Giant Helena Bay Hill slip creates 20,000 truckload challenge

A massive slip, including a boulder covering two-thirds of the road, is blocking Russell Rd at Helena Bay, Northland. Photo / Denise Piper

Up to 20,000 truckloads of clay and debris will potentially need to be removed to clear the giant Helena Bay Hill slip.

And authorities are looking at where to dump up to 100,000 cubic metres of clay, vegetation and debris from the slip.

The slip came down last Wednesday after overnight rain, after a weekend weather bomb dumped more than a summer’s worth of rain on the coast on January 17 and 18.

About 100,000 to 200,000 tonnes of heavy wet silt and debris have collapsed in the slip.

WDC infrastructure chair Brad Flower said it will mean potentially between the 50,000 to 100,000 cubic metres of debris that came down across Russell Rd on Helena Bay Hill had to go somewhere.

The council has estimated it could take up to three months to repair.

Flower said the slip material could not be pushed over the edge of the site at Russell Rd.

The material would simply go downhill and sediment would flow into the settlement of Mokau and out to sea, he said.

It also risked creating a dam, which could collapse and flood the tiny community northeast of Whangārei.

Flower said sites for the debris were being investigated.

These included local areas where a community wanted to build its whenua (land) above flood height or on suitable farm valleys.

He said the job was not just about what could be seen on the road.

There were big cracks in the land at the top of the slip.

“We might have to go 50 to 100m back from the slip,” he said of the nature of the repairs.

Specialist equipment has been brought in to assess the slip.

Flower said there was a huge amount of background planning happening.

“People might think there’s nothing going on because they can’t see anything happening on the ground.

“But there’s a lot of preparation work being done.”

This included working with Northland Regional Council on consenting processes.

The last big Helena Bay Hill slip in 2007 took six months to clear.

■ LDR is local body journalism co-funded by RNZ and NZ On Air.