Estimation of annual storm runoff coefficients by continuous simulation

A continuous simulation technique, based on the Soil Conservation Service (SCS) method, is used to determine annual storm runoff coefficients (ASRCs) for Orlando, Florida using 13 years of daily rainfall data. The ASRC, which is defined as the ratio of annual runoff to annual precipitation, is used to determine annual runoff volume (or depth) and annual pollutant loads in storm-water models under wet conditions. Although simulated ASRC values are very similar to values measured in other studies, they are significantly lower than the values predicted by other existing models. Estimating ASRC values by the continuous modeling approach has several advantages over existing models; relevant watershed characteristics such as soil type, cover, hydro-logic condition of the soil, and antecedent moisture conditions neglected in existing models are taken into consideration, and the annual precipitation that does not produce runoff is determined precisely. Meaningful statistical comparisons can be made between the annual pollutant loads estimated using simulated ASRCs. The technique is cost-effective since continuous simulations can be done on spreadsheets, and require easily available daily rainfall data from a nearby climatological station.