Equilibrium beach profile with net cross-shore sand transport

Abstract

Periodic beachfill placement and frequent overwash result in net offshore and onshore sand transport, respectively. Three tests consisting of fifty 400-s runs were conducted in a small-scale wave flume to examine the effect of net cross-shore sand transport on an equilibrium profile. The foreshore of an equilibrium profile with no net sand transport shifted seaward after periodic sand placement near the shoreline. Frequent sand overwash resulted in the landward shift of the shoreline. The profile changes among the three tests were relatively small and the shoreline shifts were less than 0.1 m. An analytical model for an equilibrium profile with net cross-shore sand transport is developed by approximating existing formulas for onshore bed load and offshore suspended sand transport in the inner surf zone. The model predicts the horizontal shift of the equilibrium profile under net cross-shore sand transport, which is the maximum at the shoreline and approaches zero at the closure depth. The model calibrated using the three tests are used to estimate the seaward shift of the shoreline on periodically-nourished beaches of prototype scale. The estimated shift is of the order of 1 m or less but will need to be verified using field data.