Terrestrial water load and groundwater fluctuation in the Bengal Basin

Abstract

Groundwater-level fluctuations represent hydraulic responses to changes in groundwater storage due to aquifer recharge and drainage as well as to changes in stress that include water mass loading and unloading above the aquifer surface. The latter ‘poroelastic’ response of confined aquifers is a well-established phenomenon which has been demonstrated in diverse hydrogeological environments but is frequently ignored in assessments of groundwater resources. Here we present high-frequency groundwater measurements over a twelve-month period from the tropical, fluvio-deltaic Bengal Aquifer System (BAS), the largest aquifer in south Asia. The groundwater level fluctuations are dominated by the aquifer poroelastic response to changes in terrestrial water loading by processes acting over periods ranging from hours to months; the effects of groundwater flow are subordinate. Our measurements represent the first direct, quantitative identification of loading effects on groundwater levels in the BAS. Our analysis highlights the potential limitations of hydrogeological analyses which ignore loading effects in this environment. We also demonstrate the potential for employing poroelastic responses in the BAS and across other tropical fluvio-deltaic regions as a direct, in-situ measure of changes in terrestrial water storage to complement analyses from the Gravity and Climate Experiment (GRACE) mission but at much higher resolution.

Security of Deep Groundwater in the Coastal Bengal Basin Revealed by Tracers

“…Remote from cities, shallow groundwater levels over the last 20 years in the BAS have remained constant or risen (0.4 to 2.5 cm/a), commensurate with rising sea levels (Shamsudduha et al, ). Piezometric heads from multilevel monitoring sites presented here (Figure d) reveal downward hydraulic gradients within the uppermost 200 m below ground level (mbgl) of the BAS whereas deeper within the BAS >200 mbgl upward hydraulic gradients dominate (Burgess et al, ), see supporting information.…”

Security of deep groundwater against arsenic contamination in the Bengal Aquifer System: a numerical modeling study in southeast Bangladesh

“…Furthermore, the model was validated regionally against groundwater heads monitored by the Bangladesh Water Development Board at shallow levels, < 75 m depth within the study area (BWDB 2005;Zahid 2008;Zahid et al 2015) for the depth-distributed pumping scenario with pumping quantities for 2004 (BADC 2005). Additionally, Burgess et al (2017) show that groundwater levels in BAS are greatly influenced by terrestrial water Fig. 2 The spatial distribution of groundwater abstraction for domestic supply and irrigation for the 2003-2004 dry season, illustrated the depth-dependent groundwater abstraction strategy loading and unloading at the surface and thus calibration of numerical models of transient groundwater flow using groundwater-level records is questionable.…”

Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products

“…In addition, direct comparisons between in situ observations of SMS, SWS, and GWS and gridded GRACE TWS anomalies are complicated by substantial differences in spatial scales, which need to be considered prior to analysis (Becker et al, 2010). For example, individual groundwaterlevel monitoring boreholes may represent, depending on borehole depth, a sensing area of several tens of square kilometres (Burgess et al, 2017), whereas the typical GRACE footprint is ∼ 200 000 km 2 . The disaggregation of GRACE TWS into individual water stores can also propagate errors to disaggregated components.…”