Coastal Erosion and Protection Measures at the German North Sea Coast
Keywords:Reach nourishment, coastal erosion, barrier island, structures
The German North Sea coast consists mostly of loose sediments of Pleistocene and Holocene age, including glacial till, beach and dune sand, and tidal silt and clay. Young barrier islands, marsh islands (formerly parts of the mainland), as well as islands of morainic hills (in the north) protect the low-lying mainland coast which is composed almost entirely of low marshland. Spring tides are 1.8 to more than 3.5 m (in the inner parts of the German Bight), but during winter storms from the west sea level can rise to more than 3 m above the spring tide datum. Coastal erosion can be measured directly from good maps over a period of 120 years and attains rates of more than 2 m/year as long term averages. Coastal change is now restricted only to about 10-15 percent of the coastline (only on the islands), because most of the coast is protected by high and strong dikes. At the exposed parts of the islands, coastal erosion endangers settlements and touristic infrastructure. For over 100 years groins or tetrapod walls as well as concrete sea walls were constructed, but since 1972 the method of artificial beach nourishment has become more common. This is cheaper than the other measures and has less impact on the natural coastal environment. The low-lying leeward parts of the islands as well as the mainland are protected by dikes which have a total length of more than 1,000 km. Since 1955, a total of $3.3 billion U.S. was spent for coastal protection of the German North Sea coast. The current annual rate is about $100 m U.S. This paper gives some general information and specific data for Sylt island (the largest German North Sea island) as a regional example.