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New Orleans levee report blames Army Corps

By: Dr. Jeff Masters, 3:37 PM GMT on March 23, 2007

The Army Corps of Engineers is largely to blame for the disastrous flooding of New Orleans during Hurricane Katrina, according to a 475-page report commissioned by the state Department of Transportation and Development that was released Wednesday. The five major findings of the report by "Team Louisiana":

Figure 1. Team Louisiana researchers discuss forensic developments at a section of the 17th Street Canal breach. Image credit: Team Louisiana.

1) The Army Corps failed to follow the 1965 Congressional mandate to protect against the "most severe combination of meteorological conditions reasonably expected." This mandate specified a "1 in 100 year storm" that the New Orleans levee system must protect against, which was set as a Category 2 hurricane with winds of 107 mph. In 1972, the National Weather Service adjusted the expected "1 in 100 year storm" to be a Category 3 hurricane with 129 mph winds. This was adjusted again in 1979 to a Category 4 hurricane with 140 mph winds. The Army Corp never revised their protection plans based on these new estimates, despite their mandate to do so and their awareness of the requirement to do so.

2) The New Orleans levees were built 1-2 feet too low, because the Army Corps used elevation estimates taken in 1929 to design the levees. The city has sunk over the years, and was already 1.3-1.6 feet lower than the 1929 elevation estimates in 1965 when the levee system was designed. Continued subsidence of the land resulted in levees that were up to five feet too low when Katrina struck. The Corps was aware of the subsidence issue, but did not correct for it. The levees being too low caused many of the failures that flooded New Orleans, the report asserts: Crown elevation deficiencies ranging up to 5 feet at the time Katrina struck resulted in prolonged overtopping of floodwalls and levees along the Inner Harbor Navigation Canal (IHNC) and to the east in the Lake Borgne funnel that otherwise would have been overtopped only briefly. Prolonged overtopping led to catastrophic breaches into the Lower 9th Ward on the east and into Orleans Metro on the west, and contributed to the early failures of levees along the Gulf Intracoastal Waterway (GIWW)and MRGO. Early failure of the MRGO levee allowed the 32,000 acre wetland buffer between MRGO and 40 Arpent back levee to fill and overtop the 40 Arpent back levee while the surge was still rising, and resulted in catastrophic flooding in St.Bernard to an elevation of 11 ft.

3) The Army Corp did not follow existing engineering practice and guidance for construction of levees and floodwalls.

4) The free-flowing deep draft navigation channel on the east side (MRGO and GIWW channels) compromised system performance.

5) The levee system was "managed like a circa 1965 flood control museum", and was not maintained or upgraded properly.

The Army Corps yesterday issued a press release defending themselves, saying that all levels of government were involved in the poor decision making for New Orleans' levees, and the Corps should not be singled out for their failures. Regardless, the release of the Team Louisiana report will bolster the legal efforts to sue the Army Corps for damages from Katrina. These claims are currently at $400 billion and growing, including a claim of $77 billion from the city of New Orleans, and $200 billion from the state of Louisiana.

Next week, I plan to post a review of the Hurricane Katrina book by Team Louisiana's leader, Dr. Ivor van Heerden of Louisiana State University: The Storm: What went wrong and why during Hurricane Katrina--the inside story from one Louisiana scientist.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.