Validity of a moving boundary finite element model for salt intrusion in a branching estuary

A previously developed scheme for modelling of salt intrusion in estuaries with significant flow channel boundary variations during tidal cycles has been applied to a narrow branching estuary. It is shown that realistic simulations for complex tidal water systems can be obtained with this scheme provided that a suitable modification to the solution algorithm is implemented. The required modification is explained in detail and the model is applied to simulate salt intrusion in the Upper Milford Haven estuary in Wales, UK. Essentially, this moving boundary scheme introduces a distinct procedure for transient mass balance to ensure logical division of flow at an estuary junction and tracking of fluid particle trajectories along various branches of the estuary. Computational results and available field survey data for depth-averaged salinities are compared to determine the accuracy of the developed model. It is shown that the numerical results converge closer to field values than those previously reported. The method promises to provide new insights for environmental assessment, such as the determination of more accurate effluent discharge policies for estuaries.