Tsunami Modelling Study 2

Executive Summary

Northland Regional Council contracted NIWA to undertake an initial study on the risk of tsunami inundation facing communities in the Northland Region. The following credible sources were identified:

• Remote source: South American origin. Return period 50-100 years. This represents the most probable tsunami risk in the next 100 years.
• Local/Region: Tonga Kermadec. Two events were modelled, Mw 8.5 and Mw 9.0. The return period of these events is much longer (500-2000 years) but these represent a worst-case scenario for a tsunami striking the Northland coast.

Tsunami propagation from these scenarios to the Northland coastline was simulated using a computermodel and subsequent inundation at fifteen specific communities was modelled. The simulations were performed for current sea levels and for a mean sea level elevated by 50 cm, representing the 100 year projection by the IPCC Fourth Assessment Report.

The remote South American tsunami did not cause significant inundation for most of the settlements studied; however, some inundation was predicted at Waipu Cove and Marsden Point. Elevated water speeds could also cause erosion of dunes and scouring of estuaries. The Tonga-Kermadec subduction zone tsunamis caused considerable inundation (especially the larger of the two) and the high water levels would cause extensive damage, erosion and scouring of most of the fifteen communities. These effects are further exacerbated in the sea level rise scenario.

The simulation results presented here cover the likely range of tsunami that might be expected in Northland, increasing from the relatively common but smaller South American tsunami to the largest likely event emanating from the Tonga-Kermadec subduction zone, and therefore provide information on the likely range of impacts on which to base local contingency planning.

The modelling study is dependent on, and therefore limited by, the initialisation of the tsunami for each earthquake source, the quality of the LiDAR topographic data and also the quality of bathymetric data in inshore waters. Despite these limitations, we believe that the current modelling exercise provides the best possible estimate of inundation in Northland from remote and regionally sourced
tsunamis available to date.

Download the report

File size: Please note that this report is very large due to the number of maps and graphs. It has been separated into sections to make it easier to download. The Table of Contents .pdf outlines what information is in each section. 

Find out what a tsunami is and what we are doing to prepare for managing one if it does happen: www.nrc.govt.nz/tsunami