Image: The works included internal welding, jointing, seepage pipe connections, annulus grouting, flange construction and reinstatement, all completed while managing live water conditions and restricted access.
A project demonstrating practical problem-solving, technical judgement and disciplined delivery renewals has won the Category 1 award – for projects up to $2 million – at this year’s Civil Contractors New Zealand Hirepool Construction Excellence Awards.
The Paremuka Dam Culvert Rehabilitation project in Henderson, Auckland, was not straightforward. Original design details had to be challenged and refined; temporary works were adapted to changing water conditions and biosecurity and environmental requirements were incorporated into the final solution. Adding to this, the project was delivered in a live water environment beneath Paremuka Dam and in an active KiwiRail corridor.
Pipeline & Civil was contracted by Auckland Council to rehabilitate a deteriorating double-barrel culvert within a confined and irregular structure, while managing fluctuating winter water levels, constrained inlet and outlet access, rail interface risks, environmental and biosecurity requirements, and rescue planning for confined-space works.
Risk management
Constraints shaped the project setup from the outset. Rather than treating the works as a standard culvert renewal, Pipeline & Civil established the project around early risk identification, controlled access planning, constructability review, environmental compliance, and stakeholder coordination. Site inspections, survey checks, design review, resource consent review and coordination with landowner KiwiRail were used to confirm the key risks and opportunities before works progressed.
This planning helped determine the site establishment strategy, access controls, constructability checks, environmental planning and temporary works approach needed to deliver the project safely.
These constraints were compounded by the need to keep one culvert barrel active while the other was isolated, requiring water to be diverted and controlled throughout construction.
Construction complexity and challenges
The project saw the installation of DN1500 steel and HDPE liners within the existing double-barrel culvert. The pipe installation was done with steel rollers, pulling heads, and winching systems to move each section into position with precision.
The works included internal welding, jointing, seepage pipe connections, annulus grouting, flange construction and reinstatement, all while managing live water conditions, restricted access, pipe movement, welding access and emergency response requirements within the culvert environment.
Works were sequenced around two work fronts: the inlet and outlet sides. The inlet side supported scaffold access, winch control, power supply and rescue arrangements. That was made more difficult because of the limited space on this side, as well as resource consent constraints that required a reduced-footprint methodology that avoided entering the lake and minimised works in sensitive areas.
The outlet side operated as the main site yard within KiwiRail land and a busy maintenance yard, with other contractors and rail activities operating around the site.
The existing culvert geometry was tight, irregular, and difficult to work within, resulting in limited room to manoeuvre DN1500 steel and HDPE liner sections. However, by carrying out its own survey and 3D modelling before installation, Pipeline & Civil identified constructability issues, which confirmed that elements of the original fabricated pipework would not fit as intended.
Working with the designer, the team amended the design, resolving issues with pipe fit, flange details, seepage connections, and the steel-to-HDPE transition before they became site delays.
This constructability review also prompted several practical design refinements, including simplifying the steel pipe profile to reduce internal welds, redesigning complex flange details, replacing the impractical PE flange with an in-situ concrete flange and modifying seepage connections where the original couplers couldn’t be used due to constant water flow.
The complexity of the construction work was heightened by the culvert’s location underneath an operational rail corridor. Any settlement, uplift or structural movement could have affected KiwiRail’s live track above.
This was mitigated by securing KiwiRail access approvals, installing track monitoring prisms, undertaking regular settlement checks and coordinating the works around KiwiRail’s active maintenance yard.
Managing weather risks
Rain events created one of the most significant live-water risks, particularly as the works extended through winter, when water levels were more difficult to predict and control. The dam could surcharge quickly, especially when flows were being channelled through one culvert barrel while the other was kept dry for works. This created a serious flood and evacuation risk for workers inside the culvert.
When initial sandbagging proved insufficient for flow control, the flood management methodology was revised to include timber barriers and engineered inlet controls designed by a temporary works engineer to manage water levels up to 1.8 metres. Standovers were also used to monitor water levels and trigger evacuation when required.
Protecting the environment
Environmental controls were planned early due to requirements around the dam, downstream creek, surrounding reserve and biosecurity. Environmental risk was managed as an active construction control, rather than a one-off planning requirement.
The team managed fish rescue, lizard management, vegetation controls, resource consent compliance and protection against grout entering the downstream environment.
They also supported Auckland Council’s biosecurity objectives by designing and installing a bespoke fish grill at the culvert inlet, helping contain carp introduced to manage Cabomba weed while preventing them from escaping downstream.
Early planning also allowed Pipeline & Civil to reduce the original consented vegetation removal by around 60 percent, significantly reducing the project footprint around the dam environment and limiting disturbance around the inlet.
Communication is key
Pipeline & Civil maintained close communication with Auckland Council through weekly, then fortnightly meetings covering programme, risks, forecasting, environmental controls, quality records and design changes.
The client later noted that Pipeline & Civil’s involvement marked a turning point after years of earlier project delays, with the team’s planning and practical problem-solving helping move the project into successful delivery.
Through careful planning, constructability review, responsive methodology changes and strong collaboration with Auckland Council, consultants Stellar Projects, KiwiRail and environmental stakeholders, Pipeline & Civil delivered a high-quality renewal ahead of the revised programme and within the final $1.9 million contract value.
The content of this article was taken from Pipeline & Civil’s award entry.
Beneath the BLACK ART