Assessment of Increased Flood Vulnerability Due to the Canterbury Earthquake Sequence

The earthquake sequence in Canterbury from September 2010 to December 2011 caused widespread land damage to Christchurch. The earthquakes affected the flood hazard in Christchurch due to changes to ground levels and watercourses from tectonic changes, subsidence and lateral spreading. The Earthquake Commission (EQC) is responsible for compensation of land damage to residential land due to particular natural disasters. Tonkin & Taylor worked with EQC to assess potential increase in flood vulnerability for residential land due to onsite ground surface subsidence caused by the earthquake sequence. Flooding was assessed with models developed for flood hazard management in the Styx, Avon, and Heathcote catchments by Christchurch City Council. Two types of flood models were used; a river flooding model and an overland flow model (rain-on-grid approach). The flood models were used in conjunction with ground levels based on LiDAR to identify properties with potentially affected properties. This paper describes the engineering methodology and issues that have influenced the methodology.