Evaluating baseflow contribution to stream flow using stable water isotopic signatures in Kameng river basin, North Eastern India.

The detailed assessment of water resources and hydrological cycle component are very critical for attaining sustainable development goals (SDGs) in a region. One of the critical challenges in water cycle science is to understand the source of water in a river which vary seasonally and spatially. Here we deal with the spatial pattern of a river in the North Eastern Himalayas, which receives groundwater and snow meltwater supply to meet the perennial flow regime. We used stable water isotopes of oxygen & hydrogen in the river water sampled during pre-Monsoon season. This study focusses on the region of West Kameng District of Arunachal Pradesh, India covering drainage basin of 2 tributaries of Kameng river basin viz. Tenga & Dirang as shown in Figure 1. Our study used isotopic method to trace the sources of which forms river water at the headwater regions.

The Local Meteoric Water line (LMWL) for the region is defined by δD = (8.046 ± 0.03). δ¹⁸O + (11.644 ± 0.5‰) as derived from analysis of water samples collected in March 2021. This LMWL is almost identical to the signature of precipitation collected during April – October, 2007 from station at Cherrapunjee Meghalaya, India as obtained from IAEA-GNIP data [δD = 8.068 δ¹⁸O + 12.347‰] as shown in Figure 2. The d-excess signatures from the two set of observations near similar, 11.21± 1.79 ‰ & 11.41± 2.21‰ respectively implying that river and rainwater in the study region are indistinguishable. Based on the observation we commented on the baseflow contribution of the river. Result suggests places where groundwater contribution to the river water is significantly high during dry time and overall enrichment of river water composition due to this process. We will provide estimate of base flow contribution based on mass balance equation, which is prominent more than 90% at higher elevation. The volume of the aquifer is large given the long residence time & can be estimated by timebound analysis of stable isotopes and tritium isotope.