Landslide-channel feedbacks amplify channel widening during floods

Channel widening is a major hazard during floods, particularly in confined mountainous catchments. However, channel widening during floods is not well understood and not always explained by hydraulic variables alone. Floods in mountainous regions often coincide with landslides triggered by heavy rainfall, yet landslide-channel interactions during a flood event are not well known or documented. Here we demonstrate with an example from the Great Colorado Flood in 2013, a 1000-yr precipitation event, how landslide-channel feedbacks can substantially amplify channel widening and flood risk. We use a combination of DEM differencing, field analysis, and multiphase flow modeling to document landslide-channel interaction during the flood event in which sediment delivered by landslides temporarily dammed the channel before failing and generating substantial channel widening. We propose that such landslide-flood interactions will become increasingly important to account for in flood hazard assessment as flooding and landsliding both increase with extreme rainfall under climate change. We also demonstrate the role of multiphase models such as r.avaflow in simulation of flood dynamics in cases of high lateral sediment supply and recommend that these are further tested for more accurate modeling of flood hazard in catchments where floods typically coincide with high sediment supply.

This study has been accepted for publication in npj Natural Hazards: Bennett, G.L., Panici, D., Rengers, F.K., Kean, J.W., Rathburn, S.L., Landslide-channel feedbacks amplify channel widening during floods, npj Natural Hazards, https://doi.org/10.1038/s44304-025-00059-6