends to an important degree on whether strengthening has been carried out recently Other hard constructions 100% *4) 0 10 to 40% 40 to 140% 15% Sand suppletion 100% *4) 0 50 to 100% 100 to 300% 10% (incl. Dunes) Salt marsh works 100% *4) 0 5 to 10% 10 to 25% 30% Efforts to maintain 100% 0 20 to 50% 50 to 200% + discharge capacity Salinity ground water 0 0 to + + Dredging effort 100% 0 -5 to 0% -10 to -5% 0 to +

Wadden Sea Ecosystem No. 13 - 2001 33

induce a (insignificant) reduction of the cross- intensifying) salt marsh cliff erosion at the sea- sectional area due to silting up of the channels. ward edge of the salt marshes. If this process con- However, the changes will probably remain with- tinues, the salt marshes might be eroded by (lo- in the natural variability of the system. cally) up to 4 m/y until they finally disappear. How- 5.2.4 Salt marsh accretion ever, as with flooding time and surface area of the intertidal flats, the working group stresses that Present day accretion rates on the salt marshes large regional differences may prevail depending may vary from about 0.5 cm/yr on the barrier salt on the exposition of the salt marshes to incoming marshes to more than 2.5 cm/yr on some main- (storm) waves. In the Dutch and German sectors land salt marshes. With increasing sea level the of the Wadden Sea cliff erosion is prevented or time of tidal inundation and, subsequently, accu- hindered by the construction of salt marsh works mulation will increase. Hence, up to a certain limit that dissipate the incoming wave (and current) (vertical) salt marsh accretion will be able to bal- energy (Table 5.1, Ch. 3.4). ance a stronger sea level rise. It is expected that under the highest sea level rise scenario (50 cm 5.2.6 Barrier retreat in 50 years) the salt marshes with low accretion A final parameter to characterize possible mor- rates will start to drown. An increase in stormi- phological consequences of hydrological changes ness and, consequently, increased amounts of sus- along the outer North Sea coast is barrier retreat pended material may cause a stronger sediment (i.e., the coastal strip from the dune crest to the transport towards the salt marshes. A stronger foreshore). Under present conditions, a large range accretion (counteracting the drowning tenden- of morphological reactions to present sea level rise cies) might be the result. Depending on which (from retreating to prograding) exists, depending process dominates, the salt marshes will drown on the sediment availability or, rather, the long- or balance sea level rise. shore drift. In general, barriers retreat in response 5.2.5 Salt marsh cliff erosion to sea level rise. Thus, an increase in sea level rise and/or storminess will accelerate this trend. How- Although salt marshes with a perennial halophytic ever, a number of barriers like Fanø, Rømø and vegetation cover are rather robust to hydrologi- Amrum, are rather stable or even prograde in a cal changes (they even depend on a rising sea seaward direction. This is the result of a strong level, see 3.1.2, 3.5.3), the fronting pioneer zones sediment input towards the beaches from the are much more sensitive, especially to changes in longshore drift. The working group estimates that storminess. An increase in wave-impact during under the “worst case” scenario the accretion storms will, under natural conditions, result in (an

Figure 5.2. Cross-sectional diagram of “Lister Tief” tidal inlet.

Wadden Sea Ecosystem No. 13 - 2001 34 5. Impact of Changes

might turn into erosion. In the Dutch and the Ger- Increased storminess will reduce mussel beds, in- man sector of the Wadden Sea, barrier retreat is cluding the quite rich benthic fauna associated mostly balanced by sand suppletion (Table 5.1, Ch. with these beds. Also the possibilities for restor- 3.1.3). ing mussel beds will be reduced as a result of in- creasing storminess. 5.3 Biological consequences 5.3.2 Birds A central factor in the assessment of the conse- Feeding possibilities are central for the birds in quences for biological parameters are the fore- the Wadden Sea. Possibilities are regulated by seen morphological changes. As mentioned in 5.2, water depth and bottom substrate. Most bird spe- these will be only minor up to a 10 cm sub-sce- cies are specialized to a limited range in these nario. With higher values for sea level rise and, two parameters and prefer to feed on emerged consequently, morphological changes, most bio- flats, where they select their specialty from the logical parameters are expected to respond, and benthos. A shift in flooding time will affect the often the response will be abrupt, indicating a time available for feeding and a change of sediment break-down of interrelations formerly in a buff- composition affects the composition of food items ered balance. These “break points” will be reached available. at different sea rise levels in the different tidal Birds, mainly waders, will also be affected at basins (see Figure 5.1). the lowest sub-scenario. But up to some 25 cm of Another central factor is the sediment compo- sea level rise the effect will be difficult to isolate sition. It is generally assumed that sea level rise from general stock fluctuations, perhaps with the alone has no major influence on the sediment exception of small waders, which will have mark- composition. Increase in storminess, however, will edly less feeding time. Ducks and geese will not generally result in coarser sediments and increased be affected to a measurable extent. With higher turbidity. Because coarser sediment has, general- sea level, the number of waders will decrease, ly, a lower productivity, an increase in area with mainly due to increase in flooding time. An excep- coarser sediment will lead to a general decrease tion is the greenshank (and perhaps also the redshank), in biomass input to the entire biological system. which may benefit from the expected increase in Mussel beds will be reduced with more storms. channel width, resulting in a larger area of channel The decrease in biomass will become visible in a slopes where the greenshank feeds. decrease in the number of migrating and breed- A sea level rise of 50 cm in 50 years will result ing birds. Storms in (late) spring will have severe in a marked decrease in all waders, owing to an consequences for breeding birds. expected increase in flooding time, leaving less Sea level rise and increased storminess are ex- time for the birds to feed on the intertidal flats. pected to have a clear effect on the following bi- Duck and geese stocks will also go down because ological indicators: salt marshes will be flooded more frequently, leav- • Benthic biomass; ing less time for feeding. • Birds; Increased storminess will have an effect mainly on breeding birds. Oystercatchers and other bird • Fish; species feeding on blue mussel will be affected, • Seals; also when migrating. Birds breeding on low lying • Salt marsh vegetation. areas will be at higher risk (e.g. avocet, little tern), where a sequence of late spring floods can erad- Other parameters will also be affected, but the icate a whole colony and, in worst cases, the whole CPSL working group does not have sufficient in- Wadden Sea breeding population. dications to allow a prediction. 5.3.3 Fish 5.3.1 Benthic biomass Fish stocks in the Wadden Sea are not expected to be affected by sea level rises below 25 cm. Above Benthic biomass is expected to decrease slightly this, the increase in flooding time could affect with a sea level rise up to 25 cm. Under the 50 cm living conditions for flatfish hatchlings negatively, scenario some decrease in total benthic biomass e.g. by reducing tidal pools and the surface relief. is foreseen, but not in a scale that could be termed Fish migration could be impaired under the 50 cm “catastrophic”. The interspecific distribution could sea level rise scenario, because the sluice opening well be affected, resulting in effects on the stocks periods will be shorter. But the anticipated increase of birds and fish feeding on special food sources. in sluice capacity will (probably) balance the neg-

Wadden Sea Ecosystem No. 13 - 2001 5. Impact of Changes 35

ative effects. Increased storminess could lead to 5.4 Socioeconomic increased loss of fish eggs and thereby affect breeding fish stocks. consequences 5.3.4 Seals 5.4.1 Safety Seals are not expected to respond to sea level rise Under the category safety the existing strategies in general. A decrease in fish stocks at higher sea to maintain present safety standards in coastal levels due to a lack of suitable habitats for juvenile defense are categorized as follows: flatfish may affect seal population size. This effect • dikes; could be (partially) compensated by the seals finding new foraging areas. At the highest sea level rise • other hard constructions (revetment, groynes, scenario also a shortage of haul-outs may affect stone walls); the populations. • sand suppletion incl. complementary biotech- An increase in storminess will have a negative nical measures in dunes, such as planting mar- effect on the grey seal (breeds early, pups vulner- ram grass and installing brushwood fences; able to spring storms), whereas no effect is ex- • salt marsh works. pected on the common seal. 5.3.5 Seagrass A comparison of the current relative expendi- ture for each of the four coastal defense catego- The seagrass area will decrease with increased ries is in Table 5.2. For all four strategies, the in- storminess because higher water turbidity leads crease in intensity is expected to be insignificant to a decrease in light influx to the bottom. No for the lowest sea level scenario (10 cm in 50 effect is expected from sea level rise itself. It should years). Further, the expected changes do not in- be noted that the seagrass area has fluctuated crease linearly with sea level rise. It is suggested strongly over the last century. that, somewhere between 25 and 50 cm of sea 5.3.6 Salt marsh vegetation level rise in the next 50 years, the costs to main- Salt marsh plants are adapted to a harsh climate. tain present safety standards with traditional The lack of shade requires resistance to extreme measures may start to rise more than proportion- temperatures and they must tolerate high salt ally. concentrations in the soil. Artificial drainage has For dikes (maintenance and strengthening) the changed the natural habitat of most salt marsh- expected increase in costs for the most realistic es. Natural processes will eventually lead to less sea level scenario (25 cm in 50 years) is expected salty environments at some places, but not to the to be in the order of 5 to 15 % for the German extent seen today. Wadden Sea. In the Dutch and the Danish Wad- The salt marsh vegetation will become more den Sea the relative increase is estimated to be “typical” with a sea level rise above the 25 cm much higher. The main reason is that at present scenario and also with increased storminess. Both dikes are only maintained in these two countries, factors lead to more frequent and longer-lasting not strengthened as in Schleswig-Holstein and inundations with salt water, favoring the special- Niedersachsen. For the high sea level scenario (50 ized, typical salt marsh plants. Moreover, the typ- cm in 50 years) the costs to maintain present dike ical morphology of the salt marsh with meander- safety in the year 2050 may rise by up to 75 % ing creeks and salt pans will be promoted, leading (Germany) and even more in The Netherlands and to increased variation in habitats within the salt Denmark. As an example, the present yearly ex- marsh.

