Morphodynamic evolution of the kink of an offshore tidal sandbank: the Westhinder Bank (Southern North Sea)

This study looks at the complex interactions between sedimentology, morphology and hydrodynamics near a kink in an offshore tidal sandbank (Westhinder) and combines all these data to understand the kinkʹs characteristics. The Westhinder sandbank lies in the northern part of the Belgian continental shelf, where the main hydrodynamical agents are the tidal currents. The data sets include two multibeam surveys, 59 surficial Van Veen grab samples and a hydrodynamical and sediment transport model (set up by MUMM). The different data sets point to a triple division of the kink region. The parts north and south of the kink are covered with larger dunes, culminating at the bankʹs crest into a symmetrical very-large dune. Here, the bank is actively maintained by a net sediment transport up both bank flanks and by higher residual water transport strengths. The kink part of the bank lies deeper, is characterized by a steeper eastern flank and by a faster and eastward movement of the very-large dunes over both bank flanks. Coarse sediments west of the kink reveal that the peak flood current is hindered by the changing orientation of the bank northward into a more rectilinear N–S position. The finest sediments are found on the lee slope and might be washed out from the kinkʹs stoss slope. A combination of all the results points to a possible breakthrough in the kink, a hypothesis which is worked out into a scheme.