CONSTRAINING DECADAL-SCALE EROSION OF POST-WILDFIRE DEBRIS FLOW DEPOSITS

Debris flows generated from wildfire pose significant risk to increased sedimentation to river networks, degradation of water quality, and accumulated sediment behind downstream reservoirs. Despite an abundance of research investigating the probability of debris flow generation and the constraints on deposit initial volume, there remains a significant knowledge gap in understanding the temporal scale at which debris flows supply sediment to river networks after deposition. To provide reliable estimates of sediment delivery from debris flow deposits over time, two important metrics must be constrained: 1) how does sediment delivery to river networks from post-wildfire debris flow deposits change over time, and 2) which local, reach-scale hydrogeomorphic features influence the relative magnitude of debris flow sediment delivery over time? With a combination of remote analysis and fieldwork of 58 identified debris flows in the state of Utah, we have compiled a dataset representing volume loss from debris flow deposits through time. We identified three major erosional processes responsible for removing sediment from debris flow deposits; surface deflation of the deposit, tributary channel incision through the surface of the deposit, and lastly toe erosion resulting from fluvial processes of the axial river. We analyzed the factors responsible the initial delivery of deposits to the axial river, the relative volume loss due to each of these erosional processes, and variability in exponential decay rates due to each dominating erosional process. Additionally, we revisited initial delivery models and constructed a new initial delivery predictive model with reliable accuracy estimating the initial volume of sediment delivered to the river network. We developed a new metric, the Debris Flow Delivery Potential, for estimating initial deposit delivery into a river network and the volume remaining through time. Additionally, we verified the hypothesis that volume loss of debris flow deposits can be modeled with an exponential decay function. These models provide in-depth investigation in debris flow, valley bottom, and channel morphology influence the sediment delivery from post-wildfire debris flows through time. This dataset will improve post-wildfire rehabilitation and understanding of excess sedimentation to river networks and downstream reservoirs.