Water quality modelling of the western Scheldt estuary

1n 1987 the National Institute for Coastal and Marine Management (the Netherlands) initiated the SAWES project (Systems Analysis WEstern Scheldt). The main goals of the project were to acquire knowledge with respect to the pollution problems in the Scheldt estuary and to apply this knowledge to management issues of the Scheldt on an operational level. The main interest was to understand quantitatively the relation between inputs of polluting substances and effects on the ecosystem. In the framework of the project, a water quality model for the Scheldt estuary was made. In 1995, the model area was expanded to include the Belgian coastal region at the mouth of the estuary. The model calculates the fate of discharged substances and establishes the relation between pollution inputs and the resulting water quality, including general water quality (oxygen, pH, alkalinity, major ion chemistry and nutrients) as well as pollutant concentrations. The model incorporates all chemical processes which affect these concentrations, including the precipitation/dissolution of metal sulphides which to a large extent controls the fate of trace metals. Based on calibration and verification exercises, it has been shown that the model provides a good presentation of the physical and chemical processes taking place within the estuary and can therefore be used to support policy development for the estuary. For example, the model can compute how the water and sediment quality in the estuary will respond to reduced inputs of waste or to such human activities as dredging