Mayor Tracey Collis and the council team presenting to the public last week. From left, CEO Bryan Nicholson, Chris Chapman (infrastructure manager), Roger Earp (senior project manager impounded supply) and Dewi Knappstein (Tonkin and Taylor engineer).
Mayor Tracey Collis and the council team presenting to the public last week. From left, CEO Bryan Nicholson, Chris Chapman (infrastructure manager), Roger Earp (senior project manager impounded supply) and Dewi Knappstein (Tonkin and Taylor engineer).
“It is clear from recent discoveries the Tararua District Council cannot delay permanent repairs to the Dannevirke Impounded Supply until the summer of 2024-25.”
This was the message delivered at a public meeting last week.
Mayor Tracey Collis assured the group that the council’s absolute focus was to ensure a resilient water supply for Dannevirke but went on to say recent discoveries have indicated this is a pretty complex challenge.
Council chief executive Bryan Nicholson introduced the team and called on Roger Earp, senior programme manager for impounded supply and Three Waters representative, to describe the events which have taken place.
Roger said a remotely operated vehicle (ROV) with a camera was put into the dam six weeks ago to find leaks which were causing it to lose 25 litres per second. This revealed two tears in the protective membrane in the east wall, one the size of a mobile phone and the other barely a pin-hole, plus other potential sites.
The tear in the dam membrane that needed urgent repairs.
Action was taken immediately to reduce the water loss to five litres per second and a diving team of four, supported by 15 other staff, worked day and night and over the weekend to effect the repair which was successful.
In the six weeks it took to assemble the dive team the largest tear had grown to almost a metre. The council decided the long-term permanent repairs set for summer 2024-25 would have to come forward.
The dam is now being monitored daily and another ROV will go in next week.
Dewi Knappstein of Tonkin and Taylor explained the complex engineering challenges ahead and said monitoring was essential to prevent a sequence of events which would lead to “an uncontrolled release losing the dam water and having downstream consequences”.
The council has considered four options: Remedy the impounded supply; monitor and mitigate; decommission the impounded supply and build alternative storage; decommission the impounded supply and construct an alternative source, storage and treatment facility.
General consensus leans towards option one - remedy the impounded supply - as the most practical.
Regardless of the option chosen, infrastructure manager Chris Chapman said the impounded supply will be offline for the summer of 2023-34 while repairs are being made.
He said the shortage of time to provide alternative supplies had made it very difficult and finding an alternative supply for Dannevirke had not been successful. Building a tank farm was also not practical as it was expensive and not possible in the timeframe.
Council is working with the Alliance Freezing Works to find its own water supply and the Tamaki River intake was being upgraded to handle water in more turbid conditions.
Leaks and other non-regulated users of the water supply line from the Tamaki to town are being investigated.
What you need to know about water next summer.
Residents are being requested to conserve water over summer by concentrating high water usage activities to spring, installing tanks for gardens, repairing any leaks and reporting any others noticed.
A crowd of over 70 attended the meeting.
Speakers at the meeting raised issues in question time.
One resident asked if Dannevirke will be in the same predicament in five years’ time. The response was that the problem will be resolved.
The number of consultants used was questioned and the public was told council needed the best advice to do the job correctly.
The prospect of building two more big reservoirs next to the treated water reservoir was brought up and it was acknowledged as a possibility, but not before summer.
Another resident brought up building a tank farm on council land, but was told that, apart from the expense, it couldn’t be done without demolishing the dam first and a similar answer was given to the question of building a shallower but wider dam.
A suggestion was made to build another deeper infiltration gallery at the Tamaki intake to lessen turbidity and increase supply and it was acknowledged as a possibility but would need research.
Residents also asked if Tonkin and Taylor backed their advice with a guarantee and were told they backed their performance with reputation.
The cost was also questioned, but the reply from council was that this had not been assessed yet, and would be presented to council on July 19.
In response to a question about the public being better informed, Mayor Tracey said all the information was on the council website, on Facebook, and on Radio Dannevirke on Fridays after 11am, as well as in print media.
