LAUSR

Abstract The surface water and groundwater interaction in the Imphal River Basin in Northeast India using hydrogeology, hydrochemical and isotopic constituents has examined to elucidate hydrochemical evolution, surface water and groundwater mixing and recharge condition. Groundwater is characterized by Ca2+–Cl-–HCO3-facies while surface water exhibits Ca2+–Cl- type. Surface water prevailed the intermediate stage of chemical evolution while groundwater characterizes the late stage of chemical evolution. Analysis of flow net combined with hydrogeologic sections revealed significant relationship of surface water and groundwater in the basin. The upper and lower reaches are characterized by contour heads showing an upstream pointing curvature due to depression induced by groundwater discharge where contour lines cross a gaining stream. The middle reach is marked by contour curvature pointing downstream owing to mounding induced by groundwater recharge where it crosses a losing stream. Groundwater shows markedly depleted isotopic composition than surface water. Both surface water and groundwater fall below Global Meteoric Water Line and Local Meteoric Water Line indicating the source of water through infiltration of modern precipitation. The slope of the evaporation line and the original composition of water are identified as 4.92 and −6.58‰ and −42.17‰, respectively. Isotopic d-excess values revealed isotopic composition of semi-arid climate.