A quantitative risk-based planning approach for managing life risk from slope instability: adaptation of the Christchurch District Plan approach

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Gunnell, S. 2019 A quantitative risk-based planning approach for managing life risk from slope instability: adaptation of the Christchurch District Plan approach. Lower Hutt, N.Z.: GNS Science. GNS Science report 2018/31. 21 p.; doi: 10.21420/NWC0-2758.

Abstract:

Following the Canterbury Earthquake Sequence that occurred over 2010–2011, comprehensive geotechnical investigations were undertaken in the Port Hills area of Christchurch. This research allowed the risk to life posed by the most prevalent types of land movement caused by the earthquakes, being rockfall, cliff collapse and other types of mass movement, to be quantified. In a New Zealand first, this quantitative risk assessment methodology has been integrated into the planning framework of the operative Christchurch District Plan, to inform the risk-based approach taken. The methodology utilises an Annual Individual Fatality Risk metric, which is the probability of an individual occupying a specific site being killed as a result of slope instability in any one-year period. Previous ‘It’s Our Fault’ research by Saunders and Massey (2016) has detailed the process of incorporating landslide risk into the Christchurch District Plan, and while briefly explored here, this report is more focused on considering if the risk assessment methodology developed for the Christchurch context could be adapted to other regions, using Wellington as an example. It was found that the use of a life loss metric, such as Annual Individual Fatality Risk, is a potentially valuable tool for land use planners when managing the risk to life posed by not only land instability, but other hazards also. It can successfully be adapted to different areas but may not be appropriate where there is high uncertainty in the model parameters that inform the risk assessment. Where there is high uncertainty, investigations into slope response to seismic events, such as that undertaken after the Christchurch and Kaikoura earthquakes, can provide valuable data to inform the models for regions that have similar geology and slope morphology. (auth)