After three floods within a decade, the St. Mary Levee District (SMLD) decided to build a permanent $80 million Bayou Chene Flood Protection Structure to protect several Louisiana communities from high river dangers.

“The permanent structure is operational,” says Tim Matte, Executive Director of SMLD. “We are prepared for high-river issues.”

The floodgate was installed in Bayou Chene south of Amelia, Louisiana.

“This region has relied on temporary measures to prevent backwater flooding since the 1970s,” said Governor John Bel Edwards at the floodgate's ribbon cutting ceremony. “With the completion of this decades-long effort, the people of St. Mary and the five surrounding parishes can rest easier knowing they're protected by a permanent flood control structure.”

The Need for the Flood Structure

The Mississippi River and its distributary the Atchafalaya River flooded to historic proportions in 2011, and SMLD installed temporary sea walls by driving sheet pile flood walls anchored with steel piles, riprap and HESCO baskets to protect the parishes of St. Mary, Terrebonne, Lafourche, St. Martin, Assumption, and Iberville from back flow from the river. About 30,000 people live in the region.

The next year, SMLD contracted with APTIM of Baton Rouge, Louisiana, to design a permanent floodgate. The district obtained the necessary permits to build the structure.

In 2016 and 2019, the area experienced significant flooding. SMLD again installed temporary, emergency sheet pile flood walls. Once the water receded, the district hired multiple contractors to remove the sheet pile and open up the waterway again. Those temporary structures cost millions of dollars each to build and remove when the threat passed.

“That motivated everybody to push the permanent structure project along,” Matte recalls.

The state agreed it was a regional project and contributed $80 million toward the construction through the Coastal Protection and Restoration Authority, using Gulf Of Mexico Energy Security Act funds.

The Permanent Floodgate

APTIM was the engineer of record for the permanent floodgate. Engineering firms T. Baker Smith of Houma, Louisiana, and Miller Engineers and Associates of Franklin, Louisiana, assisted with the design.

The permanent flood wall is more than 1,000 feet long with a 400-foot opening to allow for navigation on the commercial waterway. In the event of flooding, SMLD can close the 400-foot opening with a 29-foot-tall, 80-foot-wide, and 400-foot-long floating floodgate, which rests on a pivot pole near the opening.

“It's swung over the opening and pumped full of water, so it sits on a sill across the bottom,” Matte explains. “Once it's locked into place the waterbody is shut off from flow from the Atchafalaya River and affecting our region.”

Matte reports these structures are common in south Louisiana, but this is the largest such installation. This represents one of four such structures in SMLD.

In the event of a high water, the district will empty the barge-like floodgate causing it to float and allowing it to swing into place, using wenches and tugboats. Then it fills with water again to sit on the sill and block flood water.

Multi-Phase Construction

SMLD divided the project into several phases, expecting to receive funding over a multiple year period. However, after phase one, the district learned funds were available to construct the project.

Patriot Construction of Duson, Louisiana, began the clearing and grubbing of the Tabor canal in 2019. The company also completed the dredging and spoil placement for the new levee, under two contracts totaling $3.4 million.

Rigid Constructors of Butte La Rose, Louisiana, received the contract to work on Avoca Island road and the Tabor Canal levee. The work also included elevating Avoca Road and an earthen levee from Avoca Road to the floodgate structure to 8 feet; and earthen levees from the structure to the Tabor Canal and along the Tabor Canal with geotextile fabric, all to 8 feet; and a weir structure at the end of Tabor Canal to 6 feet. Everything had to be hauled by barge.

In February 2020, SMLD awarded Sealevel Construction of Thibodaux, Louisiana, the $46 million contracts for construction of the flood wall and the 8-foot-tall steel receiving structure on the north and south banks of Bayou Chene, along with installation of the barge and pivot pile.

At the remote location, all of the piling installation took place working off of barges. The pilings to support the floodgate were driven 135 feet deep into the ground and grouted into place.

Sealevel, founded in 1997, subcontracted construction of the floating barge to Bollinger Shipyards of New Orleans. The floating floodgate was towed about one mile to the site of its permanent location.

“It was good to see these dollars spent on local contractors, contributing to the local economy,” Matte says.

SMLD will be responsible for operating and maintaining the floodgate. The floodgate was designed to work off generator power, since it is located in a remote location. However, SMLD later realized it was possible to connect to electrical power. The last phase will bring electrical service to the floodgate, enabling it to operate on power, with generator backup.

The movable barge structure will remain docked parallel to the land and when high water is expected, it will be moved into place between the two steel structures and across the bayou, creating a 10-foot barrier for high river waters.

“In a high-water event, we can close it on a day's notice,” Matte concludes. “It's a phenomenal project and we're thankful to have it.”

Photos courtesy of St. Mary Levee District