Step 2: Characterize Your Watershed (cont.)
Watershed Modeling
Models provide another approach for estimating loads and evaluating various management alternatives. A model is a set of equations that can be used to describe the natural or human-made processes in a watershed system, such as runoff or stream transport. By building these cause-and-effect relationships, models can be used to forecast or estimate future conditions that might occur under various conditions. Models can be highly sophisticated, including many specific processes such as detailed descriptions of infiltration and evapotranspiration. Models can also be very generalized, such as a simple empirical relationship that estimates the amount of runoff based on precipitation. Some models are available as software packages, whereas simple models or equations can be applied with a calculator or spreadsheet. Compared to using monitoring data or literature values, models add more detailed procedures that represent the separate processes of rainfall, erosion, loading, transport and management practices. By separately addressing each process, models can be adapted to local conditions, and the simulation can be made more sensitive to land use activities and management changes.
For more details on the types of models available and how to select the ones most appropriate for your watershed planning effort, see Chapter 8 of the Handbook for Developing Watershed Plans to Restore and Protect Our Waters.
You might also want to review the Watershed Modeling Module or the Overview of Watershed Monitoring Module.