Response of deeper groundwater in the delta area to intensive pumping — case study

Figure 1: hourly groundwater levels in three boreholes at Lakshmipur site in Bangladesh.  Note these groundwater level data are not corrected for atmospheric pressure and water density.
Figure 2. Groundwater sampling in Bangladesh field area.

Deep groundwater (more than 150 m below ground level) in the Bengal Basin is being increasingly exploited as an alternative to shallow, arsenic-rich groundwater.

This study assesses the impacts of abstraction on the recharge and the quality of deep groundwater within the Bengal Basin. Of particular interest are salinity and arsenic (As) concentrations.

Key objectives

Key components to this analysis are an improved understanding of:

  1. the extent of aquifers and aquitards across the basin
  2. hydraulic connectivity of groundwater at different depths (shallow, intermediate, deep) within deltaic deposits
  3. the residence times and chemistry of groundwater with depth

Research approach

Field Activities

  1. Correlation of borehole lithologs
    Borehole lithological data from the Bengal Basin are being correlated to produce a uniform interpretation for hydrogeological analysis and mapping of aquifers.
  2. Installation of data loggers
    Automatic data loggers have been installed in eight nested, multi-level piezometer sites to monitor at high frequency (hourly) groundwater levels at various depths as well as groundwater salinity (Figure 1).
  3. Groundwater sampling
    Groundwater samples are being collected from multi-level piezometer sites and individual abstraction boreholes to analyse the chemical composition including As and salinity, stable isotopes, and residence time indicators (Figure 2).

Analysis of climate change models

Climate change projections from multi-model ensembles compiled under the Fourth and Fifth Assessment Reports of the IPCC (CMIP3, CMIP5) are being assessed to evaluate changes in rainfall intensity — a key influence on recharge — over the Bengal Basin for three future epochs, representing the early (2021–2050), mid (2035–2065) and late (2070–2099) 21st century.

This will enable assessment of the projected impacts of climate change impacts on storage and quality of the deep groundwater resource.

Project team

The case study involves researchers from the British Geological Survey, University College London, University of Dhaka and Indian Institute of Technology Kharagpur.

Contact

Contact Dr Alan MacDonald for further information.