Posted on June 29, 2020
Dredging the Vermilion River would do little to reduce flooding in Lafayette Parish and would do little harm to buildings downstream, a study by the Louisiana Watershed Flood Center at the University of Louisiana at Lafayette suggests.
Findings of the study, authorized by the Corps of Engineers and previously released in February, were briefly presented Wednesday to the Louisiana Watershed initiative Region 5 Steering Committee in Lafayette.
Mark Wingate, deputy district engineer for programs and project management with the Corps of Engineers in New Orleans, said when word got out a few years ago, after the massive 2016 flood, that he was going to ask for federal money for dredging, he received calls from Vermilion Parish residents and officials concerned that dredging the river in Lafayette would flood them to the south.
At that time, Wingate said he promised not to request dredging funds until a study was done on the impact on Vermilion Parish. That led to the UL Lafayette study.
UL researchers used a model they had already created of the Vermilion River to model the impacts dredging the river from Bayou Fuselier to Vermilion Bay would have during a 10-year storm and a 100-year storm like the August 2016 deluge. They also modeled the impact of dredging just in Lafayette Parish, he said.
The models, Wingate said, showed very low impact in all scenarios.
“No negative and not much positive,” he said.
Partial dredging in Lafayette Parish would cost about $50 million while full-scale dredging would cost about $150 million or more, Wingate said, with modest impact on lowering the flood stage of the river. Increasing the cost is the fact that the dredged material would have to be loaded on barges then trucks and disposed of on land local governments in Lafayette and Vermilion parishes would provide.
Dredging the entire length of the river would produce enough material to fill the Cajundome 5 1/2 times, according to Jeffrey Varisco, senior project manager with the Corps’ New Orleans District. It would lower the river on average less than a foot, preventing the flooding of 327 homes that flooded in 2016.
When Wingate and Congressman Clay Higgins of Lafayette in February announced the study results, Wingate said dredging the entire river would prevent the flooding of 175-200 Lafayette Parish homes that flooded in 2016.
Emad Habib, UL professor of civil engineering with the Louisiana Watershed Flood Center, said the modeling of the 2016 flood shows the river has a good slope north of Lafayette, but has a bump at Lafayette due to shoaling. In addition, four or five major coulees dump water into the river simultaneously during heavy rainfall. Combined, he said, they make the river flow north, creating flooding in Lafayette Parish.
Dredging the river can make the channel bigger, Habib said, but it still would fill with rainwater quickly in a 2016-like event. One inch of rain falling across the watershed equals 50 million cubic yards of water. The main solution, he said, is to hold the water back from entering the river.
Higgins concluded the presentation by suggesting additional modeling of flooding scenarios based upon the observations and suggestions of long-time Lafayette residents such as Dave Dixon and Harold Schoeffler of the group Dredge the Vermilion.
The study results are expected to be published soon. Meanwhile, Varisco said, the Corps is drafting a memo of understanding with the Louisiana Watershed Initiative, committing the federal agency to share models and other information with the state.
The LWI was formed after the 2016 floods. The goal is to study floodplain management in multi-parish regions based on watersheds instead of political boundaries and to build projects or procedures for water management regionally.
Source: theadvocate
