New Orleans channel may have exacerbated post-Katrina floods

Floods in New Orleans following hurricane Katrina were made worse by a channel dug by a U.S. government agency, according to testimony heard by a federal court. The hearing, in which the government is being sued for allowing the channel to be built, could lead to payouts to hundreds of thousands of flood victims. It may also lead to massive reforms in flood protection.

The evidence comes from the most detailed modeling of Katrina’s storm surge to date. “Science is the most critical factor in this courtroom,” says Pierce O’Donnell, lead attorney for the plaintiffs. “To win the day, one side has to provide the judge with a more compelling scientific case than the other.” The court case is being brought by two residents of the Lower Ninth Ward, a resident and a business in St Bernard’s Parish and one resident of New Orleans East.

New Scientist’s Celeste Biever writes the U.S. government cannot be sued for the failure of flood protection measures. This court case got the go-ahead because it concerns a channel, called the Mississippi River Gulf Outlet (MRGO, or “Mister Go”) dug by the U.S. Army Corps of Engineers (USACE). The channel was built in the 1960s to bring shipping into the city.

That MRGO might exacerbate flooding is not a new concern — it was known as a “hurricane highway” by many residents of New Orleans. Shortly after Katrina struck in 2005, a computer model run by coastal ecologist Paul Kemp, then at Louisiana State University, and colleagues indicated that MRGO combined with another waterway to create a V-shaped trap that funneled Katrina’s storm surge, causing the levees to be overtopped and breached. Other reports, however, have concluded that this funnel effect made a minimal contribution to flooding compared to the other dynamics of the hurricane.

Another factor is that vegetation and marshes were lost when MRGO was built. The channel’s construction sliced through fresh water marshes and destroyed trees and other vegetation that coastal scientists claim would have otherwise provided a key natural barrier against Katrina’s surge. Others say the effect of such vegetation in mitigating a storm surge is still poorly understood.

Biever writes that since then, Kemp and other researchers have created an improved model which accurately simulated the timing of the flooding and levee breaches, as well as the magnitude. They claim it provides the best estimates yet of storm surge, waves and currents during Katrina. They plugged their storm figures into the new model, which was similar to the original except MRGO was filled in with marshes and vegetation known to have been there before 1958. “We wanted to see what Katrina looked like with a GO and without a GO,” says Robert Bea of the University of California, Berkeley, who was part of the team.

The results showed that without MRGO, the storm surge which battered levees protecting the neighborhoods concerned in the court case led to fewer breaches and less overtopping. In the model, flooding of the plaintiffs’ properties was reduced by almost 9 feet. In St Bernard’s Parish, flooding was reduced from 11.5 feet to 3 feet in plaintiff Tanya Smith’s home, and from 10 feet to 5 feet at the Lattimore and Associates business. In New Orleans East, it was reduced from 9.5 to 2 feet. In the Lower Ninth Ward, it was reduced from 11 feet to 3 feet in the home of Anthony and Lucille Franz. “We have shown that MRGO spelled the difference between survivable flooding and catastrophic flooding,” O’Donnell claims.

The team began presenting its evidence on 20 April. “Finally, we are having our day in court,” says Kemp. If the plaintiffs win, others in their neighborhoods should be able to claim damages too. O’Donnell says that more than 200,000 people and groups have already filed such claims.

The USACE, in a brief filed to the court, maintains that “this catastrophe would have occurred regardless of the MRGO and regardless of the way the channel was maintained prior to the flood.”

Many New Orleans residents are convinced that such a court case is long overdue. Oliver Houck, a law professor at Tulane University in New Orleans says: “This opens the door to the government doing what it should have done in the first place — a massive reconciliation and compensation program.”

Other coastal scientists are reserving judgment about MRGO’s role. The decision in the case will rest with district judge Stanwood Duval. “It is fascinating to see what will happen,” says Denise Reed at the University of New Orleans. “In my experience, Duval is a pretty smart guy.”