One River, Two Floods

June 3, 2011 5:45 AM

Mary Ann Travis

Levees and spillways designed to protect New Orleans from Mississippi River flooding worked as they were designed to work this spring. That’s good news in the short run. “But we have to keep in mind that we have one river and two floods,” says Mark Davis, director of the Tulane School of Law Institute for Water Resources Law and Policy.

river fishing

The swollen Mississippi River recently crested at 17 feet in New Orleans. (Photo by Paula Burch-Celentano)

The 20-foot-high levees holding back the river throughout the city had 3 feet to spare when the river crested at 17 feet in New Orleans last week. But it wasn’t the levees alone that kept water from inundating the city. It was the diversion of the floodwater upriver into the Atchafalaya River Basin and Lake Pontchartrain through the Bonnet Carre and Morganza spillways.

River flooding is an occasional crisis and a fact of life in south Louisiana. It also is what naturally built the land of coastal Louisiana during the past 7,000 years. During times of high water, the river would leave its channel and spread out sediments, nutrients and fresh water, nourishing marshes and swamps.

But the extensive levee system constructed during the past hundred years to prevent flooding in populated areas has walled the river off from the coastal plain and contributed to the other flood — coastal flooding — confronting south Louisiana.

“Ironically, coastal flooding is caused substantially because of the absence of the river,” says Davis.

Coastal flooding — chronic and everyday — is worsening. “Time is not our friend,” says Davis.

But something can be done. The coast can be restored using the cycles and rhythms of the river. Rather than funneling sediment and fresh water out into the Gulf of Mexico, as it is now, controlled flooding in low-lying areas and mechanical devices such as pumps and dredges can build up the land, Davis says.

“We’re the generation that has to make this commitment, or we’re the generation that loses,” he says.

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Tulane University, New Orleans, LA 70118 504-865-5000