Numerical Investigation of River Discharge and Tidal Variation Impact on Salinity Intrusion in a Generic River Delta Through Idealized Modelling

Abstract

Salinity in deltaic systems is expected to increase in the near future due to sea level rise. This will cause severe environmental consequences because salinity can be detrimental to agriculture, aquaculture and human consumption. Tidal dynamics are important in regulating salinity in river deltas. However, there is still uncertainty about the influence of different tidal amplitudes on deltas’ salinity. This paper investigates the impact of various tidal amplitudes on the spatiotemporal salinity distribution in deltas through three-dimensional idealized modelling. Numerical simulations are carried out with a common hydrograph and different tidal ranges. Both tide-influenced and river-dominated cases were considered. Results suggest that small increases in the tidal amplitude in river-dominated or low tidal regimes cases can have positive effects against salinization. Tide-induced mixing helps to increase freshwater areas and volumes. The water in the delta remains fresh for longer periods in scenarios representative of microtidal regimes. Further increases in the tidal amplitude to meso- and macrotidal levels reverse these effects and reduce freshwater areas and volumes. Results were used to test how salinity correlates with channel orders and river discharge in the presence of tides. These correlations are controlled more by bathymetry than tidal forcing. This study provides important insights into how changes in tidal range could impact spatiotemporal salinity distributions in deltas.