Wave Reflection from Beaches: A Predictive Model

Abstract

A model to predict reflection of random waves on a beach, including dissipation due to breaking, is presented. The evolution of the local reflection coefficient and the incident and total wave height is computed. Two initial conditions are needed; the incident H_rms and the reflection coefficient, R, far offshore. The expected value of the wave breaking dissipation is estimated following BATTJES, and JANSSEN, (1978). The expected value of the reflected energy flux per unit area of beach profile is obtained hypothesizing that (1) wave reflection may be considered a linear process dependent only on the local profile geometry and wave period and (2) only the non-breaking waves contribute to the reflected flux of energy (BAQUERIZO, 1995). These results are compared with wave parameters measured during the SUPERTANK Project and with the reflection coefficient estimated by three different methods. Measured and computed data agree well for barred and non-barred beach profiles. It is shown that the local reflection coefficient evolves along the beach profile. An overall beach reflection coefficient should be defined only offshore of the depth where waves start to break and where the contribution to the wave reflection process is negligible.