Mayoral Column - Plans for the Dannevirke Impounded Supply.
Published 11 Sep 2023
Council staff and experts from Tomkin & Taylor continue to be extremely busy working on the repairs to Dannevirke’s Impounded Supply. This is a multi-faceted and complex project with many moving parts.
Staff have provided regular updates to Council through the Infrastructure, Climate Change and Emergency Management Committee. I encourage anyone with an interest to visit our website which provides a wealth of information including these updates. I will however take a moment to provide a summary of some of the key actions.
Council is waiting on the results of soil samples taken mid-August from a second geotechnical investigation to quantify the stability of the Dannevirke dam, specifically the eastern embankment. The outcome of the soil analysis will determine the works, if any, which must be completed on the dams’ eastern embankment.
As part of the ongoing supply monitoring regime, a remotely operated vehicle underwater inspection was conducted on August 24. It identified further deterioration has occurred in the sub-soil drains under two previously identified depressions and an additional depression was also located. However, no holes or tears in the liner were found and the seepage coming out of the sub-soil drainage network has not increased and has remained consistent, between 3-5 litres per second. This most recent inspection has reinforced the urgency to commence remediation works as soon as possible.
Draining of the dam is scheduled to begin in January and it is likely to take up to five months depending on a variety of factors, including the condition of the supply under the liner and weather conditions over summer and autumn.
Detailed design of the repairs to the sub-soil drains and to rectify the hydraulic deficiencies of the supply are well underway, including preparing two building consent applications to fast-track the process. A water sample of the Tamaki River in high turbidity has been analysed and indicates additional water treatment to treat this very fine material will be required.
We are continuing to identify alternative water sources for the Alliance Meat works and for Dannevirke from the Tamaki River immediately south of the Impounded Supply. Staff also continue to investigate the installation of a second treated water reservoir.
We are all in this together and we are working with landowners to locate and quantify unmetered water extraction. All these actions will help build a resilient and reliable water source for the Dannevirke community.
New Zealand has moved into a El Nino weather pattern which indicates stronger and more frequent winds from the west. El Nino has been associated with historically significant droughts which we experienced back in 2020. The best way to prepare for any potential drought is to have a plan, harvest rainwater and think about water conservation in our daily lives.
Noho ora mai, All the best,
Tracey Collis - Mayor