2022 – Assessment of Long-Term Erosion Damage in Pukaki Dam Spillway Stilling Basin

David Menéndez Arán – Damwatch Engineering Ltd, Viculp Lal – Damwatch Engineering Ltd, Grant Webby – Damwatch Engineering Ltd, Jim Walker – Meridian Energy Ltd.

Concrete erosion is a common safety concern present in many stilling basins and energy dissipators around the world, but generally not well documented. Pukaki Dam in the South Island of New Zealand has been in service for 43 years. The spillway for the dam is constructed on an erodible foundation (glacial outwash gravels) and, over the years, the surficial condition of the spillway chute has gradually deteriorated and required ongoing repair. More recently, abrasion damage was observed in dive inspections of the atypical stilling basin. This paper describes the abrasion damage in the stilling basin, including detection, quantification, classification, and opportunistic repair of the observed damage. The experience at Pukaki Dam highlights that progression of abrasion erosion is difficult to estimate during design, and all possible damage scenarios should be considered in the design and reviewed periodically thereafter. The authors believe that the case study presented in this paper will likely assist engineers and asset owners in developing
surveillance and maintenance plans for other vulnerable stilling basins and energy dissipators.

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