The protection solution options and costs were used to determine the direction of the Christchurch Port Hills rebuild process and were critical in the Red Zoning and Section 124 Notice decisions. At the time the work was carried out this was the largest 3D rockfall modelling project undertaken.

The 3D and 2D analysis were equally critical - the 3D presenting the lateral extent of the issue and helping define what areas are exposed to risk, while the 2D analysis is where energies and impact velocities are calculated to help define what level of risk those areas ascertained in the 3D analysis are subject to. Typically between 15 and 20 cross sections per kilometre were analysed for the 2D analysis varying depending on the risk presented at individual locations.

Geovert worked in collaboration with our Austrian and Italian counterparts Hannes Salzmann from Freefall and Professor Giovani Crosta from University of Milan to deliver this progressive rockfall assessment.

The scope included:

Field work: visit the site, check available datasets collected by the PHGG, and CCC
Analysis of rock fall inventories available for the earthquake from PHGG and historical from GNS
Analysis of available data (topography, geology, land use, lithology, etc.) and implementation of datasets from CCC
Preparation of database for buildings and population distribution from CCC
Attribution of a rockfall onset susceptibility on the basis of available geotechnical/geomechanical studies
3-D Rockfall Model calibration, at least one calibration per subarea required
3-D Rockfall Modelling (linear or polygonal source areas) for different rock fall scenarios (block sizes, shape etc)
Detailed hazard analysis
2-D Rockfall Modelling including implementation of mitigation structures
3-D Rockfall Modelling including effects of mitigation measures on the final hazard and risk (if required)
Completed report to CERA, inclusive of options for remediation used in the final risk assessment.
CERA's article on this project including the detailed reports are available on this link [http://cera.govt.nz/port-hills-3d-rockfall-modelling-report](http://cera.govt.nz/port-hills-3d-rockfall-modelling-report)