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Posted on 12/08/2005 10:09:15 PM PST by caryatid
When the New Orleans Sewerage and Water Board developed a plan in 1981 to improve street drainage by dredging the 17th Street canal to increase capacity for Pump Station No.¤6, residents across the city applauded. Increasingly heavy rains were not only flooding streets, but pushing water into homes. Action was needed. It seemed like a no-brainer.
Today forensic engineers investigating the levee breach that flooded much of city during Hurricane Katrina aren’t so sure. The search for the cause of the failure keeps returning to that dredging project as the probable starting point for a series of mistakes they believe ultimately led to the breach.
[...]
(Excerpt) Read more at nola.com ...
Among other problems, they say, the dredging sharply reduced the distance water had to travel to reach the canal wall; left the canal too deep for existing sheet pilings that were suppose to cut off seepage; may have removed some layers of clay that sealed the canal bottom; and reduced support for the wall on the New Orleans side.
Investigators believe the storm surge water pushed into the canal from Katrina seeped through porous soils under the floodwall, causing the earth to shift and taking the wall with it.
“The more you look at this, the worse it gets,” said J. David Roberts, the University of Missouri-Rolla professor who is an expert on levee failures, and part of the National Science Foundation forensic team. “Dredging is always a prime suspect in these failures. And when you look at this project, the alarm bells go off.”
The dredging was done as part of a joint-venture between the New Orleans Sewerage & Water Board, the Orleans Levee District, and the East Jefferson Levee District. Officials at the time hailed it as a sterling example of cooperation for the public good.
Records show the U.S. Army Corps of Engineers issued permits to the New Orleans Sewerage & Water Board to do the dredging in 1984 and 1992. The corps was not a partner in the project.
Before the project, the canal formed a roughly symmetrical “U” shape common to most canals. In the sections that would later fail during Hurricane Katrina, its average depth was about 12 feet below sea level and, at normal water levels, the Orleans side had about a 20-foot buffer of mud between the water and what was then a bare steel flood wall. That wall of sheet piling ran through the center of the levee to a depth 9.8 feet below sea level.
After the dredging, the bottom was 18.5 feet below sea level, and the canal-side levee had been shaved so narrow, water now touched the wall on the Orleans side. The “U” was now lop-sided and the water in the canal had shorter paths to the outside of the levee.
A review of records maintained by the two levee districts hasn’t yet revealed why more extensive dredging was done on the Orleans side of the canal than on the Jefferson side.
“I’ve never seen a canal profile unbalanced like that, and I can’t account for why it was done that way,” said Bob Bea, a University of California-Berkeley professor and member of the Science Foundation team. “The dredging probably removed some layers of clay that had formed a seal on the canal bottom, exposing the more porous layers of peat to seepage. That’s always a risk you run when you dredge, especially in the soils they were working in.”
Records show those concerns were known to consulting engineers on the project.
In 1982 Eustis Engineering did soil investigations on the canal bottom and levees to determine the impact dredging might have on a stretch of the canal from just south of the Veterans Highway bridges to just north of those structures. In an August report to Metairie-based Modjeski and Masters, identified as the consulting engineers for the project, Eustis found that “the planned improvements to deepen and enlarge the canal may remove the seal that has apparently developed on the bottom and side slopes, thereby allowing a buildup of such pressures in the sand stratum” to cause a failure.
Concerns that a land side “blow-out” of the levee could occur after the dredging in this area were high enough that Eustis recommended a test dredging be done before finalizing design plans. Failing that, it recommended sealing the bottom of the canal with a concrete liner, installing pressure relief wells near the land side toe of the levee, or putting a seepage cutoff wall, such as sheet pilings, to a depth of 65 feet below sea level.
That report has grabbed the attention of investigators because it concerns a section of the canal with soil layers they consider stronger than those found in the section that would fail after Katrina.
“If they were concerned about problems caused by disturbing seals in that section, one would think they would be even more concerned about something like that happening over weaker layers like humus that are found at the breach,” Bea said.
