RISK ASSESSMENT ANALYSIS OF TEHRI DAM

Abstract

In India and worldwide large population lives near and downstream of dams. The dam failure results in large economic losses and loss of human lives living in the downstream areas of dams. In the present study, risk assessment analysis of Tehri dam has been carried out. Tehri dam is located in Uttarakhand, India. All the data required for Risk assessment analysis have been collected from THDC office, Rishikesh (Uttarakhand), India. Digital Elevation Model data is downloaded from USGS earth explorer for analysis. HEC-RAS is used for model development of Tehri dam. Risk assessment analysis is done by performing level pool routing for different gate conditions and initial reservoir level of Tehri dam in HEC-RAS model. Tehri dam has five gated spillways and two ungated spillways. Mechanical and electrical failure of gates is possible and hence its failure probability has been considered for risk analysis. Initial reservoir levels for this analysis are taken as 810m, 815m, 820m, 825m, 826m, 827m, 828m, 829m and 830m. Level pool routing has been performed for different gate conditions i.e. zero gate working, one gate working, two gates working, three gates working, four gates working and all the five gates working. For level pool routing probable maximum flood is taken as the inflow to the reservoir of Tehri dam. Level pool routing is performed for different cases to find out the downstream consequences and overtopping height of water above the dam body. Failure probability is calculated by using Quantitative risk model architecture. Based on the level pool routing, the situations under which overtopping of dam is possible have been worked out. The results indicate that if all the gates are functional during the incoming flood, the dam is able to safely pass the PMF without overtopping. However, if one or more gates of the dam are not functional then overtopping of the dam is possible. Flood inundation mapping has been carried out for different scenarios using HEC-RAS 2-D model and the inundated areas have been computed. Dam breach analysis has also been carried in the dissertation and the downstream inundated areas has been computed.