Wairakei tsunami safe

The city's latest residential development area at Wairakei will be tsunami and flood proof – at least within the parameters required to obtain the development's resource consent, city councillors learned this week.

Taurang City councillors approved the required natural hazard risk assessment, which gives Wairakei a pass for development because of its height and distance from the sea.


An inundation map showing inundation expected from a 4m tsunami. Photo: TCC.

The five metre, four metre, and 3.5 metre tsunamis modelled in the study will not inundate the new housing at Wairakei itself, unlike the existing housing between Wairakei and the beach.

The Tauranga City Plan requires all houses and attached garages in Wairakei to be built 5.1m above mean sea level.

Wairakei lies between existing housing at Papamoa East and the TEL highway.

Tonkin and Taylor's computer modelling results are considered conservative as they don't take into account landforms, roads, reserves and stormwater ponds and swales all of which would reduce the impact of a tsunami and help dissipate wave energy.

The computer model also makes no allowance for roughness, the computer model virtual tsunami doesn't encounter any resistance to a likely future design, it operates like a sheet of ice with water over it, says the report.

The study uses the same tsunami waveform as used for the Te Tumu modelling a little further along the coast, based on the waveform developed by GNS (2012) for a magnitude nine earthquake within the Southern Kermadec Trench.

For a 5m, 2500-year return tsunami event, the areas under investigation and part of the Wairakei Urban Growth Area have been shown not to be potentially susceptible to inundation by tsunami.

According to the regional council's risk assessment methodology, even though these two areas may be considered as falling within a Hazard Susceptibility Area as defined by a maximum credible event, no parts of the subject areas would be inundated in a 2500 year, 1000 year (4m) or 500 year (3.5m) average return interval tsunami evenL

As a result, the risk is considered to be acceptable (i.e. a low level of risk), and the policy requirements of the Regional Policy Statement, satisfied in terms of tsunami risk.

Because the model tsunamis won't inundate the computer model of the land under investigation, there's no requirement to undertake any additional analysis in regard to buildings being functionally compromised, lifelines at risk or loss of life.

For flooding the area is considered proof against all levels of flooding, up to and including the once in every 500 years flood.

When fully developed about 75 per cent of the Papamoa catchment will drain to the Wairakei Stream with the balance draining naturally to the coast, the Kaituna River or be self-contained.

The water levels used in the model were derived from Moturiki datum for 2014 sea level plus 0.687m for neap high tide plus 0.8m for an anticipated sea level rise by 2100.

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3 comments

then.......

Posted on 28-09-2016 10:02 | By Smilarkie

...... why did the TCC spend 1.6 million dollard (I believe) on a stupid Tsunami raised platform (pile of dirt) at the Gordon Sprat reserve.


Mmmmm

Posted on 28-09-2016 16:07 | By The umpire

Let's hope the wave knows the council rules before coming ashore


Disillusioned

Posted on 28-09-2016 19:42 | By awaroa

You stupid people.. Keep telling yourselves the area is tsunami proof.. This is the most stupid thing that I've heard all year. Winners, the lot of you, including Tonkin Taylor's "experts".. Plain stupid.


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