Spatial variability of floodplain sedimentation at the event scale in the Rhine-Meuse Delta, the Netherlands

This article addresses spatial variability of comtemporary fllodplain sedimentation at the event scale. Measurements of overbank deposition were carried out using sediment traps on 11 floodplain sections along the rivers Waal and Meuse in The Netherlands during the high-magnitude flood of December 1993. During the flood, sand sheets were locally deposited behind a natural levee. At distances greater than 50 to 100 m from the river channel the deposits consisted mainly of silt- and clay-sized material. Observed patterns of deposition were related to floodplain topography and sediment transporting mechanisms. Though at several sites patterns were observed that suggest transport by turbulent diffusion, convection seems the dominant transporting mechanism, in particular in sections that are bordered by minor embankments. The average deposition of overbank fines ranged between 1.2 and 4.0kg m^-2 along the river Waal, and between 1.0 and 2.0kg m^-2 along the river Meuse. The estimated total accumulation of overbank fines (not including sand sheets) on the entire river Waal floodplain was 0.24 Mton, which is 19% to the total suspended sediment load transported through the river Waal during the flood.