Workers from the Army Corps of Engineers finish the last part of the new flood wall at the 17th Street Canal in New Orleans, La., on July 2, 2007.
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Now the Gulf has advanced some 20 miles (32 km) inland, thanks in large part to the Army Corps. The Corps started as a Revolutionary War regiment, fortifying Bunker Hill, but it evolved into an all-purpose engineering unit, eventually overseeing local flood control on the Mississippi. The Corps ordered communities to imprison the river in a narrow channel with a strict "levees only" policy, rejecting calls to give the river room to spread out. So levees rose, and the Corps repeatedly declared the river floodproof. But the constrained river also rose, and its jailbreaks repeatedly proved the Corps wrong. In the epic flood of 1927, crevasses shredded the entire valley and nearly destroyed New Orleans.
Congress rewarded this failure by allowing the Corps to seize control of the entire river and its tributaries, an unprecedented Big Government project that foreshadowed the New Deal and established the Corps as the U.S.'s manipulator of water and manhandler of nature. It built dams, floodways, revetments and pumped-up levees throughout the Mississippi basin, caging the beast in its channel, safeguarding riverfront cities, creating a reliable web of liquid highways. But by walling off the river, trapping its sediments behind giant dams and armoring its erosive banks with concrete, the Corps inadvertently choked off the land-building process. The straitjacketed river now carries less than half its original sediment load down to Louisiana. So there's little new land-building material to offset the natural erosion of the coast, much less the unnatural rising of the sea fueled by global warming.
The result is that New Orleans is sinking, and about 30% of the coast's wetlands have slipped into the Gulf, jutting Louisiana's chin even further into the path of Mother Nature's fist, endangering the U.S.'s largest offshore oil and gas fields, a lucrative seafood industry, a busy network of ports and about 2 million people. If Mexico had seized all that land, we'd be at war. lsu hydraulic engineer Hassan Mashriqui says just 100 yds. (91 m) of cypress trees can reduce wave energy 95%; he has seen a similar phenomenon with mangroves in his native Bangladesh. Katrina and then Hurricane Rita confirmed that marshes knock down surges as well. "Basically, we found that none of the levees that failed were protected by wetlands or trees," Mashriqui says.
Oil and gas canals have accelerated the land losses. But so have Corps navigation canals, especially the notorious Mississippi River Gulf Outlet, a shipping shortcut to the Port of New Orleans that was a larger dirt-moving project than the Panama Canal when it opened in 1965. The canal never carried many ships, but it has carried plenty of saltwater into freshwater marshes and cypress forests, killing nearly 100 sq. mi. (259 sq km) of wetlands. Shortly before Katrina, Mashriqui called it a "critical and fundamental flaw" in New Orleans' defenses; after Katrina, his modeling found that the outlet boosted Katrina's surge 2 ft. (0.6 m) and increased its velocity 10-fold, overwhelming St. Bernard Parish and the Lower Ninth Ward. "This was a disaster created by the Corps," Mashriqui says.