Predicting Cumulative Watershed Effects of Fuel Management with Improved WEPP Technology

The increase in severe wildfires in recent years is due in part to an abundance of fuels in forests. In an effort to protect values at risk, and decrease the severity of wildfires, forest managers have embarked on a major program of fuel reduction. Past research has shown that such fuel reduction may have minimal impact at a hillslope scale, but when numerous hillsides are disturbed within a watershed over a number of years, the cumulative effect of such disturbances may be unacceptable. In addition, road networks are necessary to support fuel management activities by providing access for thinning crews, small diameter timber extraction, and fire crews. These road networks were frequently designed and constructed to minimize cost, and do not necessarily minimize adverse watershed impacts. Research findings from wildfire, fuel management, and roads will be presented to provide a context for predictive modeling. There are some new predictive tools to aid in watershed analysis. These include the GeoWEPP GIS wizard, the online WEPP:Road Batch processor and WEPP FuMe fuel management analysis tools, and a revised WEPP hillslope model with improved water balance and lateral flow capabilities. In this paper, we use these new technologies to explore the sources of sediment and runoff within a typical forested watershed. The paper shows improvements in runoff prediction with the revised WEPP model, as well as the relative importance of roads, wildfire, prescribed fire, and thinning operations in generating sediment at the hillslope and watershed scales. The analysis of the performance of the modified WEPP interface showed that there are problems within the WEPP Watershed stream flow routing routines that will need to be addressed before use of this modified model can be recommended.