Flooding will only get worse
Wednesday August 31, 2005
Mark Schleifstein
Staff writer
The catastrophic flooding that filled the bowl that is New Orleans on Monday and Tuesday will only get worse over the next few days because rainfall from Hurricane Katrina continues to flow into Lake Pontchartrain from north shore rivers and streams, and east winds and a 17.5-foot storm crest on the Pearl River block the outflow water through the Rigolets and Chef Menteur Pass.
The lake is normally 1 foot above sea level, while the city of New Orleans is an average of 6 feet below sea level. But a combination of storm surge and rainfall from Katrina have raised the lake's surface to 6 feet above sea level, or more.
All of that water moving from the lake has found several holes in the lake's banks - all pouring into New Orleans. Water that crossed St. Charles Parish in an area where the lakefront levee has not yet been completed, and that backed up from the lake in Jefferson Parish canals, is funneling into Kenner and Metairie.
A 500-yard and growing breach in the eastern wall of the 17th Street Canal separating New Orleans from Metairie is pouring hundreds of thousands of gallons of lake water per second into the New Orleans area. Water also is flowing through two more levee breaches along the Industrial Canal, which created a Hurricane Betsy-on-steroids flood in the Lower 9th Ward on Monday that is now spreading south into the French Quarter and other parts of the city.
New Orleans Mayor Ray Nagin warned Tuesday evening that an attempt to plug the holes in the 17th Street Canal had failed, and the floodwaters were expected to continue to rise rapidly throughout the night. Eventually, Nagin said, the water could reach as high as 3 feet above sea level, meaning it could rise to 12 to 15 feet high in some parts of the city.
Louisiana State University Hurricane Center researcher Ivor van Heerden warned that Nagin's estimates could be too low because the lake water won't fall quickly during the next few days.
"We don't have the weather conditions to drive the water out of Lake Pontchartrain, and at the same time, all the rivers on the north shore are in flood," he said. "That water is just going to keep rising in the city until it's equal to the level of the lake.
"Unless they can use sandbags to compartmentalize the flooded areas, the water in the city will rise everywhere to the same level as the lake."
This isn't the first time that the 17th Street Canal has proved to be a hurricane-flooding Achilles heel. Following a 1947 hurricane that made a direct hit on New Orleans and Metairie, officials were unable to clear floodwaters from Metairie through the canal for two weeks.
Sewage from a treatment plant that stagnated in the canal created enough sulfuric acid fumes that nearby homes in Lakeview painted with lead-based paint turned black.
The slow-motion flooding of the south shore mirrors a similar flooding event during Tropical Storm Isidore, when weather conditions blocked water from leaving the lake as heavy rainfall pushed its surface higher and higher, causing extensive flooding in low-lying areas of Slidell a day after the storm had passed by.
Van Heerden said water flowing through New Orleans. back door used a weakness that he and many others have been concerned about for years: a V-shaped funnel formed by the joining of the Mississippi River-Gulf Outlet and the Inner Harbor Navigation Channel. Storm surge as high as 18 feet pushed through the funnel, into the Industrial Canal and on to the lake. It's that surge water that is thought to have caused breaks in the Industrial Canal levees breaks that lake water is now flowing through into the 9th Ward.
Water entering that funnel also is thought to have topped levees surrounding Chalmette and eastern New Orleans, causing extensive flooding in both places.
Van Heerden said that if there's a silver lining to this disastrous event, it's that the eye of Katrina didn't go directly over or to the west of the city. If that had happened, the storm surge could have been much higher and would have directly topped levees all along the lake and much more rapidly filled the bowl, which would have meant an even higher death toll than is anticipated from this slow-moving event, he said.
This flood event contains many of the features used by federal, state and local planners early this year to begin shaping what was supposed to be a catastrophe recovery plan for New Orleans: failed pumping stations, breached levees, rooftop rescues, makeshift medical triage zones.
In drawing the plan, officials assumed that it would take several days to a week before enough manpower and equipment could be staged to deal with many of the problems they're facing now, such as how to close the breach in the 17th Street Canal.
There, the problem is how to close the hole quickly. Strategies suggested during tabletop exercises indicated it could take several days to position barges and cranes in place to more permanently fill such a gap, assuming it was part of the worst-case, storm-surge-driven flooding scenario.
The slow-motion reality of the collapsing canal wall has the state Department of Transportation and Development and the Army Corps of Engineers working into the night to plug the breach and try to stem the flooding in Lakeview, West End, Bucktown and large swaths of East Jefferson.
A convoy of trucks carrying 108 15,000-pound concrete barriers - like those used as highway construction dividers - was en route to the site Tuesday night, said Mark Lambert, chief spokesman for the agency. Helicopters will lift the barriers above the hole and drop them in place, even as another 50 sandbags, each weighing 3,000 pounds, are also being maneuvered into place.
"That's 800 tons of concrete," Lambert said. .What we are trying to do is just stop the water from going into the city."
More difficult will be the overtopping of levees along the Industrial Canal caused by the high lake water flowing in. Lambert didn't say how the state would address that problem.
The problems caused by floodwaters will only get worse, according to van Heerden and the earlier tabletop exercises. For one, if the water in the city does rise to the height of levees along the lakefront, it may be difficult to open floodgates designed to keep the lake out that would now be needed to allow the lake to leave. Van Heerden said the rising floodwaters also would cause major pollution problems in coming days, as they float dozens of fuel and chemical storage tanks off their fittings, severing pipelines and allowing the material to seep into the floodwaters.
"In our surveys of the parish, a lot of the storage tanks we looked at weren't bolted down with big bolts," he said. "They rely on gravity to hold them down. If an industrial property is 5 feet below sea level and the water gets to 5 feet above sea level, that's 10 feet of water, and I'm certain many we looked at will float free.
"You'll see a lot of highly volatile stuff on the surface, and one spark and we'll have a major fire," he said.