New floodgate being shut to fight against rising Atchafalaya | Business News
A permanent gate that blocks backwater flooding from affecting 30,000 people in six parishes began to be closed Monday morning ahead of expected high water on the Atchafalaya River.
The closure of the 405-foot-long Bayou Chene floodgate is the first time the three-year-old structure has been used due to high water in the Atchafalaya, a St. Mary Parish levee official said.
The $80 million floodgate finished in April 2022 was first used last fall for Hurricane Francine. Levee district operations crews began moving the submersible gate shortly before 7 a.m. Monday and were expected to be finished in the afternoon.
Tim Matte, the former mayor of Morgan City and the levee district director, said the levee district decided to move the gate more than a week sooner than its operational plan calls for — when the Atchafalaya gauge at Morgan City hits 7 feet.
The Atchafalaya at Morgan City was a little over 4 feet on Monday and isn’t predicted to hit 7 feet until April 23, according to a National Oceanic and Atmospheric Administration forecast Monday.
A relatively quick rise is predicted for the Atchafalaya and, as that water rises, the flow in Bayou Chene moves more quickly, creating a challenge to move the gate that’s longer than a football field and about as tall as a four-story building.
“We think by closing it a little bit earlier that it will accomplish two things. One, it will be safer, and we won’t put the equipment at any risk by closing it a little earlier and, number two, the quicker you can do that, the more water you can block from getting into the basin,” Matte said.
Crews must empty water from inside the floodgate so it floats up from its resting location along the shore and can be swung on its hinge, known as a pivot pile, into position in Bayou Chene and resubmerged.
The gate closes off the bayou, becoming the central piece of a 1,100-foot long floodwall that goes across the bayou and ties into levees that head off into Terrebonne Parish and Avoca Island.
The gate and its levees can hold back a rise of about 6.5 feet, based on current water levels in the bayou, Matte said.
The floodgate south of Amelia protects St. Mary, Terrebonne, Lafourche, St. Martin, Assumption and Iberville parishes from backwater flooding in the basin.
Temporary submersible barges and sheet piles have been used four other times in roughly the same location in Bayou Chene to block high waters in the Atchafalaya — 1973, 2011, 2016 and 2019.
In 2019, Gov. John Bel Edwards announced that the Coastal Protection and Restoration Authority would finance the floodgate with federal revenue sharing from offshore oil and gas production.
Heavy rains in the Midwest are filling watersheds that drain into the Mississippi and its related waterways, like the Atchafalaya.
The Atchafalaya is projected to peak at 7.5 feet at Morgan City on April 25, and stay at that height until the pre-dawn hours of April 26, when waters will begin to fall, NOAA says.
Last week, state officials suggested high water in the Mississippi was leading to evaluation by the U.S. Army Corps of Engineers about partially opening the Bonnet Carre’ Spillway upstream of New Orleans.
But Corps officials said the river is not expected to reach the required streamflow to trigger opening of the venerable series of floodgates near LaPlace.
The spillway opens when Mississippi streamflow hits 1.25 million cubic feet per second, or roughly 17 feet on the Carrolton gauge in New Orleans. Forecasts last week put the peak just below that level but within the forecast’s margin of error.
The Mississippi at Baton Rouge is expected to hit 40.6 feet, or just into major flood stage, on April 23. The river last reached that height or greater in Baton Rouge in April 2020, when it peaked 4 feet higher. It was also the last time the Bonnet Carre’ was opened.