EFFECT OF WILDFIRE ON RILL EROSION

Wildfire can alter hillslope hydrologic processes which in turn can alter the erosional processes. This becomes a problem if new, incisive erosion begins to operate in regions of the watershed that were previously only subject to diffusive erosion. Such erosional regimes, incisive versus diffusive, can be delineated by the relationships between slope and drainage area by assuming certain hydrologic conditions. The purpose of this study is to determine if rills, which commonly occur after wildfires, exist in regions of the watershed that are not typically subject to incisive erosion. This is accomplished by mapping the topographic position of new rills in two recently burned watersheds and determining if their origination points plot in modeled diffusive regions of a slope-area plot. Where the rills plot on the slope-area graph indicates the state of equilibrium for that hillslope. If the rills plot in areas dominated by erosion by overland flow, it indicates that there is a correlation between the erosional process and the erosional feature. If the rills plot in areas dominated by diffusive erosion, it indicates a state of disequilibrium between the erosional process and the erosional feature. The contributing area and slope of seven channel heads and forty-two rills in a burned watershed near Los Alamos New Mexico, and of three channel heads and twenty-one rills in a burned watershed near Bailey Colorado were plotted. Preliminary results show that the channel heads in both New Mexico and Colorado lie in the region predicted to dominated by overland flow. This result verifies the validity of the predictive nature of the slope-area plot. The rill data for both sites lies in the region predicted to be dominated by diffusive erosion. The occurrence of rills in this region indicates that wildfire is affecting the location of the rills by disrupting the hydrology of the hillslope.