An assessment of groundwater resources in the Banke district of Nepal
Using groundwater balance approaches on case studies and seasonal groundwater table fluctuation estimates
P.A. van Sabben (TU Delft - Civil Engineering & Geosciences)
Thom A. Bogaard – Mentor (TU Delft - Water Resources)
OAC Hoes – Graduation committee member (TU Delft - Water Resources)
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Abstract
Groundwater extraction has increased significantly in Nepal. In combination with climate change, this might lead to accelerated groundwater resource depletion. No recent research has been done in the assessment of these resources in the Banke district development area in the Terai. This study aims to assess whether the intensification of extractions has led to a depletion of groundwater in the upper aquifer. We investigated six local case studies during the dry season with a sole focus on the upper aquifer. The hydrological fluxes were quantified at every location. Evaporation and recharge were estimated using remote sensing data and locally obtained meteorological data. Domestic extractions, irrigation return flow and irrigation extractions were approximated by fieldwork. The groundwater storage change over the period was estimated using a recorded groundwater table time series and the Water Table Fluctuation method. The net subsurface flow- and percolation were estimated by closing the water balance for every case study. Subsequently, the fluxes at local case studies were extrapolated using Groundwater Response Units. The groundwater table replenishment was estimated using the relation between effective precipitation and groundwater levels over two years. The net extraction from the groundwater was insignificant compared to the contribution of evaporation. The approximate minimum precipitation needed for the monsoon season to recover the shallow aquifers after the dry season was on average comfortably exceeded over the last ten years. Thus, the groundwater resources are currently not depleting due to the intensification of extractions in the upper aquifer. However, the current extractions from deeper aquifers might decrease the pressure in deeper layers increasing percolation. Eventually, this endangers the groundwater resources in the upper aquifer. The limited number of measurements in deeper wells already indicated potential depletion in deeper layers. Further research is therefore recommended in deeper aquifers.