Dikes Other hard Sand Salt marsh Table 5.2: constructions nourishment works Current national relative expenditure (%) for four The Netherlands 35 10 50 5 categories of coastal Niedersachsen 80 10 5 5 defense measures in the Schleswig-Holstein 50 10 15 25 Wadden Sea. Denmark 90 5 0 5

Wadden Sea Ecosystem No. 13 - 2001 36 5. Impact of Changes

penditures on dikes in Schleswig-Holstein of about the Dutch coastlines in the year 2050 might 24,0 million EURO may maximally increase to increase to more than 10 million m3 for the “worst- about 42,0 million EURO in the year 2050. This case” scenario (50 cm of sea level rise in 50 years, figure may still be about 15 % higher (i.e. 48.3 combined with increasing storminess). For the million EURO for Schleswig-Holstein) if stormi- most realistic sea level scenario (25 cm in 50 years) ness increases as well. Under this “worst-case” the estimated amount of sand needed would scenario the necessary costs to keep the present increase to about 8 million m3. dike safety could double! Under the strategy “salt marsh works” the tech- Under “other hard constructions” several mea- niques to stabilize (and in some places create) salt sures like revetments, groynes and stone walls are marshes in the Wadden Sea are combined (Figure combined. The crests of these constructions are 5.4). One of the basic requirements for salt marsh- situated near or only a few meters above present es to persist is a moderate sea level rise. Without sea level. With rising sea level they will increas- sea level rise a vegetation succession towards fresh ingly be exposed to tides and waves. Therefore, it water biotopes would prevail. Hence, the expect- is suggested that the costs may (relatively) in- ed increase in the intensity of salt marsh works crease more than the expenditures on dikes. As under the different sea level scenarios is rather the present expenditures on these measures are modest compared to the other strategies. One of normally much lower than on dikes, the absolute the most destabilizing factors for salt marshes is increase in costs will not be so high. However, wave attack along the outer edges (Ch. 3.4). As a under the BAU-scenario it may become necessary result, cliffs may develop and the salt marsh may to build new or to strengthen existing hard con- be eroded from its seaward side. An increase in structions, which could raise the costs significantly. storminess and, correspondingly, wave attack will One of the main measures to keep the coastline thus result in much higher efforts to protect salt in its present position is the suppletion of sand marshes. In Schleswig-Holstein the costs could on the beach or in the nearshore (Figure 5.3). rise from about 12 to 20 million EURO. For the According to present knowledge (the so-called most realistic sea level scenario on the other hand, Bruun rule) the upper nearshore and beach will the yearly costs in Schleswig-Holstein would rise increasingly erode with increasing sea level and, by about 1 million EURO. consequently, the coastline will retreat faster. Some larger harbors, especially in the estuar- Therefore, more sand is needed to maintain the ies (e.g. Hamburg, Bremerhaven), have extensive coastline. At present, about 6 million m3 of sand out-of-dike areas. The efforts to maintain these is suppleted each year along the total Dutch areas will certainly increase with rising sea level. coastline (incl. the provinces of Holland and However, considering the huge investments in Zeeland). The volume of sand needed to stabilize these areas, the working group expects that the

Figure 5.3: Schematic presentation of sand nourishment on the isle of Sylt. beach nourishment sand reservoir

wearing part storm surge reserve

GOL +5 m GOL +7 m

GOL German Ordnance Level (GOL)

30 m 30 m

Wadden Sea Ecosystem No. 13 - 2001 5. Impact of Changes 37

Legend:

Main drainage ditch Drainage ditch Ditch Old ditch Brushwood groyne Salt marsh

Sea wall about 200 m

Figure 5.4: Schematic presentation of salt marsh works in Schleswig-Holstein.

Salt marsh Accretion zone Turbulence zone

relative increase in costs will remain low. Further- nels towards the tidal gullies. However, at some more, it is assumed that an increase in sea level places pumping stations already have to pump rise is already anticipated in the planning schemes the water into the channels. With increasing sea for these areas. level, the tidal low water level will probably rise as well. As a consequence, the water stored in 5.4.2 Fresh water run-off, harbors/ the basins during flood may not be able to flow shipping, tourism, agriculture and out naturally during ebb any longer. Moreover, salinity. the time during which discharge can take place Although the working group concentrated on the will become shorter. Extra pumping stations, as effects of changes in sea level rise and storminess well as, more and larger storage basins (and even- on coastal defense, it was decided to consider tually dikes along the lower courses of some Dan- some other relevant aspects as well. Efforts to ish rivers) may become necessary. In consequence, secure fresh water run-off from the hinterland the efforts to secure fresh water run-off are esti- and the functionality of harbors and shipping mated to increase by 50 to 200% for the highest routes are often closely connected to coastal sea level scenario (see box text on Lake IJssel in defense measures. Further, as stated in the terms Chapter 6). An increase in storminess will proba- of reference of the working group, tourism and bly result in more storm rainfall and, therewith, agriculture are two significant uses in the Wadden higher peak water discharges. Further, a more in- Sea with direct interrelations with coastal defense tense silting up of the discharge channels is ex- and nature conservation. pected under an increasing storminess. The ef- To secure fresh water run-off into the North forts to secure fresh water run-off will increase Sea or, rather, to prevent the coastal lowlands from correspondingly. drowning by rainwater (e.g. during storm floods) One further problem that is closely linked to the following combination of measures is used: fresh water run-off and sea level rise is increased (1) water storage basins behind the dikes; salinity behind the dikes. Available data do not give indications about significant changes in sa- (2) gates/sluices in the dikes; linity. (3) discharge channels through the salt marshes The navigability of the main shipping routes and tidal flats towards the tidal gullies. in the Wadden Sea is mainly secured by dredg- ing. This artificial deepening of gullies has direct Normally, the sluices are opened during ebb implications for the hydrology and morphology (tidal low water) and the fresh water, stored in of the Wadden Sea. Vice versa, changes in the the basins during flood, runs off through the chan- hydrology will influence tidal gullies morphome-

Wadden Sea Ecosystem No. 13 - 2001 38 5. Impact of Changes

try and, therewith, dredging activities. It is ex- tion of the public to sea level rise and increase in pected that an increase in sea level rise will gen- storminess is expected to be rather complex or erally result in deeper channels and, consequent- even divergent. For example, an increase in storm- ly, in a (small) reduction of dredging efforts. In iness may result in an emotional negative atti- contrast, an increase in storminess may induce a tude towards the Wadden Sea as an unsafe holi- stronger sedimentation in the channels and har- day region. Another example is mud flat walking bors. The efforts to maintain shipping channels that might be negatively affected if flooding time and harbor access would increase corresponding- of the tidal flats increases. At the same time, how- ly. Which of the two effects (deepening or sedi- ever, increasing storminess may induce a new kind mentation) would prevail under the “worst case” of active tourism during winter (watching and scenario cannot be predicted with present knowl- experiencing storm surges). Agriculture may, on a edge. The situation is even more complex in the small scale, be influenced by an increase in sea estuaries. For example, salt and fresh water meet level and/or storminess. If the present fresh water and mix here which strongly influences local sed- run-off is to be secured, extra arable land needs imentation patterns. A shift in the position of this to be set aside for fresh water storage basins. Fur- mixture zone resulting from sea level rise may have ther, an increase in storminess (during summer) unknown implications for the navigability of the might result in more damages to the crops. In gen- estuaries. eral, it is expected that, for the hydrologic sce- Two important uses/interests in the coastal narios, the effects on tourism and agriculture may zone that affect coastal defense and nature pro- be neglected. Other factors like atmospheric con- tection are tourism and agriculture. Tourism has ditions (e.g. precipitation, hours of sunshine) or become the most important source of income in EU-policy will dominate the future development. many parts of the Wadden Sea region. The reac-

Flatwalking in the Wadden Sea. (Photo: H. Marencic)

Wadden Sea Ecosystem No. 13 - 2001 39

6. BEP Options

Best Environmental Practice (BEP) Options

6.1 Introduction slightly negative scoring for the criteria impacts In the previous chapter 5 an analysis was made on natural dynamics and habitats was considered of, amongst others, the consequences of increas- acceptable. ing sea level and storminess for present coastal It is stressed that the selection of BEP mea- defense practice, taking as a starting point that sures has not taken into account aspects which today’s safety level would be maintained. are relevant for their feasibility. Because feasibil- In this chapter several technical measures and ity aspects will, in general, play a dominant role practices are being evaluated with a view to their in the decision whether or not to apply the mea- possible application in future coastal defense sure, the working group has also made a scoring strategies. It concerns not only the „classical“ for the following feasibility criteria: measures covered in chapter 5, but also a large • Technical: Technical possibility to carry out the number of alternative measures, most of which measure, also considering the time it will take are not being applied yet. The assessment was for the measure to become effective; carried out by the working group with a view to having a broader array of measures and practices • Financial: Indication of costs; available for future choices, especially in the light • Legal: Agreement with current laws and rules; of increasing sea level and storminess. The measures and practices have been evalu- • Public opinion: Acceptance by the public. ated on the basis of two main criteria, namely • Spatial: Applicability on a local or wider scale. their contribution to maintain safety and their impact on the environment. These criteria are An evaluation of all individual measures, ac- called „Best Environmental Practice“ (BEP) crite- cording to running number, is given in 6.2. A brief ria. description of the measures is given in the box on The following BEP criteria were applied in the the following page. The measures have been struc- evaluation: tured according to Sandy barrier coast (6.2.1), Tidal basins (6.2.2), Salt marshes (6.2.3) and Mainland • safety: the contribution to coastal defense; (6.2.4). Brief descriptions of all measures are in • Impact on habitats; the Box. An overview of the scoring of all mea- sures is in Table 6.1. • Impact on natural dynamics. In 6.3 the main conclusions of the evaluation All measures with a positive scoring for these and the selected Best Environmental Practice op- criteria have been selected as Best Environmental tions are presented. Practice measures (BEPs). In some cases also a

Wadden Sea Ecosystem No. 13 - 2001 40 6. BEP Options

Sandy barrier coast 14. Mussel bed reinstallation: Promoting the set- 1. Artificial reefs: Reefs of hard constructions in tling of mussels in order to stimulate accumula- the foreshore in order to reduce wave impact on tion of mud including protection of existing beds the shore. or potential locations for these beds: 2. Beach drainage: Draining the beach by tubes 15. Sea-grass bed reinstallation: Creating sea- and pumps in order to stimulate sedimentation grass meadows in places with low hydrodynam- of the beach. ics in order to try to stimulate sedimentation. 3. Enhance dunes creation: The stimulation of Salt marshes sedimentation by marram grass and sand-trap- 16. Revetments: Hard constructions protecting ping fences and thus accumulation of sand trans- the salt marsh edges in order to prevent cliff ero- ported by the wind. sion. 4. Dunes relocation: The building up of new dunes 17. Creation marshes from dredged material: landward of the eroding old ones. In practice this Deposition of dredged material on intertidal ar- will mean a gradual retreat of the dune front. eas along the mainland or Wadden-sea side of 5. Natural dune dynamics: The transport of sand the barrier island. from the North Sea shore to the inner part of the 18. Outbanking of summer polders: Opening sum- barrier island where accumulation causes a grad- mer dikes in order to get a more frequent flood- ual landward shift of part of the barrier island ing of the area and higher sedimentation rates. with rising sea level. 19. Groyne fields: Areas, sheltered by groynes, 6. Overwash creation: Allowing water and sand with reduced waves and in which accumulation transport across unprotected parts of barrier is- of fine sediments is stimulated. lands through wash-over channels. As with nat- 20. Artificial drainage: Digging ditches in the salt ural dune dynamics the transport of sand from marsh in order to stimulate water run-off after the North Sea shore to the inner part of the bar- the area has been flooded and vegetation growth rier island and accumulation there causes a grad- in the lower parts of the salt marsh. ual landward shift of part of the barrier island 21. Grazing: Grazing by sheep and cattle with with rising sea level. the aim of keeping a short vegetation and re- 7. Revetment building: Protecting the dunes ducing the amount of flotsam. against erosion by hard constructions. 8. Groynes: Constructions perpendicular to the Dikes coast into the foreshore. Comparable to revet- 22. Revetments: Using hard material at the dike ment building. surface to protect the slope against damage by 9. Sand nourishment: Taking sand from outside wave impact and currents. the sand sharing system deeper water and pump- 23. Enforcement: Heightening and/or strength- ing it on the beach or on the foreshore with the ening the dikes in order to maintain safety stan- aim of stabilizing the beach. dards. 10. Spatial planning: Spatial planning aiming, in 24. Second dike line: A dike, situated behind a the long term, at creating and maintaining buff- primary sea wall, that serves to limit the area er zones between land and sea where safety is flooded after the primary sea wall breached. not guaranteed under all circumstances. 25. Relocation of first dike line: Building a new dike landward of the old one. Tidal basins 26. Spatial planning: See running number 10. 11. Dam building: Building dams between the mainland and the islands in order to stabilize tidal Mainland basins. 27. Pumping stations: Pumps for active discharge 12. Dredging reduction: Reducing the dredging of fresh water from the inland to the to the sea. of shipping lanes. 28. Sluices: Constructions allowing passive dis- 13. Gullies damming: Diversion of tidal gully by charge of fresh waters from the inland to the 1) closing off the old gully with a sand dam and sea. 2) dredging a new gully on another location in 29. Storage basins: Inland basins for storing fresh order to obviate hazardous gully meandering (e.g. water in periods when sea level is too high for gully approaching a dike foot). the passive discharging the fresh water.

