Indication of subsurface seawater intrusion into the Indus delta, Sindh, Pakistan

Abstract

Due to climate change impacts, seawater intrusion is a major issue in various river deltas around the globe, including the Indus delta, Pakistan. The seawater intrusion has severely affected the freshwater resources as well as the livelihood of the people living in the Indus delta. Thus, this study was aimed to evaluate the subsurface seawater intrusion into the Indus delta based on the groundwater quality data. Around 180 groundwater samples, randomly collected from the study area, were analyzed for chloride, carbonate, and bicarbonate concentrations. Based on these concentrations, the indication of subsurface seawater intrusion was determined using Simpson’s ratio and ionic analysis, such as the ratio of chloride to bicarbonate. Also, an interpolated map using the analysis results of these ratios was developed using ArcGIS 10.5. Overall, the present study revealed that about 88% of the Indus delta is affected by the subsurface seawater intrusion. Also, the impact of subsurface seawater intrusion was observed in the wells near the Thatta and Sujawal towns of the study area. However, about 12% of the delta is still unaffected by the subsurface seawater intrusion. Various factors such as reduction in freshwater flow into the delta, climate change, sea-level rise are potential causes of subsurface seawater intrusion in the study area. This study may be taken as a baseline by the policymakers to start mitigation measures against the degradation of the delta to save the environment from further deterioration. Also, further an isotopic analysis of subsurface seawater intrusion in the study area is recommended.