GROUP D: Source 1

Excerpt from Travis, John (2005) “Scientists’ Fears Come True as Hurricane Floods New Orleans”, Science 309, 1655-1659.

Because much of the city is below sea level, New Orleans is particularly vulnerable to a storm surge moving through the gulf and into Lake Pontchartrain. Over the past few decades, several computer models have shown how strong hurricanes on the right track could cause massive “overtopping” of the levees that, averaging almost 5 meters high, keep the lake from the city. The National Oceanic and Atmospheric Administration’s (NOAA’s) official storm surge model SLOSH (Sea, Lake, and Overland Surges from Hurricanes) was developed in the late 1960s, and Leuttich and several collaborators have created a more sophisticated model called ADCIRC (Advanced Circulation) that has been adopted by the Army Corps of Engineers and other groups. Last year, in an exercise simulating a direct hit by a slow-moving category 3 hurricane, both models showed that the levees would not prevent the flooding of New Orleans.

According to these models, Katrina’s storm surge should not have submerged the city. Joannes Westerink of the University of Notre Dame in Indiana, who helped develop ADCIRC, says it estimated that the southern shores of Lake Pontchartrain only rose about 3 meters during Katrina. (The various models estimate that the Mississippi coast received a peak storm surge of about 7 to 9 meters, which would be the highest in U.S. history.)

Instead of overtopping, the catastrophic collapse of several levees—ones that had been upgraded with a thick concrete wall—apparently sealed the city’s fate. Stephen Leatherman, director of FIU’s hurricane research center, suggests that the lake’s raised levels may have increased water pressure to the point that water flowed through the earthen levees on which the concrete walls sat. “Then the whole thing collapses. This is how an earthen dam collapses during a flood,” he says.