Monitoring geohazards and trigger level response on Deans Head in the Port Hills, Christchurch

Following the recent Canterbury Earthquake, GNS Science have identified numerous mass movement areas in the Port Hills with a potential risk to nearby infrastructure and life lines. Deans Head, a Class I mass movement area near the Sumner suburb, comprises of an approximate modelled 46,000m3 soil (loess) landslide on a steep sloping site. Different to other mass movements, the Deans Head landslide could be triggered by relatively frequent rainfall events. During the land clearance phase of works carried out by Land Information New Zealand (LINZ; formerly Christchurch Earthquake Recovery Authority, CERA), the Deans Head project has proven to be challenging including overcoming the multiple site constraints. These constraints include CERA Red Zoned structures, a key lifeline route below the site, cliff collapse and landslide hazards both susceptible to weather. During the land clearance phase, mass movement hazard monitoring has formed an integral part of the health and safety for personnel working on site. This paper will identify the numerous site hazards on Deans Head and provide an overview of the hazard monitoring techniques including ground movement, laser scan monitoring and groundwater monitoring used during LINZ’s land clearance phase of works. An overview will be provided on the emergency management if trigger levels are exceeded and the importance of procedures and reporting during hazard monitoring throughout the project.