“Huge sea level rises are coming – unless we act now” – James Hansen, head of NASA’s Goddard Institute for Space Studies in New York. He gives a frank and disturbing answer to the question “Why might scientists be reticent to express concerns about something so important?”

http://environment.newscientist.com/channel/earth/mg19526141.600-huge-sea-level-rises-are-coming–unless-we-act-now.html

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jh, If I understand the Richter Scale correctly the energy release at the fault line would be 10 times greater than Inangahua and two or three times greater than Murchison or Napier. In each of these quakes less than 100 km of faultline ruptured. The Great Alpine Earthquake will affect five times more land area than the Napier quake.

At one point the Great Alpine Fault is less than 150km from Christchurch and combined with the geology of the Canterbury plains parts of Christchurch and North Canterbury could experience collapse of masonry buildings. If the quake happened today the waterlogged soil would cause quite a bit of liquifaction in Kaiapoi and slope failrures in the Port Hills suburbs.

It is more equivalent to the Great Wellington quake circa 1850 that lifted much of the CBD above sea level.

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An earthquake like that would be equivalent to the Inangahua or Murchison Earthquakes?
jh

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Cool

I designed something very similar for my parents place on the beach in Sag Harbor… we didn’t build it (I was not yet an engineer and there was never any money), but aside from using regular pontoons rather than foam filled, it was exactly the same.

After everyone stopped laughing they realized I was serious. Eleven year olds often are more serious than you expect.

respectfully
BJ

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“Dutch Answer to Flooding: Build Houses that Swim”
http://www.spiegel.de/international/spiegel/0,1518,377050,00.html
and
http://www.ecoboot.nl/artikelen/floating_houses.php
and
http://www.csmonitor.com/2005/1026/p13s02-lihc.html
and
http://www.treehugger.com/files/2007/03/floating_ecohom.php
and
http://www.inhabitat.com/2006/08/29/interview-koen-olthius-of-waterstudionl/

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jh, Predicting when the sea level rise will occur and by how much is a bit like predicting when the next Great Alpine Earthquake earthquake will occur and how big it will be.

Preditions for sea level rise will be less precise than predicting faultline earthquakes because scientists can’t simply look at the past to narrow down the range of options for the future. Your guesstimate of sometime between next week and next century is reasonable given the limited knowledge currently available of the various causal mechanisims and there potentially cmplex and non-linear interactions.

To date the best prediction paleoseimologists have been able to cme up with for the Great Alpine Fault is 50% probability within 30 years, 90% probability within 100 years, 95% probability it will register 7.9 +/-0.25 and involve betwee 300km and 500km of the northern most portion of the Great Alpine fault.

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Brookhaven

What sort of time frame are we talking here? Sometimes I’m not sure whether the sea will rise next week or next century.
jh

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To your list of refugees you can add people living in places named Marshlands, Riverlands or ending with lagoon, port or mouth, and anywhere with a high water table.

Those sea level maps show that a 1 metre rise can affect river levels up to several hundred metres inland. In most pleces this will be like having a permanent spring tide. This is going to dramatically reduce peak river flow capacities so there will be more frequent floods in places like Greymouth, Blenheim, North/east Christchurch and across the Napier/Hastings Motorway. We are going to have to make the hard decision that London has made and actually return much of our flood plains to the role nature intended them to have instead of trying to build ever higher stopbanks.

A one metre increase in sea levels is effectively a one metre reduction in the height of groynes, sea walls and other coastal defences. This is going to be major problem on some of our most important tourist highways particularly in south Westland and north of Kaikoura where roads (and the railway) can’t be moved away from the ocean.

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Forget about environmental refugees. What about all the NZ citizens currently living overseas who have an absolute right to come home any time they choose? If things get rough in Aussie or Europe, we would be welcoming a lot of expats home. See what that does for Auckland house prices…

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I think one of the biggest effects of rising sea level will have on countries such as New Zealand will be that there will be millions of environmental refugees. Where will these people go, who will feed and house them?

