MODELING SEDIMENT TRANSPORT AND SEDIMENT QUALITY IN A SHALLOW DUTCH LAKE (LAKE KETEL)

Lake Ketel is a shallow Dutch. lake, part of the river Rhine delta, with a surface area of 38 km2. Between 1960 and 1980 15 x 10(6) m3 contaminated sediment accumulated in the lake. After 1980 the ContaMinant load started to decrease. A common hypothesis was that the. relatively clean solids supplied now, would slowly cover the contaminated sediment layer. Research indicated however a serious erosion of old and polluted bottom sediments. To quantify resuspension and sedimentation fluxes the sediment transport model STRESS-2d has been applied. Simulation results show a net sedimentation of 300 x 10(6) kg year-1, but an erosion of old and polluted sediment of 350 x 10(6) kg year-1. In large areas in the lake net sedimentation is only a few millimetres a year, while high resuspension and sedimentation fluxes lead to an intensive interaction between sediment and water. Spatial variability in resuspension and sedimentation fluxes will lead to spatial gradients in the response of the bottom sediment to the reduced contaminant load. Based on the simulated resuspension and sedimentation fluxes, a simple model for the Cd concentration in the bottom sediment has been developed. Simulation results show a relatively fast decrease of the Cd concentration in the upper sediment layer areas with high net sedimentation and/or (brute) resuspension and sedimentation fluxes.