2019 – Low Level Outlets: Necessary Evil or a Nuisance?

Philip Winter, Thomas Fritz

Many dams have low level outlets, most of them put in place as diversion structures during construction. However, once dam construction is complete and reservoir filling begins, the reality is that low level outlets are used very infrequently, and sometimes not at all.
This paper will discuss the merits of decommissioning low level outlets vs maintaining them as operational dam safety critical equipment. In this context the paper will examine the criticality of low level outlets in relation to the type of dam, the Potential Impact Category of the dam, the ratio between outlet capacity and mean reservoir inflows, possible resource consent issues and required maintenance and testing regimes.

Trustpower’s dam portfolio consists of a variety of dam types with multiple different types of low level outlets. Case studies from the portfolio will be used as arguments for maintaining or decommissioning the low level outlets in order to develop evaluation criteria for low level outlets and provide a basis for how to treat them from a wider dam safety perspective.

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