A semi-empirical model for beach profile evolution in the vicinity of reflective structures

Abstract

In order to consider the effect of reflective structures on beach morphology, a number of experiments have been performed in front of a partially reflective seawall located in the surfzone. The main objective of these experiments was a quantitative comparison of near-bed velocities in two cases (i.e. with and without the reflective structure).The velocity measurements have been complemented by beach profile measurements performed with different sizes of sand. The results obtained from the profile evolution measurements in front of reflective seawalls indicate that a seawall located well landward of the active shoreface will behave in much the same way as a natural beach whereas seawalls located in the active shoreface will modify the near-shore beach profile because of the effects of reflected waves. Based on the results obtained from the measurements, a beach profile evolution model has been developed, using the measured probability distribution of near-bed horizontal velocities as input, to predict the short-term bed-level changes in front of reflective structures. The main conceptual innovation of the model is taking the probability density functions of the near-bed velocities into account and integrating them to calculate the sediment displacements across the profile using a threshold criterion for initiation of sediment motion. The results obtained from the model and comparison with the experimental results are promising and encouraging for further developments of the preliminary model.