The rockfall risk
Christchurch Earthquake 2011
As the final zoning decisions are announced for the Port Hills, The Press examines how demolition workers will be kept safe in the hillside suburbs, how Christchurch has lost a playground and how tumbling boulders reached speeds of nearly 100 kilometres an hour in the February earthquake.
Red zoned homes in the Port Hills will have to be cautiously demolished for fear of triggering deadly landslips or rockfalls.
Demolition of hillside homes in the residential red zone will take longer than those on the flat, the Canterbury Earthquake Recovery Authority (Cera) has warned.
Residential red zone security manager for Cera, Brenden Winder, is urging private demolition companies to be cautious of rockfall risks. He said demolition contractors working for insurance companies will be given safety advice.
''There are cross boundary risks that are broader than the site you are working on. We want to alert people to the fact that if you have a house on a property and you are going to demolish it, that is permitted, but neighbours could be affected,'' he said.
''You could set off a landslip. The hazard could be 150 metres long and 200 metres wide and you could be standing on top of it and not even know it. We want people to take a global view of the hazard and take their time. We don't see a huge urgency.''
Demolition firms working for Cera will only start work once geotechnical and engineering assessments have been completed.
''It is a much smaller volume, but likely to be more complex demolition. Port Hills demolitions are likely to take longer,'' he said.
''There is a lot of work that needs to go into how we will approach those demolitions. We need quite a lot of geotechnical and engineering advice before those demolitions start. The last thing we want is for demolition people to go in and have an avoidable accident.''
Private security guards patrolling the Port Hills red zones would also have to be cautious, Winder said.
Cera spends $1,000 a day on private security guards that patrol residential red zones to prevent burglary and arson.
''The security team don't go into any properties in the Port Hills. There are life risk issues, which is different to the residential red zones on the flat.
''We don't want to put our boys in any risk so we will have safety protocols about putting people in those areas. Some of the buildings up there are not in great shape. We don't want them to go into those buildings unless there is a very good reason. We would give them engineering advice on how best to do that.''
The security guards do not enter any red zoned Port Hills properties as Cera does not yet own any of them.
Police inspector Richard Bruce said the Port Hills were challenging because of ''risks in the hill areas''. He said regular police and community patrols would help keep the area safe.
''The nature of the area also creates some opportunities for Police as it can be easier to control traffic and people going in and out of the area.''
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- © Fairfax NZ News
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