Understanding river – subsurface water interactions in upper Ganga basin, India

Abstract

In the upper Ganga basin particularly in Himalayan terrain, precipitation and/or snow/glacial melt contribute towards the flow of the Ganga river in the form of surface and sub-surface water. In the present study, river–subsurface water chemistry is compared to infer river–subsurface water interactions in higher Himalayan region. Forty-one water samples from the Ganga river and its small tributaries between Gomukh and Dabrani section as well as subsurface water were collected during the months of March, May, September, October and November 2016 with in-situ measurements of pH, Electric Conductivity, temperature and bicarbonates. The samples were analysed for major ions and isotopes of oxygen and hydrogen. The results revealed that major ion chemistry of sub-surface water and river water is influenced by seasonal mineral dissolution and rock weathering reactions in the sub-surface water. A dominance of Calcium (36–43% in surface and 61–71% in sub-surface water), bicarbonate (13–66% in surface water and 45–85% in subsurface water) and sulphate (31–86% in surface water; 15–47% in sub surface) is observed. High carbonate dominance is observed in surface water during the pre-monsoon (May 2016) suggesting more carbonate dissolution while high sulphates are found in March and September. The isotopes characterization of the surface and sub-surface water indicated highly evaporated sub-surface water in pre-monsoon season while in post monsoon season the slope and intercept values of δ18O and δD plot was more close to that of surface water suggesting its influence. The study helps understand to river–subsurface water interactions in the Himalayan terrain of the Ganga basin. The understanding of river–subsurface water interactions can help in management of the Ganga river water and in addressing downstream environmental issues associated with the river.