Linking geomorphic change due to floods to spatial hydraulic habitat dynamics

Large flood events have the capacity to induce geomorphic restructuring that can impact riverine ecosystems. However, the detailed morphodynamics associated with infrequent, high-magnitude floods are variable and difficult to capture, and more research is needed into potential relationships between geomorphic change, flow organization, and aquatic habitat dynamics. In this study, we focus on the reach-scale response of a gravel bed river to a large flood, employing a combined remote sensing, field measurement, and numerical modelling approach to measure and interpret conditions bracketing the flood. Documented geomorphic turnover was extensive, reworking low-flow channel patterns and causing widespread bank erosion and sediment deposition. This resulted in a shift to wide, shallow flow conditions in the post-flood morphology and a loss of hydraulic diversity, particularly in ecologically important pool and riffle units identified using a fuzzy statistical classification method. These impacts are most evident at low flows; higher discharges display relatively similar hydraulic conditions despite geomorphic change. Smaller-scale adjustments in the year following the flood appear to be driving the reintroduction of hydraulic diversity, which is interpreted as beneficial for in-stream brown trout. Results from this study highlight the utility of applying flexible and objective remote sensing and modelling methods to measure fluvial change and provide a real-world example that can inform broader theoretical understanding of large flood ecohydrology.