Identification of surface water and groundwater interaction in a non perennial river using hydrogeochemistry and stable isotopes

Studying of surface water and groundwater interaction is crucial in understanding the changes in the ecosystems, thus affecting the quality as well as the quantity of hydrology of the catchment. Non -perennial rivers account around 50% of the world’s rivers and such interaction plays a prominent role in determination of seasonal availability and quality of such catchments. The present study aims to identify the river water and groundwater interaction using hydrogeochemistry and stable isotopes in Cauvery, a major non-perennial river of southern India. The river water as well as groundwater was collected once in four months from 2013 to 2021. The samples were analysed for major ions from 2013-2021 whereas stable isotopes δ¹⁸O and δ²H were analysed during 2018 and 2021. Inverse modelling was carried out to understand the hydrogeochemical reactions during surface water and groundwater interaction. Both river water and groundwater was  dominanted by Ca-Mg-HCO₃ and Na-Cl type. Seasonal variation of major ions in river water and groundwater shows similar variation. The inverse modelling indicates the weathering of hornblende, plagioclase, biotite, K-Feldspar into stable clay minerals along with the leaching of major ions into the water. The stable isotopes indicates that both 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 that groundwater contributes to the river water. Also, the interaction between river water and surface water is more evident during wet seasons, whereas during dry periods the interaction persists in headwater regions. 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 that groundwater contributes to the river water. The present study on river water and groundwater interactions acts a baseline framework in developing sustainable water management in non-perennial rivers. 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 that groundwater contributes 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.