Ōtaki Reservoir
We received a $29.3 million contribution from Kāinga Ora’s Infrastructure Acceleration Fund to help fund water and transport infrastructure to improve resilience and support new homes in Ōtaki. You can read more about this on our A blueprint for Ōtaki page.
The first project to be built is a new reservoir for Ōtaki. The reservoir will improve the resilience and fire-fighting capability of the Ōtaki water supply.
Artist impression of the Ōtaki Reservoir with trees near fully grown.
Ōtaki has limited water storage and is reliant on bores and pumps to supply the community. This system does not meet good practice standards. If a problem occurred with the pumps or the treatment station, then most of Ōtaki would lose their water supply. The new reservoir will provide 24hours of water storage.
Council has been investigating a new reservoir for Ōtaki for approximately 20 years. A site at Te Manuao Road was determined to be the best choice due to its elevation, and proximity to the existing water supply network. Also, the site is out of hazards zones such as flood plains and earthquake fault lines.
The reservoir by the numbers:
|
5.5 million litres (5,500m3) |
volume of the reservoir |
|
35 metres |
diameter of the reservoir |
|
6 metres |
depth of water in the reservoir |
|
7 metres |
height of the reservoir |
|
53 metres |
maximum height of the reservoir above sea level |
|
267 |
the number of native trees that will be planted around the reservoir |
|
100 years |
reservoir design life (length of time the reservoir can be used with maintenance but without major repair being needed) |
|
2,500 years |
reservoir designed to withstand an earthquake of this frequency (making it the strongest structure in the area) |
|
4 kilometres |
length of pipes to be installed, made up of 1.8km to convey water from the County Road pump station to the reservoir, 1.8km to carry water from the reservoir back to join the reticulation network at the County Road pump station, and 0.5km of pipes for overflow or flushing from the reservoir to join the stormwater network |
|
$6 million |
estimated cost of reservoir (TBC when tenders are received) |
Ōtaki Reservoir planting plan.
Construction
Earthworks were expected to get underway in April 2023 but have been deferred pending further investigation into the siting of the reservoir. Earthworks will include levelling the area where the reservoir will be built, installing stone column foundations, and building an earth bund to help screen the reservoir. Stone columns (6 to 8 metres long) will be installed to help strengthen the ground and support the weight of the reservoir.
A tender to find a contractor to build the reservoir is planned for June. We expect construction will take 12-to-18 months but this will be confirmed once a contractor is on board.
Seismic design
The reservoir is designed to withstand a one-in-2,500-year earthquake, making it one of the strongest structures in the area. During a major earthquake, the tank is designed move a small amount. Movement of around 25mm to 100mm can be expected to occur in a 2,500-year earthquake. Designing for some movement results in better seismic performance compared to a reservoir that is totally locked in place. Pipework will include flexible joints to allow for any movement of the tank.