Increasing water levels as a result of heavy rain in the Mississippi and Ohio river valleys are prompting the U.S. Army Corps of Engineers to operate the Bonnet Carré Spillway to ensure safe passage of the Mississippi river through the greater New Orleans area.
Operation of the structure will relieve pressure on main line levees, maintain river stages, and regulate the flow downriver from the spillway. The decision to open Bonnet Carré was issued by Maj. Gen. Richard G. Kaiser commander of the Corps’ Mississippi Valley Division in Vicksburg, Miss.
Opening procedures will begin on Wednesday, Feb. 27 when the river is expected to reach the operational trigger of 1.25 million cubic feet per second.
Environmental, hydrologic, structural, and navigational considerations all bear on the decision to open Bonnet Carré. Other factors that affect the decision are the overall condition of the levees and the ability of the river to pass flows, and the effects high water and river currents may have on vessels navigating the river. The Corps has a detailed environmental monitoring plan in place that will assess water quality, dissolved oxygen, sedimentation, recreation, and natural resources such as the pallid sturgeon, both within the spillway as well as Lake Pontchartrain.
All third-party users and grantees should take immediate steps to remove their movable property and protect existing facilities and immovable property within the spillway. 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 U.S. Hwy. 61 will be closed beginning on Wednesday, Feb. 27, 2019, until further notice.
The Bonnet Carré Spillway, located 28 miles above New Orleans, is a vital element of the multi-state Mississippi River and Tributaries (MR&T) system, which uses a variety of features to provide flood risk reduction to the alluvial Mississippi Valley from Cape Girardeau, Mo., to Head of Passes, La. 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 cfs, the equivalent of roughly 1,870,000 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,” for a total of 7,000 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.