Improved hydrological process understanding of a mountain spring catchment in the lesser Indian Himalayas: A stable isotope and hydro-geochemistry based situational assessment.

Código

I-EBHE0034

Autores

Bhargabnanda Dass, Sumit Sen

Tema

WG 1.14: Droughts in Mountain Regions

Resumo

Groundwater springs serve as important sources of water for the inhabitants of the Indian Himalayas for domestic and commercial consumptive use. These life-supporting springs have either dried up or become seasonal over the last two decades causing water scarcity and hydrological imbalance in the fragile montane regions. This situation is due to a rapid, unplanned urban growth and the mismanagement of natural resources, further worsened by a changing climate. Quantifying and understanding aquifer dynamics is challenging as the hydrologic cycle in catchments is time variant and groundwater transmission is a highly complex nonlinear process. In this study, we characterize the springs and its flow properties in a sandstone catchment - Paligaad (59.7 km2 ) in Uttarakhand, India. Sampling was conducted for rainfall, springs (S02, S06, S07, S08, S09, S13, S14, S15, S16, S17), and streams (St01, St02, St03, St04, St05) from December 2021 till September 2023 and were analyzed for their isotopic (?18O and ?2H) and major chemical compositions (pH, TDS, cations : Na+, K+, Ca2+, K+, Mg2+, Na+, NH4+, and anions : Cl-, HCO3-, NO3-, SO42-, F-). The temporal isotopic and chemical signatures in rainfall, springs and streams was used to estimate Mean Residence Times (MRT) and to conduct spring water quality index modelling (SWQI) while also understanding groundwater evolution mechanisms. Results indicate that the Paligad catchment, and on average, exhibits an MRT ranging from 17 to 55 days for streams and 26 to 53 days for springs with a moderate goodness-of-fit (R2 = 0.47 to 0.77). It is observed that higher elevation springs display shorter MRT than lower elevation springs. The MRT ranged from 17-30 days in high elevations; 26-33 days in mid elevations while MRT varied from 33-55 days in lower elevations. Among high elevation springs, S06 and S02 showed the lowest MRT (28 and 30 days, respectively), followed by mid-level springs S07 and S09 (27 days), and low elevation spring S13 showed MRT of 40 days. These results indicate a rapid, flashy response of springflows to rainfall, attributed to the heterogeneous sandstone geology and the formation of preferential flow paths activating groundwater flow networks, resulting in complex, tortuous flow systems. The studied quality parameters were within the WHO guidelines and reports no contamination with heavy metals (Co, Cu, Cr, Ni, Zn and Pb). Based on the SWQI modelling, all the samples were classified as ?excellent? water category, with S04, S05, S06, S11, S14, S15 representing ?pristine? class. Results suggest Ca?HCO3 and Ca-Mg-HCO3 type waters and indicate silica degradation, groundwater mixing, and ion exchange process as the major controls on groundwater chemistry. Such a study addresses the need to garner science evidence-based derivation of quantitative information on spring hydrology in mountainous catchments and helps bolster the understanding of mountain hydrological processes. It supports site-specific catchment management decision-making and in scaling pilot studies across the Indian Himalayan region, for spring rejuvenation, drought remediation, aquifer characterization and co-designing interventions to build capacity and climate resilience.