What happened in New Orleans, and what is being done to stop it from happening again?
On August 29, 2005, Hurricane Katrina hit the Gulf Coast of Louisiana, Mississippi, and Alabama. The devastation in many communities was nearly complete, but parts of one city—New Orleans, much of which lies below sea level—flooded to a depth of 20 feet when breaks occurred in the levee system that surrounds the city, and remained flooded for weeks afterward. Although many communities rely on levees to protect them from nearby waterways, New Orleans was more dependent than most.
Forty-three Days of Unwatering
Larry Banks, a hydraulic engineer and chief of the Watershed Division of the US Army Corps of Engineers' Mississippi Valley Division, was instrumental in the unwatering effort and the initial planning to determine the fastest course of action. "I was on one of the initial flights the day after the storm," he says. "We took a recon and looked at the situation, then went back with a helicopter flight with General Crear [Brigadier General Robert Crear, commander of the corps's Mississippi Valley Division] and laid out a plan to get the water out."
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Banks describes a three-step process to accomplish the unwatering: first allowing some of the water to flow back across the barriers into Lake Pontchartrain by gravity until the water level in the city and the lake equalized, which in places meant enlarging the breaches to let the water flow more quickly; next, closing the breaches; and, finally, getting the waterlogged pumps back into operation and bringing in additional portable pumps to remove the rest of the water. It took 43 days—far less than the three months originally estimated—to drain all but small pockets of water; on October 11 the corps announced that it had removed 224 billion gallons of water from New Orleans. (In the corps's terminology, "unwatering" refers to removing standing water and "dewatering" to removing water below ground.)
In what seemed like a paradox to many watching in the days after the hurricane, crews used backhoes and other equipment mounted on marsh buggies and barges to cut new breaches in floodwalls along Lake Pontchartrain, but the new or enlarged openings allowed water to flow back into the lake. Several methods were then used to attempt to close the breaches. "If we could get to them with large stones or concrete rubble, we attempted to close in that fashion," says Banks. "If we could not get to them with stones, we used large sandbags dropped by helicopters." Sandbags, some as large as 7,000 pounds, were dropped with US Army Chinook and Black Hawk helicopters. Steel sheet piling eventually was used to repair some of the walls and, in the case of the 17th Street Canal, to seal off the mouth of the 200-foot-wide canal from the lake entirely.
Access to the breaches was a problem from the ground as well as from the water. "It was a real nightmare," recalls Banks. "We had barges that were on top of bridges"—washed up by the storm—"that had to be opened up to get river traffic through. We had to manually operate bridges because there was no power source. There were some barges sunk in the channel, so you couldn't get barge loads of large riprap stone to the site, which we'd have done in a normal operation; we'd have just carried barge after barge of stone in there and closed off the breaches with a crane, which would have been the easy way to do it." State transportation workers used tractors, and other equipment was used to create land access to the most critical areas.
Heavy equipment was used to salvage the sunken barges and clear the channel. "There were actually ships—large ocean-going ships—that ended up on top of the Mississippi River levees down in Plaquemines Parish," notes Banks, adding that water also overtopped the river levees in that area. Plaquemines Parish lies between New Orleans and the mouth of the Mississippi River.
The final stage, pumping out the remaining water, presented its share of challenges as well, including the same river access problems for the barges carrying portable pumps. Most of the city's existing pump stations were flooded and inoperable; their wet electric motors had to be dried out. "Pump station number 6, which is at the head of the 17th Street Canal, was the first that came out of the water so that it could be operated within the system right there downtown," says Banks. "We were also operating pump station number 19, which had a diesel generator, so we were able to lower the water in the city enough that we could start getting other pumps online." He describes it as a phased approach: "We used one pump to pump water down enough to be able to put another pump in operation.
"There was a complicating factor in New Orleans in that many of the large pumps use 25-cycle power, not 60-cycle power which is commercially available," he adds. "So the initial pumps that were put online when the power started to come back were 60-cycle pumps, and it took a couple weeks before we could get the 25-cycle power plant, which was also flooded, online." He credits the Sewerage and Water Board of New Orleans with getting the plant online as quickly as possible. The portable pumps that were brought in handled about 10% of the water, and the rest was removed using the city's own pumping stations.
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On September 23, Hurricane Rita caused storm surges that overtopped the temporarily repaired Industrial Canal. "The Ninth Ward went back underwater, as did parts of Saint Bernard Parish," says Banks, "and we had breaches on the west side that started putting water in New Orleans. But since the breach on the west side was near pump station 19, we were able to continue running the pump and recycled that breach water so that it did not have a major impact on the area west of the Industrial Canal."
A major concern early on was the effect of the polluted water that flooded the city, containing raw sewage, household and automotive chemicals of all sorts, and, potentially, chemicals released from oil refineries along the coast, on the waters of Lake Pontchartrain. In an October 14 press release, the Louisiana Department of Environmental Quality (DEQ)—which, along with the US Food and Drug Administration (FDA), the USEPA, and other agencies, had been sampling water from Lake Pontchartrain—reported on the testing to date. Tissue samples of fish and other aquatic animals people would be likely to eat were being sampled at the FDA's labs in Atlanta.
