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

 

Presented by

Tingting Zhu

Ph.D. Candidate

Center for Applied Coastal Research

 

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 by volume) can be reproduced by the numerical model which is modified to account for sand loss associated with the alongshore gradient of longshore sand transport.  The computed cliff recession rates depend on the incident wave angle and the alongshore gradient.  The sand loss is affected by the beach material (fixed or sand) when the incident significant wave height exceeds about 0.6D  with D being the toe depth of the cliff.  The effect of sediment cohesion on cliff erosion is examined using the numerical model extended to cohesive sediment containing sand.  For cohesive sediment with weak resistance against wave action, the cliff recession rate is limited by the rate of sand removal by longshore and cross-shore sand transport.  The recession rate decreases when the resistance of the cliff material exceeds a critical value.  These findings will need to be verified using experimental and field data.

 

REFERENCE

Zhu, T. and Kobayashi, N. (2019), “Numerical Study on Erosion of Soft Cliff by Oblique Breaking Waves on Cohesionless and Cohesive Beach.” Research Report No. CACR-19-05, Center for Applied Coastal Research, University of Delaware, Newark, Delaware