Modeling of Soft Cliff Erosion by Oblique Breaking Waves during a Storm

Abstract

Soft cliff (bluff) erosion during a storm is investigated using available wave basin data and a cross-shore numerical model for dune erosion. The measured cliff recession rates under oblique breaking waves for cliffs built of wet sand and a sand/clay mixture (90.8% sand) can be reproduced by a numerical model that is modified to account for sand loss associated with the alongshore gradient of longshore sand transport. The sand loss is affected by the beach material (concrete or sand) when the incident irregular waves break on the beach and cause sand transport seaward of the cliff toe with small depth. The effect of sediment cohesion on cliff erosion was examined using the numerical model extended to cohesive sediment containing sand. For cohesive sediment with weak resistance against wave action, the cliff recession rate was limited by the rate of sand removal by longshore and cross-shore sand transport. The recession rate decreased when the resistance of the cliff material exceeded a critical value. These findings will need to be verified using experimental and field data.