All posts in the topic Impacts of sea level rise (Short link)
Summary
- There are 11 posts — by 7 authors — in this topic.
- Latest post made by Brian Sandle at Jul 12 22:37 UTC
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| Brian Sandle | Heights above MSL.doc | Jul 11 10:56 UTC |
On Tue, 2008-07-08 at 19:45 +1200, Brian Sandle wrote:
> I just wanted to be sure that no-one thought that meant we do not have
> to plan here in Canterbury for sea level rise.
Good point, Brian. I'd be interested to know if anyone's done any
analysis of the impact of a reasonable rise in sea level on Christchurch
in particular. I used Google Earth a while back to find out that here in
Bryndwr I'm about 10 metres above current sea level, which is somewhat
comforting :-) But then, how much is the sea level predicted to rise
over the next, say, decade ?
Hi Andrew Your position at 10m is not only impacted by average rises but also by minimum and maximum - i.e. shoreline surge is greater than mean sea-level rise so while you may not be dipping your heals all year you may be mopping up after extreme events - you know those one in one hundred year events that seem to be happening consecutively? The mean increase is predicted at around 480mm by 2100 but there are lots of assumptions based on methane emissions and the reflection indexes from sea uncovered by melting Artic Ice so is the rate increasing or decreasing? There's an article here http://www.nwrc.usgs.gov/hurricane/Sea-Level-Rise.pdf There seems to be a lot of discussion about the Artic melt but what people forget is that the Artic ice is already floating in the ocean and therefore will not substantially raise the mean sea level - however if glaciers and marginal ice melts and flows off the Antartic continent then we will see greater inundation. What is more likely to effect the Canterbury fringes is a combination of faulting (the land lowers along the continental fringe which runs through the Main Divide), coastal subsidence especially around braided rivers (Waimak, Rangitata, Rakaia) and breaks in natural sea defences i.e. our sand dunes along the Brighton coast. Also there is the possibility, which has never been suggested (that I have seen), that if we were to empty our aquifers they could cause some lowering of land levels - though how you could predict or measure this impact would be difficult as we don't measure the aquifers that well - mainly based on outflows. The article I've cited suggests that saving coastal fringes (the example is New Orleans) requires: "Minimize drain-and-fill activities, shallow subsurface fluid withdrawals, and other human developments that enhance subsidence" On the up side of all of this doom and gloom is that you might have a beach side property to retire to without having to move...... The other issue, of course, is can we reverse the trend? In other words is this climate change due to carbon pollution or just a trend since the last ice age 20,000 years ago. That opens a whole other debate as to whether you even believe in climate change and I'm sure we'll have someone come on here and tell us of we get rid of cattle in Canterbury we'll save our coastline. If you don't believe its happening then ask the Germans when their 7 best summers were - not hard - its the 7 most recent years - but that's not a trend just a one in one hundred year event! Unfortunately climate change has brought benefits to some areas so its unlikely we'll see Germany wanting to sign up to something to reduce what is giving them a better climate.... The greatest issue I think though is the effect of extreme events and how we deal with them in Canterbury - but that's for another post Michael Campbell
In terms of extreme events, the issue here is less about what might happen when
rather, what is the quantifiable risk to infrastructure when it does. NSW did
some interesting analysis looking at mean sea-level rise but recognises that it
is 'event issues' that correlate to the highest risk scenarios.
So what might threaten Canterbury..
An increased energy in the atmosphere tropical depression bringing moisture
laden south pacific nor'easterly winds onto our porous alluvial and sand soils
with upper range precipitation over short time frames onto winter wet plains,
coastal and inland foothills and up to the main-divide creating a significant
spring melt - coupled with 'low pressure' storm surge on top of a king tide
starts to look pretty darn risky.
The hydrodynamics of this would just move what ever is in its way... away!
Tell me this can't happen. Please tell me this is not probable, likely or even
possible. Then assure me of your qualification...
No wonder the Insurance industry loss adjustors and actuary's are saying to
territorial authorities "if you don't take a precautionary approach, we'll
sue".
And they have very very deep pockets.
