John Howell’s column

Published 12:00 am Tuesday, May 3, 2011

Flood waters threaten from Panola to NOLA

During these weeks of violent and wet weather that have passed through north Mississippi, New Orleans has been windy and dry. Warm, moist air has been rushed north from the Gulf headlong into the waves of cool air coming down from the north.

We were close to a couple of those collisions of hot and cold last week in Panola County. Fortunately we were spared the violence of that conflict that we saw further east and in Alabama.

Meanwhile, our attention has turned to flooding on the Mississippi River and its tributaries, especially local tributaries including the Coldwater River. Another long train of thunderstorms marching across the Mississippi and Ohio valleys on Monday threatens to bring more rain for already saturated watersheds.

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River forecasters are predicting a crest at 45.0 feet for Memphis on May 10, 11 feet above 34-foot flood stage. That’s compared to 48.7 feet during the 1937 flood, 45.8 feet in 1927 and 40.5 feet in 1950 and 1973.

Crests downriver are forecast at 60 feet for Greenville (48-foot flood stage) on May 15, 53.5 feet for Vicksburg (43-foot flood stage) on May 18 and 60 feet for Natchez (48-foot flood stage) on May 20.

The crest forecast for New Orleans on May 22 is 17 feet, which is the flood stage for the city. However, levees are believed to protect the city to 20 feet. That assumes opening the Bonnet Carre spillway upriver from New Orleans to divert the river’s floodwaters into Lake Pontchartrain, sending them around the city, through the lake and then to the Gulf through the Rigolets T.

But floodwaters don’t always behave as predicted. In 1973, the Old River Control Structure at the divergence of the Mississippi and Atchafalaya Rivers was weakened and threatened to allow waters from the Mississippi to flow to the Gulf through the Atchafalaya River basin. Given that the path to the Gulf is shorter and increasingly steeper through the Atchafalaya route, that’s what the water wants to do. The control structure completed in 1963 diverts 30 percent of the Mississippi’s water into the Atchafalaya basin and forces 70 percent of the water to continue down the traditional route of Mississippi by Baton Rouge and New Orleans.

Without that, those mighty river ports could become backwaters.