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PostPosted: Fri Aug 03, 2012 9:39 am 
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Yes normal sea walls are very expensive. That is because they are in situations where the fury of storms has to be countered.

In the case of a sand bar where the land has been stable for hundreds of years without any human help and will indeed not need any further human interferance at all but the sea wall is still desired for psychological/political reasons a far cheaper wall will do absolutley fine.

The sea wall around an exposed deep water harbour which sits in 40 foot of water is a different matter. A 2 foot high thing is easy.


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PostPosted: Fri Aug 03, 2012 9:54 am 
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Tim the Plumber wrote:
Yes normal sea walls are very expensive. That is because they are in situations where the fury of storms has to be countered.

In the case of a sand bar where the land has been stable for hundreds of years without any human help and will indeed not need any further human interferance at all but the sea wall is still desired for psychological/political reasons a far cheaper wall will do absolutley fine.

The sea wall around an exposed deep water harbour which sits in 40 foot of water is a different matter. A 2 foot high thing is easy.


The land has not been stable for hundreds of years, which is an assumption you should not make.

The height will not be 2 feet because that would not be stable. The height will be several times that amount just to reach a stable footing and will be higher above ground to provide protection from storm surge. The thickness will be proportional to the height too.


That is why I mentioned the cost discussions on a short seawall on a canal for a residence being much more expensive than your estimated costs. A canal has very little surge or wave action and probably has somewhat better footing but has a higher cost than you propose for a sound or sea side defense.

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PostPosted: Sat Aug 04, 2012 5:15 am 
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It's managed fine with no help for long enough that people have built on the sand bar.

Since there has been so far no significant sea level change an additional bit of protection starting above the high tide point will be easy.


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PostPosted: Sat Aug 04, 2012 7:35 am 
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Tim the Plumber wrote:
It's managed fine with no help for long enough that people have built on the sand bar.


Because of the size of the islands and the relative stability of the sea level over the period people have built there, but that changes even without sea level increases.

http://nc1812.ncdcr.gov/history_forthampton.htm

For the next several years the erosion at Bogue Point progressed and eventually lopped off an extensive portion of the beach. Included in that portion, at last, was Fort Hampton. There seems to have been no exact record of when the little fort actually met its end. Local tradition claimed it disappeared virtually overnight in a summer storm. Undoubtedly, it was the early season hurricane of June 3-4, 1825, that finally claimed the fort. The exact sequence of its demise is not known, but the sea undoubtedly surged around the walls of the fort, undermining and crumbling its parapet. Once a breach was made, the tide swept through the weed-choked parade ground to topple the empty shells of the barracks and magazine. It is known that by February, 1826, the high tide mark lay over 200 feet in the rear of the spot where the little fort had stood. By 1834, the site lay in the inlet along the line of a 12-foot deep ship channel.

The site of the new fort on Bogue Point, Fort Macon, was initially fixed by the engineers about 130 feet southwest of Fort Hampton. By the time construction was ready to begin in 1826 the site was in the possession of the sea. A new site had to be chosen 300 yards west of Fort Hampton and here Fort Macon now stands. Even then, Fort Macon was saved from its predecessor's fate only by the building of brick and stone sea jetties over the years that followed.





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Since there has been so far no significant sea level change an additional bit of protection starting above the high tide point will be easy.


Neither easy nor inexpensive for the barrier islands nor any of the places I have given as examples found. The only easy aspect seems to be in your assumptions. You have no other evidence of the ease or cost than your personal opinions.

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PostPosted: Sat Aug 04, 2012 8:39 pm 
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Tim the Plumber wrote:
In the case of a sand bar where the land has been stable for hundreds of years without any human help and will indeed not need any further human interferance at all but the sea wall is still desired for psychological/political reasons a far cheaper wall will do absolutley fine.



According to the IPCC and others one of the major costs will be the loss of agricultural land as the sea level rises. The water table along the coast will rise to the point where the salt will be too close to the surface to grow crops. This is going to be worst on river deltas and places where the water can seep through the ground as in sandy areas.
http://www.iuss.org/19th%20WCSS/Symposium/pdf/0419.pdf
It also suggests to me that your idea that a sand banks will solve the problem is wrong. the water level behind the sand barrier will rise because the water table rises. This will undermine buildings, infrastructure, roads etc.

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PostPosted: Sun Aug 05, 2012 6:24 am 
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warmair wrote:
Tim the Plumber wrote:
In the case of a sand bar where the land has been stable for hundreds of years without any human help and will indeed not need any further human interferance at all but the sea wall is still desired for psychological/political reasons a far cheaper wall will do absolutley fine.



According to the IPCC and others one of the major costs will be the loss of agricultural land as the sea level rises. The water table along the coast will rise to the point where the salt will be too close to the surface to grow crops. This is going to be worst on river deltas and places where the water can seep through the ground as in sandy areas.
http://www.iuss.org/19th%20WCSS/Symposium/pdf/0419.pdf
It also suggests to me that your idea that a sand banks will solve the problem is wrong. the water level behind the sand barrier will rise because the water table rises. This will undermine buildings, infrastructure, roads etc.


Yeah..... oh how do the Dutch make all that land below sea level by 10 meters formed out of the deposits of the Rhien river so fertile, they must be so clever.


