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.

Background

Ōtaki has limited water storage and relies 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 24 hours of water storage.

Council will be building a new 5.5-million-litre reservoir on Te Manuao Road. We chose this site because of its height above sea level, and closeness to the water reticulation network.

We’ll work with the community to develop a plan to screen the reservoir from homes.

The new reservoir will:

• improve the resilience of the Ōtaki water supply
• improve firefighting capability for Ōtaki
• provide water storage for emergencies and times of high demand
• support the significant housing growth planned for Ōtaki
• be more energy efficient.

We’ll be designing and building the reservoir to Aotearoa New Zealand earthquake standards. It will be strong enough to stand up to a one-in-2,500-year earthquake. The project includes laying approximately 4 kilometres of pipes to carry water to the reticulation network.

We expect to start earthworks in October 2023, and construction of the tank in early 2024.

Ōtaki Reservoir planting plan.

---

Key features

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
$9.1 million	estimated total cost of reservoir project including associated pipework

---

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.

Latest updates

Work on the new reservoir will begin in October. Here’s the high-level timings of construction.

Expected construction timings for the reservoir
Stage	Estimated Dates
Earthworks – clearing the area and building earth bunds to help screen reservoir	October/November 2023
Trenching from tank site to Te Manuao Road for pipework	November
Ground improvements to provide a strong foundation for the tank	November/December
Build concrete pad for reservoir	January 2024
Construct tank and control equipment	February to June
Install pipes from site to County Road pump station	February to June
Plant native trees to screen the reservoir and create a natural environment	April/May
Fill and calibrate tank	July/August
Reservoir fully operational	Late 2024