CHARACTERIZATION OF SURFACE WATER-GROUNDWATER INTERACTIONS IN THE UPPER JHELUM BASIN, HIMALAYAS, USING AN INTEGRATED GEOCHEMICAL, ISOTOPIC, AND MODELING APPROACH

Abstract

Surface water and groundwater have been regarded as separate components of the hydrological cycle for centuries in water resources management. However, surface water and groundwater are hydraulically connected and function as a single resource. The interactions between surface water and groundwater in the Himalayan basins remain poorly understood. Understanding the mechanisms of interactions between surface water and groundwater is essential for attaining sustainable development. This thesis presents a systematic approach to quantitative analysis of temporal and spatial interactions between surface water and groundwater in the Upper Jhelum River Basin (UJRB) with hydrogeochemical, isotopic, and modeling approaches. The first topic focuses on the spatio-temporal variability of isotopic signatures of stream water, rain, winter fresh snow, snowpack, glaciers, springs, and wells to identify the water sources and conceptualize the streamflow dynamics in three catchments (Lidder, Sindh, and Vishow). The snowmelt dominated the streamflow, with spatially averaged snow meltwater contributions across the entire catchment varying between 59±9%, 55±4%, 56±6%, and 55±9% in Lidder, 43±6%, 38±6%, 32±4%, and 33±5% in Sindh and 45±8%, 40±6%, 39±6%, and 32±5% in Vishow during the spring, summer, autumn, and winter seasons, respectively. The glacier melt contributions can reach ~30% of streamflow near source regions during peak summer. The findings suggests that if the glacier contribution were to completely disappear in the future, the annual average streamflow in Lidder and Sindh would decrease by up to ~20%. The depletion of the cryosphere in the region has caused an increase in runoff (1980-2000) but also shows a significant reduction of streamflow due to the loss of glacier mass and changes in peak streamflow over the past two decades (2000-2020). The second topic focuses on the identification and quantification of Mountain Front Recharge (MFR) and Mountain Block Recharge (MBR). MFR and MBR recharge are challenging to distinguish and are the least quantified, considering the lack of extensive understanding of the hydrological processes in the mountains. This study used oxygen and hydrogen isotopes, electrical conductivity (EC) data, hydraulic head, and groundwater level data to differentiate MFR and MBR. The results suggest that Karst springs (KS) and Deep groundwater (DGW) recharge are dominated by snowmelt (47%±10% and 46%±9%) as MBR from adjacent mountains, insignificantly affected by evaporation. The hydraulic head data and isotopes indicate a Quaternary shallow aquifer system as MFR of local meteoric water with significant evaporation. The KS and DGW suggest no evaporation effect as they plot on Local Meteoric Water Line (LMWL), while most of the Shallow groundwater (SGW) samples plotting between LMWL and Global Meteoric Water Line (GMWL) and below GMWL show an evaporation effect. The estimated recharge elevation for KS ranges from 2300m to 3500m (average: 2900m asl). The estimated recharge elevation for springs emerging from alluvium ranges from 1900m to 3500m (average: 2700m asl), whereas for springs emerging from Panjal-Traps ranges from 3100m to 3400m (average: 3250m asl). This study employed an integrated approach from hydrochemical data, isotopes (2H, 3H, and 18O), and hydro-meteorological data to advance the understanding of regional-scale water origin, residence time, hydrochemical evolution, and SW-GW interactions. The surface water and groundwater in the basin are controlled by seasonal recharge sources, demonstrating interacting linkages between SW-GW recharge systems. The river gaining zone was identified along the Alluvial Plain (AP) and Lacustrine Plain (LP) of the basin. The groundwater plays a vital role in maintaining winter–spring baseflow, with a spatially averaged contribution of 66±7% in winter and 39±10% in spring. The SGW system primarily relies on recent meltwater and rain with rapid recharge. The hydrochemistry of SGW is dominantly controlled by carbonate dissolution, cation exchange, and agricultural inputs from irrigation return flow, resulting in slightly alkaline water with TDS values < 500 mg/L and Ca2+-Mg2+-HCO3⁻ facies. The intermediate flow evolves from Ca2+-Mg2+-HCO3⁻ type from the recharge area (near MF) to Ca2+-Mg2+- SO42⁻/Cl⁻ type at the discharge areas of AP and LP. Evaporation also plays a significant role in the geochemical processes of SGW and lake water in LP, leading to enriched isotopic values and mineral precipitation (aragonite, calcite, and dolomite). The DGW in the basin is recharged directly by river water seepage and mountainous lateral inflow from meltwaters. Due to longer residence time in the aquifer, the chemistry of deep confined groundwater is also influenced dominantly by mineral dissolution and less commonly by cation exchange compared to river water and SGW, and it exhibits a trend of increasing solute inputs and evolves more likely as SGW from Ca2+-Mg2+-HCO3⁻ type to Ca2+-Mg2+-SO42⁻/Cl⁻ type along the flow path. These results led to the formulation of a coherent conceptual flow model that demonstrates the effectiveness of an integrated approach for determining SW-GW interactions in a transboundary basin that has significant implications for water security across the basin.