An overview of geomorphic responses to high-magnitude floods: insights into river dynamics and implications for hazard mapping

Abstract

In recent decades, the frequency of high magnitude floods has increased across many regions of the world. Such events can trigger geomorphological processes that significantly alter river channels and floodplains, with important implications for flood hazard. This is especially relevant in mountainous and hilly areas, where channel dynamics (e.g., major widening) and sediment transport (e.g., debris floods) play a key role in shaping flood risk. This paper provides an overview of major scientific advancements related to two core aspects: (i) understanding how river channels respond geomorphologically to extreme flood events, and (ii) developing geomorphic tools for assessing and mapping flood-related hazards. Beyond hydraulic variables like stream power, several geomorphic factors are critical in driving channel changes during floods. Key controls include lateral confinement and sediment availability, while the type of sediment transport (e.g., debris floods versus normal water flows) can greatly influence the extent of channel widening. In highly dynamic systems, flood hazard stems not only from inundation but also from channel instability. Recent tools such as morphodynamic corridors delineation have shown promise in predicting these dynamics, although their application remains limited compared to traditional hydraulic methods. Integrating geomorphic approaches into land use planning and river management can improve hazard assessment by considering the natural variability and evolution of river systems, ultimately supporting more resilient communities and infrastructure.