Sea level rise and the Canterbury coastline

by Gareth on July 31, 2013

What are the prospects for the shorelines of Pegasus Bay as sea level rises, river flows change, and wave directions change? Someone who really knows her erosion from accretion is Sonny Whitelaw, the Hurunui Council’s biodiversity ambassador1. She’ll be talking to the Food For Thought Hurunui group on Monday night at the Memorial Library in Amberley, kicking off at 7-30pm. This is a presentation that Sonny has already given to the Waimakariri and Hurunui Councils, and comes highly recommended — especially if you live in or near a Canterbury coastal community.

  1. And SF author, writer, photojournalist, and Hot Topic reader. []

{ 23 comments… read them below or add one }

Kiwiiano July 31, 2013 at 9:55 pm

I’d love to attend but am working till 7pm. Which Monday is it?

Gareth July 31, 2013 at 10:08 pm

Sorry Ian, this Monday – the 5th. I thought it was obvious from the context… ;-)

Bob Bingham July 31, 2013 at 10:29 pm

I worry about the feasibility of rebuilding Christchurch in its current location. It is a very flat area and a one meter sea level rise puts the sea behind the CBD. I would want a pretty quick payback before investing money in a new building. Try this web site with the level set at one meter and try a few vulnerable areas. The East coast of the UK is very vulnerable.
http://flood.firetree.net/

Kiwiiano July 31, 2013 at 11:40 pm

I’m not sure about Firetree, Bob, the high tide mark in the Avon is between the Barbados and Kilmore St bridges (personal observation) well within the 4 Aves, but Firetree doesn’t show any effects in the area until a 4m rise, which puts a single pixel well upstream at Victoria Sq. By my reckoning 4m rise would put Cathedral Sq underwater in a Spring high/storm surge.
That being said, I’d be reluctant to invest $$$ in anything below the 50m contour (McLeans Island) or even 100m (Sandihurst Winery) to be safe….. “Safe” being a relative term if it came to a 90m oceanic rise. I doubt that civilisation would survive such an onslaught.

Kiwiiano July 31, 2013 at 11:56 pm

Not trying to pre-empt Sonny, but there is one crumb of comfort regarding sea level rise in Canterbury. While a dump of Greenland’s ice would eventually affect NZ quite badly, a big melt in Antarctica wouldn’t be as bad, or so I’m lead to believe. Our current sea level is apparently somewhat higher than it would be if there wasn’t that huge volume of ice to the south sucking the oceans toward it by it’s sheer gravitational mass. Apparently, if it melted and dissipated our sea levels wouldn’t change much, or as much as areas further from Antarctica. The same situation as Iceland, Scandinavia, Scotland and Canada who would see a fall in sea level if Greenland melted.

Thomas August 1, 2013 at 6:30 pm

Not sure if I share your relative optimism. If Antarctica melts Greenland will go too if it not goes first anyway. Overall NZ will not fare particularity well in according to the models, gravity included.
Postdam Institute Paper

Bob Bingham August 1, 2013 at 7:55 pm

A lot of articles deal with sea level rises of ten and twenty meters because big numbers grab more attention. A one meter sea level rise would be catastrophic as eleven of the Worlds fifteen largest cities are at the one meter level and its not the poor nations who are going to suffer, Big lumps of the UK, Holland, Florida, New York and vital areas of California up to Sacramento and big lumps of Texas and New Orleans.
New Zealand is fairly hilly and so only places like Aukland airport, Christchurch CBD, Tauranga port and a few others are vulnerable.
I suspect that the next IPCC report will increase the expected forecast to be nearer two meters by the end of the century but there is still a lot more to learn about the glaciers..

Macro August 2, 2013 at 11:57 am

Downtown Auckland – where the majority of the latest expensive infrastucture (Britomart, new tunnels, etc) is based – is certainly under threat dig one metre down on Franshaw Street and you are into water from the Viaduct just 100 metres away; as is Wellington – “Lambton Quay” is not called that for nothing! But nothing will be done until the water is lapping on the steps of Parliament and flooding the Beehive car park.

Copie August 1, 2013 at 9:48 pm

Perhaps someone will be kind enough to provide evidence that Canterbury residents are being affected by sea level rise caused by man made global warming!

Kiwiiano August 1, 2013 at 10:29 pm

Um….they’re not. YET! We haven’t suffered much in the way of wacky weather here in ChCh and the global sea level rises to date have been comparatively minor. In fact ChCh has had greater ill-effects from the February earthquake dropping significant parts of the city leaving them especially vulnerable to storm surges and flooding following heavy rain.
However, given the increasingly erratic weather around the world and the speed with which polar regions are reacting to rising GHG, we can reasonably anticipate problems in the not-too-distant future. Enough that the Scientific community, Insurance Industry and Military are concerned, even if the politicians are resolutely keeping their heads where the sun don’t shine.

As an aside, it occurred to me that I’ve seen climate change in action personally. I haven’t seen the official figures but have noticed that in ChCh the heaviest frosts in the last decade have been maybe -3°C. When I was a kid in Bryndwr back in the 50′s I clearly recall repeated “12 degrees of frost” which is -6.6°C. We regularly experienced still-frozen gutters where we could walk/slide on the ice when coming home from school at 3.30pm. I haven’t seen iced-up gutters for years.

Bob Bingham August 2, 2013 at 9:41 am

According to NASA sea level is rising at 3.16 mm a year. http://climate.nasa.gov/ and a shallow beach has a gradient of 50:1 so the land is disappearing at 150 mm a year. Does anyone notice? I doubt it..

noelfuller August 3, 2013 at 12:18 am

Keep in mind that erosion effects will be noticeably greater than simple sea-level rise or spread.

