Estimation of Annual Pollutant Loads under Wet-Weather Conditions

Abstract

The Continuous Simulation Method (CSM) has been used to predict average annual total nitrogen storm-water loads, under wet-weather conditions, for various sites in Tampa, Florida. Predicted loads are compared to those predicted by other existing “spreadsheet” models, namely the Storm Water Management Model (SWMM) Level I—Preliminary Screening Procedure, the Simple Method, and the U.S. Geological Survey (USGS) Regression Model. Comparisons showed that the USGS Regression Model predictions were vastly different from those of the other models. The predictions by SWMM Level I, the Simple Method, and the CSM were closer, although there were substantial differences under certain conditions. Of the four models, the CSM provides the greatest flexibility to a model user; it has the capability to (1) model different soil types within a watershed; (2) model loading variations due to geographical (location) and demographic (land use and cover) differences between watersheds; and (3) simulate confidence intervals around the predicted average annual loads.