Can someone enlighten me, I am still not quite sure the reasons those levees in NOLA broke ? Was it the force of the wind or the water that broke the levees? If they said the levees were designed to withstand Cat 3 hurricanes then it sounded like the wind caused it. Hadn't Katrina passed and the wind died down by then? A more important question that bothers me: when you have a levee that protects your home, I think you monitor it constantly for leaks and try to fix them before they became too big to fix. Force of water does not work instantly, you probably see leaks, or the soil that makes up the levee moves or falls off into the water or some other indications. I could undertand it if the engineers responsible for the levees made some attempts and failed but I didn't hear any report if there were such activities taking place. You watched the news all day long and all of the sudden you heard a levee broke and the next minute water was all over the whole city. Does it sound like someone dropped the ball here?
My understanding is the levees broke for two reasons. One was that the storm surge pushed the water over the level of the levees and would cause them to collapse from the top the other was that the force of the water undermined the levees. I remember seeing a few years back when there was major flooding on the Mississippi some levees breaking and when they go they go pretty quickly. It is a gradual process but not one that's always visible as water infiltrates into the bottom of an earthen levee it turns to mud and eventually the whole bottom of the levee slides right out and water comes rushing in. Wind action on an earthen levee wouldn't do much to it because they are designed with a low wide profile but its primarily the water pressure which in a storm surge is strong enough to wipe concrete buildings off of their foundations. All that pressure is both pushing on the levee and also pushing water into the levee so its not a matter of waves lapping on the levee eroding it away like a sand castle on the beach but more like trying to block a hose with a piece of cardboard. Eventually the cardboard gets waterlogged and falls apart.
new orleans is built on a swamp, below sea-level. that makes it unique , as a major American city. they have been vulnerable since the day new orleans was settled in the 1700's... http://www.cnn.com/2005/WEATHER/09/01/orleans.levees/index.html The widespread damage to the city has much to do with its topography, or "lay of the land," English said. New Orleans sits mostly below sea level on swampland on the east bank of the Mississippi River and south of Lake Pontchartrain. "A lack of coastal irregularities," such as substantial barrier islands or hills, and the Gulf of Mexico's flat bottom make southern Louisiana "ideal for wave damage," according to the National Weather Service Web site. "Storm vulnerability is made worse by ongoing wetland loss and barrier island erosion," according to the U.S. Geological Survey Web site. To prevent flooding, a system of pumps, canals and levees was put in place by the Army Corps of Engineers. Construction of levees along the river and lake over the centuries has led to a rise in the water levels, according to the National Weather Service. Each increase of the level of water puts more pressure on the levees. The levee system is quite extensive, but had been built only to withstand a Category 3 hurricane, English said....
Erosion seems to be the big force here. Unless it is not visible, I would think you can temporarily repair the smaller leaks or breaks. You've seen it before, people hand-carry bags of soil to pile on top of levees or dams to plug the breeches. Maybe if they had used those 3000 lb bag early, it might make a difference?
You're not going to notice the smaller breaks when water's already going over the levee. THey said there was a five hundred foot hole in one of them, it apparently happened very fast.
When the Levee Breaks --------------------- If it keeps on rainin', levee's going to break If it keeps on rainin', levee's going to break A-when the levee breaks, have no place to stay Mean old levee, taught me to weep and moan and moan Mean old levee, taught me to weep and moan It's got what it takes to make a mountain-man leave his home Oh, well-a, oh, well-a, oh, well-a, ooh-ooh A-don't it make ya feel bad when you're tryin' to find your way home and ya don't know which way to go If you're goin' down south and they've no work to do then ya go north to Chicago, ah, 'eah, 'eah, hey Cryin' won't help ya, prayin' won't do ya no good Now, cryin' won't help ya, prayin' won't do ya no good A-when the levee breaks, mama, you got to move, a-woo-hoo All last night, sat on the levee and moaned All last night, sat on the levee and moaned Thinkin' 'bout my baby and my happy home, oh-hoh Ah-ah-ah, ah-ah-ah, ah-ah-ah, ha Ah-ah-ah, ah-ah-ah, ah-ah-ah, ha Oh, oh Goin', I'm goin' to Chicago, goin' to Chicago Sorry, but I can't take you Goin' down, goin' down, now, goin' down, a-goin' down, now Goin' down, goin' down, goin' down, goin' down, yeahh Goin' down, goin' down, now, goin' down, goin' down, now Goin' down, goin' down, now, goin' down Goin' down, down, down, down, down Ooh-woo-ooh, ooh-woo-ooh
How many people are going to post this? Seriously.. makes me wish there were other songs about levees..
There are some more songs that use the word levee, but they are Blues and not well known to most people.
I just heard on 60 Minutes that the earthen levees didn't fail but that the floodwalls bordering the canals failed. Those walls are 2' thick concrete and what happened was that the storm pushed water over them and then knocked them over. Thse walls were designed for a cat. 3 hurricane and when Katrina landed it was a cat. 4.
Yeah, I saw that on 60 minutes. Its amazing people keep saying that, because they aren't showing levees on tv, they're showing walls. The levees are earthen dams that were built a long time ago.
If you'd like to get a good look at the dynamics look at either the Johnstown Flood or the failure of the St. Francis Dam. The St Francis Dam was concrete, but failed because of the earth surrounding the dam was like the composition of the levees, and the Johnstown Flood resulted from the failure of an earthwork "dam" in which the owner had blocked off the spillover. Once you begin to notice leaks in construction like the levees, it's probably already too late, because the earthworks between the leak and the wall of water have already been compromised by the influx of water. It's like the proverbial iceberg, where 90% of the problem is where you can't see it. The water soaks into the earthworks and alters it's solidity, and increases internal pressures. That is what really causes the failure, and leaks are like the symptoms of the disease, not the cause.