Taupo Control Gates Erosion Repairs

MERCURY'S TAUPŌ CONTROL GATES EROSION REPAIRS.

Mercury owns and operates the Taupō Control Gates. It is a reinforced concrete structure built in 1941, on the bed of the Waikato River at the outlet of Lake Taupō.

The Control Gates regulate flows out of the lake and down the river to nine power stations downstream operated by Mercury, which form the Waikato Hydro System Catchment. The hydro system generates about 10% of New Zealand’s renewable energy demands.

While Mercury owns and operates the Control Gates, the surface of the bridge is owned by Taupō District Council for transport purposes.

Project background

As part of Mercury’s ongoing Dam Surveillance programme, regular inspections of the Control Gates are carried out to ensure the structure is maintained and structural integrity is ensured.

The inspections show work needs to be done now to address erosion on the river banks around the structure. To repair the erosion spots, we are planning work to take place between August-December 2024 and February-June 2025. We will also use this opportunity to complete the planned refurbishment of one set of Control Gates in the structure.

There are no immediate safety or operational risks to the road, to the bridge or the way the water flows are managed through the Control Gates. But it is important this planned work is advanced now to ensure the Control Gates can operate reliably.

Rending of Grouting Platform at Mercury Taupo Control Gates

Grouting Platform - A temporary platform will support a small rig which will drill holes that will be pumped full of grout that sets on contact with water. This work is part of the downstream erosion repairs work. Image rendered by MᶜConnell Dowell.

Project overview

The work we have planned will be done in two phases.

Phase 1 is between August and December 2024. Initial work will involve installing new dam safety instruments around the structure. We will then work to fill in an erosion spot (sink hole) which has formed downstream from the Control Gates, on the river's southern side. A drilling rig will be used to pump grout, which sets when it contacts the water, to fill the hole.

We will also use this time to refurbish one of the six Control Gates.

Phase 2 of the work is between February and June 2025 and will involve erosion protection upstream of the Control Gates, on both sides of the river. Specialist equipment will be used to install 12m-long sheets to protect the riverbanks from erosion.

Please watch this page for updates. People can also contact the project team via email: MercuryControlGates@mercury.co.nz

FAQs

Have you consulted Mana Whenua and the Tūwharetoa Māori Trust Board?

Yes, we have a working party which is assisting with the engagement with Mana Whenua Hapū on both sides of the river.

Will there be lane closures during these works?

Yes, but we’ll keep them to a minimum.
The first closure will occur during the refurbishment of one of the six Control Gates underneath the bridge in October 2024. Access to the Control Gates for maintenance is on top of the bridge in the centre island of the road. We will have traffic management in place so we can use a crane to remove the gate during the night. Lane closures will occur for up to two nights, for times between 8pm to 6am with full road closure for brief periods during this time. The second closure is planned for early December 2024 to reinstall the gate, lane closures will be in place for up to two nights.

Electronic signage on the roadside will provide relevant information to the drivers. Additional lane closures may happen when we repair some erosion on each side of the river adjacent to the Control Gates structure. We are currently working through traffic management requirements with the contractors, with outcomes to be communicated closer to the time of starting that work around March 2025.

How will people be informed of the lane closures?

We will use digital message boards on both sides of the bridge at least two days prior to the closure to let everyone know. We will also place advertisements in local newspapers, and inform emergency services, Taupō District Council and the Tūwharetoa Māori Trust Board. We will endeavour to make the night closures as short as possible. A traffic management plan will be completed prior to work starting, it will be approved by Taupō District Council.

When are you planning to do the work?

For phase 1- the downstream erosion repairs on the Southern side, we aim to begin work on 3 September 2024, and complete work by the end of December 2024.

For phase 2 - the upstream retaining wall installation on both sides, we aim to begin work on 10 February 2025, and finish by end of June 2025. Work on these projects will take place between 7am and 5.30pm, weekdays, and Saturdays if needed.

For the maintenance work on the Control Gates, this will be done from 28 October to 6 December 2024. Once the gate is removed at night, there will be contractors working under the structure, from 7am-5.30pm, Monday to Saturday. We will also be working nights when traffic management is operating on the bridge.

Why did you select these dates to do the work?

We selected the phase 1 dates to avoid doing the work during the peak demand for electricity during winter, and when we need flexibility to operate the Control Gates. Maintenance work on the Control Gates will follow on from phase 1.

We wanted to start the phase 2 work after the 2024-25 summer concert season, and after Waitangi Day events.

Why is phase 2 much longer than phase 1?

Phase 2 involves a more extensive work programme. It will also require more time to set up at the start of the project, and more time to complete checks at the end. During some phases of phase 2, we will need to work on both sides of the river and this will have to be managed carefully to ensure safety for our contractors and the public.

Will this work impact on any public walkways or bike tracks nearby?

A bike and walk track from Waikato Street to the Control Gates will be diverted around our work site during phase 1 and reinstated when the work is completed. The diverted track is still off-road and will not add much to your journey time. See the map attached.

What will be the impact of building the access track?

We have planned a track route with minimal impact on the environment. A few tree stumps pushed over by the cyclone and some exotic trees will have to be removed and have been selected to minimise the impact. We will reinstate the site to its original condition at the end of the work.

How will the contractors access the work site for phase 2?

Our contractors will access the site via Tongariro Street, but they will use the area around the existing gatehouse for site offices.

Won’t this impact on people using Tongariro Street?

We plan to move heavy machinery and equipment to and from site at night to reduce the impact on the public, in terms of road use and noise.

How noisy will the work sites be?

We are always careful about the noise our construction work might generate. We will be guided by the New Zealand standards on acoustic noise as well as the Taupō District Council’s District Plan. Upper limits for construction noise, from 7.30am to 6pm, are between 75-90 decibels, for work lasting between 14 days and 20 weeks.

How will you keep the public safe during these works?

We have experience working near the river and keeping our operations safe for everyone. Each work site will be fenced off from the public and there will be site security operating. We are working with the Taupō District Council to ensure safety is paramount.

Won’t this work generate silt, sediment or cause more erosion to enter the Waikato River?

We have worked around the river for many years and understand the need to take care of the Awa and its environment. We will have a plan in place to monitor control of sediment and erosion during the work and we will be guided on this by the Waikato Regional Council who we have been engaging with about the works.

How can I keep up to date with the progress of this work?

Information signs will be displayed near the work sites and we will have a project webpage set up so you can read updates on the work. You can also contact the project team on email: MercuryControlGates@mercury.co.nz.