Modelling hydrodynamics and sediment flux within a macrotidal estuary: problems and solutions

A model of estuarine circulation and sediment transport is described. The model uses a 2-D longitudinal and vertical grid to predict the distribution of tidal elevation, current velocity, density and sediment concentration. It has been developed for relatively narrow estuaries that have a large tidal range and potentially high river flow. The advantage over simple 1-D and depth-averaging 2-D models is that it can give reasonable representation of both gravitational circulation and the vertical distribution of suspended sediment concentrations, thereby providing better estimates of the bottom stress and sediment flux, particularly in the deep channel. The model has been developed as a management tool to provide some of the advantages of a full 3-D model, but with smaller development and running costs. It can be used to predict concentrations of contaminants in estuaries that have a significant load of suspended cohesive sediment, and can differentiate between dissolved contaminants and those that are attached to suspended sediments. It is a potentially useful tool for predicting the distribution of relatively short-lived contaminants that are affected by sediment concentration, such as bacteria and some radionuclides.