Controls on groundwater flow in the Bengal Basin of India and Bangladesh: regional modeling analysisContrôles de l’écoulement de l’eau souterraine dans le Bassin du Bengale en Inde et au Bengladesh : analyse d’une modélisation régionaleControles sobre el flujo de agua subterránea en la cuenca de Bengala de India y Bangladesh: análisis de modelado regional孟加盆地地下水流动的控制因素 : 区域模拟分析Controladores do fluxo de água subterrânea na Bacia de Bengala (Índia e Bangladesh): análise de um modelo regional

Groundwater for domestic and irrigation purposes is produced primarily from shallow parts of the Bengal Basin aquifer system (India and Bangladesh), which contains high concentrations of dissolved arsenic (exceeding worldwide drinking water standards), though deeper groundwater is generally low in arsenic. An essential first step for determining sustainable management of the deep groundwater resource is identification of hydrogeologic controls on flow and quantification of basin-scale groundwater flow patterns. Results from groundwater modeling, in which the Bengal Basin aquifer system is represented as a single aquifer with higher horizontal than vertical hydraulic conductivity, indicate that this anisotropy is the primary hydrogeologic control on the natural flowpath lengths. Despite extremely low hydraulic gradients due to minimal topographic relief, anisotropy implies large-scale (tens to hundreds of kilometers) flow at depth. Other hydrogeologic factors, including lateral and vertical changes in hydraulic conductivity, have minor effects on overall flow patterns. However, because natural hydraulic gradients are low, the impact of pumping on groundwater flow is overwhelming; modeling indicates that pumping has substantially changed the shallow groundwater budget and flowpaths from predevelopment conditions.