Assessment of the effects of marine aggregate extraction on the coastline : an example from the German Baltic Sea coast.
Résumé
The German Baltic Sea coast between Warnemünde and Darss is rapidly eroding. In this area, extensive sand extraction takes place at water depths of 8-13 m, for both local beach nourishment and industrial use. Sand resources in the area are restricted to a layer of <2 m of Holocene sand, whilst contemporary input of sand is limited to erosion of the cliff sections. To investigate if sand extraction in this area has any effect on the coastline, bathymetric data from two particular time periods were compared, as well as the location of the coastline over 5 different years, ranging from 1953-2002. Waves and wave-induced sediment transport were simulated using the integrated coastal zone model, Sistema de Modelado Costero (SMC). Results indicate some primary areas of concern: small changes in bathymetry of approximately 10% are sufficient to cause significant modifications in sediment transport potential at the coast; and, thus, alternations in the patterns of erosion and accretion. Sediment transport by both wave action and currents, induced by the inflow of North Sea water, is in a NE direction towards Darss. Here, deposition takes place in a National Park, where dredging is prohibited. There is very little input of sediment in the system. Any sand that is removed by marine aggregate extraction, for industrial use, will have a negative effect on the total sediment budget at the shoreline