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, wi th a surface area of 38 km2. Between 1960 and 1980 15 x 10(6) m3 conta minated sediment accumulated in the lake. After 1980 the ContaMinant l oad started to decrease. A common hypothesis was that the. relatively clean solids supplied now, would slowly cover the contaminated sedimen t layer. Research indicated however a serious erosion of old and pollu ted bottom sediments. To quantify resuspension and sedimentation fluxe s 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 eros ion of old and polluted sediment of 350 x 10(6) kg year-1. In large ar eas in the lake net sedimentation is only a few millimetres a year, wh ile high resuspension and sedimentation fluxes lead to an intensive in teraction between sediment and water. Spatial variability in resuspens ion and sedimentation fluxes will lead to spatial gradients in the res ponse of the bottom sediment to the reduced contaminant load. Based on the simulated resuspension and sedimentation fluxes, a simple model f or the Cd concentration in the bottom sediment has been developed. Sim ulation results show a relatively fast decrease of the Cd concentratio n in the upper sediment layer areas with high net sedimentation and/or (brute) resuspension and sedimentation fluxes.