Simulated Dynamics of Mixed Versus Uniform Grain Size Sediment Pulses in a Gravel‐Bedded River

Mountain rivers often receive sediment in the form of episodic, discrete pulses from a variety natural and anthropogenic processes. Once emplaced river, movement this depends on flow, grain size distribution, channel network geometry. Here, we simulate downstream bed elevation changes that result inputs (∼10,000 m3), differing volume under medium high flow conditions. We specifically focus comparing responses between mixed uniform pulses. This work builds Lagrangian, bed-material transport model applies it to 27 km reach mainstem Nisqually River, Washington, USA. compare observed change accumulation rates lake simulation results. Then investigate magnitude, timing, persistence due introduction synthetic by results against baseline condition (without pulse). Our findings suggest response is primarily influenced sediment-pulse distribution. Intermediate mixed-size (∼50% median gravel size) are likely have largest impact because finer sizes translate quickly coarser (median larger) disperse slowly. Furthermore, pulse, with smaller than bed, increases mobility more uniform-size pulse. has important implications for river management, as allows us better understand fluvial geomorphic variations supply.