‘Distressing’ letter warns of West Coast landslide risk

Granity residents have been called to a surprise briefing after the Buller District Council commissioned a geological report on landslide risk following a heavy rainfall event in February.

“We acknowledge that this may be distressing for some and encourage you to come along to ask questions,” regulatory services group manager Sean Judd said in a letter hand delivered to affected residents in the small town northeast of Westport late last week.

The council briefing on 17 August encompasses about two dozen residences or commercial buildings identified at high risk from “debris flow” landslides or “translational type” landslides.

It includes the Northern Buller Museum, a site built in 1909 for receiving coal from the Millerton Plateau above.

Museum chairman Derek Lord described the report as “scaremongering” and said it would cause unnecessary stress in Granity.

As far as the museum was concerned they would just carry on.

“What are they going to tell us to do, close? We’re going to tell them to take a flying leap,” Lord said.

The report was “putting the fear of God” into the community unnecessarily about its future.

Lord’s Torea Street home of about 30 years was also affected by the landslide report.

He noted there had been a long history of drains bordering residential properties under the hill at Granity backing up when they reached the road due to lack of regular maintenance by the authorities.

“They’re calling it a major weather event! It’s just the coast rain. We get water spouts along here – it’s just the weather from the Tasman. It’s nothing new.”

The letter was accompanied by a fact sheet titled “Granity landslides” and a further sheet outlining “options, decisions and actions.”

“That discussion will need to take into account the community’s risk tolerance levels and availability of resources, and will facilitate the development of a risk management plan,” the executive summary says.

In February, 166mm of rain fell on Granity in 24 hours, causing several slips on the steep escarpment immediately above Granity and Ngakawau townships.

The Granity Landslides Preliminary Risk Analysis, by England and Co, covers the entire area south of the Ngakawau River to the southern edge of Granity, with State Highway 67 forming the western boundary of the identified risk area.

“The preliminary risk analysis identifies two distinct types of landslide … and it presents corresponding risk zone maps delineating the risks associated with each of these landslide types,” the report says.

The Northern Buller Museum, four houses and some outbuildings or sheds have been identified in a “high risk zone,” for landslides and were vulnerable to “impact damage.”

There was a 57 percent risk in the 50-year design life of a building.

About 20 residential dwellings and some outbuildings are at medium risk, or 22 percent, of being damaged in that timeframe.

The risk to life in both the high and medium risk zones was higher than the level for new build homes under the current building code.

Ten houses and the museum were at high risk of debris flow damage, with “a possible risk of harm” to residents.

A further 15 homes, three commercial properties and some outbuildings were judged to be at medium risk from debris flow.

The report says the risk to life and property will increase “as climate change progresses”.

Lord said while floodwaters sent debris through the museum building in February, that was because a 600mm culvert in a drain slightly uphill was blocked and this had diverted the floodwaters toward the complex.

“It’s really a flood event, it’s not a slip.”

Another slip slightly south of the museum site now formally identified by the council had been there about 20 years but minimal debris had come down from that area in February, Lord said.

“We’re not worried about it.”

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