Wonder how this structure behind me came to be? This is the Bonnet Carre Spillway. It is an essential part of flood control in the Lower Mississippi Valley. The Bonnet Carre Spillway stands in St. Charles Parish, Louisiana. It is about 12 miles west of New Orleans. The spillway lets floodwaters from the Mississippi River flow into Lake Pontchartrain. From there, the water flows into the Gulf of Mexico.
The Bonnet Carre Spillway has a fascinating history. The Great Mississippi Flood of 1927 devastated the region. In response, engineers constructed the spillway between 1929 and 1931. The American Society of Civil Engineers has designated it a National Historic Civil Engineering Landmark.
The Bonnet Carre Crevasse was an issue. It caused levee breaches in 1871. Local drainage systems couldn’t handle the floodwater. Strong winds pushed water into Lake Pontchartrain and nearby urban areas. The river levee wasn’t fixed until 1883.
The 1927 flood led to the spillway’s construction. It first opened during the flood of 1937. In 2007, crews began extraction operations on a section of the spillway. This 7600-acre area provides sand and clay. This material is vital for construction projects. Post-Katrina, the clay helped raise levees in St. Charles and east Jefferson Parish.
However, the spillway’s openings have impacted marine fisheries. The Mississippi Sound suffered. This resulted in a federal award of damages in 2011. Ongoing litigation addresses the spillway’s management.
In 2019, the Bonnet Carre Spillway opened on February 27. River levels were rising. They predicted minor flood stage in New Orleans by March 19. The Army Corps of Engineers opened 38 of the 350 bays initially. They increased this to 206 bays as the flood crest arrived. The spillway closed on April 11, 2019. It reopened on May 10, 2019. That marked the first time it opened twice in one year. In April 2020, it opened again for 29 days.
The Bonnet Carre Spillway has two main parts. There is a control structure by the Mississippi River’s east bank. Then there is a floodway. The control structure sits between Montz and Norco. It’s a long concrete weir running parallel to the river. When open, it allows overflow into Lake Pontchartrain. The lake connects to the Gulf. This opening can handle significant flood flow. The water from the Mississippi splits. Part stays in the river. The other part diverts through the channel. This reduces stress on New Orleans’ levees.
The floodway stretches almost six miles to Lake Pontchartrain. It can handle 250,000 cubic feet per second. U.S. 61 and Interstate 10 cross the spillway.
The Bonnet Carre Spillway also serves as a recreation area. People enjoy off-road vehicles, biking, boating, hiking, hunting, and fishing. The Louisiana Department of Wildlife and Fisheries manages it as a protected area. Clay extraction pits were filled with water. They stocked them with fish like bluegill and bass.
The floodgate is set into the Mississippi River bank. This location had natural flooding for centuries. The concrete design minimizes settling. Opening and closing involve removing up to 7000 wooden beams. These beams are arranged in 350 bays. Two rail-mounted cranes do this work. The number of beams removed controls the water flow. Removing all beams takes about 36 hours.
The Bonnet Carre Spillway is part of the Mississippi River and Tributaries Project. This is a multi-state plan by the Army Corps of Engineers. It protects the alluvial valley from Missouri to Louisiana. Levees, floodways, and channel improvements are all part of this project. It also includes reservoirs and pumping stations.
There are two cemeteries within the Bonnet Carre Spillway. These cemeteries hold the remains of enslaved persons and free African-Americans. These sites flood when the spillway opens. The Kenner and Kugler Cemeteries are on the National Register of Historic Places since 1987.
The success of other freshwater diversions has led to more studies. A diversion within the Bonnet Carre Spillway could direct water and sediment into Lake Pontchartrain and the Mississippi Sound. This would help reduce marsh loss and provide storm surge protection.
The Bonnet Carre Spillway stands as a testament to engineering ingenuity. It protects communities and offers recreational opportunities. It reminds us of the ongoing challenges of managing the Mississippi River.