Potential for managed aquifer recharge in southwestern Bangladesh based on social necessity and technical suitability

In southwestern Bangladesh, clean drinking water is scarce, since rainwater is only available during the monsoon, pond water is often bacteriologically polluted, and groundwater may exhibit high salinity and arsenic levels. Managed aquifer recharge (MAR) might potentially provide safe drinking water by storing abundant freshwater from the wet season in aquifers for year-round use. Regional potential for MAR was determined by combining assessments of (1) social necessity for MAR by mapping areas with insufficient drinking water of acceptable quality; (2) regional technical suitability by determining the (a) impact of density-driven flow on freshwater recovery efficiency, and (b) vulnerability of recovered water to mixing with contaminated groundwater. These assessments were based on the largest groundwater quality dataset compiled to date in southwestern Bangladesh, which contains 3,716 salinity and 827 arsenic measurements. The results show there is some mismatch between social necessity and technical suitability. In some northern areas, necessity is low because good quality groundwater is present and hence, despite the high technical suitability, potential for MAR is reduced. In other northern areas, groundwater with unsafe arsenic levels or brackish groundwater is likely used for drinking. There, MAR is a technically suitable and safer option. In southern areas, where saline groundwater is widespread and people consume bacterially unsafe pond water, the high groundwater salinity calls for careful evaluation of MAR design, for which this study presents practical guidelines. The approach developed may be useful for mapping MAR potential based on social necessity and technical suitability in other saline deltas worldwide.