'You Don't Know What You Don't Know' - Inspecting Spillways and Assessing Potential Failure Modes

摘要

The February 2017 incident at both the principal and auxiliary spillways of Oroville Dam has brought considerable attention to potential failure modes associated with concrete chute and unlined spillways. Based on the lessons-to-be-learned from this event and the subsequent findings of forensic investigations, many dam owners with similar spillways have initiated their own assessments. The Oroville incident also put a spotlight on the traditional understanding of "potential failure mode" which has been defined as the uncontrolled release of stored reservoir water, regardless of other consequences to the owner and the public, or the ability to manage the reservoir. The Oroville Dam incident also raises the question, especially for auxiliary spillways, on how much damage to a spillway during an extreme event is acceptable? The most common failure modes for lined and unlined spillways using actual case studies will be presented. Emphasis will be placed on deficiencies and weaknesses in historic spillway designs, and how the integrity of lined spillways can change over time. Early warning signs for inspectors will be illustrated. The need to assess spillway exit flows and how they can adversely impact other dam features and reservoir operation will also be discussed using case studies.