GIS data widely available today can be used to better estimate watershed parameters for the SWMM model. An interface was developed to create SWMM input files from spatial data. The interface delineates watersheds and allows update of land-use parameters.

SWMM performs continuous simulation but it assumes a time-invariant land use. A "hot-start" technique was developed that uses end values from one year's simulation to initialize state variables for the next year. This technique allows for dynamically changing the land use model parameters to reflect changes in time.

Based on the simulation results, three regression models were developed to adjust constant land-use model results to account for land use changes in peak discharges, baseflow, and total phosphorus loads. These adjustments use imperviousness as an index of land use changes. The regression equations adjust streamflow and water quality results from a constant land use SWMM simulation to conditions with time-varying land use.