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
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