Kapiti Island no barrier to tsunami
Wave could crash back and forward
BY ALASTAIR STEWARTLarge sections of the Kapiti Coast are at risk during a tsunami, according to new maps made public days after New Zealand was put on high alert.
The maps, put together by Greater Wellington Regional Council in co-ordination with Kapiti Coast District Council and Civil Defence, show sizeable sections of Paraparaumu, Te Horo and Otaki will be subject to mandatory evacuation in the event of a tsunami. Even greater sections of all Kapiti's coastal communities are part of voluntary evacuation zones that could be damaged in the event of a once-in-2000-years tsunami.
The maps show that Kapiti Island, as opposed to acting as a barrier, would be likely to trap the wave and send it crashing back and forward between the island and mainland several times, said Greater Wellington natural hazards analyst Iain Dawe.
The maps, created by Mr Dawe, were released last week, following Sunday's scare when much of New Zealand was put on high alert amid tsunami concerns from a massive 8.8 magnitude earthquake in Chile.
Though the warnings were largely directed at the east coast, the Kapiti Women's Triathlon at Raumati Beach on Sunday, was postponed for more than an hour as organisers waited for the all-clear from Civil Defence. Police were also out in force warning beach-goers to stay away. Most were co-operative, Sergeant Noel Bigwood said.
The risk of a distant tsunami reaching Kapiti is considered low, with earthquakes near the Solomon Islands posing the highest degree of risk.
But locally-generated tsunamis, from either earthquakes or underwater landslides, could strike Kapiti quickly and residents would have little or no warning, KCDC emergency management officer Tom Finnimore said.
"If you're at the coast and you feel a large earthquake or hear a noise or you see the sea suddenly go out, go for your life up the hills."
Knowledge of the maps will prove invaluable in those cases, and he urged residents to study them and locate safety zones and escape routes.
Mr Dawe, said the maps were intended to strike confidence, not fear, in residents.
"It's very easy to feel panic by these. It's certainly not the aim to generate panic but rather [for people] to feel that they can take matters into their own hands."
Mr Finnimore said Sunday's tsunami exercise ran smoothly. Though there was little chance the tsunami would strike Kapiti, Civil Defence was concerned sea level fluctuations could pose a risk and "erred on the side of caution".
The potential reach of a tsunami on the Kapiti Coast:
The potential reach of a tsunami in Otaki:
The potential reach of a tsunami in Paekakariki:
The potential reach of a tsunami in Paraparaumu:
- Kapiti Observer
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My mum has asked never to argue with an idiot because they drag you to their level & then beat you with experience but I suppose Eddie & Ozzel points need clarification: 1)"how far inland did it get as it is too shallow in the tasman to get very big ". Shallowness increases the velocity as it ramps from deeper water into shallower water therefore incresing spread. 2)"Since when do any tsunamis come from the Tasman Sea?" Not often but they can eminate from any direction around the Pacific trench. Looking at plate techtonics the earth is a patchwork of colliding plates including the Tasman.
Its important to note Tsunamis can have periods of over an hour and move at speeds of 600-700 km/hr in the open ocean & when confined into a basin such as Wellington harbour can have a sluicing effect magnifying the effect. The probabilistic wave height with a 500 year and 2500 year return period, from regional and distant sources (i.e. >1 hr travel time away), was used to define the orange and yellow evacuation zones. The 84th percentile wave height was used from this modelling to allow a margin of safety. The probabilistic wave heights were derived from a large study conducted by GNS Science in 2005 “Review of Tsunami Hazard and Risk in New Zealand” by Kelvin Berryman, and updated for the Wellington region for this project. The orange zone represents the area where authorities may reasonably expect to provide official warning and/or evacuation for now or in the foreseeable future. The yellow zone represents the maximum credible event from all sources, local (i.e. < 1hr travel time), regional and distant. This zone encompasses an event for which there would only be a natural (i.e. earthquake) or informal warning. The zones were produced by taking the probabilistic wave heights and doubling these to take account of the on-shore run-up inundation as a tsunami flows inland. Then the attenuated elevation-distance relationship was applied taking into account local variations in coastal geomorpholgy/inland topography. Thus, whilst a wave may have the potential to reach 5 m elevation, it may never reach that height if that elevation is several kilometres inland. Conversely, very smooth surfaces (asphalt, roads, concrete, paved surfaces) have much lower friction and allow water flow to proceed with much less hindrance. This effect is particularly critical to take into account around river mouths and coastal lakes/lagoons, where the water body acts as a near frictionless surface for the advancing tsunami flow. In summary, red zone denotes wave heights in the order of a 1.0-1.5 m such as could possibly result from the likes Chile. Orange denotes the forecast tsunami wave heights in the order of 2.0 m, based on 1 in 500 year event. Yellow will be localised event where there is little/no warning using infrequent/worst case scenario & deep water wave heights in the order of 7-8 m.
Proof? Check out the science anytime on GWRC website. Nope, tsunamis dont exist, neither does global warming and the Mafia never orchestrated JFK assinination. All just conspiracy theories eh?
#3 only you are a thick you are gessing but still dont have proof of a tsunami or when unless you can ansewer that dont start calling names as for the wave action we get that now in large sea swells & storms. PS cant even put your name to you reply shows you dont know.
Where is the map for Waikanae?
What's next - how much of Petone is going to be swamped by a tsunami miraculously bursting up in the middle of Wellington Harbour?! Since when do any tsunamis come from the Tasman Sea? There is no evidence whatsoever of significantly high tsunami waves coming from that direction (going around NZ from the Pacific loses a lot of energy).
It sounds to me like these people are only trying to justify their jobs with all that scaremongering (conveniently these maps are finished just right after the Chile earthquake ;-).
This is based upon elevation, wave height, hide tide & velocity over the coastal geomorphology
Thanks Civil Defence, Kapiti - your real troopers. I had hoped to have been involved in Emergency Response Team coordination in Kapiti. Unfortunately, I tired out but no real opportunity arose for me in that field - blocked pathway? Nevertheless, I for one am feeling better informed as my own un-informed guess would have been that Kapiti would provide it's usual shelter from inclement weather. Especially like this simple three step message. IF caught on the coast (can easily happen) and feel a large earthquake, hear a noise or see the sea suddenly go out (I have seen the latter, but never knew at that time, as was a child, and uninformed) - then, go for your life up hills. Will be spreading the information with local children and community. Nice job.
When was the last tsunami in Kapiti perhaps these map makers will be able to tell us along with the proof neaded plus how far inland did it get as it is too shalow in the tasman to get very big so come you so called experts and wiz kids go back to the moa days to find one.
#8 you still are name calling but ok you letter only cofirms that only a 1 to 2m wave as I said we allready get in storms and some times 3m as for one in 500 years you have not said it was on this coast or were to find proof it ever happend then you state 2500 years ago well no one has ever said or proven that so now who is the idiot so your mum is right dont argue with yourself and show or tell me were to find proof it happened on the Kapiti coast as the land has always risen then been eroaded back into the sea by winter storms.