Seasonal fluctuation of spring outflows in contrasting lithological and geomorphological environments of the western mid-hill region, Nepal

Abstract

Springs are vital water sources in the mid-hill region of Nepal, yet understanding of their seasonal outflow variability and the hydrogeological controls remain limited. This study analyzed 175 perennial springs in the western mid-hill region of Nepal, with seasonal outflow (discharge) measurements conducted during the post-monsoon high-flow periods in 2022 (Q1) and 2023 (Q2), and the pre-monsoon low-flow period in 2024 (Q3). Spring outflow was measured using volumetric gauging and weir methods depending on outflow conditions. Mean outflow declined from 36.44 lpm in Q1 to 31.97 lpm in Q2 and 15.66 lpm in Q3, indicating strong dry-season recession. The Friedman test confirmed significant seasonal variation among Q1, Q2, and Q3 (χ2=298.16, p<0.001), while Wilcoxon signed-rank tests showed significant differences between all seasonal pairs. The Q1–Q2 decline was partly linked to interannual rainfall variability, as monsoon rainfall decreased by 27.4% from 2022 to 2023. During Q3, nearly two-thirds of springs shifted into the minimal discharge class (≤10 lpm). Carbonate-dominant regions showed higher and more variable outflows, reflecting fractured/karstic aquifer storage. These findings support priority-based springs conservation and recharge enhancement for dry-season water security. The study emphasizes the need to distinguish seasonal spring recession from long-term groundwater depletion through sustained monitoring.