The combination of a rainfall event model and a continuous simulation model for a brtter assessment of nonpoint source pollution

摘要

One method for the assessment of the release and movement of nutrients and pollutants within a watershed can be performed using hydrologically based simulation models. The main goal of modeling watershed hydrologic systems is the development of a mathematical structure that can be performed using the complexity of hydrological processes and their interrelations. To achieve this goal, state-of-the-art modeling techniuqes take advantage of GIS technology to provide a useful manner to collect, store and retrieve huge quantities of data for watershed scale assessments. GIS tools satisfy the assessment of distributed characteristics of the landscape and of the associated hydrological variables. This is particularly important using nonpoint pollution models for the assessment of the effects of agricultural activities that overlay intrinsic hydrological attributes. Temoral patterns of release of nutrient and chemicals is directly conencted with rainfall events. Particularly, most chemicals are delivered to waterbodies during only a few large runoff events. Two USDA-ARS models have been developed for the assessment of nonpoint pollution loading from ungaged watersheds: WAT (Soil and Water Assessment Tool) and AGNPS (Agricultural Nonpoint Pollution Source model). Each model performs distributed assessments on a watershed scale: with SWAT devoted to continuous long time simualtions and AGNPS devoted to the analysis of the effect of single representative rainfall events.