Wadden Sea Ecosystem No. 13 - 2001 6. BEP Options 41

6.2 Evaluation Revetment building (7). This is an existing method of stopping retreat of the coast and guar- 6.2.1 Sandy barrier coast anteeing safety. It is technically well feasible, ac- Artificial Reefs (1). Artificial reefs may be an op- cepted by the public but very unnatural. Erosion tion to reduce wave impact on the shore. Their at the edges of the constructions make it neces- contribution to safety is estimated as medium. sary to extend the measures at those edges. Ris- Reefs form substrate and shelter for flora and fau- ing sea level will lead to an increase of finances na but they interfere with natural dynamics. The needed. construction of artificial reefs is technically un- Groynes (8). This method is comparable to re- problematic and can be done at medium costs. vetment building. They will be only locally applicable, and no sub- Sand nourishment (9). Sand nourishment is, stantial legal problems or public resistance are in general, a technically and financially feasible expected. measure for coastal defense which has only slight- Beach drainage (2). Beach drainage is expected ly negative impacts on nature. It can be applied to have a medium contribution to safety and some on a large scale. impact on both the habitat (impact on the Spatial planning (10). This is considered a interstitial fauna) and natural dynamics. It is only good political instrument for a no regret policy. It locally applicable and considered very expensive. is a useful tool by creating buffer zones where no No substantial legal problems or public resistance building or rebuilding is allowed. This can work are expected. positively both from a financial point of view, as Enhance dune creation (3). Very locally it is well as, for natural dynamics. The fear of loss of possible to create new dune areas by catching safety and the limitation of uses in buffer zones wind driven sand. More often stimulation of dune will lead to difficulties in public acceptance. growth will take place in the vicinity of existing eroding dunes. From the past there is already a 6.2.2 Tidal basins lot of technical experience. On strong eroding Dam building (11). Although technically good beaches accumulated wind driven sand will be applicable and positive for safety, this practice is eroded by waves and currents. Dune creation will considered negative for the environment, espe- interfere with natural dynamics and existing cially in a nature conservation area. From the pub- habitats will be replaced by others. The public lic resistance is expected. opinion is expected to react positively on the Dredging reduction (12). In estuaries the re- enlargement of dune areas. duction of dredging in the channels will result in Dunes relocation (4). This forms a cheap and lower high water levels in the upstream parts. technically practical way of sea defense but is only Reduction of dredging will also lead to a more applicable if human interests in the dune area or natural development of the estuarine morpholo- the area behind it are low (no buildings, no infra- gy. From legal and public opinion points of view structure etc.). this option is not regarded feasible. Natural dune dynamics (5). By allowing nat- Gullies damming (13). Very locally damming ural dynamics, sandy areas lost by erosion will be off gullies can prevent constructions or salt marsh- replaced by sandy areas somewhere else. It is only es to become unstable by gully erosion. It inter- applicable in uninhabited areas where safety is feres however with natural dynamics. From not at stake, but even then public resistance can Schleswig Holstein one example is known. be expected. On the long term natural dune dy- Mussel bed reinstallation (14). In general ac- namics contributes to the shifting of islands with tive reinstallation of biota is seen as gardening rising sea level. in a nature conservation area and therefore in- Overwash creation (6). This measure is locally terfering with natural dynamics. Because these applicable in uninhabited areas and provides, in beds stimulate sedimentation and stabilization of the long run, a positive contribution to keeping the sediment they may diminish wave attack at areas above normal high water levels. It is also the mainland shore. However during storm surges positive from a viewpoint of natural dynamics and this effect is reduced to zero because of the large may, on the long term, be beneficial because it water depth. Favorable conditions for recovery of stimulates island growth on the Wadden Sea side. mussel beds can be achieved by limiting human Public resistance is expected if areas with vege- exploitation of the area. tation are replaced by sandy areas. Sea grass bed reinstallation (15). Compara- ble to mussel bed reinstallation.

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6.2.3 Salt marshes interferes with natural dynamics. In some coun- Salt marshes can have both a nature protection tries there will be legal problems. and a coastal protection function (compare 3.4.2). Creation of marshes from dredged material The main functions in coastal defense are the re- (17). Creation of new marsh lands may be posi- duction of wave energy input at the dike and the tive from a safety point of view because an extra prevention of a scour hole and water flowing buffer is created between sea and land. Using through the dike after a dike breach. Preservation dredged mud can make this option financially at- of existing salt marshes can therefore be relevant tractive. However, it interferes with natural dy- from both perspectives. namics and may only be applicable on a local scale. Revetments (16). If there are big height dif- Outbanking of summer polders (18). Outbank- ferences between tidal area and salt marshes, the ing of summer polders can compensate for the surface area of salt marshes can efficiently be pro- loss of salt marsh areas through cliff erosion or tected by revetments. By preventing cliff erosion drowning caused by accelerating sea level rise and of the smaller salt marshes also the mainland shore is therefore interesting from the point of view of behind them is safeguarded. Preventing erosion nature protection. In the working group opinions differed strongly about the technical feasibility of this measure, ranging from very negative to Spatial planning in Schleswig-Holstein very positive. In Germany the generally small In the new master plan “Coastal Defense in summer polders have a function in sea defense. Schleswig-Holstein” of 2001, ten strategic Outbanking would lead to higher expenses for goals are formulated. Goal number three guaranteeing safety. Here the feasibility is thought states: “Relocation or abandonment of sea to be low. Public resistance may be expected if walls is only possible as an exception”. Con- summer polders are private property. In these cases sidering the protection of human lives, hous- finances are needed for acquisition. Outbanking es, economic assets and inhabited land against of summer polders in the inner parts of the storm floods as the primary goals, the reloca- estuaries may reduce storm surge levels because tion or abandonment of primary sea walls may the storage capacity is augmented. However, in only be an alternative if, order to be effective, the surface area of the - the existing safety standard is maintained, outbankment should be substantial compared to including (if present) a second dike line (see the total surface area of the inner estuary. option 24; [Definition of a second dike Groyne fields (19). The construction of groyne (Schleswig-Holstein State Water Act): A fields is an accepted, already existing measure, dike, situated behind a primary sea wall, which is technically very good applicable. At the that serves to limit the area flooded after moment brushwood is frequently used to build the primary sea wall has breached]). the groynes. In future, with a rising sea level, hard - the people directly affected (i.e., the in- material may become necessary. Up to a certain habitants of the protected lowland) agree, level of sea level rise the extra sedimentation will and prevent salt marshes from drowning. Although the - coastal defense administration is kept free measure is positive for maintaining and extend- of extra costs. ing the habitat salt marsh, it interferes with nat- ural dynamics. Secondary sea walls that do not protect Artificial drainage (20) Artificial drainage of human lives have a lower safety standard. For salt marshes may be positive for soil stabilization these sea walls, relocation or abandonment and resistance against erosion and, by this, en- may be appropriate if socio-economic argu- hances the vertical accretion of the salt marsh. It ments, especially the cost-benefit relation, is technically good applicable. It interferes with supports this. natural dynamics. For some lowlands along the Baltic Sea Grazing (21). The opinions about the effec- coast of Schleswig-Holstein the relocation of tiveness of grazing in reducing the amount of flot- sea walls is or was planned. However, the right sam and, therefore, the costs of coastal defense, of every individual on its property and on eco- differ (compare 3.4.2). Grazing with low to medi- nomic development (as defined under the Ger- um intensity causes diversification in vegetation man Basic Law), combined with the unwill- which is interesting for biodiversity but may be ingness of the affected people to move, has, regarded as undesirable from the point of view of until today, prevented such a measure interference with nature.

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6.2.4 Dikes 6.2.5 Mainland Revetments (22). Revetments are a classical Pumping stations (27). The use of pumps for the and technically feasible method of preventing discharge of fresh water is regarded positive from erosion of constructions. In areas with strong hy- both safety, technical feasibility and public opin- drodynamics revetments are necessary for the pro- ion points of view. If high capacity has to be in- tection of the dikes. Revetments interfere with stalled for incidental peak discharges this option natural dynamics. becomes more expensive. Pumping stations ac- Enforcement (23). Dike enforcement is a clas- centuate the separation between the mainland sical technical solution, accepted by the public and the sea. Fish traps should guarantee the mi- and applicable on a broad scale. It forms the guar- gration of fish between fresh and salt water. antee for safety in future if alternatives are in- Sluices (28). Sluices are positive for safety, sufficient or not accepted. The costs for main- technically good applicable and accepted by the taining safety in this way will grow with a rising public. With rising sea level the sluice capacity sea level. The separation between land and water has to be enlarged in order to maintain the same will get stronger. discharge capacity. As with pumping stations Second dike line (24). In the long run it may technical measures should guarantee the migra- become cheaper to maintain the same safety stan- tion of fish between fresh and salt water. dard by constructing a second dike line. A pre- Storage basins (29). By applying this option condition is that there is no expensive investments for pumping stations and sluices can infrastructure, either existing or planned, in the be reduced because of lower necessary peak dis- potential buffer zone between the two dike lines. charge capacities. It guarantees the storage of Such a buffer zone with a low level of human fresh water after high precipitation. Depending exploitation may be positive from the nature on the design of the basins, they can have positive protection point of view. functions for nature. Relocation of first dike line (25). With rising sea level relocation of the dike may become cheap- er compared to maintenance and enforcement of the dike. Legally this is not considered feasible. Also the public will be strongly against it. From a nature point of view it is a positive option be- cause it means an extension of the Wadden Sea area. Spatial planning (26). As in 10.

Enclosure Dike In 1932 the Enclosure dike was built, separating the “Zuiderzee” from the Wadden Sea. Since then fresh water from the newly formed Lake IJssel had to be discharged into the Wadden Sea through sluices in the Enclosure Dike. 70% of the water in Lake IJssel comes from the river Rhine. Because of bottom subsidence the expected accelerating sea level rise and growing river discharges, the dis- charge capacity for water through sluices in the Enclosure Dike has to be doubled from 5500 m3/s to 11000 m3/s. Already in the last 25 years it became more and more problematic to keep the water level of the Lake IJssel at the normal level. In 1998 the water level of Lake IJssel rose up to 1 meter above the normal level. The possibility of combining the extension of discharge capacity with a more gradual transition from fresh to salt water by creating a brackish water zone, is included in the research program investigating options for the doubling of the discharge capacity.

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Table 6.1: Relative scoring of coastal defense practices for feasibility and Best Environmental Practice (BEP) criteria.

