For a second time in less than five years, high, slow-draining floodwater in the Bluff Swamp will force Ascension Parish workers to cut a drainage path through Alligator Bayou Road, shutting it potentially for weeks longer.

Parish officials announced Wednesday that crews plan to cut the drainage route where the road crosses over Fish Bayou either Friday or Saturday. The path will allow more water to drain from the Bluff Swamp and greater Spanish Lake area.

Homes in the huge, bowl-shaped basin of roughly 17,000 acres are either flooded or surrounded by high water, which is draining slowly through a handful of existing floodgates and portable pumps recently installed by Ascension crews.

Ascension and Iberville officials took a similar course in the aftermath of the August 2016 flood, cutting Alligator Bayou and Manchac roads to allow the swamp basin to drain more quickly. The area flooded because water draining from East Baton Rouge Parish and backed up water downstream poured over a levee road into the basin.

Ascension officials on Wednesday could not say how long Alligator Bayou Road, which is already closed to due the pumping operations, will remain shut due to drainage path soon to be cut through it.

"I wouldn't expect that road to be open any time soon," said John Connelly, a parish spokesman.

In 2016, the closure lasted for a few months and drew complaints from people who live in the area and use it for access to Interstate 10.

Also on Wednesday morning, Iberville Parish officials reopened their floodgate at Alligator Bayou, further increasing drainage from the basin into Bayou Manchac, Ascension officials said.

The gate can't be opened until water is low enough in Bayou Manchac to prevent bayou water from flowing back into the swamp basin.

In 2016, an estimated 17 billion gallons of water flowed over the road and into the swamp basin until the high water could be stopped with large sandbags and other measures.

In the latest incident, only some water got over the road before Iberville Parish was able to install inflatable AquaDams on the road, Iberville officials have said. The dams extend into Ascension Parish.

Alligator Bayou and Manchac roads, which are actually the same two-lane road with different names, rest on a levee along Manchac's southern bank that holds back most of the high water in the basin.

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The latest bout of high water stems from heavy rains that caused severe flash flooding in Baton Rouge and Ascension parishes last week and the subsequent drainage from those areas -- where rain approached 14 inches in a short span -- into the Bayou Manchac area.

The area has gradually become a runoff site for fast-growing parts of Ascension, East Baton Rouge and Iberville parishes but has a limited and congested path for all that drainage water to exit toward the Amite River, the ultimate runoff outlet for much the Baton Rouge region. 

With U.S. Army Corps of Engineers funding, East Baton Rouge officials are also planning a major clearing of creeks and bayous that dump runoff into Manchac and the Amite.

Though the plans have raised worries in downstream parishes, like Ascension, the Corps of Engineers has said analyses show the work won't worsen flooding. 

Even before the mid-May storm, residents of the Ridge Road area inside Ascension's Bluff Swamp had aired worries about rising water in the swamp basin from earlier rains in April, council members have said in public meetings.

In the statement Wednesday, Ascension Parish officials said that workers would monitor weather forecasts and have Public Works crews station at the site of the road cut to fill it and block water flow if Bayou Manchac again rises to 14 feet. At that height, water in the bayou would start to flow back into the swamp basin.

Parish official said they currently have set up and are running six pumps at Alligator Bayou Road, four 24-inch tractor pumps and two 30-inch axle driven pumps. Two additional 30-inch pumps were expected to arrive later on Wednesday.

Since the 2016 flood, Iberville has completed an expansion of its floodgate where Alligator Bayou joins Bayou Manchac.

On May 19, Ascension Parish officials approved the construction bid for two new floodgates where Fish Bayou joins Bayou Manchac just downstream from Iberville's gate. The parish already as a floodgate at nearby Frog Bayou and Manchac.

Officials in both parishes have seen having larger floodgates as a way to speed up drainage of the basin, but permitting for the gates took a significant amount of time.


Email David J. Mitchell at dmitchell@theadvocate.com

Follow David J. Mitchell on Twitter, @NewsieDave.