Dannevirke Impounded Water Supply

Baner impounded water supply

In July 2021, leakage was discovered in our impounded supply. An extraordinary Council meeting was held in October 2023 to discuss the next steps for the impounded supply, which included funding for raw-water treatment and extra storage for both raw and treated water. Council also decided to delay the decision whether to repair the impounded supply due to outstanding geotechnical investigations, supply challenges, and issues relating to the impounded supply liner system.

In September 2024, a report to Council included the following:

  • Tonkin and Taylor geotechnical report and impact classification assessment
  • Damwatch geotechnical interpretation report
  • New Plymouth Underwater inspection – this showed 3 depressions in the liner that required further attention
  • Rationale – assessment of options

These reports are available below under the 25 September 2024 update.

Since September 2024, several steps have been taken to improve the Dannevirke Impounded Water Supply. It was advised that the impounded supply is functioning as it was designed, and the focus has been on building resilience. Peer review was sought, and it was agreed that this was the best approach as opposed to replacement. It was noted that while there are risks, there are no immediate risks and monitoring is continuous.

Divers have patched 3 pinholes in the liner. At this stage, no additional holes have been identified. Water leakage of the Impounded Supply is currently the least it has been since monitoring has started.

A potential plot of land has been identified for the construction of an additional reservoir for treated water. Once this is installed and filled, we can undertake any necessary repairs to the current reservoir, and it will also serve as a buffer when needed.

Samples have been taken of the Tamaki River during turbid conditions (which occurs after heavy rainfall) to investigate the NTU (Nephelometric Turbidity Units) of the water. Currently, our water treatment plant can only treat water with an NTU level of 10 or lower. When the river is in a turbid state, we cannot take and treat the water, which means we have to rely on our reservoir and impounded supply. The results of this testing will inform the decision on whether a clarifier or membrane plant upgrade is required to treat water with an NTU level above 10.

Due to the original design of the impounded supply, we are currently unable to use the lower 6 metres of water without pumping, and a temporary pump is currently on site. To address this, a permanent solution with large submersible pumps is being designed to enable us to draw the remaining water so that it can be treated and used by the town.

We will continue to monitor the situation of the impounded supply, including conducting 6 monthly underwater drone inspections, to ensure the depressions and patched pinholes in the liner do not deteriorate.

Dannevirke Impounded Supply Inforgraphic

Testing of turbid water from the Tamaki River took place in March 2025.

New Plymouth Underwater Report - February 2025

A copy of the Dive Works report completed by New Plymouth Underwater in February 2025 can be found here:

Council Meeting - Dannevirke Impounded Water Supply - 25 September 2024

Mayors Update - Dannevirke Impounded Water Supply - 8 July 2024

The peer review of the Tonkin & Taylor Geotechnical Interpretation Report is due for completion by early August which will provide us with the necessary advice of our four critical considerations: The stability of the eastern dam embankment and the western reservoir rim, the degree of urgency of remediating the existing liner and underlying subsoil network, along with understanding the potential for internal erosion of the eastern dam embankment, including the dam foundation and around the subsoil outlet pipe. Please watch the Mayors video update to find out more (below):

Public Water Meeting - Dannevirke Impounded Supply - 28 November 2023

On Tuesday, 28th of November, a public meeting was held to provide the community with an update on the Dannevirke Impounded Water Supply, and to answer your questions.

Please refer to the following documents:

Presentation 28 November 2023 - Dannevirke Impounded Supply - Public Water Meeting

Information Pack 28 November 2023 - Dannevirke Impounded Supply - Public Water Meeting

This meeting was recorded and can be viewed below.

Extraordinary Council Meeting - Dannevirke Impounded Supply  - 31 October 2023

An extraordinary Council meeting was held on 31 October 2023 to discuss next steps for the Dannevirke Impounded Supply. Please watch the video of this meeting below.

Overview of important documents

Public Water Meetings

On Tuesday, 27 June 2023 a public water meeting was held in Dannevirke. The purpose of the meeting was to update community members about the recent temporary repairs and to discuss the critical decisions that have to be made with regards to a permanent fix for the impounded water supply.

The meeting has been recorded and is available below.

Overview of News articles about the Dannevirke Water Supply

Infographic about the temporary repairs carried out between 13-19 June 2023

Infographic which provides an overview of the Dannevirke Impounded Water Supply

This infographic provides an overview of Dannevirke's Water Supply system; from source to tap

From source to tap

A full page spread on the Dannevirke Water Supply appeared in the Bush Telegraph Newspaper on 20 June 2022, including this infographic. This page can be downloaded here.