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.