Mobile sand deposits and shoreface sediment dynamics in the inner German Bight (North Sea)

This paper presents a conceptual model for the net bedload transport regime on the shoreface of the German Eight. The model is based on the spatial distribution of the surficial sediment cover (North Sea sands) which is identical to the uppermost layer in the seismic recordings. Sediment thickness was measured using very high resolution seismic profiling (chirp sonar) and vibrocoring. The three-dimensional sediment distribution was estimated using geostatistical methods (cokriging). The results demonstrate a longshore sand distribution with three distinct zones. In Zone 1 (0-10 m water depth) the sediments attain their maximum thickness of 10 +/- 2.5 m. Between 10 and 15 m water depth a relatively thin sand layer of 0.4-1.5 m is observed within Zone 2. The seaward adjacent Zone 3 (15-20 m water depth) is characterized by an averaged sand thickness of 2-3 m with local maxima of 5-6 m. Further offshore, the sand layer decreases to about 1-2 m thickness. The net bedload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in Zone 1 which results in a substantial sediment supply to the innermost part of the German Eight due to bedload convergence. Shore-normal bedload transport shifts sand to and fro across the coastal profile although the net directional transport is seawards. This results in sediment depletion between the 10 and 15 m-isobaths (Zone 2) and an adjacent sediment accumulation in deeper waters (Zone 3). (C) 2000 Elsevier Science B.V. All rights reserved.