A series of three summary brochures have also been prepared. The brochures explain with the use of graphics key technical terms and concepts.
1. Understanding life safety risk concepts for rockfall and cliff collapse in the Port Hills [PDF 300KB]
2. Life-safety risk from cliff collapse on the Port Hills [PDF 600KB]
3. Life-safety risk from rockfall on the Port Hills [PDF 1.7MB]
Canterbury Earthquakes 2010/2011 Port Hills Slope Stability: Geomorphology mapping for rockfall risk assessment
This report provides information on the nature of surface geological materials (soils) and the processes that formed them. The information is compiled as geomorphic maps at a scale of 1:500. The nature and extent of the various surface materials on the Port Hills helps explain the erosion and deposition processes that have occurred in the past, including earthquake initiated large scale boulder roll and cliff collapse, and high intensity/long duration rainfall initiated landsliding. The maps also illustrate those active processes that we can expect in the future. Aerial photograph interpretation, satellite images and digital terrain models, with limited field work, were used to create the maps.
Geomorphology mapping for rockfall risk assessment - reduced resolution whole report [PDF 17MB]
Parts: Geomorphology mapping for rockfall risk assessment - pp 1-25 [PDF 4MB], Appendix 4 maps A6-D16 [PDF 10MB], Appendix 4 maps E2-J6 [6MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Principles and criteria for the assessment of risk from slope instability in the Port Hills, Christchurch
This report gives an overview of the issues that need to be considered in completing a risk-based approach to the management of slope instability hazards in the Port Hills. A framework and process for managing risk is described, international and New Zealand policy is outlined, and the risks faced by New Zealanders is summarised. Assessment criteria that could be adopted by the City Council are discussed along with options for treating the risk. The report recommendations include levels of annual individual fatality risk that the City 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 (Summary Series 1/3).
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Principles and Criteria for the Assessment of Risk from Slope Instability in the Port Hills, Christchurch [PDF 1.4MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from cliff collapse
The purpose of this pilot study was to develop a methodology to assess 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. The risk to life, between Redcliffs and Scarborough, is calculated for both cliff top recession and cliff base debris deposits. The report recommendations include the need for ongoing investigations to better determine the nature and extent of damage to the ground at the top of cliffs.
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from cliff collapse [PDF 24MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from cliff collapse in the Port Hills
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. The risk to life is calculated as the annual individual fatality risk and is applied to an individual’s occupation of their residence. The report details the methodology used and the inherent uncertainties. Important technical aspects of the report are summarised in Life-safety risk from cliff collapse on the Port Hills (Summary Series 2/3).
Canterbury earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from cliff collapse in the Port Hills [PDF 15MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Additional assessment of the life-safety risk from rockfalls (boulder rolls)
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. A new set of maps show how the reduction in earthquake activity with time changes the risk zone boundaries. The report includes a range of recommendations including the need for the City Council to consider both the original rockfall modelling results and the results from the sensitivity analysis in its decision making. The rock roll zoning decisions were based on maps associated with this report.
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Additional assessment of the life-safety risk from rockfalls (boulder rolls) [PDF 1.5MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from rockfalls (boulder roll)
The purpose of this pilot study was to develop a methodology to assess risk to life from rockfall (boulder roll). The risk is expressed as the annual individual fatality risk. Rockfall triggered by earthquakes and other mechanisms such as rainfall is considered. The assessment includes an analysis of historic and potential future events. The report explains the field verification process used and the required changes made to the risk zone boundaries. Maps showing four classes of annual individual fatality risk are included in the report for select locations on the Port Hills.
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from rockfalls (boulder rolls) [PDF 29MB]
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from rockfalls (boulder roll) in the Port Hills
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 those areas of the Port Hills not assessed in the pilot study. These areas are Hillsborough, Richmond Hill Road, McCormacks Bay, Mt Cavendish, Taylors Mistake, Moncks Bay, Cass Bay, Governors Bay, and some parts of Lyttelton, Bowenvale, Sumner, Vernon Terrace and Avoca Valley. The report provides recommendations to the City Council including the need to continue monitoring the rockfall source areas as further instability is likely to occur. As for the pilot study report, this report contains maps showing the zones of risk, potential rockfall source areas and building locations. Important technical aspects of the report are summarised in Life-safety risk from rockfall on the Port Hills (Summary Series 3/3).
Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from rockfalls (boulder rolls) in the Port Hills [low res PDF 14MB]
Parts: Main report pp 1-25 [PDF 300KB], Appendices A-B pp 26-37 [PDF 8MB], Appendix C pp 38-108 [PDF 10MB]
Separate maps associated with the reports
Maps series A to G that are associated with how the reduction in earthquake activity with time changes the risk zone boundaries.
Maps used for CERA Zoning decisions:
Maps A - Risk Model Yr 1 2012 [PDF 15MB]
Maps C - Risk Model Yr 5 2016 [PDF 15MB]
(In a very small number of cases some discretion was applied)
Maps showing sensitivity of the rockfall modelling:
Maps B - Risk Model Yr 3 2014 [PDF 8MB]
Maps D - Risk Model Yr 7 2018 [PDF 8MB]
Maps E - Risk Model Yr 8 2019 [PDF 8MB]
Maps F - Risk Model Yr 9 2020 [PDF 8MB]
Maps G - Risk Model Yr 10 2021 [PDF 15MB]
Frequently Asked Questions and enquiries
We have compiled a series of FAQs and answers. [PDF 80KB]
Please note:
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.
