Influence of Rarely Mobile Boulders on Channel Width and Slope: Theory and Field Application

Abstract Large, rarely mobile boulders are observed globally in mountainous bedrock channels. Recent studies suggest that high concentrations of could be associated with channel morphological adjustment. However, a process‐based understanding large boulder effects on morphology is limited, and data scarce ambiguous. Here, we develop theory steady‐state width slope as function concentration. Our assumes adjusts to maintain two fundamental mass balances: (a) grade, which the transports same sediment flux downstream despite acting roughness elements (b) erosion, by erodes at background tectonic uplift rate. Model predictions normalized reference, boulder‐free slope, accounting for variations due supply, discharge, lithology. Models tested against new set from Liwu River, Taiwan, showing steepening widening increasing Whereas one explored mechanisms successfully explains trend, none models accuratly account variability. We propose this contrast arises different adjustment timescales: while bed within few floods, takes much longer time. Overall, find represent significant perturbation fluvial landscapes. Channels tend respond forming differs The general approach presented here can further expanded explore role other hydrodynamic large, boulders.