Environment Measure Feasibility BEP Aspects Tech Finan Legal Public Spatial Impact on Habitat Impact on Safety nical cial opinion natural dynamics Sandy barrier coasts 1 Artificial reefs 4 3 3 3 1 2 2 3 2 Beach drainage 4 1 3 3 1 2 3 3 3 Dunes creation 4 4 3 4 2 3 Replace one 2 4 habitat by another 4 Dunes relocation 4 4 3 2 2 3 3 4 Relocation=retreat 5 Allowing wind 4 5 3 2 2 4 5 2 Possibly positive on a driven sand long time scale and transport strongly dependent on locality 6 Overwash creation 4 4 2 2 2 4 Loss of fresh 4 2 On a very long run water species 7 Revetment building 4 3 2 3 3 2 2 4 8 Groynes 4 3 3 3 3 3 2 3 9 Sand nourishments 4 4 4 3 4 3 2 4 Extraction from outside the sandsharing system 10 Spatial planning 4 3 3 2 4 3 4 4 (create buffer zones) Tidal basins 11 Dam building 4 2 2 2 3 2 2 4 12 Dredging reduction 4 4 1 1 1 4 4 3 In estuaries 13 Gullies damming 3 3 2 3 1 3 3 3 One positive example from SH 14 Reinstallation and 4 3 3 3 3 4 2 Reinstall 2 In the long run protection of mussel 4 Protect beds 15 Sea-grass beds 3 2 3 3 2 4 3 2 In the long run reinstallation Salt marshes 16 Revetments 4 3 2 3 2 3 2 4 17 Creation from 3 3 3 3 2 3 2 4 dredged materials 18 Outbanking of 4 2 3 2 2 5 4 1 Site specific in estuaries summer polders 19 (Brushwood) 4 3 4 4 4 3 2 3 groynes 20 Artificial drainage 4 3 3 3 4 3 2 3 21 Grazing 4 4 3 3 4 3 2 3 Reducing flotsam Dikes 22 Revetments 4 3 4 4 4 2 2 4 23 Enforcement 4 2 4 4 4 3 3 5 24 Second dike line 4 2 3 3 4 4 3 5 25 Relocation of first 4 1 1 1 2 4 4 2 dike line 26 Spatial planning 4 4 3 2 4 3 4 4 In the long run Mainland 27 Pumping stations 4 2 3 4 3 3 3 4 28 Sluices 4 2 3 4 3 3 3 4 29 Storage basins 4 3 3 3 2 3 3 4

Legend Technical: 1 (almost impossible) ...... 5 (very practical) Financial: 1 (very expensive) ...... 5 (very cheap) Legal: 1 (very problematic) ...... 5 (unproblematic) Public opinion: 1 (very negative) ...... 5 (very positive) Spatial: 1 (site specific) ...... 5 (everywhere) Impact on habitat: 1 (large scale destruction of ...... 5 (large scale creation of typical Wadden Sea habitats) typical Wadden Sea habitats) Impact on natural dynamics: 1 (large scale reduction of natural dynamics) ...... 5 (large scale increase of natural dynamics) Safety: 1 (low contribution) ...... 5 (substantial contribution)

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6.3 Conclusions of a successful application of this technique. 6.3.1 Sandy Barrier Coast Where human activities have morphological con- sequences comparable to those of sea level rise, Sand nourishment (9) is in general a good prac- the reduction of such activities will cause less tice for coastal defense with slightly negative im- changes and a postponement of the moment that pacts on nature. It can be applied on a large scale. changes in the system will become distinguish- In addition to the classical methods of coastal able from natural variability. This holds for mining defense many of the other suggested practices causing bottom subsidence and sand and shell for the sandy barrier coast may prevent erosion, extraction. stimulate accumulation of sand or enhance safety In the estuaries both sea level rise and dredg- on a local scale. This holds for artificial reefs (1), ing works cause an easier penetration of the tidal beach drainage (2), overwash creation (6) and dune wave and storm surges. A reduction of dredging creation (3) or dune relocation (4). In general, these (12) will diminish this effect leading tot a reduc- measures are more or less neutral for nature. Al- tion in costs of maintaining safety along the in- lowing natural dune dynamics (5) and overwash ner parts of the estuaries. On the other hand this creation (6) on the uninhabited parts of the is- will give problems for navigation between the lands is positive from a viewpoint of natural dy- North Sea and the harbors. This makes this option namics and may be beneficial on the long term not feasible from a legal and public point of view. because island growth at the Wadden Sea side is However, in the long term, stimulating the increase stimulated. In this way disappearing ecotypes at of harbor capacity along the more outer deep the North Sea side of the islands are recreated at water parts of the estuaries instead of the inner the Wadden Sea side. parts might be a preferred option. Spatial planning (10) is a useful tool through The measures selected as BEP for the tidal area which buffer zones are created in which no build- are reinstalling mussel beds and seagrass beds, ing or rebuilding is allowed. In these areas safety gullies damming and dredging reduction. must no longer be guaranteed. This can work out in a positive way both from a financial and a na- 6.3.3 Salt marshes ture protection point of view The fear of loss of Outbanking of summer polders (18) can compen- safety and the limitation of human activities in sate the loss of salt marsh area caused by cliff buffer zones will lead to difficulties in public ac- erosion or drowning as a result of accelerating ceptance. sea level rise and is, therefore, a good option from The measures selected as BEP for the sandy the point of view of nature protection. However, coast are artificial reefs, beach drainage, dunes in Niedersachsen, where summer polders are im- creation, relocation and allowing natural dune portant for coastal defense, outbanking will lead dynamics, overwash restoration, sand nourishment to higher expenses for guaranteeing safety. Here, and spatial planning aiming at creating buffer the feasibility is therefore considered low. The out- zones. banking of summer polders along the inner parts 6.3.2 Tidal basins of the estuaries will cause a reduction of storm surge levels because the inundation area and, The selection of BEP measures for the tidal basins therewith, the storage capacity is increased. The depends, first of all, on the political choices that surface of the outbanked area should, however, have been made for the area under consideration. be substantial compared to the total surface area One extreme is not accepting any change in the of the inner estuary. character of the tidal basins and the other ex- Applying the already existing method of groyne treme is accepting all changes as a consequence fields (19) will safeguard salt marsh areas when of changed hydrodynamics. In addition, it must sea level rise accelerates. If applied, it is clear that be realized that, on the scale of whole tidal ba- a choice has been made for safeguarding the hab- sins, preventing changes in morphology induced itat at the cost of natural dynamics. It is an al- by accelerating sea level rise is an impossible job. ready existing measure which is technically very On a local scale, however, safeguarding intertidal good applicable. At the moment brushwood is fre- areas from drowning can be done by (re)-install- quently used to build the groynes. In future, with a ing mussel beds (14) or seagrass beds (15). Local- higher sea level, hard materials may become ly erosion and damage of constructions or loss of necessary. The extra sedimentation prevents marsh salt marsh area can be prevented by damming lands from drowning, also, up to a certain level, gullies (13). Schleswig-Holstein has an example with an accelerating sea level rise. Although it may

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be positive for certain habitats, it interferes with this may become attractive from a financial point natural dynamics. of view, provided no large infrastructural invest- Artificial drainage (20) and low intensity graz- ments take place in the potential buffer zone. From ing (21) stimulate root and swath growth and, con- a nature protection point of view such a buffer sequently, the stability of the salt marsh. There zone with low human exploitation must be re- are different opinions about the effectiveness of garded as positive. grazing in reducing the amount of flotsam at the Relocation of the first dike line (25) with rising dikes and thus reducing the costs of coastal pro- sea level may be cheaper than guaranteeing safe- tection (compare 3.4.2.). From a nature protec- ty forever and everywhere. Legally this option is, tion point of view both measures cause interfer- however, not considered feasible. Also public opin- ence with natural dynamics. Grazing with low to ion will be strongly against it. From a nature per- intermediate intensity can, however, result in a spective it is positive because it would mean an more diverse vegetation which is interesting for extension of the Wadden Sea. biodiversity. Here political choices have to be made With appropriate spatial planning (26) in the about the desired kind of nature: natural dynam- zone landward of the dikes it can be guaranteed ics versus a high biodiversity. This choice does not that alternative options for guaranteeing safety necessarily have to be the same for the different will not be lost. In general this means that eco- countries. nomic developments in areas directly bordering The measures selected as BEP for the creation the Wadden Sea are limited. and maintenance of salt marshes are brushwood The measures selected as BEP for dikes are cre- groynes and outbanking of summer polders in es- ating different dike lines, dike relocation in estu- tuaries. aries and spatial planning aiming at preserving the 6.3.4 Dikes possibility to use stretches of land along the coast for future coastal defense. Maintenance and enforcement of existing dikes (23) and revetments (22) is the classical, techni- 6.3.5 Mainland cally feasible starting point for guaranteeing safe- An alternative for creating expensive extra pump- ty. If alternatives are insufficient or not accepted, ing stations (27) or higher sluice capacity (28) for the continuation of this kind of protection seems the discharge of increasing amounts of fresh wa- logic. The separation of land and water will, how- ter, is creating storage basins (29) on land. This is ever, become stronger. The question is whether, positive from a safety, technical feasibility and on the long term, this will still be the cheapest public opinion point of view. Dependent on the method. One possibility is, for instance, to create design of the basins they can also have functions a second dike line (24) parallel to the first one for nature. This measure must therefore be regard- with a buffer zone in between. In the long run ed as BEP.

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7. Conclusions and Recommendations

7.1 Introduction will not easily be distinguishable from natural vari- The CPSL has investigated possible impacts of ability. three sea level rise scenarios: 2. The Wadden Sea system has a high resil- ience to changes and will, up to intermediate - Scenario 1 reflects a continuation of current increases in sea level (25 cm/50 years), which is sea level rise of about 10 cm/50 years; the most realistic scenario, be able to compensate - Scenario 2, the intermediate and most realis- the increased levels. Within this most realistic tic scenario, assumes a sea level rise of 25 cm/ scenario costs for coastal defense will be higher 50 years; than today. Also changes in the ecosystem are - Scenario 3, the worst case scenario assumes a expected but these will not be substantial. sea level rise of 50 cm/50 years. 3. When sea level rises beyond intermediate levels and storminess increases, there will proba- For all scenarios also the additional effects of bly be a point between the intermediate and the an increase in storminess have been evaluated. worst-case scenarios at which the capacity of the The analysis was done under the assumption system to balance the changes will be exhausted of a continuation of current coastal defense prac- (breakpoint) and after which significant changes tices (Business As Usual, BAU), taking as the main in the system can be expected. These will be starting point that current safety standards are changes in the morphology, which will influence maintained. The main conclusions with regard to biological parameters. The most notable change the anticipated impacts on several physical, bio- will be a reduction in the size of the intertidal logical and socioeconomic parameters are given area. Consequently the Wadden Sea tidal basins in 7.2. In general, the intensity of impacts on the may start to evolve into the direction of tidal la- elaborated physical, biological and socioeconom- goons. ic parameters is expected to show a strong re- The reduction of intertidal area will cause a gional and temporal variability. reduction in population sizes of some bird spe- As a second step the CPSL has investigated a cies. Also the costs for coastal defense will in- large number of alternative measures which may crease substantially after the breakpoint has been alleviate and reduce the impact of enhanced sea passed. A more detailed description of the changes level rise and storminess and which also take into is given in Sections 7.2.2 to 7.2.4. account the environmental impact. Those options 4. In the long term, the application of current that were regarded as both positive from a coast- and future coastal defense measures may allevi- al defense point of view and acceptable or even ate impacts of sea level rise and storminess but positive from a nature protection perspective (Best will not be able to prevent such impacts, certainly Environmental Practice [BEP] measures), either on not under the worst case scenario. Policies will a local or on a larger scale, have been listed in therefore have to adapt to the anticipated changes 7.2.5 below. by starting, as soon as possible, to develop long It should be stressed that all measures, both term interdisciplinary policies for coastal defense, BAU and BEP, needed to counteract the negative nature protection and economic development in effects of sea level rise and increase in stormi- the coastal area. ness, are actually combating symptoms and not 5. There is a lack of qualified data to assess the causes. possible effects of sea level rise and increase in It should finally be underlined that the assess- storminess. ment of the CPSL is based upon best available knowledge and best expert judgement and that 7.2.2 The Tidal Area little hard facts are available. Up till an intermediate sea level rise (25 cm/50 years) it is likely that no significant changes will 7.2 Conclusions occur in the Tidal Area, at least not such which will be clearly distinguishable from natural vari- 7.2.1 General conclusions ability. Beyond the breakpoint, which may sub- 1. The Wadden Sea system shows a high natural stantially differ between individual tidal basins, variability. Consequently changes caused by ac- significant changes can be expected. The main celerated sea level rise and increased storminess changes will be:

