Coastal Protection and Sea Level Rise
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0 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 Wadden Sea Ecosystem No. 13 - 2001 4 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 Wadden Sea Ecosystem No. 13 - 2001 6 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