BAYOU MANCHAC — Brown, murky water flooding homes in Ascension and Iberville parishes flowed with ease out of Bluff Swamp Tuesday afternoon, frothing a bit near where the water flowed into Bayou Manchac in the northwestern corner of the parish.

A few hours earlier, Ascension Parish excavators dug a 1-foot-deep, 40-foot-wide cut across Alligator Bayou Road to allow the high water leftover from last week's historic storm and the accompanying backwater flooding to escape the basin.

Ascension officials announced Sunday they expected to cut the trench when the level in Bayou Manchac dropped two feet, likely Wednesday or Thursday. But Bill Roux, the parish director of public works, said they decided to move forward with a smaller cut a day early after the bayou had fallen one foot.

"Ideally, I was waiting for two feet, but once we started prepping this morning, I said, 'Hell, a foot's a foot.' I mean whatever we can let out while it's going down ...," Roux said at the site of the opening Tuesday afternoon.

Like the bottom of a bathtub, the spot where the trench was cut along Alligator Bayou Road is where the natural slope of the Spanish Lake Basin wants to drain water. The 17,000-acre swamp basin, which includes Bluff Swamp, extends west toward St. Gabriel and south toward La. 30.

Alligator Bayou Road, which separates the basin from the bayou, serves as a kind of levee that holds water in the basin, with the exception of two small floodgates that run under the elevated road.

But parish officials have said it would take months to drain off the immense amount of water now in the basin, leaving the owners of flooded homes on Ridge Road in Ascension Parish and in the Bayou Paul area of Iberville Parish stranded from homes they could not occupy and could not fix.

In addition to the rain that fell in the basin itself, backwater flowed south from East Baton Rouge Parish, through Bayou Manchac and over a three-mile stretch of Alligator Bayou Road into the basin for more than three days.

Roux said the new cut across the road works like a "control weir" one might see at the top of a dam or on other flood control structures, allowing only a specific amount of water out but more than what the floodgates can handle.

Troy Morgan, 46, who lives with his family on Manchac Road in Iberville Parish just west of the road cut, said he has had six inches of water in his house since Wednesday night.

He said he and his neighbors welcome anything the parish is doing to lower the water level in the basin.

"It's helping. I can see it going down in the front yard," Morgan said Tuesday afternoon.

Morgan, who has been living with a neighbor who did not flood, said he is running his air-conditioning in his house to keep the mold down until the water drops.

"We just talked to the (insurance) adjuster, and he's not coming in until the water's out, and then I got some people coming to help gut the house, but we're not going in until the water's out, 'cause it's sitting and getting nasty," said Morgan, who has lived in the area for 17 years and built his house above the projected height of a 100-year flood.

The Ascension digging operation on Tuesday followed the installation of three portable pumps over the weekend and on early Monday.

The pumps, which were running on Tuesday and extend across the surface of the road with pipes that funneled water into the bayou, moving about 130,000 gallons per minute. Roux said the cut into Alligator Bayou Road moves about 1.5 times that amount of water.

He said that as the water level in Bayou Manchac drops farther, parish official plan to open the nearby floodgates at Frog Bayou and Alligator Bayou.

"We're not going to do that until we make sure down stream there's not any effect," he said.

Water released from the basin and into Bayou Manchac will move past northern Ascension and southern East Baton Rouge parishes and eventually will end up in the Amite River and Lake Maurepas.

Roux said monitoring has shown no effect so far along Bayou Manchac.

He said the parish plans to dig out another foot from the 40-foot-wide trench on Alligator Bayou Road as the water level in Bayou Manchac drops. That second cut could happen as soon as Wednesday.

He said each additional foot of depth in the cut across the road exponentially increases the amount of water that can escape the basin.

Follow David J. Mitchell on Twitter, @NewsieDave.