Assessing the Effects of Extreme Rainfall Patterns and their Impact on Dam Safety: A Case Study on Indian Dam Failures

Abstract

Abstract This study investigates the impacts of extreme rainfall variations on dam safety, focusing on six Dam Failure (DF) events in India: Tigra, Khadakwasla, Pagara, Machu-2, Koyana, and Kaddem. Daily gridded rainfall data is obtained from the India Meteorological Department, and the Inverse Distance Weighted interpolation method is used to get location-specific daily rainfall data. The severity of extreme rainfall events on dam safety is highlighted by computing the average and accumulated rainfall (ACR) for 5, 10 and 15 days prior to the date of DF. Shockingly, the magnitude of 15 days ACR prior to DF exceeds 50% of the normal annual rainfall of most of the study locations. This unexpected situation may put tremendous pressure on the dams and eventually lead to their failure. Further, the Probable Maximum Precipitation (PMP) is computed at each dam location for every 30-year horizon starting from 1911. It is observed that the maximum PMP is noticed during the horizon of DF. Next, the Efficiency Factor (EF) is calculated to check the severity of rainfall prior to the DF. The annual EF values are computed, and the maximum EF value over 30 years (used to compute the normal annual rainfall) indicates the extreme most rainy day. The EF values > 0.90 indicates a great threat to the dam. The study established a robust correlation between dam failures and heavy rainfall preceding them. Some dams, like Machu-2 and Kaddem, experienced clear rainfall peaks on the day of collapse, indicating severe rainfall as the primary cause. Others, such as Tigra, Khadakwasla, and Pagara, exhibited continuous rainfall for 5 to 10 days is the principal cause of failure. The percentage of accumulated rainfall contributed nearly or more than 75% over 5 days at Pagara, Machu-2, Kaddem, and 10-days at Tigra, Khadakwasla; these resulted in the flash flood. However, EF values for Tigra, Khadakwasla, Pagara, Machu-2, and Kaddem still suggest the potential for severe rainfall events. These findings are of significant relevance to professionals in the field of dam engineering, offering a comprehensive understanding of how extreme rainfall events can impact dam failures and provides valuable insights into rainfall patterns and their implications for dam safety.