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Natural and Anthropogenic Impact at the East Frisian Coast - Last 1000 Years and Future Perspectives

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Natural and Anthropogenic Impact at the East Frisian Coast - Last 1000 Years and Future Perspectives Natural and anthropogenic impact at the East Frisian coast - last 1000 years and future perspectives Alexander Bartholomä Senckenberg Institute Development of the East Frisian Islands over the last 1000 years Past , Present and Future Past : - development of the barrier island system - land relamation and dike construction Present : - Dyke maintainance , preservation of the modern Wadden Sea system - Hazard analysis and risk managemant Future: - Intergrated Coastal Zone Managment with alternative concepts in coastal zone protection and ecosystem conservation Development of the East Frisian Islands over the last 1000 years 1 Past : East Frisian coast 800 AD Without dike line (based on historical maps, by Homeier 1969) Development of the East Frisian Islands over the last 1000 years Past : East Frisian coast 1300 AD with dikes without dikes - land reclamation - southward migration by transgression - reduction of tidal prism - tidal flats with natural salt marshes - loss of accommodation space Development of the East Frisian Islands over the last 1000 years 2 Past : East Frisian coast 1800 AD with dikes without dikes - land reclamation - southward migration by transgression - reduction of tidal prism - tidal flats with natural salt marshes - loss of accommodation space Development of the East Frisian Islands over the last 1000 years Present and Future: East Frisian coast with dikes without dikes - land reclamation - southward migration by transgression - reduction of tidal prism - tidal flats with natural salt marshes - loss of accommodation space Development of the East Frisian Islands over the last 1000 years 3 Past to present : Sea -level rise Discontinuous sea-level rise with transgressive and regressive phases Development of the East Frisian Islands over the last 1000 years Energy gradients in the Wadden Sea coarse Examples of energy gradients Spiekeroog 2.0 53°46' N y y= =- 0.04x- 0.04x + +1.28 1.28 1.5 MMando r =r =0.92 0.92 Langeoog 2.0 fine 2.0 2.0 1.4 1.0 Baltrum 1.4 0.5 1.4 1.0 Denmark 0.0 1.4 2.0 1.4 2.0 y y= =- 0.04x- 0.04x + +1.07 1.07 53°42' N PellwormPellworm r =r =0.91 0.91 1.5 1.0 1.0 mainland 1.0 0 5 km 007°20' E 007°30' E 007°40' E 0.5 Schleswig-Holstein 0.0 2.0 Sediment belts along the East Frisian coast y y= =-0.08x -0.08x + +1.24 1.24 LangeoogLangeoog 1.5 r =r =0.75 0.75 1.0 sampleP point Sea-level rise results in: regressionR line 0.5 confidenceV interval 95% East Frisland predictionV interval 95% - coarsening of sediments 0.0 settling velocity [cm/s] at 5°C and and S=3% settlingvelocity 5°C [cm/s] at 2.0 y y= =-0.05x -0.05x + +0.81 0.81 RottumeroogRottumeroog - sediment lag effects r =r =0.90 0.90 1.5 close to the dike line 1.0 0.5 - Elevation of tidal flats West Frisland 0.0 - Wadden Sea squeeze [km] island dike (all below breakpoint) back-barrier tidal flat other regions of Spiekeroog island of the Wadden Sea Development of the East Frisian Islands over the last 1000 years 4 Wadden Sea squeeze and sea level rise Development of the East Frisian Islands over the last 1000 years Reconstruction of the fully developed tidal system without dike constructions N Spiekeroog WE S Langeoog sand flats present dike line mud mixed flats mud flats content total sediment (in %) saltmarsh 100 75 53°36'N mean high water 50 level (1.4 m above chart datum) 25 10 53°34'N pleistocene sands 0 007°25'E 007°30'E 0 km 5 km - lost area: more than 50 % of the entire tidal system - mud flat and salt marsh deposits landward of the present day dike line Development of the East Frisian Islands over the last 1000 years 5 Salt -marsh erosion Preditecd salt-marsh erosion along the coastal dike line With summer dikes or dammed retention pits Under certain wave & water-level