The Effects of Seawalls on the Beach: Part II, Numerical Modeling of SUPERTANK Seawall Tests

This paper presents calculation results from a numerical model of cross- shore transport and beach profile change at seawalls. For this work, the SBEACH model was re-written to include wave reflection at a wall. The reflected waves modify the radiation stress, modulate the wave setup/setdown, and cause the incident waves to begin breaking farther offshore. However, the influence of the reflected wave on the cross-shore transport rate and the beach profile is rather minor for the dissipation- type sediment transport model employed, and in the absence of longshore processes. Profile responses to a storm for a beach with and without a seawall are surprisingly similar, except close to the wall. Predictions from the model are compared to measurements made at the large-scale seawall tests conducted during the SUPERTANK Laboratory Data Collection Project. Results for predicted wave heights across the surf zone are in good agreement with measurements. Reasonable agreement was observed for the profile change and scour at the seawall. The large-scale tests also supported the observation that the influence of reflection on the profile is minor. This paper is the second of a companion set of papers that investigate the effects of seawalls on the beach. The first paper presents a critical review and synthesis of the literature on seawalls and the beach published since a previous review in 1988.