Posted on January 24, 2017
By David J. Mitchell, The Advocate
Armed with new data from the August flood, Ascension Parish officials are going to revisit an old idea to dredge Bayou Manchac with the goal of improving drainage in the Spanish Lake and Bluff Swamp areas where water pooled for weeks last summer.
Even after water retreated from the rest of the region, allowing people to get back into their homes and start gutting, some Iberville and Ascension parish residents in those swamps had to cope with standing water that kept them from their properties for weeks.
An estimated 14 billion gallons of water flowed over a 3-mile stretch of the Alligator Bayou-Manchac road in August, as Bayou Manchac filled with backwater from the swollen Amite River and downstream runoff out of Baton Rouge.
Officials dug deep trenches across the road to get water to drain more quickly from the vast bowl-shaped swamp into Bayou Manchac. The road, which is on a 14-foot-high berm, acts like a levee, except for two small floodgates.
But, even with all the trench digging, the water still took weeks to drain, and Ascension officials believe natural and man-made blockages in Manchac contributed to the slow-going.
They say they can now make a strong case with their new model for the need to snag and dredge the historic bayou to clear out those holdups. Longer term, the officials also want to create more space for water to flow under highways and a railroad track that cross over Manchac and they’d like to see a new flood control structure on the bayou.
Ascension officials maintain that Manchac, as shown in the model produced by Baton Rouge engineer Stokka Brown, is restricted by these natural snags and highway crossings at Interstate 10, Perkins Road, Airline Highway and Jefferson Highway.
The proposed dredging and other work, parish officials say, would bolster the effectiveness of expanding floodgates that allow Spanish Lake and Bluff Swamp to drain into Manchac and eventually the Amite River.
“It proves the fact that there (are) constrictions within Bayou Manchac,” Bill Roux, the Ascension Parish public works director, said in a recent parish drainage meeting. “No matter what we do there (at the Spanish Lake floodgates), it can only benefit up to a point. If we don’t dredge and enlarge or do something with Bayou Manchac, we never will be able to get an efficient outflow from the Spanish Lake and Bluff Swamp area.”
In addition to the Spanish Lake area in Ascension and Iberville parishes, Manchac also serves as a major drainage outlet for fast-growing south Baton Rouge, receiving water from Bayou Fountain and Ward Creek.
“It’s just too much for that bayou to handle,” Roux said of all the water headed to Manchac.
Source: The Advocate
