6-Origin and Recharge Zones of Ground Water in a Himalayan Catchment - An Isotopic Approach

Abstract

Generally ground water emerges out in the form of natural springs as an important source of drinking water in the mountainous regions. An attempt has been made to study the origin and natural recharge zones of ground water by using isotopic composition (5180 and SD) of ground waters in parts of upper Ganga catchment. The 8180 in ground water varies between —12.73%o (minimum) at Gangotri (3050 m amsl) to — 4.6%o (maximum at Rishikesh (347 m amsl). The 8180 in precipitation varies —0.25%o to —0.28%o per 100 m with increase in altitude and in ground water, it is calculated to be -0.24%0 per 100 m with increase in altitude. The depletion of 8180 in ground water and precipitation with increase in altitude is due to the altitude effect. The regression analysis of 8180-0 of ground water shows that best fit line is close to Local Meteoric Water Line of Bhagirathi basin. This similarity in altitude effect and isotopic composition reveals that isotopic composition of precipitation is well preserved in the ground water and precipitation is the only source of recharge for ground water in the study area. The 5180 in ground water of Devprayag and Gangotri is more depleted than precipitation of these locations. It indicates that recharge zone is about 480 and 160 m above the sampling sites of Devprayag and Gangotri.