Response of SPM concentrations to storms in the North Sea: Investigating the water-bed exchange of fine sediments

Shallow coastal seas are subject to an increasing pressure by offshore operations. Further to a direct influence these operations impose on benthic and pelagic organisms, an indirect influence is caused by changes in sediment dynamics and morphodynamics. Temporal variations in SPM have a large effect on the timing and rate of primary production, thereby also affecting higher trophic levels. Field measurements along the Dutch coast indicate significant seasonal variations in concentrations of SPM (Suijlen and Duin, 2001; Witbaard et al., 2015). These seasonal variations originate from a marked seasonality in wind climate and the occurrence of storms. During storms, increases in SPM occur simultaneously in large parts of the Dutch coastal zone of the North Sea (Suijlen & Duin 2001), demonstrating that on short timescales, the vertical exchange between the sea bed and the water column is dominant. Model concepts with two discrete seabed layers (a fluffy top layer and a sandy lower layer) turned out to capture these fine sediment dynamics, see van Kessel et al. (2011). However, the underlying physical processes resulting in the water-bed exchange of fines are still to be unravelled. Therefore, this study aims to investigate the resuspension of fines from the bed during and after storms, accounting for the tidal variation due to the spring-neap tide cycle. This will lead to a more specific conceptualization and related parameterization of the water-bed exchange, thereby enabling to study both the direct and indirect impact of offshore operations.