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Customer: Mercury New Zealand Contract: Design & Construct Location: Taupō, Central North Island   |
Fast Facts:
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The Taupō Control Gate Erosion Repair project for Mercury was completed in June 2025 on time, to budget, and with an impressive track record.
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Zero Lost Time Injuries (LTI)
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Zero Medical Treatment Injuries (MTI)
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Zero Environmental Incidents
The project scope included stabilising the banks of the Waikato River alongside the control gates that manage water flow to the Waikato Hydropower System.
Powerful water flows erode the banks alongside the gates, and Mercury’s asset surveillance regime had identified the need for intervention to prevent further erosion.
The ECI project, awarded in April 2023, was divided into four separate portions. The first two included the design and construction of erosion remediation and prevention measures around the existing Control Gates Structure, and the second two were the construction.
SP1 entailed the detailed design and methodology to remediate the voids that had formed downstream of the existing gates behind a previously installed sheet pile wall.
SP2 incorporated the detailed design and installation methodology for sheet pile walls upstream of the gates on both riverbanks. Working with Andy O Sullivan and his team, we developed and refined a concept supplied by Mercury to incorporate efficiencies and constructability.
SP3 involved three months’ construction in conjunction with Wagstaff piling and filling the voids downstream. The careful drilling and filling of the voids and the use of fast-setting grout protected the Waikato River adjacent. We completed work in November 2024 and demobilised ahead of the busy summer tourist season.
SP4, commenced mid-February, was completed in mid-June. It involved the installation of two steel sheet pile walls, upstream of the existing gates on both banks. Due to the sensitivity and importance of the bridge and gate structure, we used specialist piling equipment to control the vibration parameters. The piling was completed on schedule in early June 2025
Cultural Collaboration
The Waikato River is a sacred entity for mana whenua, and so we worked closely with our client Mercury and local iwi to protect the river. Ngā Hapū O Te Hikuwai O Tūwharetoa provided cultural advice to the project and developed Accidental Discovery Protocols to manage potential archaeological finds.
Before work started, an iwi representative held a karakia and cultural induction for the team. At the end of Phases One and Two, we planted a tree, and local iwi held a karakia to honour the river and the completion of the job.
Innovative Engineering
The work to stabilise the riverbank downstream from the gates on the southern bank (town side) was completed ahead of schedule in November 2024.
Our in-house Engineering team and specialist geotechnical Andy O’Sullivan Consulting designed a ground stabilisation solution to support the downstream bank where voids had developed. Protecting the river from contamination was critical to the client and local iwi. We identified a special water-resistant grout mix that hardens quickly once injected into the ground, even if it is in contact with water, to minimise risk to water quality.
Specialist support was provided by Wagstaff Piling, who grouted seals between old and new structures and completed the void filling (downstream) using a compact piling rig suited to the constrained site conditions. We self-performed most of the project scope, managing challenging ground conditions, a constrained site, and environmental risks. The team also delivered the sheet pile installation within the strict vibration limits to protect the 80-year-old bridge.
