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An AquaDam has been placed along Bayou Manchac on Alligator Bayou Road Wednesday May 19, 2021, in Ascension Parish/Iberville Parish, La.

After heavy rains dropped more than 13 inches on the Baton Rouge area in less than 24 hours earlier this week, Iberville Parish sought to hold off a swollen Bayou Manchac with AquaDams. But a judge in neighboring East Baton Rouge Parish ordered the portable water-filled fabric dams not be installed, contending they would cause homes in that parish to flood.

The squabble is the latest in an ongoing battle among Iberville, East Baton Rouge and Ascension parishes over the use of the flood protection mechanism. But just what are AquaDams, and why are they so controversial? Here's what you should know.

What are AquaDams and how do they work?

AquaDams consist of two large, watertight polyethylene tubes inside another larger heavy-duty tube that holds them together. The "inner" tubes are filled with onsite water. The friction between the inside tubes and the outer container and the mass and weight of the water keeps the dam stable. During the 2016 floods, Louisiana-based Gulf Coast AquaDams stocked about 20,000 feet of the barriers, which range in height from 1 foot to 16 feet.

AquaDams come in segments, usually 50 or 100 feet, rolled around a 4-by-4. A segment is unrolled, the two inner tubes are filled with water, and the segments are connected.

Where else have AquaDams been used?

The Baton Rouge area's introduction to AquaDams came in August 2016, amid the struggle to hold back water from the first floor of Woman's Hospital. Record rainfall in the Amite and Comite basins were too much for Lake Maurepas to handle, and backwater flooding threatened to push 2 to 3 feet of water into the building if something wasn't done.

The Woman's campus has an 18-acre lake, but even it couldn't hold the water expected to come. Amid a dire forecast from the state hydrologist, Gov. John Bel Edwards directed the state Department of Transportation and Development to enter a contract with Gulf Coast AquaDams of Abbeville. The company would place more than 1,500 feet of its barriers at Woman's, along with an additional 1,600 feet along Airline Highway to keep the roadway open.

In the years since, Ascension and Iberville parish have either looked at, or actually deployed, AquaDams to hold back floodwaters from East Baton Rouge Parish. This week, Iberville Parish President Mitch Ourso sought to use the structures as heavy rain fell on the Baton Rouge metro area.

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Why is the use of AquaDams controversial in the Baton Rouge area?

On Wednesday, East Baton Rouge Parish Judge William Morvant barred Iberville and Ascension from deploying AquaDams along Manchac’s southern bank — although Ourso vowed to keep them in place.

The dams are intended to prevent high water in the bayou from spilling into the Spanish Lake basin and threatening homes there. City-parish officials contend the dams would cause homes in East Baton Rouge to flood.

Once connected to the Mississippi River, the bayou and the swamp basin through which Manchac threads have a hydrology that has been complicated by the years of human alternation. The area now receives runoff from fast-growing areas in all three parishes and dumps it into the Amite River.

Iberville officials say that runoff from southern East Baton Rouge, in particular from Bayou Fountain, winds up in Manchac.

In severe storms, that water, they contend, can force the bayou to overtop roads that normally serve as levees keeping Manchac’s water in its banks and out of the swamp basin.

High water overtopped the road in the August 2016 flood. Residents waited weeks for the slow-draining basin to drop low enough so they could rebuild.

City-parish officials say the AquaDams pose a flood risk to residents on the other side of the bayou and that the bayou is subject to backwater from the Amite River downstream of the city-parish's runoff.