Last updated 6 June 2025.
The road reopened to traffic at 12:01am on the morning of Friday 20 December 2024.
Here’s an example of the repair plan for slip A9 which was one of the critical slips on the northern end of the gorge. It was a complex fix and took approximately 8 months to complete. Each critical slip required a similar approach and took on average 5-6 months each to repair.
This has been a complex process to understand firstly the damage which occurred and then investigate and plan the best way to fix each slip.
We were working in a constrained environment with large machinery and a lot of people working across multiple sites. This meant the movement of equipment and materials around site was sometimes slow and had to be carefully planned to ensure the safety of our people and to maintain the integrity of the road.
Following the initial evaluation of the damage an extensive amount of enabling work was undertaken to ensure the gorge was safe and stable enough to accommodate the large machinery needed to carry out permanent slip repairs.
This included installing 747 soft piles (drilled and filled with concrete) and hard piles (reinforced with steel casings).
While the enabling works were being undertaken, a parallel workstream with the permanent design for all critical slips was also being undertaken and now complete.
Following the completion of the enabling works, permanent piling, excavation and anchor installation commenced.
Alongside the slip repairs, stormwater improvements have been undertaken to increase capacity of the drainage through the gorge, so it’s more suitably equipped to handle the increase in severity and frequency of future weather events.
The last stage of the repairs was to replace the damaged road surface at the slip sites through the gorge.
Since February 2023, the site has been repaired with multiple large, piled retaining walls. In total, 1,337 were installed—including 747 enabling piles and 590 permanent piles. On average, each pile is 23m deep, with the deepest reaching 32m. The total length of drilling for the piles added up to 12.8km, and more than 10,000m³ of concrete was used.
Over 300 anchors were used to fasten the piles to the hillside. We also made drainage improvements, including upgrading crossroad drainage and installing new larger culverts ranging from 0.6m to 1.2m in diameter to better manage water flow.
In total, we paved 5.2km of road and laid 50,000m² of asphalt – that’s around 6,571 tons of asphalt used.
While the risk of major slips has been significantly reduced, the area is still susceptible to slips due to the geology and varying terrain in the Maungataniwha Range.
However, the risk of major slips and long closures has been reduced due to the extensive recovery work completed in the gorge. The recent works are designed in a way that any future movement is expected to be much less severe, helping us respond quickly and minimise disruptions.
The piled repairs we completed both in 2020–2021 and 2023–2024, held up well and required no additional work in those areas during recent weather events.
Both options would require significant investment.
On average, the state highway through Mangamuka Gorge carries only about 1300 vehicles per day, as compared to somewhere like the Brynderwyn Hills, which carries approximately 10,000 vehicles per day (though this can vary depending on the season). This means the business case for such a large investment would be unlikely to meet the criteria for NZTA funding.
The nature of the terrain that the road travels through means that, as extreme rainfalls or wet weather will always cause movement in the gorge, it would not be feasible to build a tunnel through this section of SH1.
We understand that SH1 through the area is a social and economic lifeline, and we are committed to ensuring it is safe and reliable for the Far North Communities who rely on it.
SH10 is the official detour route for all vehicles whenever SH1 through Mangamuka Gorge is closed—adding up to 40 minutes to journeys. During the over two-year closure for major repairs, the increased traffic placed additional pressure on this route.
To help keep SH10 safe and functioning during this time, slip repairs and bridge strengthening work were carried out as part of the emergency and recovery response.
Since SH1 reopened, we’ve been able to carry out further maintenance and renewal work on SH10 to help manage wear and keep the route safe and reliable. Maintaining safe transport connections to and from Northland is a key priority for NZTA.
As part of the 2024–2025 Northland state highway renewal season, we’ve delivered an extensive pavement repairs programme on SH10 to repair damage and prevent potholes, including:
For the latest travel information and journey times, check out the NZTA Journey Planner before starting your journey.
