Keeping the Waters at Bay
There's no shortage of ideas on how to protect the Crescent City. But ideas are the easy part
Orleans Ave. Canal; London Ave. Canal; Outfall canals; Lake Pontchartrain ; Causeway
WHERE ALL THE WATER CAME FROM
As Hurricane Katrina hammered the Louisiana coast, it caused flooding in two major ways:
1 Water blown from Lake Borgne converged with the Intercoastal Waterway and the Mississippi River-Gulf Outlet, creating an amplified storm surge pushing west to the Industrial Canal and into surrounding neighborhoods.
2 Later, as Katrina passed east of the city, winds forced water to the southern shore of Lake Pontchartrain, shooting a surge of water into the three outfall, or drainage, canals.
[map labels]
Undamaged levees; Damaged levees; Mississippi River; Intercoastal Waterway Superdome; Garden District; French Quarter Storm surge; Storm surge; Storm surge; Lake Pontchartrain; Storm surge; Storm surge; Storm surge; Storm surge; Storm surge; Lake Borgne; Mississippi River-Gulf Outlet(MR-GO)
LENGTHY SURGE STOPPER
One long-term proposal: a system of levees, floodgates, and locks along Route 90 to help protect the 1.4 million residents around Lake Pontchartrain.
KATRINA FLOOD LEVELS
0-2 feet2-4 feet4-6 feet6-8 feet8-10 feet17th Street Canal10+ feet
Downtown New Orleans; Lakeview; Lower Ninth Ward; Industrial Canal; (also called Inner Harbor Navigation Canal)
Water pumped out of canal; PumpsGate closes to stop storm surge; Interim outfall canal pump and gate;
IMMEDIATE PLAN
Task Force Guardian; Floodwall repair/replacement; Levee repair; Minor amount of levee armoring (only where Katrina overtopping was severe)
Interim gated structures for outfall canals; Scheduled completion: June 1, 2006
IMMEDIATE PLAN
Damaged levee/floodwall; Task Force Hope Upgrading New Orleans's protection
LONG-TERM
More-ambitious levee armoring to prevent erosion due to overtopping
Floodwall redesign; Permanent gated structuresfor outfall canals
Starting the process of coastal wetlands restoration; Channel control
LONG-TERM PLANS
Close the Mississippi River-Gulf Outlet, or keep it open for shipping? One long-term solution might be a floating flood control gate, which could keep a shipping lane open yet could close to block a storm's surge.
The wetlands factor
LONG-TERM PLANS
Hurricanes Katrina and Rita transformed about 100 square miles of Louisiana's marsh to open water, according to initial U.S. Geological Survey estimates. There's widespread agreement that restoring the wetlands will provide an essential natural buffer to future storm surges and that this endeavor-however expensive-must be part of any long-term solution. Lost wetlands: 1,900 square miles (1937-2000) Levee and floodwall repair/upgrades
IMMEDIATE AND LONG-TERM PLANSTASK FORCE GUARDIAN
Levees repaired to pre-Katrina height of 15 feet. Levees with the worst overtopping damage could be reinforced with riprap or concrete, called "armoring."
TASK FORCE HOPE
Proposals include: More-extensive armoring of the leveesArmoring with: riprap or concrete Floodwall Levee River or canal
Overtopping
LAKE BORGNE'S PROPOSED LEAKY LEVEE
To blunt storm surges from Lake Borgne, a "leaky levee" skirting the western shore of the lake might be built. Its openings allowing the free flow of water and marine life would be closed during a storm.
Floating gate; Construction in progress; Undamaged levee/floodwall; Leaky levee; Proposed flood control gate; Proposed flood control gate; Proposed flood control gate; Proposed flood control gate; Erosion
Sources: U.S. Army Corps of Engineers; Bring New Orleans Back Commission; USGS; Louisiana Department of Natural Resources
GRAPHIC BY STEPHEN ROUNTREE AND ROB CADY-USN&WR
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