Snow melting from heavy winter storms up north is not expected to cause major flooding along the Mississippi and Atchafalaya rivers in Louisiana, but forecasters say it’s too early to predict the impact of any intense rains that might hit the river system this spring.
Melting snow can push up river levels down South, but the big snowstorms that made the news this winter were mainly in the Northeast, in areas that do not drain into the Mississippi River, said Jeff Graschel, a hydrologist with the National Weather Service’s forecast center for the lower Mississippi River.
“All that stuff goes off the East Coast and does not impact us,” he said.
In the Ohio River Valley, the source of much of the water in the Mississippi River, snowfall was not exceptional this winter, he said.
That being said, the Mississippi River and the Atchafalaya River, which is fed by the Mississippi, will swell in the coming weeks, pushed up by a combination of melting snow and heavy rainfall in the Tennessee and Ohio river valleys.
“We are expecting a pretty good rise in the Mississippi River,” Graschel said.
The National Weather Service released a long-range forecast Friday that estimated the crest for the Mississippi River in Baton Rouge at 35.5 feet on March 30.
That’s up from about 27 feet as of Friday but far below the 45-foot crest in Baton Rouge during the last major flood in May 2011.
In New Orleans, the Mississippi is forecast to crest at 14 feet on March 31 at the Carrollton Gauge, up from 9 feet on Friday. Floodwalls are designed to hold back the water at levels up to 20 feet.
When the river reaches 11 feet at the Carrollton Gauge, the U.S. Army Corps of Engineers begins weekly levee inspections to identify potential problem areas and starts requiring waivers for excavations, pile driving and other subsurface work within 1,500 feet of a levee, said Corps spokesman Ricky Boyett.
At 15 feet, the Corps begins daily levee inspections and prohibits all subsurface work within 1,500 feet of the levee, he said.
The National Weather Service forecast released on Friday does not consider rainfall beyond 24 hours, so a major storm in the coming weeks could push river levels higher.
The Mississippi and Atchafalaya rivers rose to historic levels in 2011, prompting the Corps to open the Morganza Control Structure north of Baton Rouge for the first time since 1973. It takes pressure off the Mississippi by diverting water into the Atchafalaya Basin.
The peak levels on the Mississippi River in Louisiana are usually seen from March to May, Graschel said, and whether the state will see significant high water this year depends on how much rain falls and where.
“It’s still too early to say where our high will be,” he said.
Follow Richard Burgess on Twitter, @rbb100.