2018 Psoda Project of the Year Award Finalist Profile: Maraetai Intake Rehabilitation Project – Mercury

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4 September 2018

Complex projects come in many shapes and sizes, but few take four years, have a $6.8 million budget, involve 500 tonnes of steel gates and require 400 decompression dives. But then few projects are as complicated as renewing a 70-year-old asset located 50 metres beneath a lake, with the full force of the Waikato River running through it.
This was just some of the complexity involved in Mercury’s Maraetai Intake Rehabilitation project, which is one of three finalists for the 2018 Psoda Project of the Year Award. As part of the annual Project Management Institute of New Zealand (PMINZ) Awards, the Psoda Project of the Year Award recognises superior performance and execution of exceptional project management.
The aim of the project was to restore five intake gates at Mercury’s Maraetai Power Station on the Waikato River and replacing submerged steel gate tracks which had become corroded over the past seven decades.

Unusual conditions, extreme risks

With each intake on the dam consisting of a 100 tonne headgate running on a pair of gate tracks – all submerged 50 metres below the surface of Lake Maraetai, the project team faced truly unusual and complex conditions, as well as extreme physical and cost risks. In addition, they had to manage 13 suppliers and contractors.
To be restored, each of the five headgates had to be lifted to the surface of the lake and removed from the water – for the first time since the late 1940s. This required a unique and specialised crane, as well as a team of divers to attach lift bags to the gates to assist with the lift.
Each gate took about three weeks to remove and then had to be partially disassembled to be light enough to be transported offsite to a local workshop for a 10-week rebuild during which they were blasted, repainted and had around 2,000 components replaced. Many of these components had to be sourced from specialised suppliers overseas – further complicating the project’s procurement plan.
Since it could not be determined which components needed replacing while the headgates were still submerged beneath the lake, the exact scope, schedule and cost to complete the work were not known beforehand. The project team had to develop numerous systems for determining and managing the condition-dependent scope with the various contractors involved, along with protocols to communicate the dynamic cost, scope and schedule implications to sponsors and stakeholders.
After all that, each gate then had to be safely reinstalled again.

Workplace safety in 50m deep water

Restoration of the gate tracks meanwhile was a far more complicated task, since the tracks are fixed to the dam and could not be brought to the surface. This meant all rehabilitation work on the tracks had to be completed by divers 50 metres below the lake surface. At this depth, divers only had about 25 minutes to do their work on each dive and on resurfacing had to spend an hour in decompression chambers.
With divers working at depths of 50m under water – along with removing and replacing five 100 tonnes steel gates – the project presented significant health and safety risks which required review, buy in and approval by numerous parties, including WorkSafe, the New Zealand workplace health and safety regulator.
In addition to the inherent danger of deep diving, there was also the risk posed by the high number of total dives needed to complete the project and diving at the entry to the dam’s penstock with the main barrier, the headgate, removed.
This was overcome by a thorough 12-month long planning process between Mercury and a specialist diving contractor, appointed following a rigorous tender process.
The health and safety plan combined the contractor’s specialised expertise of diving works with Mercury’s technical knowledge about the operation of the intake and headgates to fully quantify, understand and mitigate all the risks involved.
The project team developed, tested and implemented several bespoke pieces of equipment to improve both the safety and productivity of the diving work – which was important as it costs around $100 a minute to dive at these depths.
Overall, the divers safely completed almost 400 decompression dives to replace 2,000 structural components submerged deep beneath lake.


Ultimately the project was completed without any lost time or medical treatment injuries – thanks to the planning, monitoring and controlling of the various work streams.
According to Mercury, the identification, communication and proactive management of all the inherent risks led to a successful project which enhanced the reputation its project delivery team.
“This project showed that difficult, seemingly overwhelming problems can be solved safely, on time, and on budget by the rigorous application of project management principles,” says project delivery manager, Mark Kirsopp.
“The numerous lessons learnt on this project have been well recorded in Mercury’s information management system to assist with the planning and management of future projects.”

PMINZ Awards

The PMINZ Awards will be announced at the 2018 Project Management Conference in Auckland on 20 September. The two other Psoda Project of the Year finalists are the Ministry of Education for its Education Sector Logon upgrade and Beca for its Mangere Biological Nutrient Removal project.

Rhona Aylward avatar
Written by Rhona Aylward
Rhona is Deputy Everything Officer at Psoda, where she does everything except code. After starting life as a microbiologist she moved into PMO leadership roles around the world before settling in New Zealand with her family.

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