Improved numerical modelling of estuarine flows

Three key improvements to a widely used numerical model for predicting depth-averaged shallow water flows in estuarine and coastal waters are outlined herein. They include the adoption of a new grid layout for calculating friction and viscosity, a new method for simulating flooding and drying processes and a better representation of irregular wall boundaries. Although these improvements are currently implemented in the Depth Integrated Velocities And Solute Transport (DIVAST) model, they can easily be extended to other numerical models in the framework of a finite-difference or finite-volume method on a space-staggered rectangular grid system. Much effort has been made to keep the improvements simple and efficient so that they can be used in long-term and large-area simulations of estuarine and coastal flows. Numerical tests have been undertaken to verify the performance of these refinements for idealised bed forms, different beach configurations and irregular shoreline boundaries. The results show that for all conditions these refinements produce either the same or better results than the original model. Finally, the refined numerical model was used to simulate the tidal flow in a natural coastal basin. On the whole, the predicted variations in the inundation areas and the velocity fields were reproduced more accurately for different stages of the tide. At field measurement sites, the predicted water levels and velocities agreed favourably with the measured data.