Modeling Flow In and Above a Porous Beach

Abstract

The development of a numerical model for the simulation of water flow in and above a porous beach is described. The model, OTTP-1D, is based on a previous hydrodynamic model of the swash zone, OTT-1D, and builds on the numerical methods developed in the earlier model by the addition of a permeable layer representing a gravel beach. The porewater flow equations used in the present model are described along with the boundary layer approach used to determine the bed shear stress when the effects of exchange between the free-flow and porewater flow regions of the model are taken into consideration. These equations are transformed so as to make them amenable to solution by an upwind finite volume method in the same way as the earlier model. The model is verified against a simple analytical case of Darcy flow and an estimate of lower limit of applicable grain size made thereby. Validation against observed water depths and free-flow velocities recorded on a gravel beach at Slapton, U.K. in 2001 is also undertaken. The model accurately predicts both measured instantaneous water depths and velocities.