WATERSHED-SCALE HYDROLOGIC AND NONPOINT-SOURCE POLLUTION MODELS: REVIEW OF MATHEMATICAL BASES

Abstract

A clear understanding of a model is important for its appropriate use. In this article, eleven watershed scalehydrologic and nonpoint-source pollution models are reviewed: AGNPS, AnnAGNPS, ANSWERS, ANSWERS-Continuous,CASC2D, DWSM, HSPF, KINEROS, MIKE SHE, PRMS, and SWAT. AnnAGNPS, ANSWERS-Continuous, HSPF, and SWATare continuous simulation models useful for analyzing long-term effects of hydrological changes and watershed managementpractices, especially agricultural practices. AGNPS, ANSWERS, DWSM, and KINEROS are single rainfall event modelsuseful for analyzing severe actual or design single-event storms and evaluating watershed management practices, especiallystructural practices. CASC2D, MIKE SHE, and PRMS have both long-term and single-event simulation capabilities.Mathematical bases, the most important and critical elements of these mathematical models, were identified and compiled.In this article, a comprehensive summary of the compilation is presented in tabular form. The flow-governing equations andtheir solution methods used in each of the eleven models are discussed. The compilation of the mathematical bases of thesemodels would be useful to determine the problems, situations, or conditions for which the models are most suitable, theaccuracies and uncertainties expected, their full potential uses and limitations, and directions for their enhancements or newdevelopments. AGNPS, AnnAGNPS, DWSM, HSPF, MIKE SHE, and SWAT were found to have all the three major components(hydrology, sediment, and chemical) applicable to watershed-scale catchments. SWAT is a promising model for continuoussimulations in predominantly agricultural watersheds, and HSPF is promising for mixed agricultural and urban watersheds.Among the single-event models, DWSM provides a balance between the simple but approximate and the computationallyintensive models and, therefore, is a promising storm event model for agricultural watersheds.