University of California Water Resources Center

We investigated the surficial processes that deliver sediment from hillslopes into channels in a mediterranean landscape and determined how these processes are controlled by climate and landscape characteristics (e.g. topography, vegetation). Watersheds in semi-arid regions of the United States are subject to a variety of disturbances, including grazing, fires, and vegetation cover changes and, while the consequences of sediment loading are well documented, presently our ability to predict the spatial and temporal pattern of delivery is poor. The processes that we have investigated are: shallow landslides, overland flow, dry ravel, and bioturbation. Through field experiments and monitoring, we have developed physically-based transport equations for each individual process. These transport equations are used as the governing equations for a computer model, driven by random sequences of rainstorms and fires, that predicts the spatial and temporal patterns of sediment delivery. As downstream problems become more closely linked to watershed conditions and perturbations, this type of fundamental research is relevant to issues such as the health of riverine ecosystems and the siltation of reservoirs. We anticipate that our fieldwork and modeling results will help land managers estimate the influx of sediment from surface processes according to different land-use practices.