Drivers of stream channel erosion and deposition in post-fire watersheds

Abstract

Wildfires alter watershed hydrology and sediment dynamics, yet the relative importance of topographic, climatic, and vegetation controls on channel erosion remains poorly quantified. This study investigates the primary physical controls influencing channel erosion and following the Cameron Peak Fire (CPF) and East Troublesome Fire (ETF) in northern Colorado. Geomorphic change was quantified using digital elevation models of difference (DoDs) derived from structure-from-motion and LiDAR data, covering both cumulative (2023 – 2021/2020) and delayed (2023 – 2022) post-fire periods. Spatial stream network (SSN) models were applied to assess the influence of topographic, climatic, vegetation, and soil variables across hillslope, channel, and watershed scales. Results show that watershed and channel slopes were the strongest and most consistent predictors of both erosion and deposition. In contrast, stream power and drainage area exhibited site-specific and time-dependent effects. In CPF watersheds, high-intensity, short-duration storms increased sediment flux, whereas precipitation played a negligible role in ETF. Vegetation and soil variables—NDVI, clay content, and burn severity—were weak or inconsistent predictors across models. These results underscore the primacy of topographic controls, particularly slope, over other commonly cited drivers, and suggest that post-fire erosion risk is more strongly associated with terrain steepness than with burn severity.