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Hurricane & Storm Damage Risk
Reduction |
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Outfall Canals and Closure Structures
Outfall Canals
During hurricanes and tropical storms, three outfall canals drain water from portions of New Orleans northward into Lake Pontchartrain. These outfall canals are critical elements in New Orleans’ flood control system. Levees line the sides of the canals, and floodwalls are situated on the top of each levee. See an animated video about the outfall canals here. |
The 17th Street Canal extends 2.4 miles north from Pump Station #6 to Lake Pontchartrain along the boundary between Orleans and Jefferson Parishes. Hurricane Katrina caused a 455-foot breach in the floodwall along the east side of the canal, resulting in flooding of the Lakeview area and parts of Metairie in neighboring Jefferson Parish.
The Orleans Avenue Canal, between the 17th Street and London Avenue Canals, runs from Pump Station #7 to Lake Pontchartrain.
The London Avenue Canal runs three miles from Pump Station #3 to Lake Pontchartrain. Failure of floodwalls on both sides of the London Avenue Canal contributed to the flooding of the Gentilly area in New Orleans.
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New Orleans Outfall Canals |
During Hurricane Katrina, breaches occurred at the 17th Street and London Avenue Canals when water and waves pushing against the outside (water side) of the floodwalls (I-walls) caused the walls to shift, essentially splitting each levee into two pieces. Material on the protected side of the levee was unable to withstand the pressure from the forces opposite the floodwall and gave way, allowing water, intensified by the force of the waves, to spill into the protected areas.
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The Corps repaired and improved all three canals was improved beyond pre-Katrina risk reduction levels before the start of the 2006 hurricane season.
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Reinforced T-walls featuring deep, cross-braced support beams for stability have replaced canal I-walls in the areas of the breaches. The new walls are inverted T-shapes, concrete structures with steel sheet pile driven 55-65 feet below sea level down into the foundation soil and three rows of steel beams driven diagonally down to varying depths of 75-130 feet below sea level. In some areas, armoring or stone lines the canals’ inner banks to further reduce the effects of increased water pressure.
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Pre-Katrina: I-walls |
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Post-Katrina: T-walls |
Closure Structures
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To prevent storm surge from entering the canal, a gated steel closure structure was built at the Lake Pontchartrain entrance to each canal. The gated structures stay open during normal conditions. When storm surge threatens to exceed the safe water level in a canal, the Corps closes the gates and turns on the pumps. Pumps push rainwater around the closed gates and into Lake Pontchartrain. The closed gates prevent surge from entering the canals and going back into the city. When the surge recedes, the Corps reopens the gates and normal drainage resumes. These gated structures are considered “interim protection.” Permanent structures will replace them in the near future. Interim structures were necessary to provide risk reduction in time for the 2006 hurricane season. |
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