Port Hills mass movement decision announced

The safety of people living on earthquake-damaged land in the Port Hills at risk of mass movement is at the heart of decisions announced today.

The latest Council-commissioned GNS Science reports show 37 green-zoned homes are in areas where the risk to life from mass movement (sometimes called landslide) is considered ‘intolerable’ by the Council. This means the risk to life from mass movement in any one year is equal to or greater than one in 10,000.

These new reports follow the first GNS Science mass movement report released in November 2013, which gave mass movement areas in the Port Hills a preliminary Class I, II or III category. Class I areas are where any further mass movement could see lives lost, and homes and/or critical infrastructure severely damaged.

Since then, GNS Science have been working to get a better understanding of Class I areas. The latest reports look at what could trigger a landslide, how big it could be, where and how the land is likely to move and, crucially, the level of risk to people. As this new information has become available, some changes have been made to the preliminary classes given to areas. All Class I areas are between Mount Pleasant and Sumner and affected residents are being contacted.

The Council will make an offer to purchase the 16 green zone properties, as investigations show there is not a cost-effective engineering solution to manage the hazard and reduce the risk to an acceptable level for these properties. Some of these properties are needed to carry out engineering works to reduce or remove the hazard.

“With peoples’ safety coming first, we are making some tough decisions about land use and development in these areas,” says the Council’s Chief Planning Officer Mike Theelen.

For 21 other green zone properties within these areas, the Council has identified an engineering solution to remediate the land and reduce the risk to people and their properties to an acceptable level. This work will take place over the next 12 to 15 months.

Mayor Lianne Dalziel says she appreciates these decisions significantly affect peoples’ lives.

“While this news is very welcome for some, it is upsetting for others and we will be supporting all these Port Hills residents in the coming months.

“I am delighted we can work with the Crown to fund engineering solutions to see as many people as possible remain in their homes,” says Mayor Lianne Dalziel.

There are also 89 properties in Class I mass movement areas that have already been red-zoned by the Crown for cliff collapse or rockfall. Of these, 76 are owned by the Crown and 13 of them remain privately owned. This information does not change any red zone offer from the Crown.

While the risk to people in Class I areas was described as “intolerable,” there were no signs slope failure is imminent so residents were not being asked to leave their homes at this time, Mr Theelen said.

“We are monitoring known mass movement areas and if there is a change in the behaviour of the slope and increased risk to people’s safety, we will act swiftly. This may mean people may need to leave their property at short notice,” says Mike Theelen.

“These investigations have taken longer than we anticipated. The findings needed peer review by an international team of experts, to ensure the science was robust enough to support sound decisions about people’s lives and homes,” says Mike Theelen.

The Council is currently reviewing its district plan. These reports have fed into it and some additional controls on development may be introduced where there are natural hazards in hillside areas. See www.proposeddistrictplan.ccc.govt.nz from 27 August 2014. This is when the stage one priority chapters – including natural hazards -- will be notified to affected residents and opened for public submissions.

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