Because the corps has yet to release all documents related to the 17th Street canal project, it is uncertain if similar concerns were voiced about other sections of the canal. The fact that they were not a major issue in documents that have become available, is a troubling puzzle to investigators.
“They seem very concerned about that issue on this section, but they don’t seem to return to it, as far as we can tell,” Rogers said. “That’s another one of those mysteries about this project that concern you.”
The most glaring danger caused by the dredging is also the hardest for an engineer to miss, investigators said: The canal was now much deeper than the sheet pile wall that was supposed to prevent seepage to the land side of the levee.
That problem should have been even more obvious to engineers involved, they said, because it was well known the corps was planning to come in directly after the dredging project and increase the capacity by raising the floodwall from 10 feet to 14.5 feet.
Adding floodwalls to the canal and dredging it deeper without increasing the size of the levees or the support for the floodwall dramatically reduced its factor of safety, Rogers said.
“I can say that categorically; it’s not something (an engineer) can debate,” Rogers said. “You were heightening the levee and not broadening its base. You were increasing the load but not the support. So your factor of safety had to be going down.”
Although the Corps of Engineers was not a direct partner in the dredging project, it was aware of the work and knew it would have an impact on its later project, records show. Documents related to the dredging are incorporated in the corps’ official memorandum on the floodwall project, and the issue of the local work is discussed in some detail by corps engineers during the review phase of its own project.
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So the Atlanteans should move out of Atlantis?
The moonbats claimed it was blown up at the hearings this week. Dyan ex NAACP head for NO.
This is new:
"Concerns that a land side “blow-out” of the levee could occur after the dredging in this area were high enough that Eustis recommended a test dredging be done before finalizing design plans. Failing that, it
recommended sealing the bottom of the canal with a concrete liner, installing pressure relief wells near the land side toe of the levee, or putting a seepage cutoff wall, such as sheet pilings, to a depth of 65 feet
below sea level. "
Previous press releases have detailed design firm recommendations for sheet piles to 35 feet, which the Levee Board ignoed when it let the contracts for 17.5 foot piles before the Corps of Engineers had even inspected the plans.
From this disclosure, it appears that the Orleans Levee Board anf the Sewer and Water District ingored 65 foot tip depth recommendations, let contracts for 17.5 foot piles, and the work actually done only drove them to 10 feet.
This is why I keep repeating that the current government in Louisiana makes it mathematically impossible to fund a rebuilding effort with any chance of success.
As long as they are in office, any money spent will be stolen or bungled away, and no effective reconstruction can occur.
I get the feeling that the locals understand this, but do not see a realistic way to remove the criminal element from their government. If this is the case, I wonder if there is a way by which they could simply bypass the local and state government and directly request the feds to take charge?
I get the feeling that the locals understand this, but do not see a realistic way to remove the criminal element from their government. If this is the case, I wonder if there is a way by which they could simply bypass the local and state government and directly request the feds to take charge?
---You bring up a good point. I wish someone could take over like the Feds and put those people out of office.
That may be the only solution. Hurricane Katrina has proven that the rampant criminalty in government has dire consequences ... many lives were lost because of it. Something must be done.
If people want to live in NOLA I have no problem with that. I just object to federal tax dollars paying for the privilege or the whining when there is a flood.
----Where in my post did you read that?
My post:You bring up a good point. I wish someone could take over like the Feds and put those people out of office
and it was to jeffers. I said nothing about whining or asking for federal tax dollars.
Some people think the feds should take over. I do not. I think, just like the property owners of my community pay for canal and seawall maintanance, the people of NOLA should be responsible. They should be responsible for the engineering and the cost. If they CHOOSE to hire the CofE then the citizens are responsible.
I say keep the feds and federal money out of it.
I think most people will realize that most of NOLA is not worth it.
Rec: "Basic Economics: Thomas Sowell"
But....but....I thought it was all the Army Corps of Engineers fault.
No, don't you remember it was Bush's fault. He blew up the levee don't ya know.
Thanks for sharing your opinion with the thread. Have a great day.
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