Site-Specific Rockfall Risk Assessments and Rockfall Protection Structure Design Following the 2010/2011 Canterbury Earthquake Sequence

Abstract

The 2010/2011 Canterbury earthquake sequence triggered wide-spread rockfall, causing fatalities and damage to property and infrastructure. In response, an area-wide rockfall risk assessment was carried out to understand risk and support the recovery process. The risk assessment influenced zoning decisions, insurance pay-outs and property values and has had a significant impact on the disaster risk reduction process. Site-specific assessments were subsequently carried out on individual residential properties to confirm risk and inform rockfall risk reduction design. The characterization of site-specific rockfall source size, probability of detachment and topographic controls on run-out ultimately controlled rockfall protection structure design for residential properties in the Port Hills. Differences between the assessed level of risk to life between the area-wide and site-specific studies were in many cases two orders of magnitude different, lower and higher. This paper demonstrates the enhancement of the area-wide risk assessment with site specific mapping and source characterization to design rockfall protection structures that balance risk reduction, cost, environmental impact, and visual impact. Understanding the advantages and limitations between area-wide and site-specific rockfall assessments is integral to the disaster response, recovery and rebuild process.