Wadden Sea Ecosystem No. 13 - 2001 48 7. Conclusions / Recommendations

• A reduction of the intertidal area (because of worst-case scenarios (see 7.2.1) the efforts to keep higher sea level); today’s safety level will increase in a more than linear way and, under the worst case scenario, ef- • An Increase of flooding time (because of larger forts may double. More in particular it is expected water depths); that, under the worst-case scenario, • A deepening of the channels (because of higher • it will be necessary to strengthen dikes and tidal currents); other hard constructions (because of increase • An increase of salt marsh edge erosion (be- in water level and wave energy); cause of higher wave impact); • an increase in sand suppletion will be neces- • A decrease in accretion of sediment (because sary to combat barrier retreat; sea level rise will outbalance sedimentation • a strong increase in efforts to maintain salt capability). marshes is needed because of the higher wave These physical changes will have the following energy; impacts on biological parameters: • dredging efforts might become less because • A reduction of benthic biomass (because of of higher water levels, but this reduction may increase in dynamics); (partly) be nullified by increased efforts due • A decrease of intertidal mussel beds (because to increased sedimentation as a result of in- of increasing storminess); creasing wave energy and a higher sediment- transport capacity; • A reduction in population size of bird species (breeding birds mainly because of a reduction • increased efforts are needed to discharge fresh of breeding area; migratory birds mainly be- water (pumping, sluices, storage basins), be- cause of a reduction of feeding time); cause, due to higher water levels in the Wad- den Sea, there will be less possibilities for sluic- • A reduction of the fish nursery function (re- ing out fresh water. The situation may be ag- duction or disappearance of suitable habitats); gravated by more an more irregular precipita- • A reduction of the seal population size (unfa- tion vorable haul-out conditions due to storms); On the basis of available information no sig- • A decrease in seagrass coverage (decrease of nificant impact on salinity in areas behind the dike intertidal area, increase of turbulence); is expected. The CPSL furthermore anticipates that chang- • An increase in the diversity of typical salt es in tourism and agriculture will be influenced marsh flora (mainly in the higher salt marshes much more by other factors, such as EU policies because of a higher inundation frequency and and development of income. inundation time). 7.2.5 Best Environmental Practice 7.2.3 The barrier islands On the basis of the criteria “Impact on natural For the barrier islands the changes will have a dynamics”, “Impact on habitat” and “Contribution more linear character because this system reacts to coastal defense” a number of practices was se- more directly to the changes. lected. These so-called “Best Environmental Prac- The main impacts of increasing sea level rise tice” measures are listed below in alphabetical and increasing storminess will be: order and are described in more detail in Chapter • An increase of barrier retreat (or a reduction 6. of accretion); It is stressed that there may be considerable legal, financial and/or public perception drawbacks • For bird species breeding on beaches and in to some of these practices. These aspects will have primary dunes decreasing population sizes are to play an important role in the assessment of expected, mainly because of increasing storm- the feasibility of the measures as proposed in Rec- iness. ommendation 2. 7.2.4 Socioeconomic impacts Generally, it must be concluded that, in the long An increase in sea level rise and storminess will term, the application of these measures may alle- have considerable impacts on coastal defense. viate impacts of sea level rise and storminess, but Because of the breakpoint between the middle and will not be able to prevent such impacts, certainly not under the worst case scenario.

Wadden Sea Ecosystem No. 13 - 2001 7. Conclusions / Recommendations 49

Sandy barrier islands harmonization of coastal protection and nature Artificial reefs conservation interests. A suitable way is the im- Beach drainage plementation of regional management plans de- Dike relocation veloped in participation with the various inter- Dunes relocation. ested parties. In such management plans the ques- Overwash. tion should be addressed whether to introduce Spatial planning, aiming at creating buffer more flexibility in the coastal zone in order to re- zones where no building is allowed. duce the growing costs for coastal defense. The Wider application of sand nourishments. question should be answered which functions of Natural dune dynamics. the coast need to be safeguarded at what costs. Another question is where dynamic processes can Tidal basins be reintroduced without losing safety. Brushwood groynes Dredging reduction 2. Best Environmental Practice Gullies damming In addition, or as an alternative to regular coastal Reinstalling mussel beds defense measures, it is recommended to seriously investigate the feasibility of the Best Environmen- Salt marshes tal Practice options listed in 7.2.5, within a long- Outbanking of summer polders in estuaries term perspective and taking account of the dif- Dikes ferent sea level rise scenarios, to combat negative Building/strengthening of 2nd dike line effects of enhanced sea level rise and storminess. Dike relocation in estuaries 3. Public perception Mainland It is recommended to develop a communication Creation of fresh water storage basins strategy with the aim of starting a discussion with Spatial planning, aiming at creating buffer the general public about possible future impacts zones where no building is allowed. of increased sea level rise and the introduction of measures. 7.3 Recommendations 4. Methodology and research Because all partners in the CPSL apply different 1. Policies methodologies for assessing possible impacts of Under the currently most realistic scenario (25 cm enhanced sea level rise and storminess, it is nec- in 50 years) it is expected that the system will be essary to start a process of improving the level of able to adapt. There will be increasing costs for the qualitative assessment. It is in this respect coastal defense as well as effects on the ecosys- recommended to start a research project in which tem, but the latter will not be substantial. a detailed sediment budget study is carried out, However, there is also a chance that the worst- encompassing all natural and man induced inputs case scenario will become reality. Under the worst- and outputs of sediment and other material (sand, case scenario substantial physical, biological and mud, shells) and factors affecting transport pro- socioeconomic impacts are expected and it is, cesses. It is furthermore recommended to start a therefore, recommended to start developing or to study into the links between geomorphological further develop, as soon as possible, long-term and biological changes. interdisciplinary policies for coastal defense , na- ture protection and economic development in the 5. Monitoring coastal area, in order to anticipate on impacts It is recommended to evaluate the parameters of caused by increased sea level and storminess. Such Trilateral Monitoring and Assessment Program policies may, amongst others, include spatial plan- (TMAP) for their suitability to assess impacts of ning in the coastal zone aiming at the creation of climate change, on the basis of the outcome of buffer zones, the initiation of coastal defense targeted research mentioned under “4”. measures which will start to become effective in 6. Other BEP options the long-term and reducing or phasing out activ- It is recommended to continue to survey the lit- ities which enhance the effects of sea level rise. erature for possible additional BEP options. Obtaining a long term reliability for coastal protection planning into action requires a further

Wadden Sea Ecosystem No. 13 - 2001 50

Wadden Sea Ecosystem No. 13 - 2001 51

Annex 1: CPSL Terms of Reference

Responsibility 2.2 Changes in storminess and tidal water levels; The Working Group acts under the responsibility 2.3 The relevance of the volume of the tidal basin of the Trilateral Working Group (TWG) for sedimentation processes; 2.4 The relevance of changes of inundation area Composition (for example through outbankment of sum- The Group will consist of representatives of the mer polders) for sedimentation and/or of wave responsible administrations (coastal protection energy, as well as other factors (i.e. tourism, and nature protection) and/or members of the sci- agriculture, nature protection, biodiversity); entific community, to be nominated by the coun- tries. There is a maximum of two members per 2.5 Possible effects of fixing of (parts of) the is- country/federal state, not including the Chairper- lands under different sea level rise scenarios; son. 2.6 Changes in sediment composition in relation The secretarial work will be carried out by the to changes of inundation area (amongst oth- Common Wadden Sea secretariat. ers as a result of the past straightening of the Tasks coastline and changes in wave energy); The tasks of the Working Group can be divided 2.7 Relevance of biogenic structures (mussel beds, into three parts. seagrass beds, sabellaria reefs, shells) for sed- iment stability, reduction of current velocities 1. Definitions and administrative and wave energy; structures 2.8 Relevance a reduction of wave energy through Before starting the work on the issues listed un- salt marshes and summer polders for the pro- der ‘2’, a common understanding of technical tection of sea walls; terms must be developed. Taking into consideration the national differ- 2.9 Best environmental practices for coastal pro- ences in coastal protection, it will also be neces- tection under different hydrological scenari- sary to produce an overview of current national os; policies and administrative structures relevant for The results will be submitted to the Trilateral coastal protection. Working Group (TWG) by the end of 1999. 2. Development of a common knowledge basis 3. Development of proposals for In the past ten years, our knowledge of funda- common coastal protection strategies mental geomorphological processes has increased Pending the decisions of the TWG the Working considerably. The Working Group will, as a first Group will, as a second step, draft proposals for step, collect relevant information and work to- future integrated policies regarding the above wards a common understanding of facts concern- mentioned issues, on the basis of the commonly ing, in particular: agreed facts Specific attention should be given 2.1 The overall sediment budget of the Wadden to safety and nature protection aspects. Howev- Sea ecosystem and its subsystems (barrier is- er, other interests in the coastal zone that affect lands, salt marshes, tidal inlets, estuaries, tid- coastal and nature protection (e.g. tourism, agri- al gullies, tidal flats); culture) should be considered in an adequate way.

