SH1 Brynderwyn Hills Recovery Widening Works

Strengthening a critical corridor through innovation and partnership

The Brynderwyn Hills, a steep and slip-prone stretch of State Highway 1 (SH1). From 2022-mid-2023, this vital corridor between Northland and Auckland has been closed eight times due to landslides, underscoring the urgent need for a resilient solution. In response, NZ Transport Agency Waka Kotahi (NZTA) engaged WSP to provide detailed design services for recovery and widening works on the southern side of the Brynderwyns—approximately 2.3km of winding terrain.

This project, delivered in close partnership with Fulton Hogan and NZTA, has been a showcase of innovation, collaboration, and fit for purpose engineering. It began as a creative proposal in mid-2023, driven by the industrious efforts of WSP and Fulton Hogan staff.

The design philosophy centred on creating a minimum 12.5m road corridor, constructed over a planned 9 week full SH1 closure —wide enough to open to traffic while completing the slip repairs. This also accommodates future slope failures and maintains two lanes of traffic during remediation works. This pragmatic approach enabled a full recovery of the road and ensured the road may last another 10 to 15 years until a new SH1 route is available. The pragmatic approach also, enabled efficient construction within a short timeframe to minimise impact upon the transport network and the Northland region.

Collaborative engineering in action

WSP, Fulton Hogan and NZA worked collaboratively to achieve practical designs and deliver those in a quick and responsive manner. In this flexible, productive collaboration, WSP has provided a broad suite of engineering and advisory services, including:

Geotechnical investigations and slope stability design
Roading geometrics, pavement design, and stormwater management
Civil and structural design for retaining walls and rockfall protection
Environmental planning, landscaping, ecology, and sediment control
Cultural integration with hapū partners
Construction support including drone surveys, live instrumentation monitoring, and technical oversight

Location

Northland, New Zealand

Client

NZ Transport Agency Waka Kotahi

Project Status

Ongoing

What does this project exhibit?

Delivered in close partnership with Fulton Hogan and NZTA, has been a showcase of innovation, collaboration, and fit for purpose engineering

Standout delivery information

This project is one of the largest to be delivered from the WSP Whangārei office

Construction began in early February 2024, with a full road closure in place from 26 February-27March, and 3 April – 26 June. WSP maintained a continuous onsite presence, with teams of geotechnical, civil, and ecological specialists supporting the fast-paced works. Milestones of note include:

240,000m³ of earthworks
2.3km of corridor widening
Stormwater upgrades across 12 gullies
Over 100m of H-pile retaining walls (up to 5m high)
500m² of soil nail and mesh rockfall protection
Live slope monitoring with an active alarm system to enhance construction safety

Safety, culture and community at the core

Health and safety has remained the top priority throughout the project. WSP and the wider team worked closely with NZ HSE advisors to uphold rigorous safety standards, responding proactively to incidents and near misses. Our continued focus on health and safety in design and collaboration with Fulton Hogan resulted in 236,000 hours with no lost time incidents.
Weekly morning teas, staff lunches, Matariki awards, dinner vouchers, and team-building activities helped maintain morale and recognise the outstanding contributions of project staff.

Technological innovation

Creative technologies have played a key role in improving quality and programme outcomes. The use of Autodesk Construction Cloud enabled live collaboration on design and drafting, while SharePoint provided structured and accessible project documentation. A live slope monitoring network provided a vital reference to WSP and construction staff during rainfall events.

Looking ahead

Despite setbacks—including major slips over ANZAC weekend that delayed reopening—the project team remained transparent and responsive, earning commendation for its handling of challenges. WSP’s technical leadership and collaborative spirit have been recognised throughout, and in June 2024, the project team proudly welcomed the public back onto a safer, more resilient Brynderwyn Hills corridor. Final surfacing and line marking is scheduled for 3-4 days in November, marking the completion of the project, one of the largest to be delivered from the WSP Whangārei office.