Tsunami Strategy and Action Plans

A small team of Emergency Managers from within the Manawatu-Wanganui CDEM Group are beavering away on the first draft of our Group's Tsunami Strategy and Action Plans. This will document a consistent approach to tsunami response for the Group and will form the basis for consultation with communities that are potentially affected by tsunami run-up.

Run-up modelling has been undertaken for the Group by GNS Science and this is the foundation for the Plan. The zones shown in the picture are indicative of evacuation zones. The Red Zone is the beach and is obviously the area most at risk from tsunami (even small ones). The Orange Zone is likely to be affected by tsunami with a 500yr return period and the Yellow Zone by 2500yr return events.

In real terms, a 500yr tsunami off shore is likely to be between 2.2 and 3.1m (east coast) but when it reaches the beach, this could double in height. This means potentially 6.2m in height. An added margin for safety therefore sees the Orange Evacuation Zone for our east coast being set at the 10m contour. Attenuation has also been calculated at 0.5% = 1m less wave height for every 200m inland.

The 500yr event for Wanganui onshore height is 7.2m, the 2500yr event for our east coast is 35m and for Wanganui is 15.6m. 35m is a pretty big jump in sea level and an event of this magnitude would be massively destructive all around New Zealand.

The team will keep working on the project and we intend to test the Plan during national Exercise Tangaroa in October.