Process-Response Analysis for the North Frisian Supratidal Sands (Germany)

Abstract

The North Frisian supratidal sands are located at the seaward border of the German Wadden Sea. They occupy a total area of about 28 km² and have neither dunes nor a vegetation cover. Previous investigations have documented that the sands have been migrating landward at least since 1947. These sands have great ecological as well as coastal defense significance and as a result, were subjected to a process-response analysis. From 1947 to 1991, the sands moved in an eastward direction over a distance ranging from 250 m in the south to 1,600 m in the north. It is suggested that this movement occurred in response to a 0.49 cm/yr rise of mean high water (MHW). Consequently, 36 to 42 million m³ of sediment was released from the upper beaches of the sands. During the same period, 32 million m³ of sediment was deposited at the surface and the spits of the sands. The increase in elevation was sufficient to balance the observed MHW-rise. Thus, most of the sediment eroded from the western side raised and lengthened the sands. The actual sediment redistribution (morphodynamics) is probably controlled by overwash and spit forming processes, operating within a framework of a rising sea level and increasing storminess.