Last updated 16 December 2024
When will the road open?
The road will reopen at 12:01am on the morning of Friday 20 December 2024.
Will there be any remaining works after the road has opened?
After the reopening, some finishing work will be necessary following the holiday break.
Planned stop/go traffic management and reduced speed limits will be in place on SH1 Mangamuka Gorge from 13 January 2025 to April 2025 while the team completes final works, including anchor work on the final two slips on the northern side (A7 and A9). The road will remain open, and the team will do their best to minimise disruptions.
How were the slips fixed?
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.
What were the key stages of the project?
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.
Why don’t you build a tunnel or a new state highway?
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.
What’s happening with State Highway 10 (SH10)?
Slip repairs and bridge strengthening work on SH10 were undertaken as part of the emergency and recovery response work.
We also have teams undertaking an extensive pavement repairs programme on SH10 to repair damage and prevent potholes. This summer 24/25 season, we plan to repair about 15,000m² of pavement along SH10, which is 55% more than the average amount over the last three years. With faster response times for pothole repairs, we expect visible improvements by the end of the construction season.
We are also working on road renewals, including road rebuilding, resurfacing, and resealing, especially in areas where small patch repairs are no longer effective. Key projects include rebuilding 1km of SH10 between Pakaraka and Waipapa and resurfacing 9.9km of road, with about 5.5km of it in the Mangōnui to Taipa area.
Additionally, we are addressing subsidence issues caused by land movement under the road. This will involve long asphalt patches, ranging from 20m to 50m, to smooth uneven surfaces. One major smoothing project is planned for a bumpy section south of Taipa, where we’ve received regular feedback from drivers about the rough road.
This work is part of NZTA’s largest ever state highway maintenance and renewal programme for Northland this summer.
For the latest travel information and journey times, check out the NZTA Journey Planner before starting your journey.
Journey Planner(external link)
Will there be any more slips? How long will the road last for?
While the risk of major slips has been significantly reduced, the area is still susceptible to slips due to the challenging ground conditions in the Maungataniwha Range.
However, with the work we've done, if future slips occur, the damage should be much less severe, allowing us to reopen the road quickly and minimise disruptions. Due to these works, communities will have more safe and reliable access even during weather events.
The repairs we completed after the 2020 weather event were undamaged during the weather events of 2022, requiring no additional work in those areas. Also, during the bad weather in June 2024, there was no sign of movement on any of the completed slip sites and the slips we were currently addressing remained stable overall.
