Thursday 17 July 2014
Council decides against area-wide rockfall mitigation
Councillors today decided area-wide rockfall mitigation for Port Hills homes red-zoned by the Crown was not practical
for several reasons, including uncertainty around effectiveness and costs.
Since 2012, Christchurch City Council and the Canterbury Earthquake Authority (CERA) have investigated engineering
solutions that would reduce the risk to clusters of Port Hills homes in the path of falling rock. Today, after
considering additional reports commissioned in May, Councillors decided not to adopt or further investigate area-wide
rockfall mitigation.
Chief Planning Officer Mike Theelen said the Council's investigations had been extensive, thorough and independently
peer-reviewed.
"We've carefully considered all the various options, and received sound technical advice and costings for each.
Community-based rockfall protection structures are not feasible options, given the cost to build and maintain them, and
limits to using red-zoned land now owned by the Crown.
"The Council has a responsibility under the Resource Management Act to reduce exposure to natural hazards, so we have to
carefully consider the consequences of a rockfall protection structure failing. As the structures don't remove the
hazard posed by rockfall, some risk remains.
"We appreciate this news is unwelcome to some Port Hills residents. We're currently working with several people as they
investigate individual rockfall protection structures to reduce the risk for their home, and we're committed to
supporting others if they want to look into this option."
Christchurch Mayor Lianne Dalziel said, "I do feel for the people badly affected by rockfall, their dreams have been
shattered. Today Councillors expressed their great reluctance before voting against area-wide rockfall mitigation.
However, we have to make the hard calls to send a message that we don't accept development in areas where the level of
risk is high. The option still exists for the people who remain to pursue individual rockfall protection for their
homes."
The Council has worked with CERA to fund red-zoned buyout offers for properties where rockfall presented an unacceptable
risk to life.
Background
In December 2013, the Council requested staff urgently identify areas for community-based mitigation of rock roll risk
for red zone properties, where it would be cost-effective to do so as compared with the cost of property purchase.
Council staff produced a report detailing these investigations, reporting back to Council in January 2014 and 8 May
2014, and the Council asked for more information on the investigations and costings, including liability if rockfall
protection fails in the future.
Following the Council meeting on 8 May 2014, the Council commissioned an independent peer review of its report,
conducted by an engineering geologist experienced in the design of rockfall protection structures on the Port Hills. The
peer review agreed with Council's methodology, but said the costings were too conservative and that the structures were
likely to cost more than estimated.
The issue was discussed again at Council meetings on 12 June and 26 June 2014, before the decision was made today.
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