The Influence of Impact‐Energy‐Dependent Erosional Efficiency on Bedrock River Sediment Dynamics and the Effective Flood

Abstract

Bedrock river incision reflects the cumulative geomorphic work performed across a distribution of flood magnitudes and frequencies. Mechanistic models of bedrock incision by bedload impacts typically assume that bedrock resistance to erosion is constant with respect to particle impact energy. However, recent impact experiments demonstrate that rock resistance to erosion decreases systematically as impacts become more energetic. This study incorporates an experimentally constrained, impact‐energy‐dependent rock resistance coefficient into the widely used saltation‐abrasion model and evaluate how this modification alters predicted incision across a range of grain sizes and transport conditions. Allowing rock resistance to scale with impact energy strongly amplifies the grain size dependence of bedrock detachment, such that coarse grains remove substantially more bedrock per unit impact. Applying the model across a full discharge distribution to evaluate long‐term incision reveals that while accounting for impact‐energy‐dependent rock resistance does not meaningfully alter the flood magnitude that maximizes geomorphic work, known as the effective flood, it shifts the fraction of total incision contributed by rarer, high‐magnitude events. These results demonstrate that accounting for impact‐driven differences in erosional efficiency fundamentally alters how geomorphic work is partitioned across floods, increasing the contribution of extremes to long‐term bedrock erosion rates.