Tsunami inundation study

Emily Lane, Roy Walters, Jade Arnold, Matt Enright, Helen Roulston
Auckland Regional Council
Publication date:

• Auckland Regional Council contracted NIWA to undertake a study on the risk of tsunami inundation facing communities in the Auckland region. Tsunamis generated by large subduction zone earthquakes in South America have a return period on the order of 50-100 years. As such, a South American tsunami represents the most probable tsunami risk facing the Auckland region in the next 100 years.

• The tsunami scenario chosen has source characteristics of the 1868 Peru (now Chile) tsunami but with an earthquake magnitude of Mw 9.5, similar to that which generated the 1960 Chile tsunami. A tsunami of this size has a slightly longer return period than the average South American tsunami but in most cases represents a worst-case scenario for far-field tsunamis.

• The response of the tsunami at the shoreline is also dependent on the dominant period of the tsunami. While the modelled tsunami does not show significant impact on Great Barrier Island a tsunami with a dominant period around one hour has a much larger effect.

• The tsunami was modelled assuming a sea level of Mean High Water Spring (MHWS), representing a worst-case scenario of a tsunami arriving at high tide. The tsunami was also modelled for MHWS plus 30 cm and MHWS plus 50 cm, representing the predicted sea level rise in 50- and 100-years as assessed by the IPCC Fourth Assessment Report.

• At MHWS the tsunami causes maximum water elevations of 2-3 m above mean sea level throughout the Auckland Region (East Coast), and up to 3.5 m in some bays. Most of the inundation around Auckland is confined to narrow coastal strips, although the tsunami does cause significant inundation in some low-lying areas. Parts of the Northern motorway just north of the Harbour Bridge, the Northwestern motorway between Point Chevalier and Te Atatu, and Tamaki Drive by Hobsons Bay are major transportation links at risk of inundation.

Auckland Regional Council TR2009/113

NIWA client report: CHC2007-126-153. November 2007

NIWA project ARC07502

Last updated: 2018-07-02