MODELING THE BUILDUP AND WASHOFF OF POLLUTANTS ON URBAN WATERSHEDS

A model for urban stormwater quality was developed in this study. The basis for the model is the process by which pollutants build up on the watershed surface. For the wet climate of the study site, it was assu med that there exists an interval of time over which the pollutant bui ldup equals the pollutant washoff (no accumulation of pollutant). The buildup model was represented by a linear function of the antecedent d ry time. The buildup function was then linked with a pollutant washoff model represented by a power function of the storm runoff volume. Var ious time intervals for no net accumulation were tested to calibrate t he model. The model was calibrated to observed data for two small urba n basins in Baton Rouge, Louisiana, and model results were used to ana lyze the behavior of phosphorus concentrations in storm runoff from th ese basins over a long period of time.