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Message
Do levees get stronger or weaker over time?
Posted on 5/14/11 at 12:38 am
Posted on 5/14/11 at 12:38 am
Serious questions for a civil guy out there....are the levees stronger now that they are older? It seems like grass and tree roots and settling would make them stronger ...also some areas lined with concrete which gets stronger over time, right?
Man, if one of those levees failed, it would be catastrophic since the river would exploit the weakness and I can't see any way they could stop the water flow until it the river lowered significantly..
Also, my understanding is that the river is like 18 feet above sea level in New Orleans, right? And presumably the canals that flooded NO during Katrina were at sea level as they were equal with Pontchartrain, although maybe it was up due to southeast winds of hurricane and storm surge making the lake a few feet higher than sea level???
Man, if one of those levees failed, it would be catastrophic since the river would exploit the weakness and I can't see any way they could stop the water flow until it the river lowered significantly..
Also, my understanding is that the river is like 18 feet above sea level in New Orleans, right? And presumably the canals that flooded NO during Katrina were at sea level as they were equal with Pontchartrain, although maybe it was up due to southeast winds of hurricane and storm surge making the lake a few feet higher than sea level???
7
Posted on 5/14/11 at 1:56 am to Big L
Generally speaking, they get stronger in that the dirt packs; however, there are so many other variables that can affect that.
Posted on 5/14/11 at 2:24 am to Big L
I'm gonna guess parabolic
Posted on 5/14/11 at 7:01 am to Big L
Generally speaking stonger, vegetation for cover is good. Trees not so, the root system destroyes the soundness of the compacted dirt.
Posted on 5/14/11 at 9:07 am to Big L
The big time issue is how the long the water stays at a high level. The longer this occurs the more that weaker soils can become saturated and susceptible to failure.
Posted on 5/14/11 at 9:15 am to Big L
quote:
also some areas lined with concrete which gets stronger over time,
I think the concrete, like the rip rap in New Orleans, is to prevent scouring and sliding on the river side of the levee. But I stand to be corrected by those who know more.
Posted on 5/14/11 at 10:05 am to urinetrouble
quote:Exactly. The biggest concerns are sand boils from what I understand.
The big time issue is how the long the water stays at a high level.
The levees should hold up well but as the water rises and the force of water on the levees increase, the force of water pushing through permeable layers under the levee also increases.
This causes water to push through like a small underground stream which results in sand boils, or sandy water bubbling up beyond the levee. This in turn weakens the levee from below and increases the likelihood of levee failure.
The longer the river stays high, the more critical the problem becomes.
Unfortunately once the river crests, it will take a month or longer to subside to normal levels.
This post was edited on 5/14/11 at 10:07 am
Posted on 5/14/11 at 10:15 am to LSU Tigerhead
quote:
Unfortunately once the river crests, it will take a month or longer to subside to normal levels
Damn, I didn't know it would be that long.
I cannot see a scenario where nothing fails throught this whole situation.
I'm not saying it would necessarily be a failure that would be a catastrophy,.
Posted on 5/14/11 at 10:35 am to LSU Tigerhead
quote:
Unfortunately once the river crests, it will take a month or longer to subside to normal levels.
you sure about this? I remember in 97 and 08 the river dropping fairly quickly.
Posted on 5/14/11 at 10:37 am to skullhawk
quote:
ou sure about this?
I think that is right. The reservoirs up north are holding back more water than they would like to. They will start releasing it when the river starts to drop. That will keep the river at a fairly high level for a fairly long time. It will drop, but more slowly.
Posted on 5/14/11 at 11:04 am to skullhawk
quote:
you sure about this? I remember in 97 and 08 the river dropping fairly quickly.
That was then and this is now.
Posted on 5/14/11 at 11:35 am to Big L
I am sure over time the levees settle a bit, we were compacting eight inch layers to I want to say 95% I was QC at the time and the corp guy stayed pretty close. This was in Madison parish to raise the levees their in 08 I think we added about six ft to the levees
Posted on 5/15/11 at 1:05 pm to skullhawk
They said that this season when the river crests it will recede very slowly due to the intensities of the snowfall during the winter and the spring rains they've had up north. Said about 30 days or longer to get back to normal levels.
Posted on 5/15/11 at 6:02 pm to LSU Tigerhead
Here in MC we are expecting our crest to get here around the 24th and the colonel said we should expect it to stay around that level for 7 - 10 days before it starts retreating. Which gives us about 20 more days until the levels start dropping.
Posted on 5/15/11 at 7:01 pm to Big L
The river at Vicksburg is what we watch and per NOAA it will not be back to flood stage until June 9. That being said we also have to understand that they have the great lakes on a holding stage pattern until we all get to or below flood then they will have a controlled release so the river will b high for a long time. We don't need rain in the valley for a while
Posted on 5/15/11 at 7:29 pm to Northeast Tiger
quote:
they have the great lakes on a holding stage pattern until we all get to or below flood
quote:
then they will have a controlled release so the river will b high for a long time.
quote:
then they will have a controlled release so the river will b high for a long time.
Since the great lakes naturally drain into the Atlantic and the canals that provide access to the MS river are mainly for shipping access.
What is the need to drain the lakes until the MS river is well below flood stage? Or am I missing something?
Posted on 5/15/11 at 7:32 pm to Northeast Tiger
Double Post
This post was edited on 5/15/11 at 7:33 pm
Posted on 5/15/11 at 9:27 pm to tigerfan1974
They will wait until its below flood stage but the water will still be high when they drain it. Same thing for the large lakes in north mississippi.
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