Following the Canterbury Earthquakes, GNS Science has completed several reports on land stability for the Council, on mass movement, rockfall and cliff collapse.
The Council commissioned these reports in response to the 2010/2011 Canterbury Earthquakes.
The 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.
|Risk assessment for Clifton Terrace [PDF, 16 MB]
In response to the Canterbury Earthquakes, a series of seven detailed technical reports on slope instability on the Port Hills were prepared by GNS Science for the Christchurch City Council. The reports contain recommendations for the Council on how to address the risk from rockfall/boulder roll and cliff collapse. The findings of the reports have been used by CERA and the Christchurch City Council to assist with decisions on zoning, planning and infrastructure development, and regulatory matters.
A series of three summary brochures below explain key technical terms and concepts:
This report provides information on the nature of surface geological materials (soils) and the processes that formed them.
This report gives an overview of the considerations for completing a risk-based approach to the management of slope instability hazards in the Port Hills. The report recommendations include levels of annual individual fatality risk that the Council should consider. Important technical aspects of the report are summarised in Understanding life-safety risk concepts for rockfall and cliff collapse in the Port Hills.
The purpose of this pilot study was to develop a methodology to assess the risk to life from cliff collapse. The report considers cliff collapse triggered by earthquakes and other causes and expresses risk as annual individual fatality risk.
Since issuing the GNS Science reports in 2012, some additional rockfall and landslide related fieldwork was done in the Port Hills. From this it became apparent that in a few isolated areas the rockfall risk models (and subsequent maps generated from these) did not appear to reflect the actual ground conditions in these localised areas.
A review of the affected areas was carried out by GNS Science and Council geotechnical consultants. The review included field inspections to verify:
The reissued reports are below.
This report is based on the methodology established in Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from cliff collapse and assesses the risk to life at the top and base of cliffs.
Only the cliffs that meet specific potential failure criteria are included in the assessment. Important technical aspects of the report are summarised in Life-safety risk from cliff collapse on the Port Hills.
This report assesses the sensitivity of the rockfall modelling used in Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from rockfalls (boulder roll) and Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from rockfalls (boulder roll) in the Port Hills. The rock roll zoning decisions were based on maps associated with this report.
The purpose of this pilot study was to develop a methodology to assess risk to life from rockfall (boulder roll). The report explains the field verification process used and the required changes made to the risk zone boundaries.
This report is based on the methodology established in Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from rockfalls (boulder roll) and includes areas of the Port Hills not assessed in the pilot study. Important technical aspects of the report are summarised in Life-safety risk from rockfall on the Port Hills.
Latest Maps series A to G are associated with how the reduction in earthquake activity with time changes the risk zone boundaries - August 2013.
Maps used for CERA Zoning decisions:
The GNS Science reports published by the Council on this website have been prepared and provided by GNS Science at the request of the Council, and CERA (in some cases) for those agencies. The Reports are now published by Council to assist the public understanding of the complex issues.+
The Council makes no warranty or representation regarding the accuracy or completeness of the GNS reports. The Council is not qualified to have any view on the accuracy of the information contained in the GNS reports. The GNS reports should not be relied upon at a site-specific level without advice from a qualified professional.