MATHEMATICAL-MODELING OF WATER-QUALITY PROCESSES USING HIGHER-ORDER ACCURATE SCHEMES

Details are given relating to the increasing use of numerical hydraulic and water quality models for environmental impact assessment studies and the increasing emphasis on more accurate numerical schemes for modelling the transport and dispersion of water quality constituents. Such a numerical model has been refined to modify a higher-order accurate finite difference scheme to eliminate the prediction of negative concentrations in a computationally efficient manner. This refined model has been applied specifically to predicting flow and water quality constituent processes within Poole Harbour, in Dorset, UK, with this natural harbour being a semi-enclosed coastal embayment. Details are given of the governing differential equations included in the model, together with details of the modified scheme, and predictions of various water quality indicators across the basin. The main sources of input into the basin include three sewage effluent treatment works and two rivers, inputting nitrates from agricultural run-off, The agreement between the predicted and the model results has proved encouraging, particularly since the basin floods and dries extensively during the tidal cycle.