From hillslope runoff to channel migration: A multi-scale decision-support framework for sustainable water management in an Eastern Himalayan foothill region

Study Region The study was conducted in Baksa District, located in the Eastern Himalayan foothills of Assam, India, where intense monsoonal rainfall, steep terrain, heterogeneous land cover, and dynamic river systems pose significant challenges to sustainable water-resource management. Study Focus This study presents a multi-scale hydrological assessment to support sustainable water management in Baksa District. Event-based runoff generation in the ungauged Pagladiya watershed was estimated using the Soil Conservation Service Curve Number (SCS-CN) method. Groundwater potential was assessed across Baksa District using a Geographic Information System-based Analytical Hierarchy Process (GIS-AHP). Basin-scale hydrological processes were evaluated in the neighbouring gauged Beki River Basin using the Soil and Water Assessment Tool (SWAT), owing to the absence of streamflow observations in the Pagladiya watershed. Riverbank migration along the Pagladiya River was quantified using multi-temporal satellite imagery and the Digital Shoreline Analysis System (DSAS). The complementary findings from these analyses were synthesized to support region-specific water-management planning. New Hydrological Insights for the Region Mean runoff across the Pagladiya sub-watersheds ranged from 71.73 to 114.07 mm, with greater runoff generation observed in downstream sub-watersheds. Groundwater assessment indicated that approximately 56.4% of Baksa District possesses moderate-to-high groundwater potential, predominantly within the alluvial plains. The calibrated SWAT model satisfactorily reproduced observed streamflow dynamics (NSE = 0.82 and 0.78; R² = 0.86 and 0.81 for calibration and validation, respectively). DSAS analysis revealed persistent riverbank instability and pronounced lateral channel migration, particularly along downstream reaches, with lateral displacement exceeding 39 m in the most unstable downstream zone. Collectively, these complementary assessments provide a multi-scale decision-support framework for identifying runoff-prone areas, groundwater-potential zones, and erosion-sensitive river reaches, thereby supporting sustainable water-resource management in the Eastern Himalayan foothills.