2005 – Risk-Based Evaluation of Interim Operating Restrictions to Reduce the Risk of Earthquake Induced Dam Failure

David S. Bowles, Loren R. Anderson, Terry F. Glover, Sanjay S. Chauhan, Ronn S. Rose

A risk assessment was performed for the Sacramento District of the U.S. Army Corps of Engineers to explore the justification for imposing an operating restriction on Lake Success to reduce the probability and consequences of an Earthquake-induced dam failure. The potential for both a sudden overtopping failure and a delayed “seepage erosion through cracks” failure were considered.

The risk assessment focused on the seismic performance of the dam, the potential life loss and economic consequences of Earthquake-induced dam failure, and the estimated residual risk and degree of risk-based justification for the Existing operating regime, a range of Potential Operating Restrictions, and an Indicative Improved Warning and Evacuation System. Risk assessment inputswere supported by seismic deformation analyses under various Earthquake loadings and pool elevations, dam break-inundation modelling, and reservoir simulation.

Evaluations against tolerable risk guidelines from the USBR, ANCOLD, and the UK HSE, together with insights into the relationship between pool elevation and dam failure risk, provided important inputs for the decision to implement an operating restriction.

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