A triangular coastal element developed for use in finite difference tidal models

Abstract

In numerical models of environmental flows it is often necessary to implement impermeable boundaries of complicated shape. For example, when modelling the spread of pollutants in streams, the dispersion of contaminants in lakes and estuaries or the final coastal destination of an oil spill, the land-water boundary is not simply defined. Currently such boundaries are best represented using Finite Element (FE) techniques. However FE techniques are both computationally expensive and difficult to implement. As a result Finite Difference Methods (FDM) on rectangular grids have traditionally been used to model environmental flows. In this paper a triangular boundary element for finite difference models of tidal flows in coastal regions, which improves boundary resolution while maintaining computational efficiency, is developed and tested. Numerical predictions using the new approach are compared with predictions obtained using the traditional stepped boundary and an analytic solution for depth-integrated flow in an idealised estuary.