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Annex 2: CPSL Members

Mr. Frank Steyaert (Chairman) Mr. Aksel Voigt (as of Dec. 2000) Rijkswaterstaat Directie Noord-Nederland Sønderjyllands Amt Postbus 2301 Skelbaekvej 2 NL - 8901 JH Leeuwarden DK 6200 Aabenraa Phone +31 (0)58 2344 404 Phone +45 74 33 55 58 Fax +31 (0)58 2344 332 Fax +45 74 33 51 52 [email protected] [email protected] Mr. Albert Oost (until Feb. 2001) Ms Dagmar Fischer (until Dec. 2000) RIKZ Bundesministerium für Ernährung, Landwirtschaft Postbus 207 und Forsten (BMELF) NL – 9750 AE Haren Referat 524 Phone +31(0)50 5331331 Postfach 14 02 70 Fax +31 (0)505 340 772 D – 53107 Bonn [email protected] Phone: +49 (0)228 529 3568 Fax: +49 (0)228 529 4262 / 3477 Mr. Jaap de Vlas (until April 1999) [email protected] Min. Landbouw Natuurbeheer en Visserij Direction Noord Mr. Jacobus Hofstede Postbus 30032 Ministerium für ländliche Räume, Landesplanung Land- NL – 9700 RM Groningen wirtschaft und Tourismus des Landes Schleswig-Holstein Phone +31 (0)505 99 23 27 Postfach 7129 Fax +31 (0)505 99 23 99 D 24171 Kiel [email protected] Phone +49 (0)431 988 4984 Fax +49 (0)431 988 5172 Mr. Wim Wiersinga (as of Feb. 2001) [email protected] IKC Postbus 30 Mr. Hubert Farke NL 6700 AA Wageningen Nationalparkverwaltung Niedersächsisches Wattenmeer Phone +31(0) 3174 74943 Virchowstr. 1 Fax +31(0) 3174 27561 D 26382 Wilhelmshaven [email protected] Phone +49 (0)4421 911 281 Fax +49 (0)4421 911 280 Ms Anne Rebsdorf (until August 2000) [email protected] Kystinspektoratet Danish Coastal Authority Mr. Frank Thorenz (as of Dec. 1999) Postbox 100 Nds. Landesbetrieb für Wasserwirtschaft u. Küstenschutz, DK 7620 Lemvig Betriebstelle Norden . Phone +45 99 63 63 63 Postfach 102 Fax +45 99 63 63 99 D 26491 Norden [email protected] Phone +49 (0)4931-947 152 Fax +49 (0)4931 –947125 Mr. Jørgen Nicolaisen (until Dec. 2000) [email protected] Sønderjyllands Amt Jomfrustien 2 Mr. Hans Kunz (until Dec.1999) DK 6270 Tønder Niedersächsisches Landesamt für Ökologie Phone +45 74 33 50 94 Forschungsstelle Küste (NLÖ-FSK) Fax +45 74 72 05 66 An der Mühle 5 [email protected] D 26548 Norderney Phone +49 (0)4932 916 101 Mr. Thorsten Piontkowitz (as of May 2000) Fax +49 (0)4932 1394 Kystdirektoratet [email protected] Danish Coastal Authority Højbovej 1 Mr. Folkert de Jong (Secretary) DK 7620 Lemvig Common Wadden Sea Secretariat Phone +45 99 63 63 63 Virchowstr.1 Fax +45 99 63 63 99 D 26382 Wilhelmshaven [email protected] Phone +49(0)4421 910813 www.kyst.dk Fax +49(0)4421 910830 [email protected] http://cwss.www.de

Wadden Sea Ecosystem No. 13 - 2001 53

Annex 3: Technical Terms

Accretion Ecosystem The accumulation of mineral material in a partic- A functioning, interacting system composed of one ular locality or environment, e.g. tidal muds in a or more living organisms and their effective envi- shallow coastal sea. ronment, in a biological, chemical and physical sense. It is applicable at any scale (Fosberg 1963) Amphidromic point Natural functional unit of organism, as well as, The area around which the tidal wave is turning natural and artificial abiotic compartments which and therefore without any tidal difference itself. are interconnected concerning the exchange of Barrier island (Barrier) energy, substances and information. (Ref. Glossa- An elongated sand or shingle bank, either with or ry Stade Declaration) without dunes, which lies parallel to the coastline Embankment and is not submerged by the tide. The activity by which a former flood-prone area Best Environmental Practice (BEP) becomes protection against flooding. The application of the most appropriate combi- Erosion nation of measures, eliminating or minimizing en- The processes of wearing away the land surface vironmental impact. by the mechanical action of the debris which is Biogenic structure being transported by the various agents of ero- A structure that is created by living organisms, sion. either animal or plant. Eulittoral (eulitoral) Bottom subsidence (Subsidence) The zone between high and low spring tide marks The setting of the bottom by Eustatic sea level change 1. gravitational forces following accumulation of Change in sea level not considering changes in material, bottom level (see also sea level rise). 2. the extraction of mineral deposits, e.g. salt or coal subsidence, Flood defense 3. large-scale structural readjustment of the The protection of lowlands against flooding. Earth’s surface, as in basin down warping or rift Geostrophic wind valley formation. The wind blowing parallel to isobars and repre- Coastal protection senting the first-order approximation of the real The protection of coasts against loss of land by wind. It is a measure for the driving force of the marine erosive forces (tidal and wind waves). air pressure gradient on the real wind. Other fac- (see also Coastal Defense and Flood Defense) tors, e.g. friction an centrifugal forces, are neglect- ed. Coastal defense The protection of coastal lowlands against flood- Greenhouse effect ing by the sea, to a certain limit. The ability of the atmosphere to allow shortwave radiation to reach the Earth’s surface whereas Coastline outgoing long-wave radiation is absorbed and re- The line forming the boundary between the land radiated by water vapor, droplets, carbon dioxide and the water. and other radiative gases. Damming Intertidal flats (tidal flats) The building sea walls for the protection of coastal That part of a tidal coastal landscape that is situ- lowlands against flooding by storm surges. ated between the mean low and mean high tidal Design water level water level. Consequently, the area is submerged Storm water level with a certain frequency of oc- at high tide and emerged at low tide. currence (return interval, e.g. 100 year) that is tak- Inundation area en as a design criterion to establish/calculate the The area exposed to flooding without protective necessary dike height. measures (damming). Dredging works Littoral sand transport Works carried out in order to maintain the func- Nearshore parallel transport of sand by waves. tion of shipping channels or to maintain a certain water flow in a channel or belt.

Wadden Sea Ecosystem No. 13 - 2001 54 Annex 3: Technical Terms

Low water level (low tidal water level) Secular sea level rise The water level reached at low tide. See ”Sea level Rise” Mean Sea Level Sediment budget The average level of the surface of the sea, deter- The amount of material that is redistributed in a mined by averaging recorded tidal levels over a specific area over a certain time interval. The gross one-year interval. amount is the turnover volume, the net amount the sand balance. Mean Tidal Range (MTR) The difference between the level of the surface of Sediment importing system the sea at high tide and low tide, determined by Area with a net accumulation of sediments. averaging all high and low tidal water levels re- Storm flood corded over a one-year interval. High water caused by a storm. Mud flat Storm surge Tidal flat composed mainly of muds. The elevation of the sea water level resulting from Natural dynamics of the coastal zone meteorological forcing (wind) on the water sur- The principle by which all natural (biological, face in shallow coastal seas chemical and physical) processes in the coastal Storminess zone be allowed, i.e. no human interference. The force, duration and frequency of storms, char- Nourishment acterized by significant state variables. The activity of artificially replenishing the sandy Sublitoral = (Sublittoral) coast That part of a tidal coastal ecosystem that is per- Outer delta (ebb-tidal delta) manently water covered (subtidal area). An accumulative structure formed by the deposi- Summer polder tion of material transported into the area by ebb- Former salt marsh which is now protected by a tidal currents. As soon as the ebb currents leave low dike (summer dike) against flooding by high the tidal inlet the bulk of the load is deposited as tides during summer. a result of decreasing current velocities. Tidal basin Salt marshes That part of a coastal sea that is drained by one A coastal ecosystem, composed of marine sedi- unitary channel network. Its perimeter is marked ments, occupied by salt tolerant and/or salt resis- by tidal drainage divides, terrestrial environments tant vegetation, that is regularly inundated by salt and/or artificial constructions like sea walls. water. Tidal channel Sand balance A channel in a tidal system that functions to trans- The net amount of material carried into or out of port tidal water masses. a specific area over a certain time interval. It is often established by the comparison of high res- Tidal current olution topographic maps for different epochs. The movement of sea water in response to the rise and fall of the tide. Sand flat Tidal flat composed mainly of sand. Tidal flats See intertidal flats Sand sharing system Coastal systems and tidal basins within which sand Tidal inlet is relocated and between which sand is exchanged A large tidal channel that is often situated be- without a net lost of sand. tween two barrier islands through which the tidal waters may enter or leave a tidal basin during Sea level rise (change) flood- or ebb-tide. The long-term (secular) rise (change) of mean sea level. Different processes, e.g. eustatic, isostatic, Tidal prism etc. may be responsible for this change. The amount of water between high water and low water, excluding any freshwater flow. Sea level rise scenario A scenario for future sea level rise. It is a hypo- Tidal range thetical series of possible future sea levels that is The difference between consecutive low tide and constructed to evaluate causal correlations. high tide.

Wadden Sea Ecosystem No. 13 - 2001 Annex 3: Technical Terms 55

Tidal system Wave climate (Behind barrier islands) System of (a tidal inlet) The average wave conditions at a specific place tidal channels and tidal flats between two tidal over a lengthy period of time (> 30 years), includ- drainage divides, ranging from the dike to approx- ing absolute extremes, means and frequencies of imately the 20 m depth line. given departures from these means. Tidal volume Wind climate The sum of the amounts of water that a flood- The average wind conditions at a specific place tide carries into, and an ebb-tide carries out of, a over a lengthy period of time (> 30 years), includ- tidal basin. ing absolute extremes, means and frequencies of Tidal wave given departures from these means. The oscillation, generated by the gravitational at- Wind wave tractions on the earth’s surface of the moon and A deformation of a water surface in the form of the sun and the magnitude, in proportion to the an oscillatory movement which manifests itself planetary pull, the local water depth and the dis- by an alternating fall and rise of that surface. The tance from the amphidromic point (see also wind oscillation is generated by the wind pressure on wave) the water surface and the wave magnitude is in Tide proportion to the speed of the wind, its duration The regular rise and fall of water level in the and the length of fetch. world’s oceans, resulting from the gravitational attraction that is exerted upon the earth by the sun and the moon. Water shed (tidal divide) Hypothetical line connecting the highest points of the upper tidal flats, separating neighboring tidal basins. It is the first to fall dry on the ebbing tide.

