Upper Nihotupu Raw Watermain Upgrade

Overview

We plan to upgrade the over 100-year-old Upper Nihotupu Raw Watermain. This watermain which transports up to 22 million litres of water daily from the Upper Nihotupu Dam in the Waitākere Ranges to the Huia Water Treatment Plant, was damaged during the January 2023 storms. It also faces risks from landslides and rockfalls.

What is happening now?

Following environmental investigations, technical assessments, cultural input and community engagement, Watercare has identified a preferred option for the project, which will now progress to the next stage of planning.

We understand there is no option that completely avoids all effects. However, throughout the assessment process, opportunities to avoid and minimise environmental, community and construction effects were carefully considered alongside technical and cultural requirements.

Preferred option identified

Our preferred option is Option 3: A tunnel from Seavers Camp to the replacement Huia Water Treatment Plant, with a short section between Seavers Camp and the Upper Nihotupu Dam replaced along a similar route to the existing watermain.

This option performed strongly across a range of assessment criteria and provides a reliable, long-term solution for supplying water from the Upper Nihotupu Dam to the replacement water treatment plant.

A largely tunnelled approach significantly reduces ecological disruption compared with replacing the existing pipeline and reduces exposure to natural hazards such as slips and rockfalls, which have affected the existing watermain in recent years.

Why was Option 3 selected?

Option 3 was selected because it:

• Provides a reliable, long-term solution for transporting raw water from the Upper Nihotupu Dam to the replacement Huia Water Treatment Plant.

• Significantly reduces impacts on sensitive ecological areas compared with replacement along the existing route.

• Reduces exposure to natural hazards such as slips and rockfalls that have affected the existing watermain.

• Minimises surface disturbance by using a predominantly tunnelled alignment.

• Supports the long-term operation of the new Huia Water Treatment Plant and Auckland's future water supply needs.

How your feedback helped

Community feedback played an important role in the assessment process.

Many people told us they were concerned about environmental impacts, construction disruption, access and effects on recreational areas. These themes were considered alongside technical, environmental and cultural assessments when comparing the options.

The preferred option aligns closely with what we heard from the community, as it avoids many of the impacts associated with extensive surface construction and reduces disruption wherever practicable.

What happens next?

While a preferred option has been identified, further work is required to confirm affordability and address project risks and uncertainties.

The preferred option will continue to evolve and be refined as concept design progresses. This next phase will include:

• Affordability assessments.

• Further investigations and technical testing.

• Development of a project-specific effects management approach.

• Additional measures to avoid, minimise, remedy or offset effects where required.

We will continue to keep the community informed as the project progresses.