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Natural and Unnatural Disasters

Reflections on a city made possible and made vulnerable by reliance on technology

Brian Hayes

The Next One

As New Orleans and the other stricken communities of the Gulf Coast begin rebuilding, they will doubtless give much thought to protecting themselves from the next big storm. Levees and flood walls will be strengthened, perhaps the plan to install storm gates at the entrances to Lake Pontchartrain will be revived, and work to restore coastal wetlands may finally win funding. Protective measures for the beachfront communities of the Mississippi coast are harder to engineer, but perhaps this occasion will be taken as an opportunity to move at least some structures farther from the surf zone.

Given the century-long history of "back door" flooding in New Orleans, the Corps of Engineers and other flood-control agencies may well be criticized for devoting too much energy to the Mississippi River while neglecting the hurricane hazard. But in fact the river remains the greatest force of nature in the region. Before Katrina, the worst disaster in Louisiana—and one of the worst in the nation's history—was the Mississippi flood of 1927, in which nearly a million people were forced from their homes. In that case the city of New Orleans was spared—but only by dynamiting a levee downstream, wiping out much of Plaquemines Parish. On the Lower Mississippi, floods of this magnitude can happen only when several major tributaries (the Ohio, the Upper Mississippi, the Missouri, the Arkansas) all rise at once. Such an unfortunate coincidence is rare, but eventually it is bound to happen again.

Ironically, New Orleans also faces the contrary risk: being left high and dry. Two hundred miles upstream, the Old River Control Structure diverts flood waters into the Atchafalaya River, but the gates and weirs there have another purpose as well: They are intended to prevent the Atchafalaya from "capturing" the entire flow of the Mississippi, leaving New Orleans and Baton Rouge stranded on a stagnant backwater. The Atchafalaya takes a shorter and steeper route to the Gulf, and so physics is on its side. In 1973 the Control Structure was nearly washed away; if it had failed, the outlet of the Mississippi would now be at Morgan City—except that Morgan City would also have been washed away. Following that close call, the Corps of Engineers added another complex of gates at Old River. It is a great mass of concrete and steel, and yet it looks delicate enough when you reflect that whole cities depend on this structure for their wellbeing and maybe their existence.

© Brian Hayes

Editor's note: Brian Hayes, whose "Computing Science" customarily appears in this space, became acquainted with flood control on the Mississippi while writing his just-published book Infrastructure: A Field Guide to the Industrial Landscape (W. W. Norton). After Hurricane Katrina struck, we asked him to contribute a short essay on the battered infrastructure of New Orleans. "Computing Science" will return next issue.

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