SHEDDING SEDIMENT: POST-DISTURBANCE SEDIMENT RECOVERY AND RESILIENCE (Invited Presentation)

Small, steep watersheds in mountainous regions are key sediment sources for rivers globally. Assessing the response and recovery of headwater streams to disturbances that cause extreme sedimentation is thus essential to understanding recent and future landscape changes due to human activities and climate variability. Because damage to communities and infrastructure commonly accompanies extreme events, mitigating the effects of sediment disturbance is of broad societal interest. One metric of response to disturbance is quantifying the recovery time, or the time required to achieve background sediment fluxes. Sediment recovery was assessed following a wildfire, flood, and anthropogenically-induced debris flows in three small (1.5-100 km²) transport-limited basins in the southern Rocky Mountains of Colorado. A nonlinear response in sediment flux was measured over time in each basin with recovery varying from 3-5 years; more rapid recovery to background sediment yields occurred after an extreme flood followed a wildfire. In addition, a change in the baseline sediment flux was document at one site because of increased frequency of debris flows and a fundamental physical state shift occurred in another basin. An index of resilience is proposed as sediment recovery/disturbance recurrence interval to normalize comparisons between sites. Field observations indicate that high resilience more strongly reflects channel form complexity rather than rapid sediment recovery. As a result, management guidelines are proposed to enhance geomorphic resilience by promoting natural process that maintain physical form complexity.