Impact of anthropogenic activities on river-aquifer exchange flux in an irrigation dominated Ganga river sub-basin

Abstract

The easy accessibility of groundwater in the alluvial plains of the Kosi river basin has considerably altered the crop calendar and farmers’ irrigation response, especially in the dry years after 2004. The present study attempts to develop a framework for analyzing the spatio-temporal variation in the groundwater recharge/ extraction pattern as well as river and aquifer flux exchange due to increasing anthropogenic activities in the basin. The influence of anthropogenic activities over groundwater recharge/extraction statistics has been discussed in Laveti et al. (2021). The estimated groundwater recharge (Laveti et al., 2021) along with aquifer characteristics (hydraulic conductivity, porosity, and specific storage), and riverbed conductance were used as inputs to the groundwater flow transient model in the study. The model observed, an increasing groundwater dependency for agricultural activities, results in a continuous increase of flux from the river to the aquifer. Between 1997 and 2010, the river to aquifer flux increased by almost 1% of the average river discharge. This increase in river to aquifer flux exchange was evident, especially during the dry periods after 2004, which coincided with the government’s Million Shallow Tube Well Programme (MSTP) in the basin. The increasing trend of the river to aquifer flux transfer and the decreasing trend of the aquifer to river flux transfer observed in the Kosi basin can have disturbing long-term effects in terms of reduced river flow and river stage. Therefore, the concerned authorities and the stakeholders must take immediate notice of the observations.