Fluvial Geomorphic Resilience in Alluvial Mountain Rivers to Large Floods

Abstract

Intensification of hydroclimatic volatility increases the potential for large floods to reshape rivers and threaten infrastructure. Fluvial geomorphic resilience, defined as a river's resistance to, and recovery from, flood disturbance, offers a framework for understanding river response to extreme events and guiding management. We assessed resilience at two scales: (1) a detailed geomorphic and hydraulic analysis of the June 2022 flood on East Rosebud Creek, Montana, which was part of broader flooding in the Greater Yellowstone Ecosystem, and (2) a multiriver comparison of 13 flood‐impacted alluvial mountain rivers (East Rosebud Creek plus 12 additional sites across North America and Europe). We quantified resistance using active‐channel width ratios () and recovery using postflood channel evolution () and recovery rate (). East Rosebud Creek showed strong spatial variability in disturbance among two defined segments, with an upstream segment shifting to new forms via widening, coarsening and/or incision, whereas a downstream segment that experienced similar flow strengths adjusted more modestly, within a dynamic geomorphic equilibrium. Slope, confinement and grain size were key influences on flood response in East Rosebud Creek. In the multiriver analysis, multilevel regression showed a positive log‐transformed relationship between normalized flood peak exceedance above the () and mean and a negative linear relationship between mean slope and mean . Multiriver results suggest that slope‐driven influences on vegetation growth shape recovery. Understanding patterns of resilience can improve flood adaptation strategies and inform targeted river management.