Dam Break Analysis: A Case Study of the Tala Hydropower Plant Dam using HEC-RAS

Abstract

Dam break flood is widely recognized as a low probability but a high impact event that can pose significant risks to downstream communities and critical infrastructures. Numerous studies have focused on the significance of dam break modelling for hazard assessment, risk mitigation and emergency preparedness planning. In this study, the Dam Break Analysis of the Tala Hydropower Plant (THP) involves a systematic approach combining data collection, hydraulic modeling, and risk assessment under different failure conditions. High-resolution 2.5-meter AW3D Digital Elevation Model served as the primary input dataset for the hydraulic modelling. The analysis employs the Hydrologic Engineering Centre-River Analysis System (HEC-RAS) to model three dam-failure scenarios under both extreme flood and normal reservoir conditions: One scenario represents THP dam failure caused by overtopping during the Probable Maximum Flood (PMF), while the remaining two scenarios simulate cascade failure of the Chhukha Hydropower Plant (CHP) and THP dams under sunny-day and Probable Maximum Flood conditions. The three scenarios were selected to represent probable and worst-case scenario for emergency planning and associated flood hazard study. The analysis demonstrates varying levels of flood hazard across the three simulated scenarios, with maximum breach outflows reaching 47,364.95 m³/s, 37,469.66 m³/s and 52,771.27 m³/s respectively. Downstream regions including key infrastructure such as bridges, settlements, and the Tala powerhouse Main Access Tunnel are found to be at risk, with floodwaters potentially extending into the Indian plains up to approximately 66.18 km from the dam. A sensitivity analysis performed for the study indicates that the breach elevation is a critical factor influencing the magnitude and timing of flood impacts, with lower elevations leading to more severe and rapid flooding, particularly in regions closer to the dam. The flood inundation maps generated in this study highlights the need for effective dam safety management including identifying high-risk zones, early warning systems and effective emergency response planning.