andrew wrote: > On Tue, 2008-07-08 at 19:45 +1200, Brian Sandle wrote: > >> I just wanted to be sure that no-one thought that meant we do not have >> to plan here in Canterbury for sea level rise. >> > > Good point, Brian. I'd be interested to know if anyone's done any > analysis of the impact of a reasonable rise in sea level on Christchurch > in particular. I used Google Earth a while back to find out that here in > Bryndwr I'm about 10 metres above current sea level, which is somewhat > comforting :-) But then, how much is the sea level predicted to rise > over the next, say, decade ? > A decade being how long someone expects to keep a property? Interesting what Blair says: "No wonder the Insurance industry loss adjustors and actuary's are saying to territorial authorities "if you don't take a precautionary approach, we'll sue". And they have very very deep pockets." Properties are supposed to last more like a hundred years aren't they? So it would be the territorial authority who had approved it who has to bear the cost. In other words that is rates. It might be cheaper to put in a bit extra now. I worry about using the google earth for topographical data. The Heathcote River would seem to flow uphill in some places. Also aast of Comobo St. half way to the hills seems to have 0 elevation over a large area, too. The Brighton Libray does not seem to have a topographical map to check. Anyone? Some people are claiming that global warming is not a worry for inundation as a warmer southern ocean produces more water vapour in the air which falls out as snow on Antarctica. But when water freezes to snow heat is given out. http://www.antarctica.ac.uk/met/gjma/ shows some increased autumn cooling in afew parts (manily coastal) of Antarctica, but Vostok has not and the peninsula and some other coastal areas have warmed over 35 years in autumn, and most places except the south pole seem to have warmed in other seasons. Whatever process causes the Antarctic glacial ice to slide into the sea may be enhanced by such higher temps. Then the warm currents from the north will eat away more underneath, about which some studies may be starting - the International Polar Year ones. Not too much data about that exists compared to the Artic where the Cold War subs of USA & USSR used to frequent. Ground-based ice sheets, or some partly floating ice shelves may actually lower sea levels a bit when they melt as the water they process has less volume than the ice had. (I asked about that on the groups 10 years ago but got no reply.) Volcanoes like Pinatubo may have also slowed global warming. I think we need to be ready for a surprise rise as that smoke clears and also our heat sinks run down. Back to Andrew's 10 years, is it worth bothering to paint the house sort of thing. The picture gets very complicated by people's desire to avoid thinking about tomorrow. I think I should paint my coastal house as insurance against the chance it will survive for a while. But I have never been good at selling so I cannot say to be sure it is a good idea to buy it from me and invest in intensified permanent dwellings on the section. But who knows?
If you look over the past brazilion years you will notice a series of
"inter-glacial" periods that last for around 10,000 -15,000 years. There
were a couple of exceptions - two periods of roughly 5,000 years... one
after the other - with slightly shorter than normal glacial periods between.
So, to all intents and purposes we are reaching something like the end of
the current intergalcial period. Whether it will end in the next 10 years...
or temperatures continue to rise over the next ten years is a moot point.
However, by the time we have all stopped mooting the issue, actual data may
show where we are going (as apart from climate change modeling.)
Even if "average" sea levels increased there are many separate issues
relating to a little house in Bryndwr. For example although water naturally
"finds its own level", in reality the level varies on a world scale. One
side of the Pacific Ocean for example may be "higher" than the other.
So, on one hand, If we are subjected to many Nor-easters the water level may
rise and lap on the boundaries of a little house in Bryndwr... but if the
prevailing winds continue to blow from the north-west the little house may
be OK.
On the other hand.. the geological level of the Canterbury Plains may drop
in relation to the level of the South-western Pacific Ocean because dairy
farmers have taken up all the water under the plains to clean their cowsheds
and the wind has changed from a Nor-Wester that blows dust and stuff off the
Southern Alps and distributes it on top of the Canterbury Plains...to a
Nor-easter that raises sea level undercutting the coastal fringes and the
weight of that water as it rushes through the North Beach sand hills will
press upon the remnants of the Canterbury Plains thereby converting the
little house in Bryndwr into a beach house....
In sum, it may be best to come to a compromise vis-a-vis painting the little
house in Bryndwr. One compromise I'd suggest is pick up a can of white paint
on "special" - and give a few bob to a uni student to paint the place for
you. Thus you would have a cheap, acceptably attractive (if you don't look
too closely) house that will last until it is innundated...
And should ten years pass by and the house is still sitting a couple of Kms
from the beach you could then consider a professional paint job...
However, as we are now "overdue" for a major earthquake you may want to take
this into consideration in relation to changing sea levels.
Maybe just don't bother painting the house...
Hi Guys, if you want to talk about sea level rises we're well overdue for an
asteroid so I wouldn't worry too much about the the paint job on the
house...but I'd get a gun licence :-). Tongue and cheek comment.
The reality is that the "fear" of all these things - climate change, fuel
peaking, asteroids, war - all of these are going to be driving forces that will
affect our pockets locally and nationally in the future. Regardless of whether
or not there are sea level rises. If I was a Cantabrian living close to the sea
I would be moving as far inland as possible before insurance companies begin to
get serious about the prospect of sea lapping on my doorstep.
