Flood-ravaged town 'will be hit again'

A house destroyed in Matata in May's flood. Picture / Rotorua Daily Post

Geological experts have found that some parts of flood-hit Matata are unsafe to live in because of the danger of further landslides.

Areas of the Bay of Plenty town are at risk from "debris flows" - flood waters churned up with silt, sand and rubble to the consistency of wet concrete and able to carry huge boulders, they said.

"It's definite, a similar event will happen again," senior water resources engineer Tom Bassett told 200 people at a public meeting in the Matata Rugby Club tonight.

Mr Bassett and a team from the Institute of Geological and Nuclear Sciences and local and regional councils found that the May 18 disaster was a "debris flow disaster". It destroyed 27 homes, damaged a further 87 properties, and closed State Highway 2 and the local railway.

They discounted earthquakes in the disaster, despite residents' fears a swarm of quakes plaguing the town since early this year contributed to the disaster.

The comment provoked angry outbursts from several residents.

"Those slips have been coming down those bloody creeks for years," said a man who hunts in the hills behind the town.

Another man said: "All these slips are following the same faultline as in 1987 (the year of the Edgecumbe earthquake) so you can't tell me that these earthquakes haven't had an effect."

One woman said there were five to six earthquakes a day in April.

But Mr Bassett said none of the quakes at Matata was big enough to trigger landslides, instead blaming debris flows and associated flooding.

Debris flows are dense flows of water and debris. They move more quickly than floodwaters and are capable of carrying huge boulders. Boulders up to 7m in diameter were moved at Matata.

The geologists found the debris flows came from landslips triggered by exceptionally heavy rain in the catchments behind the town.

More than 94mm of rain was recorded in one hour at nearby Awakaponga.

The area received a quarter of the year's rainfall in the two hours between 4pm and 6pm.

The rainfall was labelled a 500-year event.

"These debris flows have a consistency like wet concrete," geologist and geotechnical engineer Dick Beetham said.

Further debris flows were possible whenever there was rain of a high enough intensity to trigger landslides on the steep catchment slopes, the experts said.

A leaflet given to residents said engineering works could reduce the danger from debris flows to acceptable levels, but there were some areas in the town where that was not feasible.

Emotions ran high among residents of destroyed homes, who now fear they may never be able to rebuild on their properties.

Narelle Boonen, now living in Whakatane, wanted to know when she would be told the fate of her land.

Whakatane mayor Colin Holmes said more work needed to be done before it was known if properties were write-offs, but it was likely any residents in that situation would be told before the next public meeting in July.

"I'd think that we'd be talking to these people individually," he said.

Another woman made a plea to the Earthquake Commission to ensure claims for properties written-off are processed quickly.

Others who are allowed to live in partially damaged homes, but who the council says must leave when there is more than 50mm of rain, wanted to know how long the order stood.

"How long will that embargo stay on me?" asked a man who said his insurance company had given him the go-ahead to rebuild.

Wayne Maloney asked why town planners had allowed people to build next to flood-prone streams in the first place.

"I knew it [the stream next to his house] was there, but I never imagined it'd be shooting cannonballs into town," he said.