Reservoir infill by hyperpycnal deltas over bedrock

We propose a simple morphodynamic theory of reservoir deltas prograding over bedrock under the influence of turbid underflows. The theory models the geomorphic actions of fluvial and hyperpycnal flows as diffusion processes, and treats bedrock‐alluvial and river‐lake transitions as moving internal boundaries. It yields self‐similar analytical solutions for the co‐evolving river and lake bed profiles, under different slope and influx conditions. These include a special case in which delta deposits are swept underwater to prograde into a subaqueous turbid pool. The theoretical predictions are in good agreement with microscale experiments, and should help interpret and anticipate longitudinal sedimentation patterns in mountain reservoirs.