A simplified model of rip currents systems around discontinuous submerged breakwaters

Although in the last years, several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers, only few simple methods of practical use are available for estimating main flow parameters, like the current intensity and the mean water levels, in terms of geometrical (barrier and gap dimensions) parameters and wave characteristics. The aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters. The model, which is based on rough simplifications, considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap. Four equations (mass and momentum conservation across the barrier, free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore) are used to derive one single model equation that can be solved for the wave set-up and subsequently used for rip current velocity calculation. Two free parameters appear in this equation which respectively account for energy losses at the gap (C-v) and bed friction (mu). The proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters, that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches. (C) 2004 Elsevier B.V. All rights reserved.