It may be the first week of July or later before all the water in the upper Mississippi River from last month’s record rainfall finally makes its way past New Orleans and into the Gulf of Mexico.
At Cairo, Illinois, where the Ohio and the Mississippi rivers meet, the water is supposed to crest just under moderate flood stage Friday, and that’s a little unusual.
“Typically, we are not that high at this time of year,” said Jeff Graschel, service coordination hydrologist at the Lower Mississippi River Forecast Center in Slidell, Louisiana.
This is what comes from a record wet May in the contiguous 48 states, ongoing thunderstorms and a weekend of rain from the remnants of Tropical Storm Bill. While the water has had a small impact on shipping, the biggest outcome may be the trouble it causes for farmers working on land between the levee system and the rivers.
The Mississippi River watershed drains all or parts of 31 states, about 40 percent of the contiguous U.S., as well as two Canadian provinces, according to the National Park Service.
Green flood warnings spread the U.S. weather map like veins on a leaf, showing where those rivers are.
“Some years they get lucky and there is no flooding,” said Bob Anderson, spokesman for the U.S. Army Corps of Engineers, which maintains the river and leads the fight against flooding when the water gets too high.
Then there are years like this one. “They will pretty much have to replant once the waters recede,” he said.
This year hasn’t been a repeat of 2011, when flooding crimped shipping on the river, or 2012, when low water was just as damaging to barge traffic.
Too much water can make barges hard to control, which means tugs have to cut back on the number they push through the channel. Too little and barges will run aground, so they need to carry less freight.
About 900 million tons come into or leave the inland waterway system annually, Anderson said. The total may actually be higher because statistics are about 18 months old and more grain is on the water since railroads have been hauling more crude oil, he said.
The Mississippi and its tributaries are a superhighway for everything from fuel to chemicals to food. About 60 percent of all the grain exported from the U.S. moves down the Mississippi, the Park Service said.
Some locks and dams have been closed by flooding on the Red River, which runs through Texas and Louisiana, and on the Illinois and Kaskaskia rivers.
More than 3 inches (8 centimeters) of rain were forecast to fall Monday across parts of Iowa, Wisconsin and Illinois as severe thunderstorms and damaging winds swept the region.
With luck, the recent pattern of heavy rains at the northern end of the system will slack off and give the crest a chance to make it through the channel, said Graschel.
The Mississippi at St. Louis reached a peak of 36.94 feet, less than 3 feet below major flood stage, on Sunday. It will dip a little before rising back up to 36.5 feet on Wednesday.
The river at Memphis will be near flood stage by Friday. At Cape Girardeau, Missouri, the Mississippi is forecast to crest 5 feet below the record set in August 1993.
The flooding on the upper end of the Mississippi, even with the flow from the Missouri, can usually be handled by the lower end of the river. Things start to get interesting, though, if the Ohio gets involved.
After Cairo, 60 percent of the water in the Mississippi has started out in the Ohio.
Graschel said his office will be gathering more information to get a better idea of how the Mississippi will react as the water moves through it. The crest from the north should reach New Orleans about July 7.
Of course, a little rain here and there could change all of that.