We only need to look to our nearest neighbour to see how they deal with tens and hundreds of refugees. Is that how we are going to treat the millions of people currently living in low lying areas?

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Has anybody seen any research on what effect rising sea levels will have on water tables?

Seems from this map that Blenheim will become a lakeside town with a 2 metres rise in sea level flooding most of Riverlands. As will much of North-east Christchurch east of Marshlands Rd between the Avon and Waimakariri rivers.

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BucolicOldSirHenry, Wine buffs will be alarmed to see that 1m-2m rise will flood most of Riverlands, the historic centre of Marlborough wineries.

You might have underestimated the impact on Christchurch and surrounding areas.
The entire area between Marshland Rd and the coast, from the Avon to the Waimakariri, is at moderate risk with just a 1 metre rise. I presume this is the result of the effect on the water table.
Lake Ellesmere has the potential to cover sections of the Akaroa Highway.

Ironically Transit is probably in the best position to frighten New Zealanders into taking the consequences of rising ocean levels serious. A few years ago Transit had to hastily build a boulder sea wall to stop the ocean from underscouring the highway at Bruce Bay. Transit has been progressively building a sea wall 100 metres away from the highway but a summer storm removed that coastal strip in less than 3 days. At Kaikoura they have had storms rip the tarseal right off the road. Rising sea levels don’t actual have to flood your bach to be a problem. On a steep 1 in 10 slope a 1 metre height increase results in a 10 metre increase in the distance storm surge will travel. The sorts of events that have flooded or damaged coastal highways were rare in the past but could increase exponentially with every extra centimetre of sea level.

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jh, Pegasus Town and a proposed iwi subdivision straddle the original motorway alignment, circa 1964. Transit is currently negotiating with the community for a new alignment to complete this project which was temporarily suspended in 1970 when stage 1 of the northern motorway (the Kaiapoi bypass and new Waimak bridges) was completed.

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Insider,

I believe these have been unsuccessfully trialled in the United States, somewhere called New Orleans.

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Maybe Woodend and Amberly are in the same boat.?. [and Pegasus Town is in the Water...only the Big Gate showing]
jh

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I think you mean Woodend, jh.

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I was talking to someone who lives in Amberly today. He said the residents wanted a by-pass but the plan was skittled because of the yet to be built gated community Pegasus Town. It seems to me that an existing community shouldn’t miss out to a community that has to import it’s residents from (eg Singapore) I hope people note it’s vulnerability to sea-level rises.
jh

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If the change is reasonably modest and takes place over a century timescale, many harbours could have barriers installed on them similar to the Thames Barrier in London. While it would be a fairly large task, it’s by no means impossible in terms of engineering, and far cheaper than moving cities around.

Planning for this kind of outcome could become fairly important. Although it is important to remember that we have not seen any sea-level changes yet, and may not- excess water may tend to flow to the equator from the poles due to centripetal force and increasing viscosity. Bit of a bummer for those on the equator though.

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>Oamaru’s historic buildings.

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Actually the guy who did the software for that site has admitted its shortcomings.

I think you can fill in the areas where there are spread pixels of blue… especially when coastal erosion is taken into account. The coastline will reach a new equilibrium, also dependent on wave energy and sediment budget etc.

Looking at Christchurch with it set to 7m, I would think that with erosion we get Banks Island again.
With climate change and possibly more intense storms> increase in average wave energy.
If as predicted there is a prevalence of drought, then alluvial sediment supply will decrease. The South Brighton tombolo will be interesting to watch. Also, even sans sealevel rise, the long term effect of hydro development on the Waitaki could well be the inundation of their historic buildings.

One metre rise would result in far more marine transgression than most people would expect. Poor Kaiapoi.

Take a look at the Taieri river area between Lake Waihola and Dunedin… 1m+ rise would cause some salinification of this area deemed to be quite removed from the coast (build a dam now – with turbines).

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