Groundwater is used intensively in Asian mega-deltas yet the processes by which groundwater is replenished in these deltaic systems remain inadequately understood. Drawing insight from hourly monitoring of groundwater levels and rainfall in two contrasting settings, comprising permeable surficial deposits of Holocene age and Plio-Pleistocene terrace deposits, together with longer-term, lower-frequency records of groundwater levels, river stage, and rainfall from the Bengal Basin, conceptual models of recharge processes in these two depositional environments are developed. The representivity of these conceptual models across the Bengal Basin in Bangladesh is explored by way of statistical cluster analysis of groundwater-level time series data. Observational records reveal that both diffuse and focused recharge processes occur in Holocene deposits, whereas recharge in Plio-Pleistocene deposits is dominated by indirect leakage from river channels where incision has enabled a direct hydraulic connection between river channels and the Plio-Pleistocene aquifer underlying surficial clays. Seasonal cycles of recharge and discharge including the onset of dry-season groundwater-fed irrigation are well characterised by compiled observational records. Groundwater depletion, evident from declining groundwater levels with a diminished seasonality, is pronounced in Plio-Pleistocene environments where direct recharge is inhibited by the surficial clays. In contrast, intensive shallow groundwater abstraction in Holocene environments can enhance direct and indirect recharge via a more permeable surface geology. The vital contributions of indirect recharge of shallow groundwater identified in both depositional settings in the Bengal Basin highlight the critical limitation of using models that exclude this process in the estimation of groundwater recharge in Asian mega-deltas.

在亚洲大三角洲中大量使用了地下水，但对于这些三角洲系统中补充地下水的过程仍知之甚少。在两个截然不同的环境下，通过每小时监测地下水位和降水量获得洞察力，包括全新世年龄的可渗透表层沉积物和上新世阶地沉积物，以及长期，低频的地下水位，河流水位和降雨记录。孟加拉盆地，开发了这两种沉积环境中补给过程的概念模型。通过对地下水位时间序列数据进行统计聚类分析，探讨了孟加拉国整个孟加拉盆地这些概念模型的代表性。观测记录表明，全新世沉积同时发生了弥散和集中补给过程，而上里新世沉积物的补给主要来自河道的间接渗漏，切口使河道与地下黏土下的上新世含水层之间直接形成水力联系。汇编的观测记录很好地描述了补给和排放的季节性周期，包括旱季地下水灌溉的开始。在上新世环境中，表层黏土抑制了直接补给，在地下水位下降和季节性下降的情况下，地下水消耗明显减少。相反，全新世环境中密集的浅层地下水抽取可以通过更具渗透性的地表地质来增强直接和间接补给。