Aerial view of one of the 26 slips that hit the Mangamuka Gorge in August 2022. Photo / Waka Kotahi
Repeated huge rain dumps and major damage have led to SH1 over the Mangamuka Gorge being largely closed since July 2020 - except for about 12 months from July 2021 to August 2022.
More than $100 million will have been spent on repairs by the time the reopening happens. By that stage, the highway will have been closed 75 per cent of the time since July 2020.
Far North District Council member Steve McNally, who sits on Northland’s heavyweight Regional Transport Committee (RTC), said the reopening delay to the Mangamuka Gorge road brought the risk of repairs costing more.
Delays to the reopening have been caused by bad weather, outlined in Waka Kotahi’s report to an RTC meeting in Whangārei on Tuesday.
“The wet weather throughout 2023 has resulted in more slips. In total there are now 35 slips to repair - 15 of these are critical slips,” the report said.
“Our crews have put extra measures in place to keep everyone safe, and at times we’ve needed to stop work when conditions become unsafe, or the numerous sensors positioned through the gorge have indicated ground movement.”
About 13km of SH1 is closed over the Maungataniwha Range south of Kaitāia, the road known locally as the Mangamukas.
Northland transport leader and RTC chairman Joe Carr said he understood the concerns of increasingly-frustrated motorists who are now facing further delays in getting the critical route open again.
“I share their concerns, everybody wants the service, but the work can’t be resourced any more than it is. It’s a major repair in challenging conditions.”
Carr, also a Northland Regional Council councillor, said 150 people were working on repairs over day and night shifts to make sure it could be fixed as soon as possible.
“I am satisfied everything that can be done is being done.”
Waka Kotahi’s report stated work towards the route’s permanent repairs had been progressing well.
More than 700 temporary piles had been installed and permanent repairs have started across a number of slips, Waka Kotahi said.
Steel and concrete capping beams to tie pile foundations together and anchors to fix structures into the ground would come next.
There were at present 242 piles needed for permanent repairs, some drilled 27 metres deep into the ground.
The crown entity said this number was likely to increase as slip repair design continued.
Sixty-three of the permanent piles will have been installed by the end of the week.
Piling rigs and cranes were in place at both ends of the Mangamuka Gorge.
Carr has been driving the Mangamukas for more than 50 years. He said rainfall patterns had changed in that time, affecting the critical infrastructure route.
“We’re getting the same amount of rain but it’s falling in huge dumps.”
McNally said extra SH1 traffic diverted onto SH10 as a result of the closure was in turn causing issues for the alternate route.
The major effects of extra SH10 traffic came to a head for hundreds of Labour Weekend holidaymakers last year, who were held up at the new $40m Kāeo bridge build.
Southbound traffic returning from the Far North at the end of the long weekend was at times backed up for up to 8km from Kāeo bridge to the highway’s Tōtara North.
In regards to the bridge, Waka Kotahi said the rebuild will include a roundabout with opening scheduled for early 2024. Three of the bridge’s four 30m spans had been completed, each built with 180 tonnes of concrete. Asphalt would be applied once the spans had been completed.
“The next focus is completing the roundabout and the new roads that approach the [bridge] intersection.”
