USDA Forest Service
200 E. Broadway
Missoula, MT 59802
WEPP is a well accepted process-based model that has been applied to the Lake Tahoe basin in recent studies like this one. For Optfuels, we have adapted WEPP functionality to pre-stage erosion rates for states that may exist now or in the future for the Lake Tahoe basin.
Modeling for erosion with known variables is reasonably straight forward with erosion models such as the FS WEPP on-line interface, but use of an erosion model to support large-scale forest planning for management activities and wildfire is challenging because of the array of surface and stand conditions and their subsequent change over several decades (with the most sensitive variable being extreme weather).
Preparing erosion prediction for all the combinations in soil, surface and stand conditions modeled by the Optfuels Decision Support Tool, we planned to provide managers with benchmark metrics that are sufficiently striking to support decisions without adding confusion. For this purpose this study provides erosion driven by significant weather event years (and only for those years).
Absolute accuracy for erosion prediction is beyond the scope of this study, primarily because assumptions or generalizations must be employed to model across large landscapes--this is certainly true for basins as large as Tahoe at 190,000 acres. Erosion predictions for individual management projects will be better served with project-scale WEPP modeling during the NEPA process (perhaps GEOWEPP for studies under under 15,000 acres or batch processing for larger).