Above: Before (L) and after (R) photos of one of the slip sites (A12) on the southern side of the Mangamuka Gorge [Photo/Supplied]

The Mangamuka Gorge has been closed since August 2022, due to significant slip damage caused by severe weather. Additional weather events and record rainfall throughout 2023 resulted in additional slips, as well as further complicating repairs on existing slip sites. In June this year, a significant new slip formed, taking the total number of slip sites to 36, with 16 of those identified as critical.

NZ Transport Agency Waka Kotahi (NZTA) Project Director, Mark Ware, says it’s a tremendous feeling to see the road opened today, just in time for Christmas.

“We know how important this road is to the people who live, work and do business in Te Tai Tokerau Northland. The team has worked tirelessly to restore this crucial social and economic connection for the Far North and ensure its resilience for the future.

“While much of the repair work is underground, with the extensive piles and anchors hidden from view, road users will notice a wider road at the repaired sites, new asphalt, capping beams, guardrails, and a new retaining wall – all part of a highly complex engineering effort. The summit will also be open, providing a spot for people to take a break, stretch their legs, and enjoy lunch at the new picnic tables.

“Alongside the slip repairs, we’ve made significant drainage and stormwater improvements to ensure the road is better able to handle any future weather events.

“Our team has worked at pace through tough conditions to meet the challenge of restoring this important connection. As they worked, they needed to continually monitor the hillside to ensure there was no new earth movement. They also faced Northland's challenging geology (Northland Allochthon, or “Northland Problematic Rock”) and the narrow terrain of the gorge itself.”

The significant work programme has led to some pretty impressive numbers for the project, says Mr Ware.

“There is a lot to be proud of in some of these figures – the sheer number of site hours the crews have put in to get us to this point, and the high percentage of locals, and local companies involved. It’s a real success story.”

A few facts about the project (February 2023 – November 2024):

People

• 560,000+ site hours
• 1,274 total inducted site staff
• 150 average daily workforce on-site

Companies

• 193 total companies involved
• 58% Far North employers
• 29 daily average companies on-site
• 50% Far North District average workforce on-site
• 68% Northland region average workforce on-site

Slips

• 36 total slips (16 critical slips and 20 minor slips)

Piles

• 1337 total piles installed
• 747 enabling piles
• 590 permanent piles
• 23m average pile depth
• 32m deepest pile
• 12.8km total length of drilling
• 10,000m3 of concrete used

Road surface

• 5.2km of road paved
• 50,000m2 of asphalt installed
• 6,571 tons of asphalt installed

12-month rainfall (Feb 2023 – Feb 2024)

• 1712mm historical average annual rainfall
• 2801mm total rainfall in the past 12 months
• 542mm rainfall in the wettest month, May 2023
• 34mm rainfall in the driest month, Feb 2024
• 72mm/hr peak rainfall per hour
• 118.8mm rainfall on the wettest day, 23 Sept 2023

Northland Inc Chief Executive, Paul Linton, says resilient roading networks are the backbone of Northland’s economy and community.

"Roads like SH1 through the Mangamuka Gorge are critical lifelines, connecting our people, businesses, and visitors to the rest of the region and beyond.

“This reopening is not just about restoring a key transport route; it’s about ensuring the resilience of our infrastructure to support economic growth, enhance tourism, and maintain the well-being of our communities. The investment in this project underscores the vital role these connections play in shaping a thriving and future-focused Te Tai Tokerau Northland," says Mr Linton.

Though the road is now open, additional works are required after the busy Christmas holiday break to finish the repairs. Workers will return to site the week beginning Monday 13 January 2025 to complete anchor work on the remaining slips. Works are expected to continue until April 2025.

“The road will remain open during these works and the team will do their best to minimise disruptions. However, people can expect to see temporary traffic management, such as reduced speeds, stop/go or traffic lights,” Mr Ware says.

A temporary 80km/h speed limit will be in place on SH1 Mangamuka Gorge until April 2025 for the safety of the construction team undertaking finishing work and while road users get reacquainted with the route, following the two-year closure. The speed restriction is not expected to impact travel.

There are also areas of new seal and Mr Ware asks motorists to adhere to posted speed limits to help keep themselves, other road users and road workers safe. The temporary speed limit also helps ensure the quality of the seal while it beds in.

“As these final repairs are completed, we ask that people help keep everyone on the road safe by driving with care, adhering to the posted speed limits and following the directions of traffic management staff and signs.”

As part of the largest ever investment in state highway renewals in Northland, NZTA is also undertaking significant pavement repairs this summer to address damage and prevent potholes on State Highway 10, the detour route used during the closure.

NZTA plans to repair about 15,000m² of pavement – 55% more than the average amount repaired on SH10 over the past three years. Key renewal sites include rebuilding 1km of SH10 between Pakaraka and Waipapa and resurfacing nearly 10km of road, with 5.5km in the Mangōnui to Taipa area.

“We’d like to thank the people of Te Tai Tokerau Northland for their patience and support of the project, and we hope everyone enjoys a relaxing Christmas holiday break in the beautiful Far North this summer,” Mr Ware says.

“Merry Christmas to all, and to all a good drive.”

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