SEDIMENTATION PROCESSES ALONG THE EAST FRIESIAN ISLANDS, WEST GERMANY

Abstract

The East Friesian Islands are located on a high energy shoreline. The average deepwater significant wave height exceeds 1.0 m and the spring tidal range varies from 2.7 to 2.9 m. A large easterly net longshore transport rate has caused eastward growth of the barrier islands. Reclamation of tidal flats has significantly reduced the backbarrier area and has resulted in a decrease in the ratio of inlet width to barrier island length from 42% to 16% during the past 300 years. The headwaters of the major channel dissecting the tidal flats erode in an eastward direction in response to tidal and wave driven currents, wave suspension, and eastward barrier island elongation. Consequently, the drainage systems of most of the inlets are highly asymmetric with 70-80% of the tidal prism coming from the east. This pattern results in a hooked main channel. The location of the channel at the inlet throat is controlled by the westward ebb flow in the main channel, the inertia of ebb flow in the tributary creeks, eastward longshore sediment transport, and the regional stratigraphy. The position and orientation of the main ebb channel controls the symmetry of the ebb-tidal delta about the inlet shoreline. This, in turn, affects the location of swash bar attachment to the beach and overall trends of erosion and deposition along the downdrift barrier.