Wadden Sea Ecosystem No. 13 - 2001 56

Annex 4: Relevant Running Projects

1. Evaluation study of the coastal lowlands 5. PRODEICH - probabilistic design of sea in Schleswig-Holstein walls Area: coastal lowlands of Schleswig-Holstein Area: German North and Baltic Sea coasts. Project period: 1997 - 2000 Project period: 01.02.2000 - 01.01.2002. Contact: Prof. Dr. H. Sterr, FTZ Westküste der CAU Contact: Prof. Dr.-INg. Hocine Oumeraci, Leicht- Kiel, Hafentörn, D- 25761 Büsum, Tel.: +49 431 weiß-Inst. TU Braunschweig, Beethovenstr. 51a, 8802944, e-mail: [email protected] D-38106 Braunschweig, Germany, Tel.: +49 531- Contents: this projects aims at establishing the 391 3930, e-mail: [email protected]. damage potential for the coastal lowlands using Contents: this project aims at establishing prob- a GIS and a digital terrain mode abilistic design criteria for sea walls as well as 2. MERK - micro scale evaluation of the risks in increasing the knowledge about the probability coastal lowlands. of failure of coastal flood defence systems under Area: four coastal flood units in Schleswig-Hol- given hydrographic scenarios. stein. 6. NOURTEC (Innovative nourishment Project period: 01.01.2000 - 31.12.2002. techniques evaluation) Contact: Prof. Dr. H. Sterr (see address project 1). Type of project: co-sponsored by EU-MAST II Contents: this project focusses on establishing a (MAS2-CT93-0049) common method to evaluate the (future) risk of Co-ordinator and partners: RWS-RIKZ (National coastal flooding on a micro scale using GIS and Institute for Coastal and Marine Management, DTM. The Netherlands), CRS (Coastal Research Station, 3. Programs to optimize the long-term Germany), DCA (Danish Coastal Authority, Den- stability of the Wadden Sea mark) and UU (University of Utrecht, The Neth- Area: Wadden Sea of Schleswig-Holstein erlands) Project period: 1998 - 2001 Area: Terschelling (The Netherlands), Torsminde Contact: P. Witez, Landesamt für Natur und Um- (Danmark) and Nordeney (Germany) welt des Landes Schleswig-Holstein, Hamburger Project period: 1993-1996 Chaussee 25, D-24220 Flintbek, Tel.: +49 4347 Contact: dr. R. Spanhoff, RWS RIKZ, Kortenaer- 704461, e-mail: [email protected] kade 1, P.O. Box 20907, 2500 EX, The Hague, Contents: This projects aims at the prediction of Tel: +31 70 114230, morphological changes in the Wadden Sea for dif- e-mail: [email protected]. ferent hydrographic scenarios using digital ter- Contents: Description and explanation of three rain models. Further, methods to counteract pos- experimental nourishments (complete or partly sible negative developments are described and on the shoreface). Conclusions on the feasibility evaluated. and effectiveness of shoreface nourishments. Design recommendations for shoreface nourish- 4. Regeneration of sediment source areas for ments in different coastal environments. The de- beach nourishments velopment of a database for future model tests. Area: German North Sea Project period: 1999 - 2002 7. RIACON (Risk analysis of coastal nourish- Contact: Dr. Figge, Bundesamt für Seeschiffahrt ment techniques) und Hydrographie, Postfach 301220, D-20305 Type of project: co-sponsored by EU-MAST II Hamburg, Tel.: +49 40 31903240. (MAS2-CT94-0084 Contents: This project deals with the establish- Co-ordinator: RWS-RIKZ (National Institute for ment and the analysis of the long-term develop- Coastal and Marine Management, The Nether- ment (hydro-, morpho- and ecological) of sedi- lands) ment source areas for beach nourishments. Area: Terschelling (The Netherlands), Torsminde (Danmark), De Haan (Belgium), Costa Daurada

Wadden Sea Ecosystem No. 13 - 2001 Annex 4: Relevant Running Projects 57

(Spain) and Nordeney (Germany). Ongoing research Project period: 1994-1997 Sediment transport and morphological develop- Contact: dr. K. Essink, RWS RIKZ, Kerklaan 30, P.O. ment in a barrier/lagoon system: This project fo- Box 207, 9750 AE, Haren, tel: +31 50 533 1373, cuses on the Skalling barrier spit with the follow- e-mail: [email protected]. ing key issues: Contents: Evaluation of the risk of shoreface nour- Offshore: The role of flocculation in possible fluff ishments and offshore subaqueous sand extrac- layer formation during calm weather situations tion for the marine zoobenthic community of the in the North Sea. Resuspension during storm of foreshore. fluffy material and its import to the Wadden Sea. 8. NWO-ALW Outer Delta Dynamics project Coastal zone: Understanding the 3-D nature of the bar system, morphological evolution in both Type of project: NWO (National Science Founda- cross-shore and longshore directions. Sediment tion) sponsored acandemic research program. transport in the surf zone. Exchange of sediment Participants: Utrecht University, Delft University, between the surf zone and offshore. Eolian trans- Netherland Insitute for Sea Research (NIOZ), and port processes and resulting morphology on beach support from RWS-RIKZ (National Institute for face and in dunes. Hydrodynamics and sediment Coastal and Marine Management, The Nether- budget of wash-over fans. lands) and WL|Delft Hydraulics. Inlets: Examining when and how episodic trans- Area: Tidal inlets in the Wadden Sea. port takes place. Import/export balancing of sus- Project period: 2000-2004 pended matter. Bedform migration with time. Contact: dr. H.E. de Swart, Institute for Marine Tidal flats and salt marsh areas: Tidal flat dynam- and Atmospheric Research (IMAU), Utrecht Uni- ics and their role as temporal storages for fine versity, grained material. Resuspension effects of biolog- P.O. Box 80005 Utrecht, The Netherlands, e-mail: ical activity. Salt marsh development with time [email protected] and its connection to sea-level variations. Drain- Contents: The aim of this programme is to gain age pattern evolution and effects on salt marsh more fundamental knowledge about the dynam- growth. Retention of fine grained material, nutri- ics of the outer deltas by addressing the following ents and heavy minerals on salt marshes. questions: Barrier evolution: Surface sediments and their 1. what is the role of outer deltas in the sand bal- stratigraphic relations. Morphological evolution ance of the coastal zone; from cores and shallow seismic. 2. what is the morphodynamic relationship be- tween the outer delta and the inner basin; INTERMUD. EU MAST III project 3. how to model and understand the cyclic chan- The Morphological Development of Intertidal nel-shoal behaviour and related sediment bypass- Mudflats ing over the outer delta. The objectives of the project are: To investigate the characteristics of intertidal mudflats in NW 9. Delft Cluster Research program: theme Europe in order to establish a classification which Coasts and Rivers. reflects the morphological effect of variations in Type of project:: NWO (National Science Founda- such parameters as: tidal range and phase, wave tion) sponsored acandemic research program. climate, sediment physical and biological proper- Participants: Delft University, WL|Delft Hydraulics, ties, biological communication structure etc. This TNO-NITG, Alkyon and RWS-RIKZ (National Insti- will propose a series of conceptual models of mud- tute for Coastal and Marine Management, The flat development. To carry out experiments on a Netherlands). number of type-mudflats, using harmonized meth- Area: Tidal basins in the Netherlands ods, to quantify the processor, and their interac- Project period: 2000- tions, their ranges and time scales of variation. To Contact: Delft Cluster, Postbus 69, 2600 AB Delft, formalize the relationships in statistical descrip- Tel: +31 15-2693793, tions, and test the validity of the concepts by com- Contents: To identify and further develop data, puter modeling, using the experimental field data. knowledge and models regarding the medium and To provide a basis of understanding, which can be long-term morphological evolution of coast-ba- used in management of mudflats, in order to main- sin interaction based on the coastal cascade con- tain ecological health, particularly under chang- cept. The Delft Cluster Theme 3-Project Coasts ing climatic, sea level, and anthropogenic pres- focuses on the morphological interaction between sures. the coast and tidal/estuarine basins.

Wadden Sea Ecosystem No. 13 - 2001 58 Annex 4: Relevant Running Projects

DECO (Danish Research Councils Danish Environ- ton pigment and determination of their concen- mental Monitoring of Coastal Waters) The objec- tration. Determination of suspended sediment tives of the project are: The project encompasses concentrations and size distribution Sediment re- two major objectives. The first being the develop- suspension and transport in coastal waters Clas- ment and validation of the spectral fingerprint sification of different bottom types in shallow technique, and the set-up of a spectral library of waters including vegetation and mussel beds. key parameters for the Danish coastal waters. This Within RWS RIKZ (National Institute for Coastal goal will involve the integration of sea truth mea- and Marine Management, The Netherlands) several surements, remote observations, statistical anal- research projects address aspects of the subjects ysis, and modeling, leading to a unique data li- mentioned in the CPSL Final Report. The subjects brary pertaining specifically to the Danish marine include: subsidence due to ongoing and possible environment. The second major objective of this future mining projects, the future sediment bud- program is the application of the spectral finger- get of the Wadden Sea, including the effects of print information to specific problems and pro- sea-level rise, improved nourishment techniques, cesses relevant to research and monitoring ques- and more. tions. The specific questions to be addressed in- clude: Distinction between different phytoplank-

Wadden Sea Ecosystem No. 13 - 2001 59

Annex 5: Literature

Asmus, R, Gätje, C. & de Jonge, V.N., 1994. Mikro- Dijkema, K.S., 1992. Sea level rise and manage- phytobenthos - empfindliche Oberflächenhaut des ment of salt marshes. WSNL, 92/2: 7-10. Wattbodens. In: Warnsignale aus dem Watten- Dijkema, K.S., Bossinade, J.H., Bouwsema, P. & de meer. Lozan, J.IL., Rachor, E., Reise, K., v. Western- Glopper, R.J., 1990. Salt marshes in the Nether- hagen, H. & Lenz, W. (Hrsg.). Blackwell, Berlin: lands Wadden Sea: rising high-tide levels and ac- S.75-81 cretion enhancement. In: Beukema, J.J., Wolff, W.J. Asmus, R. & Asmus, H., 1998. Bedeutung der Or- & Brouns, J.J.W.M. (Eds.). Expected Effects of Cli- ganismengemeinschaften für den bentho-pelagis- matic Change on Marine Coastal Ecosystems. Klu- chen Stoffaustausch im Sylt-Romo Wattenmeer. wer, Dordrecht: 173 – 188. In: Gätje, C. & Reise, K. (Hrsg.) Ökosystem Wat- Doing, H., 1983. Geomorphology and Soil of Dunes. tenmeer - Austausch-, Transport- und Stoffum- In: Wolff, W.J. (Ed.). Ecology of the Wadden Sea,Bd. wandlungsprozesse. Springer-Verlag, Berlin, 3. Balkema, Rotterdam: 9/12-9/26. Heidelberg: S. 257-302. Austen, L. & Witte, G., 1997. Comparison of the Ehlers, J., 1988. The morphodynamics of the Wad- erodibility of oxic and anoxic sediments in the East den Sea. Balkema, Rotterdam: 397 p. Frisian Wadden Sea. Berichte - Forschungszen- Ellenberg, H., 1982. Vegetation Mitteleuropas mit trum Terramare 2: S 75-76. den Alpen in ökologischer Sicht. Eugen Ulmer, Austen, L., 1997. Temporal and spatial variations Stuttgart. of biodeposits - a preliminary investigation of the Erchinger, H.F., Coldewey, H.-G., Frank, U., Man- role of faecal pellets in the Sylt-Romo tidal area. zenrieder, H., Meyer, C., Schulze, M. & Steinke W., Helgoländer Meeresunters. 51: S 281-294. 1994. Verbundbericht zum KFKI-Forschungsvorha- Bayerl, K., Austen, L., Köster, R., Pejrup, M. & Wit- ben “Erosionsfestigkeit von Hellern”. KFKI, Kiel: 119 te, G., 1998. Dynamik der Sedimente im Lister Tide- p. (unpublished) becken. In: Gätje, C. & Reise, K. (Hrsg.). Ökosys- Erchinger, H.F., Coldewey, H.G. und Meyer, C, 1996: tem Wattenmeer - Austausch-, Transport- und Interdisziplinäre Erforschung des Deichvorlandes Stoffumwandlungsprozesse. Springer-Verlag, Ber- im Forschungsvorhaben ”Erosionsfestigkeit von lin, Heidelberg: S. 127-159. Hellern”. Die Küste Heft 58 Bijl, W., 1996. Looking for observational signs of Führböter A. & Dette, H.-H., 1992. Strandvor- changing storminess. EU-Project WASA, report spülungen vor der Westküste von Sylt. Die Küste, RIKZ/OS-96.157x. Den Haag, Niederlande: 56 p. H. 53: 51-126. Bijl, W., 1997. Impact of a wind climate change Gast, R., Köster, R. & Runte, K.-H., 1984. Die Watt- on the surge in the southern North Sea. Climate sedimente in der nördlichen und mittleren Mel- Research, 8: 45-59. dorfer Bucht. Untersuchungen zur Frage der Sed- Bruun, P., 1962. Sea level rise as a cause of shore imentverteilung und der Schlicksedimentation. Die erosion. Journal of the Waterways and Harbour Küste 40: 165-257. Division. Proc. ASCE, 88: 117-130. Gerlach, A., Brüning, T. & Brüning, K., 1999. Un- Bunje, J., 1997. Salt marshes in the National Park tersuchung zur Zusammensetzung und Herkunft “Niedersächsisches Wattenmeer”. Status, Manage- von Getreibsel (“Teek”) an der niedersächsischen ment, Aims and Results. Wadden Sea Newsletter Küste. Universität Oldenburg. 1997-1: 16-19 Haven, D.S. & Morales-Alamo, R., 1972. Biodepo- Cadée, G.C., 1976. Sediment reworking by Areni- sition as a factor in sedimentation of fine sus- cola marina on tidal flats in the Dutch Wadden pended solids in estuaries. Geol. Soc. Mein. 133: Sea. Netherlands Journal of Sea Research, 10: 440 121-130. – 460. Heuers, J., Jaklin, S., Zühlke, R., Dittmann, S., De Boer, P.L., 1981. Mechanical effects of micro- Günther, C.-P., Hildenbrandt, H. & Grimm, V., 1998. organisms on intertidal bedform migration. Sedi- A model on the distribution and abundance of the mentology, 28: 129 – 132. tube-building polychaete Lanice conchilega in the intertidal of the Wadden Sea. Verhandlungen der Dean, R.G., 1988. Sediment interaction at modi- Gesellschaft für Ökologie, Bd 28: 207-215. fied coastal inlets: processes and policies. Lecture Notes on Coastal and Estuarine Studies, 29: 412- 439.