CTG August 3, 2013 at 9:33 pm

Yes, it is noticeable. I bought a property in Waikanae ten years ago. Even in that time it is noticeable that spring tides are now regularly hitting the dune front. Storm surges are now doing more damage to the dune front – the erosion on the dunes is quite pronounced.

People in Kapiti complained when the council showed future impacts from SLR taking out most of the beachfront properties. Given how much impact there has been in ten years already, those forecasts for 100 years look to be on the optimistic side.

sonnywhitelaw August 3, 2013 at 10:15 am

In terms of evidence (responding to Copie) I’ll be happy to provide it Monday night.

noelfuller August 3, 2013 at 2:08 am

Two articles that are worth reading if you have not already done so, although this first one, a TV interview, is more concerned with flooding in Europe. It includes relevant comments on insurance and on old infrastructure.
Europe is asking for a catastrophy

“DW: So, you want people to start thinking about moving to safer spaces or building new cities rather than shoring up the ones that we have?

“The insurance sector is starting to discuss this because they’re the ones that have been picking up the bill. You are already starting to see places in the UK, for example, where houses just can’t get insurance any more. If you can’t get insurance, you can’t sell your house.

“DW: They’re not getting insurance because they’re vulnerable to catastrophes?

“Because they flooded. In fact, in the UK they built houses on floodplains. The sellers said, ‘we guarantee you can get insurance’. So homeowners got the insurance and when they flooded, they got the payout. But then the insurer said once is enough and we’re not going to pay out again. Now homeowners are stuck with houses on a floodplain that they can’t get insurance for. This isn’t one or two cases – this is potentially tens of thousands of cases and increasingly more across Europe as the floodplains change and increase.”

The second article is about vulnerability of American cities to sea level rise. At some point a city could be considered locked in to future sea-level rise:

“Hundreds of American cities are already locked into watery futures and we are growing that group very rapidly,” Strauss said. “We are
locking in hundreds more as we continue to emit carbon into the atmosphere.”

A recent study, also published in PNAS by the climate scientist Anders Levermann found each 1°C rise in atmospheric warming would lead eventually to 2.3m of sea-level rise. The latest study takes those figures, and factors in the current rate of carbon emissions, as well as the best estimate of global temperature sensitivity to pollution.

Thus, Christchurch must aready be locked into 3.9 metres of sea-level rise on the basis of current and commited warming (0.8+ 0.9) 1.7°C. Of course I could throw this at most low lying places on the NZ coast or anywhere else and this does not include further rise that is certain if we continue to do almost nothing to change our ways.

The American author got rather confused when she mistook 31.6mm SLR per decade with 31.6 cm and translated that as 1ft sea-level rise per decade – see last sentence in article. The Guardian editor should have caught that.

Kiwiiano August 3, 2013 at 9:00 am

I’m wondering how long it will be before the proponents of the ChCh Rebuild realise that all their grandiose plans are looking increasingly fragile. When the penny drops it won’t just be the residents of Rockinghorse Rd struggling to find buyers. We don’t need the tides lapping at the Cathedral steps, just the realisation that they eventually will.
I also wonder if the NZ Insurance companies are planning to curtail flood cover for any properties below 5-10-20m or at least send the premiums ballistic..

sonnywhitelaw August 3, 2013 at 1:06 pm

I asked a couple of real estate agents that question in April, when I was writing a paper for the Hurunui Council on the impact of the earthquakes to the district (available here: http://www.hurunui.govt.nz/assets/Documents/Community-Development/Earthquake-Report.pdf). My question was geared towards the migration patterns of people following the earthquakes, the subsequent housing shortage, and the known issue of liquefaction along coastal margins. Quoting from my report (page 18): In coastal areas potentially affected by liquefaction such as Amberley Beach and Leithfield Beach, purchasing property is mostly a lifestyle consideration that appears to outweigh known and potential concerns (including tsunamis and beach erosion). Insurance, while it can be more difficult to obtain, is ‘not insurmountable’.

Copie August 4, 2013 at 12:13 am

OK, so there is no proof of sea level rise affecting people in Canterbury, just some maybes and perhaps if something else happens?
Certainly nothing for the average person to worry about.

Kiwiiano August 4, 2013 at 7:19 am

The average person isn’t worrying about it, but I for one wouldn’t buy a property that could suddenly lose its resale value overnight. That’s what due diligence is all about.

RW August 4, 2013 at 10:14 am

Oh great! Our future social progress – or even just survival, as always, will be determined by the knowledge and understanding of “average persons”?

Arguing from a standpoint of faux naivete won’t work.

Thomas August 4, 2013 at 10:55 am

Copie, leave your head firmly embedded in the sand and you will enjoy the ability to deny any developments around you unless your head hole in the sand gets flooded too.
In the meanwhile others can estimate what a rise of the sea level will do their neighborhood, what it will do to property values or the ability to obtain insurance or mortgages or sell property or to the economy of the region and the country when large parts of our infrastructure need to be relocated or productive lands need to be abandoned….

Kiwiiano August 4, 2013 at 7:32 am

I’ve even wondered if Victoria Matthews’ reluctance to repair the Christchurch Cathedral is because they realise the ultimate futility of building any permanent structures so close to sea level.
Which raises the thought that Brownlee and the Nats being so focussed on ignoring the warnings of climate change are frog-marching the city into a monumental cock-up. They’ll just about get the structure restarted when it will dawn on them that it was a total waste of money.

Macro August 4, 2013 at 8:07 pm

” They’ll just about get the structure restarted when it will dawn on them that it was a total waste of money.”

Just like the total waste of money ($23 Billion to be precise) on the building of Holiday Highways.

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