VARIABILITY IN SNOW/ICE MELT, SURFACE RUNOFF AND GROUNDWATER TO SUTLEJ RIVER RUNOFF IN THE WESTERN HIMALAYAN REGION

The Himalayan glaciers are one of the major sources of water supply to Indian rivers, such as Ganges, Brahmaputra, and Indus. In recent times, a major question is being raised about the melting of glaciers and how it will impact river flows in the downstream regions. Therefore, the present study focuses on the Sutlej river basin in western Himalaya, one of the major tributaries of the Indus river system. The Sutlej river drains southern Punjab, Haryana and Rajasthan through surface water structures (such as canal). To estimate the relative contribution of the various hydrological component to river runoff, we collected water samples from the snow/ice melt, river, groundwater and rainfall from the Sutlej river basin for isotopic (δ¹⁸O and δ²H) analysis. The δ¹⁸O and δ²H values of Sutlej river water show seasonality across the study area. The present study assessed the relative contribution from snow/ice melt, surface runoff and groundwater to Sutlej river runoff at foothills of the Himalaya and downstream region of the study area using hydrograph separation approach and SNOW MOD hydrological modeling approach. Results from the present study show seasonality in relative contribution. The annual average contribution to Sutlej river runoff from snow/ice is about 58.8% at Ropar (located in foothills of Himalayas), and about 25.5% at Yusufpur (located in downstream region), surface runoff contribution at Ropar is about 23.1% and Yusufpur is about 38.8%, and groundwater contribution at Ropar is about 18.1% and about 35.6% at Yusufpur. In addition, to check the accuracy and robustness of contribution results, we used first-order Gaussian error propagation and Monte Carlo simulations methods. Assessed uncertainty values vary between 1.7% to 3.5%, and are associated with each relative contribution obtained from the three-component hydrograph separation approach. We also found good agreement between modeled and isotopic results in the present study.