Sediment characteristics and sedimentation-erosion processes on Ketenisse polder one year after levelling

TheKetenisse polder is a former intertidal brackish marsh of 30 ha situated between the fortress of Liefkenshoek and the Kallo sluice on the left bank of the Schelde estuary, Belgium. In the 19th century its central part was embanked as a polder. During the construction of a traffic tunnel in the late eighties, the excavated soil was dumped between a lower summer dike and the damming dike. The area was restored in 2002 as compensation for the construction of a container terminal on a mudflat in 1994-1995. The rubble of the summer dike and the dumped material were removed and the area was levelled with the intention of creating the optimal starting conditions for the development of new tidal mudflats and marshes. Developments concerning morphology, sediment characteristics and sedimentation-erosion processes are monitored. Six transects with sedimentation-erosion plots were placed perpendicular to the shoreline. This article discusses those monitoring results, mainly for the first year after levelling. Sedimentation as well as erosion between 0 and 30 cm was observed in the first year. Local changes in stream current patterns caused erosion on some parts of the former mudflats; sheltered depressions filled up relatively fast. Median grain size showed large variation, both spatial and temporal. Organic matter content of the sediment varied between 0.5 and 15% and was closely related to sediment median grain size.