5 Bold Ideas For A Hurricane-Proof New Orleans

Sea Gates
Hold back storm surges with giant air-filled walls

The History
Katrina's wind-driven waves weakened the levees designed to keep Lake Pontchartrain from spilling into the city eight feet below it. Some 58 billion gallons of water-about 3 percent of the lake's volume-flooded more than three quarters of the city.

Since the 1960s, engineers have considered installing floodgates that would close during hurricanes to prevent a storm surge from backing up into the lake. But the concept was scrapped in 1977 because of concerns that the gates would hinder marine life and nutrients from moving back and forth with the tides.

Similar gates already shield Holland and Britain from violent North Sea storms and tidal surges, and are under construction in Venice. Like New Orleans, Venice lies below sea level, inside a slowly sinking lagoon. By 2011, engineers in Venice will have installed an array of 78 steel-and-concrete barriers at three inlets that separate the lagoon from the Adriatic Sea. Together the string of barriers will span nearly a mile, a distance greater than what would be required to separate New Orleans from the Gulf of Mexico. "I think you could build a solution in New Orleans similar to what we are now building in Venice," says Maria Teresa Brotto, the project's managing engineer.

The Specs
A row of giant sea gates would stretch across each of the two narrow waterways that link Lake Pontchartrain to the Gulf, at Rigolets and Chef Menteur Pass. During fair weather, the hollow gates, which would together span about 3,000 feet, would be filled with water. They would rest flush against the seafloor, where they wouldn't interfere with marine life or tides.

Should a storm approach, compressor pumps would force air into sealed chambers inside the gates, making them buoyant. One side of each hinged gate would be attached to a concrete foundation on the seafloor; the opposite side would rise out of the water.

Alberto Scotti, chief designer of the Venice project, says his sea gates can withstand waves cresting to 16 feet. To fend off a category-5 storm, Louisiana's gates would need to be reinforced to handle winds upward of 160 mph. They would also have to be taller than those in Venice. "We know that Katrina had in some places a 27-foot storm surge," says Susan Jackson, a public affairs officer for the U.S. Army Corps of Engineers New Orleans District.

The Challenge
The hurdle is cost, with estimates ranging from $500 million to more than a billion.

The Status
Army Corps engineers are evaluating several concepts. Preliminary hurricane-protection recommendations
are due by early summer.