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PostPosted: Sun Aug 05, 2012 6:26 am 
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http://nc1812.ncdcr.gov/history_forthampton.htm

Nice account of how the sand bars shift about in an active estuary.

Coastal defense is a costly undertaking because we put expensive things like ports and houses on the coast.

The effect and cost of countering errosion is a lot.

The effect of a tiny sea level rise is tiny.


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PostPosted: Sun Aug 05, 2012 7:21 am 
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Tim the Plumber wrote:
http://nc1812.ncdcr.gov/history_forthampton.htm

Nice account of how the sand bars shift about in an active estuary.


Actually, it is not an estuary, it is a barrier island.

Quote:
Coastal defense is a costly undertaking because we put expensive things like ports and houses on the coast.


Which is what we have been telling you all along. There are slightly less people living in the coastal areas than are not so there are a lot of houses for their shelter. Not many have tried building port facilities in the mountains because the ships never seem to leave the water on their own.

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The effect and cost of countering errosion is a lot.


Yes, it is.

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The effect of a tiny sea level rise is tiny
.

How do you reach this jump in illogic? If the cost of erosion is a lot, more water bringing more erosion at higher points on the shore should also be expensive, as the data show us it is.

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PostPosted: Sun Aug 05, 2012 8:17 am 
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All this arguing about the cost of defending ports/towns/a few houses is moot and a waste of time if the results of the ANDRILL project is anything to go by, a few feet is nothing when they have found the sea level rises 20m above present in every interglacial so far. It is not worth wasting money and resources (or energy arguing about it) trying to defend what is going to be flooded in the longer term anyway and relocation is the only option.


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PostPosted: Sun Aug 05, 2012 10:50 am 
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Of course there is the question as to why the sea level is not higher if the that is normal for an interglacial and according to the cycle we should be nearing the end of the period unless the added CO2 changes the cycles.

Image

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PostPosted: Sun Aug 05, 2012 12:29 pm 
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Posting nice looking graphs will not alter the real situation.

The land ice is at present locked into ice sheets mostly in Antarctica. These are so cold that any amount of expected global warming will not melt them.

The one in Greenland is at high altitude and again most of it is safe from anything shy of a 15c degree temperature rise. The edges of this ice sheet may melt a bit but the maximum contibution to sea level rise is going to be a lot less than 20cm by 2100 assuming a less than 6c degree rise.

The basic mechanics of this is clear.

The other source of sea level rise is thermal expansion of the ocean. This is again at worst going to produce a less than 20 cm rise.

I know you really want to believe that we are all doomed but we just are not. Find another doomsday scenario.


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PostPosted: Sun Aug 05, 2012 1:40 pm 
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Tim the Plumber wrote:
Posting nice looking graphs will not alter the real situation.

The land ice is at present locked into ice sheets mostly in Antarctica. These are so cold that any amount of expected global warming will not melt them.

The one in Greenland is at high altitude and again most of it is safe from anything shy of a 15c degree temperature rise. The edges of this ice sheet may melt a bit but the maximum contibution to sea level rise is going to be a lot less than 20cm by 2100 assuming a less than 6c degree rise.

The basic mechanics of this is clear.

The other source of sea level rise is thermal expansion of the ocean. This is again at worst going to produce a less than 20 cm rise.

I know you really want to believe that we are all doomed but we just are not. Find another doomsday scenario.


I would like to know where you get your information, It seems related to what I know and can confirm but just not quite right.


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PostPosted: Sun Aug 05, 2012 3:29 pm 
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Wayne Stollings wrote:
Of course there is the question as to why the sea level is not higher if the that is normal for an interglacial and according to the cycle we should be nearing the end of the period unless the added CO2 changes the cycles.

Image


Image

Just wanted to put both of these in context with each other, know they are different scales but you have one clearly showing we should be nearing the end of the cycle and the ANDRILL graph is clearly showing we have a way to go.


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PostPosted: Sun Aug 05, 2012 5:05 pm 
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Tim the Plumber wrote:
Posting nice looking graphs will not alter the real situation.

The land ice is at present locked into ice sheets mostly in Antarctica. These are so cold that any amount of expected global warming will not melt them.

The one in Greenland is at high altitude and again most of it is safe from anything shy of a 15c degree temperature rise. The edges of this ice sheet may melt a bit but the maximum contibution to sea level rise is going to be a lot less than 20cm by 2100 assuming a less than 6c degree rise.

The basic mechanics of this is clear.

The other source of sea level rise is thermal expansion of the ocean. This is again at worst going to produce a less than 20 cm rise.

I know you really want to believe that we are all doomed but we just are not. Find another doomsday scenario.


You should take that up with Spongebob as the post was in reply to his reference to a 20 m higher sea level in prior interglacials when we should be nearing the end of our current interglacial.

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PostPosted: Sun Aug 05, 2012 5:10 pm 
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Spongebob wrote:
Wayne Stollings wrote:
Of course there is the question as to why the sea level is not higher if the that is normal for an interglacial and according to the cycle we should be nearing the end of the period unless the added CO2 changes the cycles.

Image


Image

Just wanted to put both of these in context with each other, know they are different scales but you have one clearly showing we should be nearing the end of the cycle and the ANDRILL graph is clearly showing we have a way to go.


But it is not just this graph that is used to determine the time between the previous interglacial periods.

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