Practical Lessons from Dam-Break Assessment: A Case Study of Larji Hydroelectric Project, Himachal Pradesh

Abstract

Dam-break assessment in the Himalayan region is challenging due to steep valleys, rapidly changing downstream conditions, limited historical data, and the potential for extreme floods. This paper presents practical experience from the dam safety assessment of the 126 MW Larji Hydroelectric Project in Himachal Pradesh, India. A UAV-based LiDAR survey, supported by DGPS observations, was used to develop a high-resolution downstream terrain model. This model improved flood-path prediction and enabled predicted flood levels and arrival times to be related to critical infrastructure, including sediment-flushing arrangements, tail-race channels, and powerhouse approaches. A two-dimensional hydraulic model was developed using HEC-RAS 7.0.1, incorporating the actual spillway gate configuration and operating conditions rather than treating the release structure as a generic opening. Three scenarios were assessed: extreme controlled release, barrage failure due to overtopping, and sunny-day failure due to piping or internal erosion. The study highlighted the importance of accurate terrain representation, realistic hydraulic structure modelling, and consideration of multiple failure mechanisms. Ultimately, the assessment demonstrates that integrating advanced surveying, hydraulic modelling, and engineering judgement strengthens dam safety evaluation, emergency planning, and operational preparedness.