Influence of storms on tidal dune mobility in the Strait of Dover

The present paper deals with dune dynamics in a zone of the Strait of Dover located in the sea lane running into the North Sea. The dunes, widespread in this 35-m depth area, are mobile sedimentary structures (up to 40 m.yr(- 1)) that culminate at a maximum of 22 m depth and endanger navigation as we ll as submarine man-made structures (cables, pipelines). Single- and multib eam bathymetric data, coupled with seismic data, allow us to follow dune di splacements over different time scales. A net bedload parting zone has been displayed and divides the area into two parts, SE and NW. However, accordi ng to the considered time-scale, dune movements present Variations in inten sity and direction. Over a long-term period (decades), sedimentary dynamics fit the regional scheme of the residual tidal currents that induce transpo rt toward the SW and the NE in the respective SE and NW parts of the studie d area. Over a medium-term period (several years), meteorological data show that a high frequency of storm winds alters the residual sand transport ch aracteristics by strengthening, slowing or reversing the effect of the tida l currents and can lead to the reversal of dune asymetry. (C) 2000 Ifremer/ CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.