Design of discharge policies for multiple effluent sources and returning pollutants scenarios in a branching estuary

For realistic simulation of contaminants’ transport in an estuary, the presence of multiple sources and circulation of pollutants returning upstream of the discharge point should be considered. These factors contribute to a complex mechanism for effluent transport in estuaries, which can be quantitatively analysed using computational methodologies. In this work, a finite element model has been used to study the transport of solute pollutants in a branching estuary with controlled discharges from multiple sources. The scheme has been applied to test five discharge policies for the Upper Milford Haven estuary in Wales, UK, a typical branching estuary. The outcomes of each discharge schedule in relation to the minimisation of the pollutants’ concentration in the estuary, has been investigated for both spring and neap tides. Geomorphological features such as meanders and the bed slope of the estuary were included in the present study. To determine the transport and dilution of effluents in the estuary, other factors such as tidal dynamics and discharge point spacing and flow reversal have also been incorporated in the model. The developed scheme is used to quantify the interactions between multiple effluent discharges for different tidal conditions in conjunction with the effects of returning pollutants. Reaction mechanisms are not considered as the conservative behaviour for the effluents is assumed. The results of the present analysis can be generalised to networks of narrow branching estuaries characterised to predict the consequences of various discharge programmes.