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Flood Mitigation: The Role Of The Amite Basin And Comite Diversion

Aug 16, 2017
Originally published on August 30, 2017 2:46 pm

Since rainfall blanketed southeast Louisiana in August 2016, residents have wondered how the state can protect its people from future floods. Answering that question begins with understanding the geography we live in.

The Amite River Basin starts in southwestern Mississippi — right above the boot of Louisiana — and runs south to Lake Maurepas.

Bob Jacobsen is a hydrologist — he's spent years studying the Basin. He compares it to a dining room table that's tilted up on one side. The higher part is in the northern portion of the Basin. "And what happens when you get big rainfalls in the upper third of the basin — and I'm talking Mississippi but also East Feliciana and St. Helena parishes — you're dumping a lot of water on part of the table that's really tilted," Jacobsen explains.

Which means that water moves south quickly, down the Basin, into lower lying, developed areas, like East Baton Rouge, Livingston and Ascension parishes. It's like spilling a cup of water on that tilted table.

"It gets down to the area where maybe it's not tilted, and it's spreading out and everybody's wondering which way that that cup is going to pour the water off the table."

Jacobsen says in the past, the main philosophy of mitigating flooding in the lower basin, especially East Baton Rouge, has been to move the water out as quickly as possible — by dredging, straightening and clearing rivers and streams. But, he says, that's become more challenging over the past few decades. "We've started to realize there's no place to move water to where we don't affect somebody else.”

That's because thousands of people now live in places like Livingston and Ascension — where water from East Baton Rouge would be moved.

At a recent flood recovery town hall in Baton Rouge, Senator Bill Cassidy explained how those areas have changed. "A lot of land that was not developed, is now developed. So land that used to absorb water now has concrete on it and instead of being absorbed into the dirt, it runs off into the drainage ditches and those drainage ditches quickly back up."

Jacobsen says that old philosophy — getting water out as quickly as possible — needs to be reconsidered. One option is retention — turning areas into green space, able to absorb more water — or larger projects like reservoirs. Retention is only a partial fix, he warns. "These techniques that you've built up to try to reduce the more frequent flooding aren’t really going to have a big effect on the really extreme events."

Dietmar Rietschier is the Executive Director of the Amite River Basin Commission. He says in order to mitigate flooding, the approach must be holistic.

"We have to look at the Amite River Basin in total, because what we do in one part of the basin affects the other," Rietschier says. "We have to consider all kinds of elements, how to minimize flood losses — and that includes what's called structural projects, like for example the Comite River Diversion Canal."

The Comite Diversion was designed following the 1983 Amite River flood. It would stretch more than 10 miles and divert high waters from the Comite River into the Mississippi, giving it another place to go rather than onto someone's property.

But after 34 years, the project still hasn't been completed. It's received increased attention since the August flood — like from Congressman Garret Graves.

"One of the things that we can do that provides one of the best recovery investments for these flood victims is investing into projects like the Comite project to help prevent repetitive floods and to help improve the resiliency of these communities," Graves says.

Rietschier says the decades-old design of the Comite Diversion should be re-examined, since the August 2016 river levels surpassed the previous record set in 1983. Despite that, he says, "I still believe it is a project that will function probably 80 percent of the time. I guarantee you that before the next 2016 event might happen, we might have 10 smaller events like the 1983 flood."

Could it protect against a major flood like 2016? That's debatable, says Rietschier. But in less severe scenarios, the Comite Diversion could help protect homeowners.

Do you have feedback or a flood-recovery story you'd like to share? We welcome your comments here.

This story was made possible by the Louisiana Public Radio Partnership, with support from the Corporation for Public Broadcasting.

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