Watershed models: Tools for management

The modeling approach has become an important tool in watershed management, especially when data is scarce and complex interactive processes are; present. In research, models have been used to direct efforts to identify; and fill in knowledge: gaps of hydrologic and non-point pollution processes; in the classroom models have been used as a teaching tool; in resource management, models have been used in identification of sources, magnitude, and pathways of pollution and in selection of BMP's and remedial strategies. Models have been developed to cover various ranges of spatial and temporal scales. The paper covers achievements, dilemmas and future challenges. The challenges focus on the weak links in the description of processes and parameters, and their implications in the application of models, and the scarcity of data for evaluation of models. Examples have been used to illustrate the application, use and misuse of models.