U'S' Army Corps of Engineers photo by Alan Dooley

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Stephen A. Nelson Dept. Earth Environmental
Sciences Tulane University
U.S. Army Corps of Engineers photo by Alan Dooley
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Estimated Flood Depths (NOAA and USACE)
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Breaches on East Side of Industrial Canal
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Barge
Floodwall Panels
Sheet Pile
Industrial Canal
Breach Repair
Photo - L. Harder
Industrial Canal South Breach - After - Lower 9th
Ward Destroyed. Floodwall and sheet piling strewn
into Lower 9th Ward
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Sinkhole on inboard side of distressed floodwall
on Industrial Canal view looking south
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Photo - IPET
Trenching at base of floodwall on outboard side
indicates overtopping of floodwall - view
looking north.
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Industrial Canal Levee Failure
Elevation (feet - relative to sea level)
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Breach on London Ave. Canal near Mirabeau Ave.
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No trenches at base of floodwall - floodwalls
were not overtopped!
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Photo - FEMA
As flood water dropped sand deposits were revealed
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Why so much sand?
Sand Ridges in back yards along London Ave Canal
Sand deposits showing cross-beds along Warrington
Drive
Depostied cars in front of house along London
Ave. Canal
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Seepage Piping at London Ave. Canal South Breach
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Breach on London Ave. Canal near Robert E. Lee
Blvd.
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Photo - USACE IPET
View looking east across north breach of London
Ave. Canal
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Sand Deposits here too!!
Peat
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Floodwall
Levee
Club house in back yard of Pratt Drive home -
before Katrina
After Katrina
Photos - Daniel Cantrell
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Heaving at London Ave. Canal North Breach
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Breach on 17th St. Canal
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17th St. Canal Breach - View looking toward south
U.S. Army Corps of Engineers photo
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A chain is only as strong as its weakest link!
Strength
Factor of Safety, F Corps of Engineers uses a
Factor of Safety of 1.3
Expected Force
That means if F gt 1, the strength is greater than
the expected force acting on the levee. A
Factor of Safety of 1.3, means that the levee is
only 30 stronger than the expected force acting
on it. If F lt 1, then the strength is less than
the expected force acting on the levee. That
means that when that force is acting, the levee
will fail because it is not strong enough.
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Values used by Corps to calculate Factor of
Safety
From http//www.dotd.louisiana.gov/administration
/TeamLouisiana/
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Assume Calculated Factor of Safety is 1.3 for
this point
From http//www.dotd.louisiana.gov/administration
/TeamLouisiana/
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Assume Calculated Factor of Safety is 1.3 for
this point
Then, with the same force acting, the Factor of
Safety for this point (based on the real
strength) is only 0.46
From http//www.dotd.louisiana.gov/administration
/TeamLouisiana/
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Failure of the 17th St. Canal Levee Floodwall
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Why did the canal levees fail?
Contributing Factors
1. Storm Surge - increased pressure on bottom of
canal on levees floodwalls 2. Weak Materials
- Permeable Sands Peat Weak Clays 3. Trees
uprooted by hurricane force winds 4. No armoring
of tops of levees to prevent erosion after
overtopping 5. Poor design of levees
floodwalls - did not consider all of the
above! (I walls instead of T-walls, Low Factor
of Safety, Short sheet pilings, not enough
consideration of complex and variable geological
environment)
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What could have prevented the failures?
Mitigation of Contributing Factors

• 1. Storm Surge - Keep the Storm Surge Out of the
  Canals
• Gates at the mouth of Canals on Lake
  Pontchartrain
• Pumps at Lake to pump water over Lakefront
  levees
• Weak Materials
• Drive sheet pilings deep enough to cut off
  possible
• seepage to outboard side of canals
• Use T-walls instead of I-walls
• Trees uprooted by hurricane force winds
• Dont allow trees with roots that may penetrate
  levees
• remove existing trees
• No armoring of levees to prevent erosion after
  overtopping
• Armor tops of levees to prevent erosion
• Poor design of levees floodwalls - did not
  consider all of the above!
• Better oversight of design construction of
  protection systems

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Contour map of breach area based on soundings
acquired on Sept. 1, 2005 Estimated Volume of
scour - 365,500 ft3 Estimated Volume of
Sandy Splay Deposit 932,000 ft3 Scour hole
can only account for 39 of volume of sand
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Photo - L. Wooten
Photo - L. Harder
Mississippi River - Gulf Outlet Levees Breached
and eroded after overtopping. Levees made of
easily erodable spoil dredged from the shipping
channel. No armoring to prevent erosion
Photo - L. Harder
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Erosion trenches along Lake Pontchartrain
floodwall, Hayne Blvd. Eastern New Orleans
Floodwalls near Lakefront Airport were clearly
overtopped but did not fail.