"Based upon the large numbers of samples from the lake and floodwaters and because of the toxicity tests' results, we do not foresee any issues with the fish, crabs, shrimp, or any other animals that need the lake to live," says Mike McDaniel, secretary of the Louisiana DEQ.
A plan to divert some of the water from the flooded city into the Mississippi River, rather than into Lake Pontchartrain, was deemed unnecessary. As Banks describes it, "The water [flowing out of the city] was very close to the same quality that it would have been after just a normal rain in New Orleans." He notes that an oil spill in Saint Bernard Parish resulted from an oil tank that was washed or blown off its foundation, but, he says, the oil company, the Coast Guard, the USEPA, and the Louisiana DEQ all moved to contain the spill. "We did cut the pumps off and did not pump that water out. It would have gone into the wetlands between the Saint Bernard Parish back levee and the Mississippi River Gulf Alley channel. We stopped the pumps, we had good weather, and they were able to skim and recover that oil."
The Role of the Wetlands
Louisiana is losing up to 40 square miles of coastal wetlands per year, and by some estimates the Gulf of Mexico will advance inland more than 30 miles over the next few decades if nothing is done to slow the loss. As this buffer and the ecosystems it contains shrink, the cities and commercial activities near the coast become more vulnerable to hurricanes.
Why are the wetlands disappearing? The Mississippi River drains 40% of the continental US, carrying silt and sediment toward the Gulf of Mexico and, historically, depositing it in the coastal marshes and replenishing the wetland areas constantly being lost to natural erosion and subsidence. The southernmost 50 or so miles of Louisiana were created by this process of sediment deposition. However, the French settlers in the 1720s began building levees—at first only about 3 feet high—to prevent annual flooding from the Mississippi River, and over the last 300 years the building has continued. In 1879, the Mississippi River Commission was formed, under the control of the Army Corps of Engineers and other agencies.
The challenge of maintaining river traffic in this busy port city required the construction and maintenance of navigation channels, and the need to protect the infrastructure led to the building of higher and more levees—more than 2,000 miles of them. Particularly after a major flood in 1927, and again for about 20 years beginning in the 1950s, construction of levees, as well as reservoirs and floodways, increased. The constrained and armored river had less frequent alluvial flooding and could no longer deposit the sediment and nutrients necessary to maintain the wetlands, and erosion and subsidence accelerated. The US Geological Survey (USGS) estimates Louisiana has lost 1.2 million acres of coastal wetlands in the last 100 years.
In a CNN interview just after Katrina made landfall but before the extreme flooding of the city occurred, New Orleans Mayor Ray Nagin acknowledged that coastal erosion is one of the biggest threats to the region and noted that for every acre of coastal wetlands lost, the storm surge from a major hurricane or tropical storm increases by about a foot. The exact relationship is difficult to define, of course, and depends on the intensity of the storm and on the coastal elevation where the storm makes landfall; some figures equate a certain number of linear miles of coastal wetlands, usually about 2 to 4 miles, with each foot of storm surge.
Assessment is ongoing to determine how much lasting damage the wetlands and the barrier islands sustained from 2005's hurricanes. Aerial surveys by the USGS in early September indicated the Chandeleur Island chain had lost half its pre-Katrina land area, although the islands may regenerate with time. Satellite images and USGS assessments show that about 30 square miles of marshland in Breton Sound in Plaquemines Parish were lost, although the losses might not be permanent.
In 1990 Congress approved the Coastal Wetlands Planning, Protection and Restoration Act, which funds wetland enhancement projects nationwide; with 40% of the coastal wetlands in the continental US and 80% of the annual coastal wetlands loss, Louisiana receives the most funding, about $50 million of project money each year.
The Army Corps of Engineers has a 10-year, $2 billion effort ongoing to begin restoring critical areas of coastal wetlands. "Now, specifically the way Katrina hit, I don't know whether this would have done much good or not," comments Banks, noting that the storm approached the city from the east. "But there are many other scenarios where the coastal wetlands restoration project would provide benefits. What we have to do is put all of this together and relook at hurricane protection in concert with coastal wetlands restoration to protect southern Louisiana."
Other programs to evaluate and restore Louisiana's coast include Coast 2050: Toward a Sustainable Coastal Louisiana, a plan that outlines 77 restoration strategies, including restoring historic river flows, and the Louisiana Coastal Area Comprehensive Ecosystem Restoration Study, which looks at how Coast 2050's strategies might be implemented. The cost of construction and implementation to carry out Coast 2050's strategies would be about $14 billion over the next 30 years, but the Louisiana Coastal Area (LCA) is concentrating on a limited number that can be undertaken in the near term, such as beneficial use of dredged materials from channel maintenance and modifying certain existing flood control structures. The LCA's study is available at www.lca.gov.
Author's Bio: Janice Kaspersen is the editor of Erosion Control magazine and Stormwater magazine.