Estimation of Annual Non-Point Pollutant Loads Using CALSIM: A Case Study

Urban non-point sources have been widely identified as major sources of pollution of surface water bodies. In 1990, the Environmental Protection Agency (EPA) published regulations that established permit application requirements for municipalities to obtain the National Pollution Discharge Elimination System (NPDES) permit prior to discharging stormwater to the waters of the United States. One of the application requirements is the estimation of annual pollutant load, during wet-weather conditions, of the cumulative discharges from all identified municipal outfalls under average climatological conditions. This paper demonstrates how the fully calibrated Continuous Annual Load Simulation model, CALSIM, was used to predict the annual total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) loads, under wet-weather conditions, for the Briar Creek drainage basin, located in the town of Malabar on the east-central coast of Florida, during an average water year. CALSIM was used to predict the annual loads under historical (1943), current, and future conditions. The stormwater from this basin discharges into the Indian River Lagoon, an estuary of national significance. There is concern that, as the basins urbanize in future, the stormwater, rich in total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP), will further degrade the waters of the lagoon. Model results will be used to design best management practices (BMPs) to reduce future annual stormwater loadings to the annual loadings that existed in 1943.