Tower 29 relocation

Location: Pukenui Ngahere, Western Hills, Whangārei

Investment: $3.06 million

Start Date: October 2022

Completion Date: August 2024

Key people involved: Colin Boggiss (Edison Consulting Group), Shaun Brown (Northpower Network)

Project partners: Te Parawhau, Clements Quarry, Edison Consulting Group, Lumen, Ecology North

Northpower / Project case studies / Tower 29 relocation

Inspection finds threat to transmission tower

In winter 2022, a routine inspection of high voltage lines between the Maungatapere and Kensington substations identified an area of land subsidence near one of the large support towers – Tower 29.

Our team were concerned that subsidence may indicate unstable ground, potentially risking the tower and it’s supported lines. Specialist inspection and monitoring of the subsidence by Northpower’s geotechnical consultants confirmed this was the case.

This prompted an immediate response from our team to devise a solution to tackle potential future supply disruption caused by subsidence.

The temporary solution

To mitigate the risk of potential land slippage, two temporary transmission towers were created as a bypass, situated to the east and west of Tower 29.

If one temporary tower were to fall, the other would still provide electricity supply to Whangārei. Sourcing transmission poles takes six months, so the team improvised by constructing the bypass line using distribution poles.

Our network team provided technical expertise in collaboration with Edison Consulting Group to project manage, and engineering design experts Lumen.

The permanent solution

The two-year lifespan of the temporary towers required the design and construction of a new permanent line, including sourcing a new 40m monopole to support a new 110kV conductor. A suitable site for Tower 29A was selected in the forest area adjacent to Clements Quarry, known to local hapū Te Parawhau as Pukenui Ngahere.

Construction works commenced in April 2024 and were completed over a four-month period by our Hamilton-based transmission crews.

In July 2024, the staged transfer of a conductor to the new section of the 110kV transmission line was completed.

Collaborating with hapū

As kaitiaki of Pukenui Ngahere, Te Parawhau played a key role throughout this project. Their significant input through a Te Ao Māori approach resulted in a construction process upholding kaitiakitanga, and a supply solution with minimal impact on the taonga species in the forest.

Throughout the project, important cultural protocols were followed. Early on, a mihi whakatau and hui was held with our executive, signifying the importance of the partnership between Northpower and Te Parawhau. Dialogue flowed between the project team and hapū – listening to each other during every step of the project – and their valued feedback on the potential designs resulted in a mutually beneficial solution.

To conclude the project, Te Parawhau blessed the site and gifted Tower 29A the name of ‘Toitū Te Hihiri’ – translated as ‘to hold up the life energy that flows through us’.

Great outcomes

The successful delivery of the project ahead of schedule is testament to the way our engineers tackle problems that arise and highlights the benefits of quality collaborations with hapū, local councils and external consultants.

Our Whangārei customers now have the benefits of an electricity supply with improved resilience.

This project was additionally recognised at the Electricity Engineers’ Association of New Zealand awards, winning the Engineering Excellence Award.