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Hofstede, J.L.A., 1991. Sea level rise in the Inner ment Group, Quality Status Report Group. Wil- German Bight (Germany) since AD 600 and it’s helmshaven. implications upon tidal flats geomorhology. In: Niemeyer, H.D., 1986. Ausbreitung und Dämpfung Brückner, H. & Radtke, U. (Eds..): Von der Nordsee des Seegangs im See- und Wattengebiet von Nor- bis zum Indischen Ozean. Franz Steiner Verlag, derney. Jahresbericht 1985 der Forschungsstelle Stuttgart: 11-27. Küste, 37: 49-95. Hofstede, J.L.A., 1996. Saltmarsh management for Niemeyer, H. D., Kaiser, R., 1999. Hydrodynamische coastal defence in Schleswig-Holstein, Germany. Wirksamkeit von Lahnungen, Hellern und Som- In: Proceedings of the 31st MAFF Conference of merdeichen. Schlußbericht zum KFKI-Forschungs- River and Coastal Eng.: 6.2.1 - 6.2.9. vorhaben ”Bemessung auf Seegang”. Hofstede, J.L.A.,1999. Process-response analysis Obert, B., 1995. Entwicklung einer neuange- for Hörnum tidal inlet in the German sector of siedelten Miesmuschelbank des Brutfalls 1991 im the Wadden Sea. Journal of Quaternary Interna- Norderneyer Watt. Ber. Forschungsstelle Küste 40: tional, 60: 107-117. 71-76. Hofstede, J.L.A. und Schirmacher, R., 1996: Vor- Oost, A.P. & Dijkema, K.S., 1993. Effecten van landmanagement in Schleswig-Holstein. Die bodemdaling door gaswinning in de Waddenzee. Küste, 58: 61-74. IBN Rapport 025. Hoozemans, F.M.J., 1989. Het windklimaat ter Oost, A.P., 1995a. Dynamics and sedimentary de- hoogte van de Nederlandse kust over de periode velopment of the Dutch Wadden Sea with em- 1907 - 1980. Nota: GWAO 89.010 phasis on the Frisian inlet. Geologica Ultraiectina, IPCC, 1995. Climate Change 1995, the science of Mededelingen van de Faculteit Aardwetenschap- climate change. Publ. for the IPCC, Cambridge pen Universiteit Utrecht, 455 p. Univ. Press. Oost, A.P., 1995b. The influence of biodeposits of Jelgersma, S. & Tooley, M.T., 1993. Sea level chang- the blue mussel Mytilus edulis on fine-grained es during the recent geological past. In: State of sedimentation in the temperate-climate Dutch the art report ”Sea level rise and their consequenc- Wadden Sea. Geologica Ultraiectina, 126: 359 - es for hydrology and water management”, pre- 400. pared for the international Workshop SEACHANGE Paterson, D.M., Yallop, M.L. & George, C., 1994. ´93. RIKZ, Den Haag: 9-41. Spatial variability in sediment erodibility on the Jensen, J, H.-E. Mügge & Schönfeld, W., 1990. De- island of Texel. In: Krumbein, W.E., Paterson, D.M. velopment of water level changes in the German & Stal, L.J. (Eds.) Biostabilization of Sediments. Bight - an analysis based on single value time se- BISVerlag - Oldenburg: S. 107-120. ries. Proc. 22nd ICCE Delft, Netherlands. Reise, K., 1998. Coastal change in a tidal back- Jensen, J., Hofstede, J.L.A., Kunz, H., De Ronde, J.G., barrier basin of the northern Wadden Sea: are tidal Heinen, P.F. & Siefert, W., 1993. Long term water flats fading away? Senckenbergiana marit. 29: level observations and variations. In: Hillen, R. & 121-127. H.J. Verhagen (Eds.). Coastlines of the southern Schmidt, H., 1997. 120 Jahre geostrophischer Wind North Sea. ASCE, New York: 65-84. in der Deutschen Bucht. Deutsche IDNDR-Reihe, Louters, T. & Gerritsen, F., 1994. The riddle of the 7: 20-23. sands. A tidal system’s answer to a rising sea lev- Siefert, W., 1984. North Sea tide and storm surge el. Report RIKZ-94.040. RIKZ, Den Haag. Pp.69. investigation. Proc., 19nd ICCE, ASCE, New York: Mai, S., Daemrich, K.-F., Zimmermann, C., 1998. 1749-1764. Wellentransmission an Sommerdeichen. Wasser Stal, L. J., 1994. Microbial mats: Ecophysiological und Boden, H. 11 interactions related to biogenic sediment stabili- Neuhaus, R. & Petersen J., 1999. Dunes. In: De zation. In: Krumbein, W.E., Paterson, D.M. & Stal. Jong, F., Bakker, J.F., van Berkel, C.J.M., Dankers, L.J. (Eds.) Biostabilization of Sediments. BIS-Ver- N.M.J.A., Dahl, K., Gätje, C., Marencic, H. & Potel, lag Oldenburg: 41-53. P. (Ed.)., 1999 Wadden Sea Quality Status Report. Stengel & Zielke, 1994. Der Einfluß eines Meer- Wadden Sea Ecosystem No. 9. Common Wadden esspiegelanstiegs auf Gezeiten und Sturmfluten Sea Secretariat, Trilateral Monitoring and Assess- in der Deutschen Bucht. Die Küste, H. 56: 93-117.

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Striegnitz, M., 1999. Verbesserung des Verfahr- Thiel, H., Grossmann, M. & Spychala, H., 1984. ensmanagements zum Interessensausgleich zwis- Quantitative Erhebungen über die Makrofauna in chen Küstenschutz und Naturschutz. 39. BWK einem Testfeld im Büsumer Watt und Abschät- Fortbildungslehrgang Küstenschutz - Analyse, zung ihrer Auswirkungen auf den Sedimentver- Probleme, Lösungen, Papenburg 28. und band. Die Küste 40: 260-314. 29.06.1999 Töppe, A., 1993. Zur Analyse des Meeresspiege- Stock, M., 1997. Salt marsh management in the lanstieges aus langjährigen Wasserstandsaufze- National Park “Schleswig-Holsteinisches Watten- ichnungen an der Deutschen Nordseeküste. Mitt. meer. Wadden Sea Newsletter 1997-1: 11 - 15. des Leichtweiß-Instituts der TU Braunschweig, H. Stock, M., Schrey, E., Kellermann, A., Gätje, C., Es- 20: 132 p. kildsen, K., Feige, M., Fischer, G., Hartmann, F., Zielke, W., Hoyme, H. & Kück, F., 1997. Auswirkun- Knoke, V., Möller, A., Ruth, M., Thiessen, A. & Vorb- gen von Klimaänderungen auf die Wasserstände erg, R., 1996: Ökosystemforschung Wattenmeer und Windverhältnisse an der deutschen Nord- Synthesebericht: Grundlagen für einen National- seeküste, Teilgebiet: Auswirkungen veränderter parkplan. Schriftenreihe des Nationalparks Windverhältnisse auf die Wasserstände. Ab- Schleswig-Holsteinisches Wattenmeer, Heft 8, pp. schlußbericht des ISER der TU Hannover zum 784. BMBF-Projekt Nr.: 03F0141A: 39 p. (unpublished). Storch, H. von, 1997. Auswirkungen von Kli- Zimmermann, C., von Liebermann, N. & Mai, S., maänderungen auf Sturmentwicklung und Ex- 1999. Machbarkeitsstudie zur Ermittlung des für tremwasserstände in der Nordsee. Deutsche IDN- den Küstenschutz erforderlichen Vorlandprofils. DR-Reihe, 7: 3-11. Gutachten im Auftrag des MLR Schleswig-Hol- Streif, H., 1989. Barrier islands, tidal flats, and stein, Kiel, 38 p. (unpublished) coastal marshes resulting from a relative rise in sea level in East Frisia on the German North Sea coast. Proc. KNGMG Symp. “Coastal Lowlands, Geology and Geotechnology”. Kluwer Acad. Publ., Dordrecht: 213-223.

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Wadden Sea Ecosystem No. 13 - 2001 63

Issues of the Publication Series „Wadden Sea Ecosystem“

No. 1: Breeding Birds in the Wadden Sea 1991. 1994. No. 2: Migratory Waterbirds in the Wadden Sea1992/93. 1994. No. 3: Guidelines for Monitoring of Breeding Birds in the Wadden Sea (in Dutch, German, Danish). 1995. No. 4: Breeding Birds on Census Arteas 1990 until 1994. Status of Shorelark, Twite and Snow Bunting in the Wadden Sea. 1997. No. 5: Migratory Waterbirds in the Wadden Sea 1993/94. 1996. No. 6: Trilateral Monitoring and Assessment Program. TMAP Expert Workshops 1995/96. 1996. No. 7: Assessment of the Wadden Sea Ecosystem. 1997. No. 8: Monitoring Breeding Success of Coastal Birds. Monitoring Pollutants in Coastal Bird Eggs in the Wadden Sea. 1998. No. 9: Wadden Sea Quality Status Report 1999. 1999. No. 10: Breeding Birds in the Wadden Sea in 1996. 2000. No. 11: Contaminants in Bird Eggs in the Wadden Sea. Spatial and Temporal Trends 1999 - 2000. 2001. No. 12: Lancewad. Landscape and Cultural Heritage in the Wadden Sea Region. 2001 No. 13: Final Report of the Trilateral Working Group on Coastal Protection and Sea Level Rise. 2001.

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Wadden Sea Ecosystem No. 13 - 2001