MORPHOLOGICAL REACTIONS OF TIDAL SYSTEMS DUE TO NEARSHORE CONSTRUCTION WORKS

Abstract

The nearshore region of the North German North Sea coast is characterised by a large area of tidal flats with a width of 10 to 30 km (Fig. 1) . The development of the structure of this coastal area in the past centuries was mainly determined by several severe storm surges, which have destroyed the formerly existing coastline. In its present state the coastal area is subdived into numerous tidal flats, islands and peninsulas of different size and more or less deep channels and small gullies. Due to its historical development, this area cannot be expected to be morphologically stable. Once people learnt to build safe dikes, the coastline existing at the time was fixed whilst the islands in the shore belt were protected against flooding during storm surges. However, the shore belt is furthermore exposed to waves and tidal currents which cause - apart from certain shlftings of gullies - extensive permanent erosion and sedimentation in parts of the shore belt with an increasing tendency in the last decades. The nearshore region at some places on the coast is extremely endangered in its function as part of the coastal protection system, consisting of the dike, the foreshore above MHW and the tidal flat area. First attempts to achieve morphological stabilisation of the nearshore region consisted in the construction of dams normal to the coastline. However, the shore belt still remained morphologically unstable and could not yet be transformed into a stable system.