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 di stribution of the surficial sediment cover (North Sea sands) which is ident ical to the uppermost layer in the seismic recordings. Sediment thickness w as measured using very high resolution seismic profiling (chirp sonar) and vibrocoring. The three-dimensional sediment distribution was estimated usin g geostatistical methods (cokriging). The results demonstrate a longshore s and 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 an d 15 m water depth a relatively thin sand layer of 0.4-1.5 m is observed wi thin Zone 2. The seaward adjacent Zone 3 (15-20 m water depth) is character ized by an averaged sand thickness of 2-3 m with local maxima of 5-6 m. Fur ther offshore, the sand layer decreases to about 1-2 m thickness. The net b edload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in Zone 1 which results in a substantial sedi ment supply to the innermost part of the German Eight due to bedload conver gence. Shore-normal bedload transport shifts sand to and fro across the coa stal profile although the net directional transport is seawards. This resul ts in sediment depletion between the 10 and 15 m-isobaths (Zone 2) and an a djacent sediment accumulation in deeper waters (Zone 3). (C) 2000 Elsevier Science B.V. All rights reserved.