Shift at-risk homes, say councils

The Kelson house, demolished after teetering on the edge of a massive slip, was developed when building plans were not subject to strict risk-assessment. Picture / Mark Mitchell

Local Government NZ is developing a plan to safeguard homes and businesses against landslips and flooding - including the option of relocating houses away from high-risk areas.

"In areas of flooding and subsidence risk, and where there are houses that were built a long time ago, there's going to have to be a solution for those houses to be relocated," said the group's president Basil Morrison.

His comments come after he visited Kelson, in Lower Hutt, where a landslip led to one home being demolished as the ground beneath it collapsed.

The group, which represents the interests of the country's 85 councils, is working with regional authorities to develop a national protocol for flood-risk management.

When completed, the group wants to work with the Government to advance it into a total catchment plan, encompassing hazards including landslides. Mitigation schemes such as relocation would be included in the plan.

But although regional councillors acknowledge many properties nationwide are ticking time-bombs, the vast majority are unlikely to fall prey to mother nature.

"Certainly if there are obvious high-risk areas, relocation would have to be an option, but the vast majority are not in that category," said Ian Buchanan, chairman of the Greater Wellington Regional Council.

"And we'd have to be realistic about relocating on the basis of a risk that's so difficult to quantify. Every slope has some risk attached to it, and there's an awful lot of buildings in New Zealand built on slopes."

But he admitted that homes on land at risk of subsidence had few protection measures other than relocation.

And the problem is worse for houses on decades-old subdivisions - such as the Kelson case - which were developed when building plans were not subject to strict risk-assessment tests.

Mr Morrison admitted the plan would be potentially costly and controversial - lots of people may not want their homes moved elsewhere.

"It will take resources and there will be tough decisions to be made and quite a bit of money to be found. But the public requires us to do better."

He said the plan still had to go through a consultation process - involving the Ministry for Environment - and would not be ready for at least another 12 months.

Environment Minister David Benson-Pope said he would be open to looking at it.

"Extreme weather events are here on an ongoing basis and we need to come up with strategies to manage them better.

He said there are historical cases where relocation should have been considered.

"If people had known that Abbotsford was about to slide down the hill [69 homes were destroyed in the 1979 landslide], relocation would have been an option. Clearly, any local government authority that knows its residents are at risk of that sort of catastrophic failure would do something about it."

Mr Morrison said a relocation deal would be an agreement between local authorities, the Crown and landowners.

He likened it to the $28 million Peninsula Project in the Coromandel, where local authorities bought and closed Waiomu Holiday Park - Auckland woman Dorothy Newall died there in 2002 during a weather bomb - as well as five other houses in a flood-prone area. But the system would never be fail-safe, he said.

"Some land might look perfectly normal, and then you get 600mm of rain, the place turns to absolute pudding and the house takes off. But there are some areas that are more obvious than others where there will be a case for relocation."

GNS Science geologist Murray McSaveney agreed that virtually everywhere was vulnerable to landslides, particularly the East Coast of the North Island and some areas in the Auckland and Wellington regions.

But it didn't put people off living there.

"There's something compelling about living on a slope with a beautiful view. It's like telling people they can't live by the sea because of a tsunami risk, or in Taupo because it's a volcano.

"No one listens. So the next best thing is to tell them what to do if Taupo erupts: get out quick."


Problem areas

Identified by local councils as potentially prone to landslips:

Auckland: 825ha of land mainly in Mt Roskill, Pt Chevalier, Otahuhu, Glendowie, Avondale, Hillsborough and Orakei, affecting 1812 homes and 30 businesses.

North Shore: No landslip danger areas, but testing of areas suspected of being unstable.

Waitakere: Several thousand households in the Waitakere Ranges, including in Titirangi, Laingholm and Glen Eden.

Manukau City Council: Coastal areas such as Orere Pt and Bucklands Beach, affecting about 200 houses.

Tauranga: About 200 properties in the older pre-1995 part of the city on steep slopes.

Gisborne: About 30 to 40 houses on the hills around city on potentially unstable land.

Wellington: Hazard areas marked for earthquakes (Thorndon) and floods (Tawa), but not slips as there has been no historical need.

Hutt City: Ongoing assessment of risk in the western hills and some populated areas in Eastbourne.

Christchurch: Only information is on a property by property basis.

Dunedin: 856ha of land containing 3850 properties in areas where land stability may be an issue; 86ha of land containing 424 properties have records of land stability hazards.