conditions, broken-wall construction patters can prevent salt-marsh erosion Mai & Zimmermann (2002) Wittig et al. (2004) Development of the East Frisian Islands over the last 1000 years Human responses to the expected sea -level rise Risk analysis: - storm-flood risks - hydraulic boundary conditions at coastal constructions - risk assessment for local environments Risk and Coastal Zone Management: e.g. by the „Coastal Protection and Sea-level Group (CPSL) Policies, Strategies, Management Projekts and Activities: COMRISK (Common Strategies to reduce the risk of storm floods in coastal lowlands) DEKLIM (German Climate Change Research Program) KRIM (Climate change and preventive risk and coastal zone management along the German North Coast) ICZM Integrated Coastal Zone Management ENCORA (Initiative for Coordination Action within European coastal research and practitioners communities) LOICZ (Land-Ocean Interactions in the Coastal Zone) Development of the East Frisian Islands over the last 1000 years 6 Breakpoint analysis (CPSL 2001/2005) Moderate increase in sea level : ≤ 3mm/year for large basins ≤ 6 mm/year for small basins ≤ 8.5 mm/year for salt marshes 3 – 6 mm/ year pioneer zone - present dynamic equillibrium still active - Increase of duration of tidal inundation implies stronger sediment accumulation on tidal flats and salt marshes (longer Major sea-level rise: settling period) - massive erosion of salt marshes - Elevation of tidal flats; and expansion of - in sandy areas, erosion rate increases between salt marshes 250% (6mm/yr) and 330% (8.5mm/yr) - fore-shore erosion, retreat of barrier islands Changes in wave and /or tide-domminated sections are not considered Development of the East Frisian Islands over the last 1000 years Main topics of coastal protection and management Sand nourishment Dike strenghening over 1200: 1.0 m / 5.5 m / 3 m³ the last centuries 1600: 3.0 m / 19 m / 32 m³ Sea dikes time: height / lenght / volume 1900: 4.8 m / 33 m / 82 m³ 1955: 5.9 m / 56 m / 149 m³ 2000: 7.8 m / 105 m / 325 m³ 2100: 8.5 m / 150 m / 500 m³ ???? Dune management Habitat maintenance Salt-marsh management Outbanking of summer polders Development of the East Frisian Islands over the last 1000 years 7 Dänemark Nordsee Reinundation of sommer dikes - Salt marsh Helgoland Niederlande Deutschland accretion in protected areas (Langeoog island) accumulation rate 5 cm/month by courtesy of Freund (2006), ICBM Marine Lab. Development of the East Frisian Islands over the last 1000 years Concept of creating artificial tidal basins in the shelter of the dikes Sea Land - controlled tidal range - slow infilling with clay Dike - new salt marsh formation - ideal breeding conditions - new clay resource - ideal for aquaculture low - tourismus dike mean high-tide level ♣♣♣ tidal basin tidal flat tidal channel new salt marshes mean low-tide level Sluice Schematic drawing of an artificial tidal basin with multiple and sustainable usages, including tourism. Development of the East Frisian Islands over the last 1000 years 8 Subdivision of an artifical tidal basin in the shelter of the dikes by multiple usage concepts Development of the East Frisian Islands over the last 1000 years Summary and Outlook Land reclamation and dike constructions already reclaimed more than 50 % of the former fully devoloped tidal system In order to the predicted sea level rise , to preserve the modern system and/or prevent further changes in the Wadden Sea environment individual solutions for a Integrated Coastal Zone Managment are essential: - Increase of accommodation space - salt marsh , dune and habitat management on individual scales - dike strenghening and retreat , reinundation of summer dike areas , - outbanking summer polders , reactivation of retention pits Therefore we need : - Individual case studies for individual sites - Collaboration between dike protection and environmental protection Development of the East Frisian Islands over the last 1000 years 9.
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