Modeling Changes in Hydrology and Sedimentation for Forested Watersheds: an Approach for Land Managers

Hydrologic changes and sedimentation have long been recognized as critical concerns for forest management. Federal and state laws commonly require land managers to compare the cumulative effects of different forest management scenarios before management plans or policy changes can be implemented. Existing operational methods tend to be simple checklists, indices, or lumped models. Physically based, spatially explicit models are available but are not widely used because they are too data intensive, costly, and complex. Our goal is to find a middle ground by providing land managers with a suite of models that are easy-to-use, spatially and temporally explicit, and scientifically based. Delta-Q and FOREST (FORest Erosion Simulation Tools) are coupled models designed to meet these criteria. They calculate the hydrologic and sedimentary effects of roads, forest fires, and forest management using GIS. Delta-Q calculates annual changes in flow from a watershed using a simple linear recovery model. Required inputs are a GIS layer of forest management activities over time, the initial changes in flow, and the times to recovery for each activity. FOREST uses conceptual and empirical models to calculate sediment production and delivery from hillslopes and roads, and to route sediment through the stream network. Required inputs include sediment production and recovery coefficients, and GIS layers of fires, roads, streams, forest management, soils, and elevation. Online help files provide detailed instructions and summaries of published data to help users select coefficients. Model results include tables of annual changes in flow and sediment yield as well as GIS layers showing the spatial distribution of sediment production and delivery over the period being simulated. The models are now being finalized and will be validated against data from five different experimental forests across the U.S. Model results should be helpful for comparing different land management scenarios, recognizing key sediment sources, and identifying stream reaches susceptible to sedimentation or in need of restoration.