The U.S. Army Corps of Engineers, New Orleans District, has announced plans to open the Bonnet Carré Spillway on Monday, May 9, at 8 a.m., to keep the volume of Mississippi River flows at New Orleans from exceeding 1.25 million cubic feet per second. The spillway is 28 miles above New Orleans.

The Corps has indicated that it may also need to operate the Morganza Floodway which is northwest of Baton Rouge. Operation of the Morganza Floodway would require the evacuation of people and livestock and removal of personal belongings for communities within the Atchafalaya River Basin.

The Bonnet Carré spillway may be open for an estimated two to four week period, according to the Corps. Operation of the structure will relieve pressure on main line levees, lower river stages, and reduce the velocity of the river current from the spillway southward. The decision to open Bonnet Carré is the responsibility of Mississippi River Commission president Maj. Gen. Michael J. Walsh.

Citizens should take immediate steps to remove their property and protect existing facilities and immovable property within the spillway, the Corps said. In addition, all public access areas within the spillway, including the public boat launches, Lower Guide Levee Road, and the St. Charles Parish recreation area near Hwy. 61 will be closed beginning on Monday, May 9, 2011 until further notice.

Bonnet Carré Spillway is located on the east bank in St. Charles Parish. It can divert a portion of the river’s floodwaters via Lake Pontchartrain into the Gulf of Mexico, thus allowing high water to bypass New Orleans and other nearby river communities. The structure has a design capacity of 250,000 cubic feet per second, the equivalent of roughly 1.87 million gallons per second.

The Bonnet Carré structure consists of a control structure and a floodway. The control structure is a concrete weir that parallels the river for a mile and a half. It consists of 350 gated bays, each holding 20 timber “needles.” When needles are removed, river water flows into the floodway and is conveyed nearly six miles between guide levees to the lake. Operation of the structure is relatively simple. Two cranes, moving on tracks atop the structure, lift timbers from their vertical position in the weir and set them horizontally across the top of the structure to allow river water into the spillway.

The Morganza Floodway, according to a Corps statement "is operated only when existing conditions, combined with predicted stages and discharges, indicate that mainline levees in Baton Rouge, New Orleans and other downstream communities will be subjected to unacceptable risk from high water.” The decision to open Morganza is the responsibility of the Mississippi River Commission president Maj. Gen. Michael Walsh.

The Corps has developed a map to depict anticipated impacts from operation of the Morganza Floodway. http://www.mvn.usace.army.mil/news/all_articles_dy.asp. As floodwaters progress through the Morganza Floodway to the Gulf of Mexico, the height of the water could reach between five and 25 feet above ground elevation, causing widespread flooding and inundation.

People living within the following parishes are encouraged to contact their public officials for further evacuation information: Pointe Coupee, St Landry, St Martin, Iberia, Iberville, St Mary, and Terrebonne parishes.

The Corps said that public notice of operation and required evacuation will be given through state and local emergency officials and other governmental authorities, as well as media outlets. Notification will be given in advance with adequate time for evacuation; however, expeditious action must be taken to protect life and property. 

Congress authorized the Morganza Floodway as a vital part of the Mississippi River and Tributaries Project, to relieve the Lower Mississippi River of excess floodwater, which would otherwise stress the limits of the system.