Environmental setting, morphology and volumetric evolution of the Middelkerke Bank (southern North Sea)

Abstract

The Middelkerke Bank, a tidal sandbank located in the southern North Sea on the Belgian continental platform has been the object of a multidisciplinary 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 morphology of the bank and of its superimposed bedforms. Large dunes cover 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 to 150 m and in most cases an asymmetrical profile. 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 present a wavelength ranging from 1 to 15 m. Flood and ebb oriented small dunes cover respectively the western and eastern flank of the bank. Bathymetric surveying of the Middelkerke Bank was carried out to assess the importance of volumetric variations of the bank mass caused by seasonal factors. Results show that changes in the bank volume can be quite important. The bank's volume decreases in periods of heavy weather after 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 range along certain sections of the bank from −21% to +26%. Despite these large seasonal volumetric variations, the bank shows a long-term dynamic equilibrium as proven by the obtained evolution trend.