Mercury's hydro control gates in Taupo

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.

Project Overview

 

Phase 1 was completed in 2024. It involved installing new dam safety instruments around the structure, filling in an erosion spot which has formed downstream from the Control Gates, on the river's southern side. We also used 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.

Traffic management will be in place during these works. At times there will also need to be temporary lane closures to enable materials and equipment to be safely delivered to the site.


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

Read more about the Control Gates here.

Taupo Control Gates Map

 

Download Map Here

 

2024 Completed Milestones

In August, we completed some ground investigation work and installed new instruments to improve our understanding of the underlying geology of the Taupo Control Gates ahead of the main erosion repairs starting.

Main works kicked off in September, working on the downstream erosion repairs on the town side of the river (Phase 1). Ngā Hapū O Te Hikuwai O Tūwharetoa provided cultural inductions to our project team before we started the main body of work.

We activated accidental discovery protocols three times during these initial works; the first two times accounted for two sets of bones we found and a third time for some old wood. After putting works on hold within the immediate area, our archaeologist quickly established the bones were from animals and wood from a tree. The Phase 1 work will be finished in November, achieving our key project objectives, and with great care taken for our people, the land and the awa.

Ngā Hapū O Te Hikuwai O Tūwharetoa cultural advisor will provide a small ceremony to close phase 1 work, and the koiwi (bones) and wood will be re-instated under the planting of a native tree in the area.

We removed one of the control gates from the bridge for refurbishment in late October during the night and plan to put it back into service in December.

Mercury's Taupō Control Gates erosion repairs

Mercury's Taupō Control Gates erosion repairs

Our team set up a temporary platform where a small rig was used to pump grout into the erosion spot behind the sheet wall. Photos: Nick Whelan | Mercury.

FAQs

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

Yes, we are working with iwi and hapū on both sides of the awa. Similar to phase 1, a Cultural Monitoring Framework will be in place for the duration of the works.

Will there be lane closures during these works?

Yes, but they’ll be at night when traffic volume is lower, to minimise disruption to the community.

The first will be at the start of March so we can deliver a crane to the northern side of the river. The second lane closure will be in mid-March so we can move the crane to the southern side of the river. The third lane closure will be in June, so we can disestablish the work site. These closures will be between 9pm and 5am.

We will also need to close a lane two more times during the work, so trucks can deliver large construction materials. These closures will also be in the evening, between 2-4 hours.

How will people be informed of the lane closures? We will use digital message boards prior to the closure to let everyone know. We will also place advertisements in a local newspaper, 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 and it will be approved by Taupō District Council.
When are you planning to do the work?

We completed phase 1 in December 2024. This involved repairing erosion along the riverbank downstream, on the south side of the Waikato River at the control gates.

For phase 2 - the upstream erosion repairs require a retaining wall to be installed on both sides of the river - we aim to begin work in February 2025, and finish by end of June 2025. Work will take place between 7am and 5.30pm, weekdays, and Saturdays if needed.

Why did you select these dates to do the work?

We completed phase 1 in December 2024. We want to start phase 2 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. Sometimes during 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? We will need to temporarily close the footpath on the upstream side of the bridge when we are using heavy machinery to install the 12m sheets to protect the riverbanks from erosion.
How will the contractors access the work site for phase 2? Our contractors will access the site via Tongariro Street. They will establish a site office on the northern side of the river.
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 our contractor McConnell Dowell 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.