The gist: The U.S. Army Corps of Engineers has contracted UL’s Watershed Flood Center to model the effect of dredging the Vermilion River. This would complete a long-awaited study — at one time expected to be finished at year’s end — that will determine the benefits and risks of digging out years of accumulated mud and debris that have shallowed the river’s bed. A report based on UL’s calculations will be ready in January, according to Corps representatives.
Get caught up, quickly: Many flood victims and public officials believe the river is essentially clogged, contributing to more frequent flooding over its banks and into homes and businesses in Lafayette Parish. Dredging the Vermilion River became a political movement of sorts, parallel to the ongoing 2019 election campaign. But there is concern that digging out the river could worsen flooding downstream in Vermilion Parish or would have limited benefit at great cost. The study, initiated by the Corps and now largely in the hands of UL, will provide a scientific baseline for what could be a difficult public policy decision in 2020.
UL has worked on modeling the Vermilion for two years. The university created the Watershed Flood Center to address obvious information gaps in how regional policymakers were tackling stormwater management and flood risk since the 2016 floods. Center Director Emad Habib and his students did preliminary modeling of dredging the Vermilion earlier this year, spurred by increasingly urgent public calls for the action. Habib approached the Corps with the center’s findings and offered up a work in progress, avoiding the need for the Corps to build its own model from scratch. The Corps will pay the watershed center $85,000 for the expanded modeling.
“If we were going to start this model from scratch, that takes quite an effort. It’s a big study area,” says Clyde Barre, a senior hydraulic engineer with the Corps. “It just seemed to be the prudent thing to do.”
UL’s preliminary study found limited impact when modeling big storms. Those calculations, which found at most a half-foot reduction in water levels, were based on an earlier version of the model that had a smaller scope of data. It remains an “open question,” according to Habib, whether dredging would have greater impact in smaller storms. UL’s work with the Corps will take a look at those scenarios and more.
The expanded model covers the entire river. Habib’s team will input virtually every variable that impacts the Vermilion from its headwaters at Bayou Fuselier in St. Landry Parish to Vermilion Bay. That includes dozens of bridges, culverts, tributaries and flood control structures. Millions of individual computations replicate how the river will react to varying rain intensities and volumes and, in turn, how dredging would change the river’s response. It should provide policy makers some clarity on the most controversial aspects of the project, namely whether it would work and whether it would cause problems for residents downstream, who have pushed back against the proposal.
“Once you present people with data, they’re actually willing to change their beliefs,” Habib says. The watershed center was created with exactly this kind of community use in mind. Beyond the contract work with the Corps, the model could be used to study other scenarios like major retention projects or the impact of development patterns and land use on flood risk.
“This is the reason we reached out to the Corps. We’d like to offer these types of tools to the community,” Habib says.
$5 million is set aside in LCG’s budget for dredging the river. Councilwoman Nanette Cook earmarked that money out of city reserves during this year’s budget process. She recently moved to re-budget those dollars from recently rededicated parish drainage funds, but withdrew her measure in the face of opposition.
“I am very adamant about making sure this money remains available for this dredging project,” Cook says. It’s not clear how much dredging will cost, but the model would inform that calculation. Spot dredging — i.e., removing only some clogs, as some advocates have called for — would be relatively inexpensive compared with dredging projects that cover miles of river, an undertaking that could cost tens of millions of dollars. The Corps last dredged the river in the 1990s to restore navigability, but a lack of funding has prevented ongoing maintenance.
What to watch for: What the study finds come January. It’s possible the results won’t make for an easy decision. The issue may not be black and white, when cost is factored in.