Onshore Migration of Emerged Ridge and Ponded Runnel

Abstract

Ridge-runnel features can comprise large volumes of sand, and their migration can have a significant influence on the coastal sediment budget and beach recovery after a storm. Numerical modeling of ridge-runnel migration is challenging partly because of the strong interactions between the hydrodynamics and morphology and partly because of limited available field and laboratory measurements. This study investigated the effect of water ponding and runnel drainage on onshore ridge migration in an experiment in a sand flume where detailed free‐surface and velocity measurements were taken in the ponded water zone of the runnel and in the intermittently wet and dry zone on the ridge crest. The test scenario with a drained runnel showed a ridge migration speed five times larger than the scenario in which water and sediment could only exit the runnel as offshore return flow over the ridge. The time-averaged numerical model CSHORE was modified to include the ponded water effect in the sediment transport formulations. Results show the capabilities and shortcomings of CSHORE in reproducing the hydrodynamics, morphological evolution, and sediment transport rates measured during the experiment.