Environmental isotope investigation to understand the groundwater recharge from irrigation tanks in Thirumal area, Madurai

Abstract

Madurai is a water scarce, semiarid region in southern part of Peninsular India. Currently, tank-fed agriculture development programme is being implemented in this region by utilizing the large number of traditionally existing minor irrigation tanks. Hence, an isotope hydrological investigation has been conducted in the Thirumal village, Madurai district to demarcate the zone of influence (i.e., the command area) of the cascade of tanks (4 tanks) and to quantify the groundwater recharge to the downstream wells. Pre (October 2011) and post (February 2012) monsoon samples were collected from the irrigation tanks, open wells upstream and downstream of the tanks etc. and analysed for δ2H, δ18O and hydrochemistry. The downstream well samples lie in a mixing line between the tank water and the rainwater in the δ18O - δ2H plot, indicating groundwater recharge from the irrigation tanks and the area of influence of these tanks were demarcated. The tanks contribution to the downstream wells varies from 97% at 20 m to 41% upto 880m for the first tank, 93% at 60m to 26% at 880m for the second tank, 95% at 30m to 18% at 940m for the fourth tank and varies from 25% at 20 m to 9% at 550m for the third tank.