Numerical investigations of change in hydrodynamics of a coastal aquifer due to saline groundwater pumping

Coastal communities in dry and semiarid areas confront a severe scarcity of potable water. To meet the requirements of a growing population by increased inland groundwater pumping, led to saltwater intrusion, which eventually rendered the available water unfit for human use. According to studies, desalination plants using saline groundwater as feed water (subsurface intake) might alleviate the problems with coastal water supply and quality. In this context, it becomes imperative to understand the saltwater transport and the associated flow and mixing process when saline groundwater is pumped from beneath the freshwater-saltwater interface. Hence to ascertain the effect of saline groundwater pumping on the hydrodynamics, a standard test aquifer was simulated using the finite difference model SEAWAT. The hydrodynamics is quantified by the entrained saltwater which will influence width of mixing zone, length of intrusion of toe and discharge of Darcy flux back to sea. Entrained water is the amount of saltwater entrained through freshwater - saltwater transition zone, for a steady and stable (lighter freshwater above heavier saltwater) flow system in an aquifer. Performance analysis were carried out to infer the influence of pumping rates on the velocity of entrainment. The results indicate that the mixing zone changed from having a sloping shape to one that was partly vertical and partially sloping, resulting in the establishment of a mixed water interface adjacent to the saline groundwater well. It is likely that there exist modest density gradients between the two fluids, but they quickly attained equilibrium due to the localized velocity change that was observed. Pumping induced more saltwater into the aquifer, which get pumped out restricting the further inland invasion of wedge. Understanding this interaction is crucial in order to determine the method's mitigation potential prior to adopting subsurface input for desalination.