In the UK, the standards which protect river aquatic life against the effect of short term intermittent pollution events are expressed in terms of river concentration/duration thresholds for return periods ranging from 1 month to 1 year. To demonstrate compliance with these standards, it is necessary to simulate the performance of a drainage system and the river impact for a number of wet weather events, chosen such that the return periods of critical concentrations/durations can be estimated with confidence. Many events must be simulated leading to long computer runs and large result files when using detailed simulation models.

This paper describes how this problem has been addressed within the UK Urban Pollution Management procedure by developing a simplified urban pollution model called SIMPOL. This model is designed to represent the key urban processes in a relatively simple way. Accuracy is preserved by calibrating the model against a small number of detailed model results. As multiple runs can be carried out easily, SIMPOL modelling allows greater account to be taken of the variability in rainfall, river conditions and foul flow quality. Potential solutions can be rapidly tested against both environmental and emission standards. A case study is used to illustrate the application of SIMPOL.

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