Mangamuka Gorge, the ‘infamous’ section of State Highway 1 in Northland, is expected to reopen by Christmas after a closure that has lasted over two years. This crucial road link was severely damaged by a series of 15 slips during a major storm in August 2022, just a year after it had reopened following a previous year-long closure.

Efforts to repair the 13-kilometre road had been underway for less than six months when another storm in April 2023 triggered an additional 20 slips, causing further delays and escalating costs. The closure forced motorists to take lengthy detours via State Highway 10 or back roads through Broadwood and Herekino, significantly extending travel times.

Hendrik Postma, a senior project manager at Waka Kotahi NZ Transport Agency, announced that the rebuilding of this vital lifeline was progressing well and would be completed in time for Christmas, assuming no major storms occur. A specific reopening date will be announced in September to allow the completion of repairs before the onset of winter rain.

The Mangamuka project, one of the largest roading recovery projects in New Zealand, faced numerous challenges due to the unstable geology and the exceptionally high rainfall of the past year. The cost of the project increased from an initial budget of $100 million to approximately $165 million due to the 2023 storm and the subsequent increase in slips.

Mark Ware, the project director responsible for rebuilding both Mangamuka Gorge and State Highway 1 over the Brynderwyn Hills, emphasised the significance of these routes as economic and social lifelines for Northland. Despite the closure impacting the local community, Ware expressed a commitment to completing the project efficiently while ensuring safety and quality.

The complexity of the Mangamuka project, characterised by slips stretching 13 kilometres and mostly located below the road, required intricate construction work. In contrast, the Brynderwyns, where slips covered a shorter distance above the road, focused on slope stabilisation.

While the closure took a toll on local families and communities, the reopening of the highway by Christmas is eagerly anticipated. The detour increased travel time from one hour to nearly two hours, hindering connections between relatives and affecting cultural events. The reopening is seen as crucial for both sides of the ranges, despite the bittersweet sentiment for those who formed bonds with workers during the project.

Repair efforts involved driving piles into the ground, capping them with concrete beams, and anchoring them using steel cables. Most of the critical slips have been repaired or are nearing completion, with extensive soil removal required for the most complex slip, known as A11. The project also includes drainage improvements, the installation of larger culverts, and initiatives to protect local wildlife, such as fish passages and relocation of endangered species.

The reopening of Mangamuka Gorge will signify a significant milestone, providing relief for residents and travellers who have endured lengthy diversions and delays.