Upriver levee breaches, failures help lower water downriver, negating immediate need for spillway opening
Plans to open a major Mississippi River spillway have been canceled, at least for the time being.
Part of the Morganza Spillway structure northwest of Baton Rouge had been scheduled to open Sunday. But the U.S. Army Corps of Engineers said Thursday that the opening has been indefinitely postponed.
Sunday’s opening had been planned to keep the river from overtopping the structure. However, Corps spokesman Ricky Boyett says the latest forecasts don’t show the river reaching levels that would require the Morganza opening. He cautioned that the Corps isn’t ruling out an opening later in the year.
The indefinite postponement is good news for farmers whose crops would have been lost by spillway flooding. The spillway covers nearly 112 square miles (290 square kilometers). Roughly one-third is used as farmland.
A forecast that the river will reach a certain level at a certain date will trigger the plans to open spillway structures.
Authorities had considered opening the Morganza as early as June 2.
Changing forecasts twice led the Corps to change projected opening dates, first to June 6, then to June 9.
At the National Weather Service office in Slidell, hydrologist Jeff Graschel said many factors contribute to forecast revisions. Those include amounts and locations of rainfall that put water into the Mississippi or its tributaries.
A big factor in the changes in the current forecasts, Graschel said, are levee breaches and over-toppings along the Arkansas River, resulting in a slower-than-forecast rate of water flowing into the Mississippi.
Any opening this year would be the second time the Morganza structure has been used to control floodwaters. Morganza was opened in 2011 for flood control. In 1973, it was used to protect an upriver flood control structure.
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