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Abstract

Understanding of groundwater and surface water interactions is essential since it provides information on the changes in their ecosystems that affects quality and quantity of both. Hence, the present study was carried out with an objective to identify the river water and groundwater interactions in Cauvery, a major river basin of Southern India. The river water and groundwater samples were collected once in four months from 2013 to 2019. The samples were analysed for major ions, trace elements and stable isotopes (δ¹⁸O and δ²H). Inverse modelling was carried using PHREEQC to understand the hydrogeochemical reactions during surface water and groundwater interaction. It was found that both groundwater and the surface water falls under Ca-Mg-HCO₃ and Na-Cl water type. The temporal variation of major ions between groundwater and river water shows similar pattern, indicating their interrelationships. The isotope results shows that groundwater and river water falls between precipitation and the evaporation during wet seasons, whereas few samples have been isotopically enriched during the dry season as a result of evaporation, suggesting the groundwater contribution to the river water. The weathering of hornblende, plagioclase, biotite, K-feldspar occurs during groundwater-river water interaction which then transforms to stable clay minerals. It was evident that at the lower part of the basin, the river water discharges into groundwater during the wet periods and vice versa during dry seasons. Thus, this current study on river water- groundwater interactions act as a baseline knowledge in developing sustainable water management plan in the river basins.