Comparison of the groundwater recharge estimations of the highly exploited aquifers in Bangladesh and their sustainability

Sudden increase of groundwater abstraction for water supply to a million forcefully migrated Myanmar nationals (Rohingya) in Ukhia and Teknaf Upazila of Cox's Bazar district has created a threat to the sustainability of the Dupi Tila and Tipam aquifers, the primary source of drinking water for the host community. Reasonable esti-mation of groundwater recharge is crucial for understanding the sustainability of an aquifer. Therefore, this study, estimates groundwater recharge employing multiple methods such as (i) WetSpass water balance model, (ii) Water Table Fluctuation (WTF), (iii) Chloride Mass Balance (CMB), and (iv) Empirical Formulas (EF) and compares it with current withdrawal. Additionally, the applicability of empirical formulas for recharge esti-mation in Bangladesh has been evaluated, which will benefit future groundwater studies requiring a rapid es-timate of recharge from precipitation. Despite a large spatial variability in recharge, the spatially mean annual groundwater recharge estimated by these methods is comparable to each other. The estimated spatially mean annual volumetric groundwater recharge for the Dupi Tila and Tipam aquifer is 135 and 122 million m3/y, respectively. Most of the estimated groundwater abstraction of 49 million m3/y in this area is from the Dupi Tila aquifer, which is about 36% of the annual recharge suggesting that the current withdrawal should be sustainable. However, since the Rohingya camp abstraction is concentrated within a small area, there is potential for a large cone of depression development in and around the camp, which may adversely impact the wells of the host population in adjacent areas. A numerical model is required to assess the extent of the cone and its impacts on host community wells. This study also finds that the Maxey-Eakin and Sehgal formulas for precipitation-based recharge estimation are the most suitable for this area and may be applied in other areas of Bangladesh.