Takiwā

Hawke s Bay Tsunami Evacuation Zones - Hawkes Bay Regional Council

Tsunamis are a threat to life and property for all people that live, work and play near the New Zealand coast. Evacuation planning is a fundamental component of emergency planning for tsunami. The Ministry of Civil Defence & Emergency Management has established a nationally consistent approach for the development of tsunami evacuation zones and mapshttp://www.civildefence.govt.nz/assets/Uploads/publications/dgl-08-08-tsunami-evacuation-zones.pdf. Local Authorities and CDEM Groups have supported the development of local tsunami evacuation zones, maps, and information that is nationally consistent. These zones have been developed from modelling undertaken by the Hawke’s Bay Regional Council and GNS Science usingtwo methods to derive the Tsunami inundation extents: 2-Dimensional modelling (Clifton to Te Ngaru, and Wairoa to Mahia), and Attenuation Rule method (remainder of coast).Three (3) zones have been defined, Red, Orange & Yellow. Whilst final zone delineation has been the responsibility of Local Authorities and CDEM Groups together with input from local coastal communities, some simple delineation rules have been applied. Snapping to:- Road center lines- Property boundaries- Natural or man-made features (e.g. stop banks)- Contours Red ZoneThe red zone is intended as a shore-exclusion zone that is designated off limits in the event of any expected tsunami. In high resolution areas (e.g. LiDAR) then the ideal way would be to use the 2m above high tide contour, extended to make sure it covers the beach and rocky foreshore in any instances that 2m elevation doesn't. This represents the highest risk zone and is the first place people should evacuate from in any sort of tsunami warning. People could expect ‘activation’ of this zone several times during their life.Orange ZoneThis is the zone which we may reasonably expect there to be official warning for now or in the foreseeable future.The regional and distant sources (>1hr travel time away) used to define the orange evacuation zone, was a wave height modelled to 5 metres, determined from the GNS Science estimate of the wave height from distant source for likely to unlikely events. Supporting scenario for a 5m distant source event for HB (orange zone), is a M8.5 earthquake on the coast of Peru resulting in a 1,000 year return period wave, which has an offshore wave height of approximately 5m.Distant source events are assigned a MCDEM forecast threat-level, with threat levels (for tsunami height at the coast) ranging from 0.2-1m, 1-3m, 3-5m, 5-8m, to 8m+. On very rare occasions if wave heights are forecast higher than 5m for a distant source event then the yellow zone can also be evacuated.The orange zone is intended to be the area evacuated in most if not all distant and regional-source official warnings (i.e., warnings that extend beyond the red zone, for tsunami from sources more than one hour of travel time away from the mapped location). Local differentiation of this zone can be achieved using terms that are familiar to the community such as street names and key landmarks.Yellow ZoneThe probabilistic wave height with a 2500 year return period (i.e. maximum credible event) from all sources, based on the 2013 National Tsunami Hazard Model (Power, GNS Science Report 2013/131), is used to define the yellow evacuation zone. This zone must encompass all credible tsunami, including those for which there will only be enough time for natural or informal warning.The yellow zone should cover all maximum credible tsunami, including the highest impact events. The intention is that the yellow zone provides for local-source maximum credible events, based on locally determined risk. People should evacuate this zone in natural or informal warnings from a local source event. The yellow zone may be removed from published, publicly available evacuation maps in a region where the orange zone includes the local-source maximum credible tsunami. In this case it is very important that the boundaries of the orange zone are particularly cautious – that is, there should be negligible chance an official evacuation will be called that requires evacuation of an area larger than the mapped orange zone.