| Popis: |
The Belgian near coastal area is characterised by shallow marine sandbanks lying more or less parallel to the shoreline. Research activities were focussed on the sediment- and morphodynamics of the Stroombank, the Nieuwpoort Bank and the Baland Bank, supplemented by a comparative investigation along the interaction zone with the Flemish Bank system. To study the sedimentological and morphological behaviour of this macrotidal environment (-5 to -15 m MLLWS) an integrated research strategy was set up covering different spatial as well as temporal scales. Sediment transport calculations showed that the tidal currents are generally competent enough to resuspend the in-situ sediments. The surficial sediments of the near coastal zone are mainly characterised by fine to very fine sands. Still, medium sands occur in the areas witnessing an intense tide-topography interaction. Striking is the correlation with the presence of bedforms. Deeper than roughly -6 m the surficial sediments are most likely enriched with mud. An interactive model is proposed whereby the transport of sediment is mainly dependent on the swale configuration. Especially when the tidal currents are funnelled, sandy deposits are being washed out and stored along the slopes of the banks. Part of the accumulated sediments is subsequently winnowed out and transported upslope the sandbanks by the combined action of currents and waves. In time, the above mentioned observations and interpretations can be confirmed. From the chronosequential measurements an indication could be given of the vulnerability of the coastal system. It can be stated that there is a clear relation between the observed morphological changes and the ruling hydro-meteorological conditions. Generally the lowest sediment budgets correspond with summer and autumn conditions, whilst the winter months witness the highest sediment volumes and are characterised by an abundance of fine sandy sediments. Sediment transport is most intense when the direction of storminess parallels with the configuration of the swales. From the observations, it can also be deduced that the duration of stormy conditions is more important than the strength. Moreover, the sedimentary pattern in the near coastal area is characterised by a quick recovery after stormy periods. From the spatial and temporal differentiation, the near coastal area can be regarded a self regulating sediment transport system dominated by longshore sediment fluxes. The origin of the Coastal Banks is likely constrained to a time period having hydrodynamic characteristics comparable to the nowadays situation |
