Prediction of Sediment Quality in Catchment Areas of the River Rhine: Operation and Use of the Horizon Model

Suspended matter and sediments in the catchment areas of European rivers are often highly polluted. A forecast of sediment quality in relation to discharges is of importance in formulating policy pertaining to emission reduction and sediment sanitation. The model Horizon has been developed to predict the sediment quality in the long term under various emission reducing scenarios. The model schematics consist of a description of the Rhine, the Meuse and the large lakes and basins in The Netherlands. The model calculates the concentration of eight inorganic and five organic micro pollutants in surface water, suspended matter and the sediment under the influence of processes such as sorption, evaporation, degradation, sedimentation, resuspension and burial. The principles underlying the model, the modelled pollutants, the schematics and the modelled physical/chemical processes are briefly discussed. The model input, calibration, validation and model errors follow. The predictions show that emission reductions more far reaching than the Rhine Action Programme (RAP) are needed to meet the Quality Objective 2000,set out in the Dutch National Policy Document on Water Management.