Managing Saline Water Intrusion in the Lower Indus Basin Aquifer

摘要

In view of the declining surface water sources for irrigated agriculture in Pakistan, formers are compelled to extract groundwater in order provide to security against uncertain canal supplies during critical crop growth periods. However saline water intrusion can be a major hindrance to the sustainable groundwater development. Against this background, a study was conducted with a three dimensional finite element model (FEMGWST) based on the Galerkin weighted residual method being developed to simulate groundwater flow and the saline water intrusion from underlying poor quality aquifer in response to groundwater pumping through low capacity partially penetrated wells. The model was calibrated with field data collected in the district Khairpur of the Lower Indus Basin. The stability of the model for transient groundwater flow and solute transport against different time marching schemes were evaluated. This study showed that the explicit and the Crank-Nicolson time marching schemes developed the numerical oscillating, the global error and the convergence problem. The calibrated model was applied to predict the impacts of different well configurations on the pumped water quality and on the development of saline water mound at the bottom of the well. It was observed that the saline water intrusion into the fresh groundwater layer was directly related to the well discharge, pumping time and inversely to the thickness of fresh-saline water interface and the number of well strainers installed. The model results suggested that intermittent pumping through multi strainer wells could effectively be used to suppress the saline water intrusion. However multi strainers wells were found to induce saline water intrusion when the thickness of fresh-saline water interface was reduced to 4 m.