Occurrence and discharge variability of Phalebas Thrust associated springs in western Middle Hill, Nepal

Geological discontinuities play a key role in groundwater movement and storage, especially in tectonically active and metamorphic rock-dominated terrains. The study area is located in the Syangja District western Nepal, with an area of 28.71 sq. km. around the Phalebas Thrust. This study focuses on the occurrence and discharge of springs with respect to the thrust. A post-monsoon spring inventory was conducted to gather information on spring location, discharge, temperature, surrounding geology, and structural discontinuities. The major lithologies are slate, dolomite, phyllite, and quartzite. Springs are classified on the basis of thrust-associated (≤ 100 m), possible associated (100–200 m) and not associated to thrust (> 200 m). Out of 92 springs of the study area, 62% of sprigs are located close to the thrust line, within 500 m, and median spring-to-thrust distance is 282 m. Similarly, 46% of the total discharge was contributed within 200 m, while the highest value of 39.97 lpm was within 100–200 m. The spring density was the highest (14 springs/sq. km.) closest to the thrust but decreased as distance from the thrust alignment increases. Thrust distance governs spring occurrence (exponential λ = 0.0021 m −1 , p < 0.001) but not discharge (Spearman ρ = − 0.047, p = 0.66). However, the discharge varies with geological contacts, size of recharge area, facture connectivity, and precipitation event. The findings emphasize the need for targeted protection of spring sources and recharge areas near major thrust zones, alongside land-use planning and community-based springshed managment for sustainable water security in the Middle Hills.