A helicopter has dropped an “enviroblanket” over a rockfall red zone on State Highway 1 near Kaikōura to regenerate growth and combat soil erosion.

Red Tree Environmental Solutions used an “engineered monsoon bucket” to “direct seed” natives over the embankment at Ōhau Point in July.

Horticultural manager Andrew Cummins believed it was the first time the enviroblanket technology had been applied using a helicopter in New Zealand, and said it had “great potential” for establishing native vegetation on inaccessible slip faces in the future.

The aerial seeding at Ōhau Point came about because of difficulties accessing the area, and safety concerns raised about sending people behind the mesh rockfall fence.

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The work was contracted by the North Canterbury Transport Infrastructure Recovery alliance, tasked with the rebuild of State Highway 1 following the 7.8-magnitude earthquake in 2016.

But Cummins said heli-seeding could also be used immediately after natural disaster land movements, to stop clay and sediment running off into rivers.

“It’s got legs for the future,” he said.

Red Tree had developed the enviroblanket technology over the past three years, originally using trucks to distribute the seed mix, in response to stabilising and revegetating natural disaster slip sites in the Canterbury region.

The helicopter used at Ōhau Point had a lifting capacity of about 800 kilograms, and carried a bucket containing locally sourced native coastal pioneer tree and shrub species, blended with a compost solution.

NCTIR project manager Taura Allen said they had originally discussed planting the area out by hand, but it was still an “active slip area”.

“We had to talk around an alternative method which meant that we didn’t need to put people in a red zone to work,” Allen said.

They discussed whether they could spray it out from a truck, but that also posed difficulties.

The aerial operation took five days to complete, and was “cost neutral” when compared to other seeding methods.

“It was really safety driven ... it was about not putting people in a hazardous zone and coming up with a new solution.”

According to NCTIR’s latest bulletin, construction on the last formal safe stopping area finished this month, with parking opened to the public at Paparoa Point on July 15.

After a string of recent weather setbacks, the team at Ōkiwi Bay were pleased to lay the final layer of seal on the site in late June, completing the project to realign the road and rail in 13 months.

The first stage of permanent rockfall protection was underway at a rockfall-prone corner between Peketa and the Parititahi Tunnels south of Kaikōura.

This initial work identified the need for additional rock anchoring to stabilise the fractured rock face, requiring two weeks of day closures for State Highway 1, finishing mid-August.