|Robichaud, Peter - USDA FOREST SERVICE|
Submitted to: Society of Range Management
Publication Type: Proceedings
Publication Acceptance Date: September 4, 2008
Publication Date: January 10, 2009
Citation: Moffet, C.A., Pierson Jr, F.B., Robichaud, P.R. 2009. Concentrated flow experiments on burned and unburned sagebrush communities: Applications for the Rangeland Hydrology and Erosion Model. 62nd Annual Meeting, Society of Range Management. Albuquerque, New Mexico, February 8–12. [oral, invited]. Interpretive Summary: Accurate hydrological and erosion predication technologies are still not available to rangelands. Research is underway to develop a new Rangeland Hydrology and Erosion Model (RHEM) and though modifications have been made to the splash and shallow flow erosion processes, it will use the same basic concentrated flow detachment and transport equations as were used in the Water Erosion Prediction Project model. Concentrated flow experiments were conducted to focus specifically on concentrated flow processes and to characterize the effect of fire on concentrated flow erosion process. This is the first step in developing new parameterization algorithms for use in RHEM.
Technical Abstract: The risk of increased runoff and water erosion is greater after fire on many rangelands. Recent experiments on steep sagebrush rangelands have shown that concentrated flow detachment and transport is the dominant postfire erosion process. Rainfall simulation studies have demonstrated that runoff after fire increases by a factor of between 2 and 5. The effect of fire on erosion on these sites was much greater and more variable, increasing by a factor of between 25 and 100. The Water Erosion Prediction Project (WEPP) model, does not predict this degree of erosion increase as a result of the measured reduction in canopy and ground cover after a fire, even when the effect on runoff has been forced. Canopy and ground cover are the primary factors used to adjust erodibility and erosivity terms. The Rangeland Hydrology and Erosion Model (RHEM) uses the same concentrated flow detachment and transport model used in WEPP. Unless new parameterization algorithms are developed for concentrated flow erodibility and erosivity terms, it will not be sensitive to fire effects on the concentrated flow erosion process. Concentrated flow erosion experiments were used to characterize the effect of fire on concentrated flow erodibility, critical shear, flow width, and Darcy-Weisbach roughness coefficients. These experiments separate the flow process from the other erosion processes that are active in rainfall simulation experiments. The results of these experiments are the first step in determining which parameters are sensitive to fire and developing parameterization algorithms to predict those model parameters from site conditions.