The recent trend of groundwater depletion in north western part of the Indo-Gangetic basin in India has posed serious threat to sustainability of the groundwater resources and the livelihood depending on it. Therefore, it become necessary to understand the groundwater dynamics of the region for proposing a sustainable groundwater management strategy. We analyzed tritium (3H) of groundwater alongwith source water (i.e., rainfall, groundwater, and surface water) to monitor the spatial and depthwise variability of 3H in the aquifer system of the Ghaggar River Basin (GRB). GRB lies between the snow and glacier fed Yamuna and Sutlej river systems of the north-west India. Total 91 groundwater samples were collected from the GRB during pre- and post-monsoon periods of 2013 and analysed at National Institute of Hydrology, Roorkee, India. Results are reported in Tritium Unit (TU) with 2 sigma error. The main objectives of the present work is to trace recharge sources and zones, flow regime and to understand relative residence time of aquifers up to sampling depth of 320 mbgl in GRB of north-west India.
Variation of tritium concentration in the groundwater of the study area was estimated between ~0.10 TU (minimum) and 12.9±0.5 TU (maximum). The groundwater samples collected up to depth of 80 mbgl show significant spatial variation in the tritium values, in the range of 0.3±0.2 to 12.9±0.5 TU. In contrast, the groundwater samples from the aquifers below 80 mbgl (deeper aquifers) in general show lesser varaiation in the range of ~0.1 to 4.4±0.2 TU. These subtle differences in TU values in longitudinal as well as deptwise indicate complex recharge sources in the study and flow regime in both shallow and deeper aquifers. The compratively higher tritium concentration in shallow aqifer (depth up to 80 mbgl) has been attributed to the influence of local recharge from the canal seepage and irrigation return flow in the study area. The range of tritium concentration of shallow aquifers indicate that the aquifer is a mixture of modern and recent recharged water. However the presence of low to moderate tritium (less than 4 TU) in deeper aquifer suggest presence of mixed recharged water from recent and old water. The presence of high tritium concentration in middle and distal part of the aquifer in the basin may be due to nested flow system where both young and old groundwater are present at the local scale. It elucidates that aquifer is heterogeneous in nature. The understanding of the variation in the recharge sources, processes and flow regime in aquifer system in the study area can be used for developing a sustainable groundwater management plan for the Ghaggar River basin.