ENVIRONMENTAL SETTING, MORPHOLOGY AND VOLUMETRIC EVOLUTION OF THE MIDDELKERKE BANK (SOUTHERN NORTH-SEA)

The Middelkerke Bank, a tidal sandbank located in the southern North S ea on the Belgian continental platform has been the object of a multid isciplinary and international research project. The morphological and hydrodynamical setting of the study area is presented. A complete side -scan sonar coverage of the bank allowed a detailed analysis of the mo rphology of the bank and of its superimposed bedforms. Large dunes cov er the flanks and summit of the Middelkerke Bank. They have a constant orientation, a height ranging from 0.5 to 5 m, a wavelength from 75 t o 150 m and in most cases an asymmetrical pro tile. The slopes of both lee and stoss flanks are very low. Small and medium dune fields occur on the entire bank and in the adjacent swales. They are 2-D and prese nt a wavelength ranging from 1 to 15 m. Flood and ebb oriented small d unes cover respectively the western and eastern flank of the bank. Bat hymetric surveying of the Middelkerke Bank was carried out to assess t he importance of volumetric variations of the bank mass caused by seas onal factors. Results show that changes in the bank volume can be quit e important. The bank's volume decreases in periods of heavy weather a fter which the process of sand uppiling acting during long periods of fair weather conditions causes the bank to restore itself. Volumetric variations of the total bank volume in a. winter-summer period can ran ge along certain sections of the bank from -21% to +26%. Despite these large seasonal volumetric variations, the bank shows a long-term dyna mic equilibrium as proven by the obtained evolution trend.