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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2018-304
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2018-304
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jul 2018

Research article | 25 Jul 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Hydrology and Earth System Sciences (HESS).

A partially-coupled hydro-mechanical analysis of the Bengal Aquifer System under hydrological loading

Nicholas D. Woodman1,a, William G. Burgess1, Kazi Matin Ahmed2, and Anwar Zahid3 Nicholas D. Woodman et al.
  • 1Department of Earth Sciences, University College London, London WC1E 6BT, UK
  • 2Department of Geology, Dhaka University, Dhaka 1000, Bangladesh
  • 3Bangladesh Water Development Board, Dhaka, Bangladesh
  • acurrent address: Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK

Abstract. The coupled poro-mechanical behaviour of geologic-fluid systems is fundamental to numerous processes in structural geology, seismology and geotechnics but is frequently overlooked in hydrogeology. Substantial poro-mechanical influences on groundwater head have recently been highlighted in the Bengal Aquifer System, however, driven by terrestrial water loading across the Ganges-Brahmaputra-Meghna floodplains. Groundwater management in this strategically important fluvio-deltaic aquifer, the largest in south Asia, requires a coupled hydro-mechanical approach which acknowledges poro-elasticity. We present a simple partially-coupled, one-dimensional poro-elastic model of the Bengal Aquifer System, and explore the poro-mechanical responses of the aquifer to surface boundary conditions representing hydraulic head and mechanical load under three modes of terrestrial water variation. The characteristic responses, shown as amplitude and phase of hydraulic head in depth profile and of ground surface deflection, demonstrate (i) the limits to using water levels in piezometers to indicate groundwater recharge, as conventionally applied in groundwater resources management; (ii) the conditions under which piezometer water levels respond primarily to changes in the mass of terrestrial water storage, as applied in geological weighing lysimetry; (iii) the relationship of ground surface vertical deflection to changes in groundwater storage; and (iv) errors of attribution that could result from ignoring the poroelastic behaviour of the aquifer. These concepts are illustrated through application of the partially-coupled model to interpret multi-level piezometer data at two sites in southern Bangladesh. There is a need for further research into the coupled responses of the aquifer due to more complex forms of surface loading, particularly from rivers.

Nicholas D. Woodman et al.
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Short summary
We show that a conventional hydraulic understanding of groundwater level fluctuation is too simplistic for the extensive floodplains of Bangladesh and West Bengal. This is crucial because 150 million people of the region rely on groundwater for drinking and irrigation. We describe a more complex situation: the coupled hydro-mechanical action of surface water coming and going as the seasons change. Our model results will assist sustainable management of groundwater resources across the region.
We show that a conventional hydraulic understanding of groundwater level fluctuation is too...
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