Dam deemed an earthquake risk
An earthquake safety review has detected a vulnerable section in an Otago hydroelectric dam, prompting its owner to establish an exclusion zone.
Trustpower owns and operates the Waipori Power Scheme, a network of four power stations.
A recent dam safety review highlighted earthquake concerns with the scheme’s No 2 dam, located 1km downstream of Lake Mahinerangi and 3km upstream of the No 2 power station.
The review found a moderate-sized quake could result in the partial or full uncontrolled release of water from lake No 2.
That was due to vulnerability found in an upper brick portion of the dam, which was added in the early 1970s.
As a precautionary measure, Trustpower lowered the No 2 lake level by 2.1 metres, which brings the level below the upper brick portion.
Trustpower also created an exclusion zone in the gorge below the dam.
The area is in a remote part of Otago, and the exclusion zone will have little impact on the public other than the closure of the Crystal Falls walking track and a portion of the Governors walking track.
Waipori Village is the closest settlement to the dam and is located higher than the No 2 power station. Local residents have been informed of the situation.
Computer modelling indicates that the water discharged from the No 2 dam would be captured behind the No 4 dam and released in a controlled manner.
Trustpower’s general manager of generation, Stephen Fraser, said internal safety measures had also been put in place to ensure the safety of staff and contractors carrying out work on site.
‘‘The technology available allows us to undertake detailed modelling and analysis of the dam. This means we can identify areas of risk much earlier and carry out work as needed in response,’’ he said.