Consequences of slope stability issues and mitigating strategies in hydropower projects of Nepal from the perspectives of Rasuwa Flashflood

Abstract

Nepal’s rapidly expanding hydropower sector is predominantly located within the steep, tectonically active, and geologically complex Himalayan terrain, where slope instability threatens construction safety, infrastructure integrity, project schedules, and long-term operational performance. Slope failures commonly result from adverse geological structures, unfavorable discontinuity orientations, steep excavations, weathering, groundwater ingress, surface-water erosion, and inadequate geological and geotechnical investigations. These factors can cause rock failures, debris movements, rockfalls, and other forms of slope instability. The catastrophic Rasuwa flash flood of August 2026 provides an example of the interaction among extreme hydrometeorological events, mass movements, river-channel processes, and infrastructure vulnerability. The event highlights the need for an integrated, multi-hazard, and risk-informed approach to hydropower planning and design beyond conventional site-specific slope-stability assessments. Lessons from Rasuwa underscore the importance of comprehensive geological and geotechnical investigations, mechanism-specific slope-stability analyses, effective excavation and stabilization designs, systematic drainage and erosion-control measures, continuous monitoring, early-warning systems, and resilient access and emergency-response arrangements. Integrating these measures into hydropower development is essential to reducing disaster risks, protecting critical infrastructure, minimizing project disruptions, and strengthening the long-term safety and resilience of hydropower projects in Nepal’s fragile Himalayan environment.