Spatial-diurnal variability of snow/glacier melt runoff in glacier regime river valley: Central Himalaya, India

Spatial-diurnal variability in the snow/glacier melt isotope signature and their influence on hydrograph separation based on mixing model received less attention. We present isotope data from a high elevation catchment (glacierized area: 286 km2) in the central Himalaya (India) and investigated the spatial-diurnal variability of snow/glacier meltwater along with inferences of groundwater dynamics. Isotope signature variation in streamflow was small during the study period. We applied a two-component mixing model using oxygen-18 and electrical conductivity. Hydrograph separation (snow/glacier meltwater and groundwater) was carried out for Bhagirathi River at three sites i.e., Gaumukh, Bhojbasa, and Gangotri, during the ablation period of 2014 (September). The Bhagirathi River is a major tributary of river Ganga, originate from Gangotri Glacier (-30 km), the largest glacier in central Himalaya. The electrical conductivity of the river is measured in-situ and varies from 10 ?S/cm to 100 ?S/cm. The river water isotope signature of oxygen was ranged from -15.53%o to - 14.32%o from Gaumukh to Gangotri, snow samples were ranged from - 17.63%o to - 15.86%o collected at Gaumukh. Groundwater samples were varied from -8.53%o to-7.57%o from Gaumukh to Gangotri. River water signature is close to snow/glacier melt runoff signature, reveal that the snow/glacier melt runoff contribution is higher in river flow. Average fractions of snow/glacier melt runoff were estimated -82% to-76%, whereas groundwater was estimated -18% to -24%. The results of this study reveal the necessity of a multiple sampling approaches to characterize the snow/glacier melt and the importance of groundwater dynamics in catchments with snow/ glacial runoff regime.

Automated summary

Spatial-diurnal variability in the isotope signature of snow/glacier meltwater and its influence on hydrograph separation using a mixing model were investigated in a high elevation catchment in the central Himalaya. Results showed that the river water isotope signature is close to snow/glacier melt runoff signature, indicating a higher contribution of snow/glacier melt runoff to river flow. The study highlights the importance of multiple sampling approaches to characterize snow/glacier melt and the role of groundwater dynamics in catchments with snow/glacial runoff regime.