Isthmus

As straight
as you can.
North Island Grid
Upgrade.

Approach

The North Island Grid Upgrade Project (NIGUP) is a 184-kilometre-long, 400-kilovolt National Grid transmission line built to assure certainty of electricity supply to Auckland. The project was given approval by a Board of Inquiry in 2009 and construction was completed in 2013. NIGUP entailed selecting a route for the line between Whakamaru (north of Taupō) and Auckland.

Right The transmission line from Whakamaru, north of Taupō, to Auckland. The line travels across the jurisdictions of nine local authorities through mostly rural land.

In 2007, New Zealand’s Transpower, the state-owned enterprise responsible for the National Grid, sought to assure the security of supply to Auckland and respond to an increasing growth of generation from renewable sources by constructing a new line called the North Island Grid Upgrade Project (NIGUP).

NIGUP is a 400-kilovolt transmission line that traverses 184 kilometres of mostly rural land from Whakamaru, north of Taupō, to Auckland. The line, which improves the reliability, capacity and efficiency of the National Grid, required pylons of greater size than those previously used. The transmission line is comprised of 426 predominantly steel-lattice pylons, with monopoles used in areas of greater landscape significance. The pylons have an average height of 60 metres, with some up to 70 metres tall.

Above and left Photo-simulations of the NIGUP line for the Board of Inquiry.

Below The ACRE (Area, Corridor, Route and Easement) process entailed analysing alternative corridors and routes at progressively finer scales.

Given the project’s scale, there was understandable public opposition towards the project. Large-scale infrastructural projects impinge not just on the landscape but also on the rights of private property holders, but without such infrastructure the country’s ability to support itself is compromised. In this case, the aim was to devise a route of least impact for the transmission line.

Early research of transmission lines provided the designers with an opportunity to ‘get inside the skin’ of the infrastructure. Close observation and measurement of existing 220-kilovolt lines allowed factors influencing prominence and the degree of effect at different distances to be distilled. The measurements showed that the degree of effect fell away at a faster rate over the first few hundred metres and then tapered off at a slower rate.

“It was exciting to develop and then apply a robust ‘least impact’ method to route this massive line from the central North Island into South Auckland, from where it could go underground.”
— Sylvia Allan, environmental planner

Left Plans drawn analysing views from homes and proposed mitigation planting as part of the ‘Augier’ condition.

The research also revealed the principle that straight lines are less obtrusive than those that weave around landforms and vegetation. Isthmus designed a set of principles for the detailed design of the line that included straight alignments, avoiding doglegs and heavy strain towers, and using small angles where changes in direction were necessary. Like ships, the larger the transmission line the more smoothly they need to turn. Consistency in tower height and spacing was another principle.

Designing the route for the transmission line meant taking a place in the inner circle of decision makers (a position not always afforded designers in large-scale projects). The approach the team followed was attributed the acronym ACRE: Area, Corridor, Route and Easement, which required assessing alternatives at progressively finer scales. The team initially assessed the entire ‘Area’ between the Kaimai Range to the east and the Tasman Sea to the west, approximately 200 kilometres long and 80 kilometres wide.

Left Specimen trees planted as a result of Augier Method mitigation on a farm near Morrinsville.

The exercise was repeated in more detail as the corridors and routes were narrowed. At the stage of designing an indicative alignment (or ‘easement’) in the two short-listed routes, the design process became more ‘analogue’, undertaken initially by three people in a car – engineer, planner, landscape architect – drawing alignments by hand on a map.

Given the great public interest in the project, transparency of documentation was a particular requirement, with an initial peer-reviewed methodology report prior to starting the project, separate reports for the Area, Corridor, Route and Alignment phases, and a technical report for the Assessment of Environmental Effects (AEE) produced. Isthmus prepared approximately 100 photo-simulations of the transmission line as part of the process.

“The project has required involvement and liaison with nine councils, more than 300 directly affecte­d landowners, and multiple government agencies and regulators.”
— Dougall Campbell, Transpower

Subsequently, NIGUP was examined by way of a Board of Inquiry, which sat for more than three months before approving the project in 2009. One of the Board requirements was that an ‘Augier’ condition relating to offsite landscape mitigation. Transpower offered landscape mitigation to residents deemed to have adverse visual effects within one kilometre of the line. Managed by Isthmus, the mitigation required the planting of trees to screen views of pylons and was carried out on approximately 440 properties over a five-year period.

The North Island Grid Upgrade Project is not categorised easily – the work does not fit neatly within either environmental assessment or design. Rather, it integrates research, environmental assessment, design and mitigation within the framework of the Resource Management Act (1991). In short, the project pushes the influence of the landscape architect on such complex infrastructure projects.

Team Members
Gavin Lister, Grant Bailey, Helen Kerr, Alan England, Matt Jones, Travis Wooller,
Past Team Members

Sarah Finlayson, Linda Kerkmeester, Kara Maresca, Jeremy Cooke, Hrace He,

Collaborators
MWH – Sylvia Allan (planner), Simon Beale (ecologist); David Watson (engineer); Simpson Grierson – Duncan Laing, Jamea Winchester, Jo Mooar;
Woodhouse Associate – Jan Woodhouse

Contractor
Belfour Beatty
UGL Limited
Mace Contractors Ltd (planting)

Client
Transpower