Ground Investigation Work at Ross Creek Begins

Dunedin (Monday, 19 October 2015) – Work will begin soon on the final stage of design in a project which will see the historic Ross Creek Reservoir dam embankment refurbished.

The dam has been closely monitored since large cracks appeared in 2010. The monitoring plan to date has included an irrigation system on the dam face and gradual lowering of the water level to prevent further instabilities occurring.

This stage of the project, which is part of a wider strategy to provide better water security for Dunedin, will involve creating a platform on the dam face. There will be extensive core sampling to confirm the properties of the dam material. Temporary track closures will be in place during the testing process.

Dunedin City Council Water and Waste Services Asset and Commercial Manager Tom Osborn says DCC is very aware Ross Creek is one of the city’s most popular recreational assets.

“We will make every effort to retain as much public access as possible during the testing and subsequent construction, but safety of the public and people working on the site must come first.”

Opus has the contract for the design and construction management for the dam refurbishment. Initial clearing and surveying has been completed for the design, but the design cannot be confirmed until ground sampling work is done.

Contractors start today and the testing work is expected to take up to four weeks. Tracks around the embankment will be closed from 27 October to 13 November. The sampling work will create noise and disturbance between 8am and 5pm, Monday to Friday.

The crest track will be closed for a week from 9 November to allow a drilling rig to take core samples of the dam.

“We will do our best to open up part of the lower track during this time so recreational users of the area can complete a full loop of the reservoir.”

After this stage of work has finished, the DCC will be able to tender the major construction works which will refurbish the dam embankment. This work is expected to last for up to 12 months. Several of the tracks around the embankment will be closed during this period, but all tracks north of the crest will remain open throughout.

Mr Osborn says, “We are looking at ways to improve track connections during construction to try to limit the impact on users of the reserve.”

Some local road closures or traffic redirections may be required as part of the major construction work next year, but the extent of these won’t be known until construction tenders close, which is expected to be in February 2016. The DCC will work closely with affected parties to minimise disruption during this period.

The Ross Creek Reservoir, which was completed in 1867, has not been used for about 20 years. The dam is the oldest large earth dam in the country, and has Heritage New Zealand category one status, but it is in poor condition and needs attention to ensure its ongoing safety. As part of the work, 15,000cu m of fill will be brought in to stabilise and extend the embankment. The DCC is working closely with Heritage New Zealand on the project.

The refurbishment of the dam would mean the reservoir’s existing capacity of 130,000cu m could be used once more, with the water level in the reservoir restored to its ‘normal’ level after several years of being lowered. The Ross Creek Reservoir dam project is a key part of an overall strategy to ensure the city has water supply options should there be any problems getting water from Dunedin’s main water sources – Deep Creek and Deep Stream.

The first part, which is now complete, was the construction of a pumping station between the Southern and Mount Grand Water Treatment Plants, at a cost of about $1 million.

The next parts are the refurbishment of the Ross Creek Reservoir dam and the construction of a pumping station and pipeline between the reservoir and the Mount Grand Water Treatment Plant.

“Once these projects are complete, water supply could be maintained to the entire city if the Deep Creek/Deep Stream pipelines were lost, for example through an earthquake,” Mr Osborn says.

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