Implications of impact-energy dependent erosional efficiency on bedrock river sediment dynamics and form: 1. Reach-scale dynamics and the effective flood

Claire C Masteller 

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. Here we incorporate 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. We find that allowing resistance to scale with impact energy strongly amplifies the grain-size dependence of detachment, such that coarse grains remove substantially more bedrock rock per impact. Applying the model across a full discharge distribution to evaluate long-term incision reveals that while impact-energy-dependent rock resistance does not meaningfully alter the effective floods, it shifts cumulative incision toward rarer, high-magnitude events. These results demonstrate that accounting for impact-driven differences in erosional efficiency fundamental alters how geomorphic work is distributed across floods, increasing the contribution of extremes to long-term bedrock erosion rates.