Trustpower owns and operates the Waipori Power Scheme, a network of four power stations located 50km south west of Dunedin.
Across Trustpower’s 44 hydro power stations, regular dam safety reviews and monitoring are carried out by certified international third-party experts and subject to peer review.
Following the most recent dam safety review of Waipori’s number two dam, which is located 1km downstream of Lake Mahinerangi and 3km upstream of the number two power station, Trustpower has lowered the number two lake level by 2.1 metres as a precautionary measure. This brings the lake level below an upper brick portion of the dam which was added in the early 1970’s and was identified in the dam safety review as being likely to suffer substantial damage if a moderate sized earthquake were to occur. The review pointed out that without taking this precautionary measure a moderate sized earthquake could result in the partial or full uncontrolled release of water from lake number two.
In addition to reducing the lake level by 2.1m, bringing the level below the vulnerable upper brick portion, Trustpower has also created an exclusion zone in the gorge below the dam. As the Waipori Power Scheme is in a remote area, 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.
Trustpower General Manager Generation Stephen Fraser says that internal safety measures have also been put in place to ensure the safety of Trustpower 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. It also means that we are able to take precautionary steps while we look at more permanent solutions to improve the performance of the dam as required.” says Fraser.
Computer modelling indicates the water discharge from number two dam would be captured behind number four dam and released in a controlled manner.
“The scenario is similar to that of many commercial buildings throughout New Zealand cities, where building owners are aware that there is an issue and are proactively taking steps to rectify or strengthen their structures. We will keep the public updated as we continue further investigations and analysis on Waipori number two dam.” says Fraser.
Waipori Village is the closest settlement to the dam and is located higher than the number two power station. Local residents have been informed of the situation, Waipori Village Chairperson Daniel Williamson says that they are pragmatic about the report.
“Waipori Village is higher up than all of this, the local staff from Trustpower have been in touch so everyone is now aware of the situation” says Williamson.
For more information:
Community, Communication and Media Manager
021 791 084