Identification of river water and groundwater interaction using geochemical and isotopic indicators in the lower basin of the Cauvery river

Understanding the interactions between river water and groundwater is crucial for the better management of water resource problems. The present study was carried out to assess the river water and groundwater interaction in parts of the lower Cauvery river basin. The samples were collected from river water and groundwater from May 2018 to August 2021, thrice in a year. The samples were analyzed for EC, pH, major, minor ions, trace elements, and isotopes. The hydrochemical facies shows that the water is of mixed Ca-Na-HCO₃ type followed by Na-Cl type in both river water and groundwater. The dominance of cations in river and groundwater is of order Na>Ca>Mg>K whereas the dominance of anions in river water was in the order of Cl>HCO₃ >SO₄ whereas it was HCO₃>Cl>SO₄ in groundwater. The rock water interaction was the dominant geochemical process followed by the evaporation process in both river water and groundwater. The temporal variation of major ions between river water and groundwater in a few locations indicates that they follow a similar pattern, thus indicating their interrelationships. δD and δ¹⁸ O isotopes shows that the river water and groundwater are in a mixing zone between recharge water and evaporation line during the wet season. During the dry season, few samples have been isotopically enriched due to the effect of evaporation, which indicates that the groundwater contributes to the river water. Therefore, it is evident that during the wet season, the river water recharges the groundwater zone and groundwater discharges into the river water during the dry season. Hence, this present study helps in better understanding of the river water and groundwater interaction through geochemical methods.

Keywords: River water, groundwater, interaction & isotopes.