WASHINGTON, DC--There's no doubt that Hurricane Katrina walloped New Orleans. And the strength of the category 4 storm has been blamed for the failure of many of the city's levees. But at a Senate hearing today, a hurricane expert said that some of the levees failed in response to much weaker parts of the storm. Other testimony from engineers delved into construction problems with the levees.
New Orleans's levees were designed to withstand category 3 storms, and eastern areas of the city were inundated as storm surge equivalent to a category 4 flowed right over their protective levees. But thousands of homes in the western part of the city were affected as water breached the levees without flowing over them. Louisiana State University hurricane expert Ivor van Heerden said that models and gauges showed that winds driving water toward this part of the city were much weaker than those of a category 3 hurricane. According to van Heerden and experts representing two other academic teams, the new findings suggest that levees failed before the surge reached its highest point in those areas, underscoring how poorly the system performed.
"If the levees had done what they were designed to do, a lot of the flooding would not have happened," said University of California, Berkeley, civil engineer Raymond Seed, who led a National Science Foundation-funded team in New Orleans to study the problem last month. Another team from the American Society of Civil Engineers contributed to the 129-page joint report.
Studies of the levees at the 17th Street canal, for example, suggest that the water rose only to 1 to 1.5 meters below the tops of the levees. Scientists said today that peat and clay layers beneath the levees might have allowed water to flow below metal pilings or been so weak as to allow the water to simply plow back the raised levee embankments. The London Avenue canal showed evidence of underseepage and tipped levees. Another problem was that junctions between sections of the levees were easily breached, with little leaks quickly cascading into major failures. Levees along the lake, by contrast, performed well as water surged elsewhere in the canals, bolstered by strong foundations.
The Army Corps of Engineers, which designed and built most of the levees, would not comment on conclusions. The corps is studying the problem and plans to publicly release its study in June of next year. Carol Sanders, a spokesperson for the corps, said that soil composition was a possible factor for some breaches. But, she noted, "we don't know what the surge was. ... We have to collect a lot more data."