2023 – Spillway Gate Reliability – Typical Values, Trends and Targets

Glen Hobbs, Richard Mannix

The ANCOLD Guidelines on Risk Assessment state that the assessment and quantification of spillway gate reliability is a critical consideration in the overall assessment of dam risk. But there is little data and guidance within the industry on typical values and targets for setting gate reliability. This paper draws on quantitative analyses for over 40 spillway gate systems both in Australia and the USA and provides data on typical values for all gate and single gate failure. The paper provides comment on the process of quantifying spillway gate reliability and discusses some of the factors that contribute to uncertainty in calculating reliability.

This paper reviews a history of gate failures in Australia both in failing to open and opening unexpectedly and discusses some of the emerging factors in Australia that may threaten reliable operation.

The paper also discusses trends in the data and investigates gate estimated reliability values against actual flood capacity of the dams and surprisingly finds that there is a random variation between the actual flood capacity (AEP) of the spillway and the estimated gate reliability, but there is reasonable correlation between the flood hazard category of the dam and gate reliability. Reasons for these findings are discussed and some conclusions are drawn, providing a pathway to further understanding and establishing practical and achievable levels of reliability.

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