Hi Craig, Needing gun licence implies a) needing a gun b) there is a government with a legal system to fear. And who knows an earth-impinging asteroid my provide enough dust in the atmosphere to ward off global warming. Isn't it that people trained in martial arts try to avoid conflict? Perhaps I cause a little conflict by discussing issues that may change the value of some land. But maybe if we can get the government, that is really ourselves in a democracy, to look ahead and around the corner then maybe bigger conflict can be averted. The URL: http://www.globalwatch.org/ungp/qc-chrono.htm refers to how a Chinese city in 1976 lost 240,000 people in a quake. 100km away in another city many buildings fell, but the people were prepared. So only one life was lost (heart attack). These people were then able to help the neighbouring city. I am glad more and more online data is becoming available for us to know our environment. Some of the Land Information maps are free online. But the topographical map elevations are no use as they are in 20 m steps, I think. But I have got a map from the CCC made by LiDAR technology. I don't know if it is commercial property and I may be breaking the law. It would be the same used at public lectures by the CCC Civil Defense section a while back. This is an interesting article about philosophy of public access to info: http://www.digitalstrategy.govt.nz/upload/Main%20Sections/Content/Working%20Papers/Access_Issues_Geospatial_Content.rtf. Take a look at the map, the properties on Marine Pde are actually mainly a bit higher above sea level than much of Brighton, and quite a bit of east Christchurch.
Hi Brian!
Hey, I have a gun (well, a rifle) and a license to operate it. I don't need
a gun - but I do need a license.
I don't think that means we have a Government that has a legal system to
fear.
I does mean though, that I picked up a firearms license back in the days
when is was OK to have a rifle, then some faceless bureaucrats made it
compulsory to pay huge fees to re-license ourselves (as apart from our
rifles) and then we have to be police-checked every ten years - which
includes checking neighbours, wives and God knows who else.
So, pardon me for mentioning this... once I could quite safely carry a rifle
through town without hitting TV1 National News and getting a bunch of armed
offenders after me. Now kids with cap guns darn near get arrested.
But I don't know what all tis has to do with the rising tides and a little
house in Bryndwr....
But unless you own an Ipod there seems little fun left in life - can't even
light up a rubbish fire!
Yes we'll note that down, Tim, oneday a few rabbits or possums might be needed.
We used to have cadets at school. We had practice on a .22 range at the school,
which backed on to the fives courts. I think the fives was more fun really. For
a few years we kept getting promised a trip to West Melton to shoot a bren gun.
It was an interesting thought but I am glad we didn't ever go. I guess quite a
few children across the world get pulled in to war as a way of life. Probably
would have gone more deaf, too.
But we need to think really hard to avoid a siege mentality developing at home.
I am guessing some of the first food raids will be on the community gardens.
I understand in some countries now farmers have to stay up at night to guard
their crops.
I don't think it would work very well just to protect our own. I think we need
to get together as good politicians outwitting the every-person-for-themself
mode. I suppose people like to compete a bit. But if there is chaos all around
when people are short it can be depressing, can't it? The odd firm will set up
to make money out of the chaos and suffering.
Anyway sorry I must have pushed a wrong button last post for the height above
sea level for various parts of Christchurch.
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- Name: Heights above MSL.doc
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Thanks for that map, but I'm having a thick moment; hdeciphering the key to
it.
My house is in a medium-blue area and looks to me that blue is slightly
above sea-level. Am I correct ? I've wondered about this ever since that
tsunami . . .
Paula Lambert wrote: > Thanks for that map, but I'm having a thick moment; hdeciphering the > key to > it. > My house is in a medium-blue area and looks to me that blue is slightly > above sea-level. Then I think it should be from 2.1 to 3 metres above average sea level. The tide tables for Lyttelton give from near 0 for very low to near 3 metres for very high. So I suppose the average would be about 1.5m. So a very high tide could rise about 1.5m above the average (or mean) sea level. I don't know what it would be for Brighton. So your property could be as little as 0.6 m above a very high tide. I should probably have weighted till Monday to check back on that. Maybe 'mean sea level' means mean high water spring (fairly high) tide. Again I think the Marine Pde dunes are not supposed to be lowered below 8m above that. And that is supposed to be 5m above road level I think , giving about 3m difference and the Marine Pde area is in the light blue making it about 3.1 to 4 m above whichever datum they mean. But whatever it is does not seem a great safety margin. My Aunt once told me that the sea water had come across low dunes on to the tram lines which used to run along Marine from the clock tower to the Ozone Hotel. The audio file from the scientific journal Nature http://media.nature.com/download/nature/podcast/climate/climate-2008-02-29.mp3 relates how new data start to tell that the Antarctic glaciers are adding to sea level. Also it speaks of high level political influence on USA government scientists not to give out their findings. > Am I correct ? I've wondered about this ever since that > tsunami . . . > The main tsunami surge from the Chilean coast arrived here at low tide. Some later surges, though not so strong, appeared to be similar since they did not come at low tide. The tsunami adds to the current sea level. The prediction for 100 years sea level rise from global warming used to be 0.45 m but now I thiink it is thought it could be quite a lot more than that. So I believe some hard thinking is needed about whether to increase population density in certain areas of Christchurch.