A STATISTICAL APPROACH TO URBAN RUNOFF POLLUTION MODELING

In evaluating the present or future state of integrated urban water sy stems, sewer drainage models are often used in calculating the expecte d return periods of given detrimental acute pollution events and the u ncertainty thereof. In the present study an urban runoff pollution mod el is developed for a Dutch combined sewer catchment. The water quanti ty model consists, in its final shape, of a combination of linear rese rvoirs in series and some physical characteristics of the sewer system . Attached to the water quantity model, a model was developed to simul ate the suspended chemical oxygen demand (GOD) concentration at the po int of combined sewer overflow (CSO). The model structure has been dev eloped on the basis of a rainfall input series and a water level and a suspended COD concentration output series. Physically interpretable p arameters have been included where this could be statistically justifi ed by the available observation. Model development has been based on a n approximate likelihood ratio test, tests for parameter significance, parameter correlation and information criteria. It has been possible to formulate a model to describe the rainfall-runoff process at the Lo enen catchment with a coefficient of determination (R-2) of 0.83 for t he water level at the overflow weir. The best model contained eight es timated parameters of which six were directly interpretable in traditi onal urban drainage terms. A three parameter suspended COD concentrati on model was developed with an R-2 of 0.44. Though considerably less s uccessful than the water quantity modelling, the results are interesti ng when viewed in relation to the small number of model parameters. Fu rthermore the model structure can be linked to existing resuspension t heory involving a critical shear stress. (C) 1997 IAWQ. Published by E lsevier Science Ltd.