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 gist: A resolution adopted unanimously by the City-Parish Council Tuesday formally urges action on dredging the Vermilion River. Council members and dredging advocates are now targeting funding and political help while the Army Corps of Engineers completes a dredging study.
There is immense political pressure to act. Facing repeated floods and sustained anxiety since August 2016, many residents say little has been done to protect them. Dredging advocates Harold Schoeffler and Dave Dixon have won the ears of officials, most notably U.S. Rep. Clay Higgins, and have rallied flood victims and politicos alike to take comprehensive steps to manage regional waters. The tip of that spear is dredging the Vermilion River to remove years of accumulated.
“The Vermilion River is in a state of emergency,” Dixon told the council Tuesday night. An August navigation depth survey by the Corps of Engineers shows clogging throughout the river in Lafayette Parish, which Dixon believes is the culprit behind increasingly more common flood events.
LCG needs a permit from the Corps to dredge the river. Before the Corps will OK dredging, it’s studying the impact it would have locally and downriver in Vermilion Parish, where officials have asked for caution.
The Vermilion has reached flood stage five times in the last year. Indeed, over the last three decades, flood events along the Vermilion have increased dramatically, a phenomenon that correlates with population growth and accompanying development.
Climate and development appear to play key roles. Some evidence suggests that rain events are getting more intense. Researchers at LSU found that southern Louisiana is getting more so-called “convection showers” — high intensity downpours that burst over shorter intervals, often overwhelming drainage systems. Meanwhile, Lafayette Parish has added acres of rooftops and pavement that shed more water more quickly into drainage channels and, ultimately, the river.
Public Works Director Mark Dubroc attributes the increase in flood events to those rainfalls. Dubroc has questioned whether dredging will have the impact touted by advocates, arguing earlier this month that there is little evidence to support claims that dredging would have substantial benefit. More to the point, Dubroc is concerned that conclusions are getting ahead of proof. He doesn’t oppose dredging in and of itself, but he questions whether the benefit would be worth the cost.
“As public works director, I need substantive, identifiable benefit,” Dubroc tells me.
UL Lafayette researchers are modeling the effect of dredging the river. Responding to the public momentum, Emad Habib, a professor of civil engineering at UL, has used a detailed river model to calculate the efficacy of dredging.
UL’s model ran a scenario in which 20 miles of the Vermilion was dredged at varying depths and widths, including leveling the shoals at Coulee Mine and Rotary Point, identified by the Corps’ August survey. In a simulation of the August 2016 storms, the most extensive dredging modeled reduced water levels by at most half a foot and only at the Surrey Street bridge and Coulee Ile Des Cannes.
“The benefit is not universal in terms of the location. How much and where you dredge” is what really matters, Habib says. It remains an “open question,” he adds, whether more routine storms would see better results. A 1995 study by the Corps of Engineers suggests that dredging could see greater benefit in smaller storms, estimating a 2-foot reduction in peak water levels after 35 miles of excavation at a cost of around $30 million. Habib’s team will run the smaller storm scenarios through its Vermilion model, which includes more recent data and conditions.
Despite the unknowns, council members are chasing funding. Councilwoman Nanette Cook proposed a $5 million line item for dredging the river in an amendment to LCG’s upcoming budget. It’s not clear how much dredging that dollar amount would accomplish and where the money would come from. Elected officials are targeting state and federal pools, including a $1.2 billion flood control package authorized by Congress last year. Local dollars could be freed up by shifting funds from a handful of road projects and into stormwater diversion, as Mayor-President Joel Robideaux suggested in his introductory budget. An aide with Higgins’ office told the council earlier this month that the Corps estimated the cost of dredging hot spots — i.e. the shoals at Rotary Point and Coulee Mine — to be $5 million. Reached for comment Wednesday, a Corps spokesman could not identify the source of that figure by press time.
People are tired of studies, but studies are underway. LCG needs a permit from the Corps to dredge the river and will not receive one until after the Corps’ impact study is completed later this year. At issue is whether dredging upstream in Lafayette Parish could cause saltwater intrusion or loss of marshland in Vermilion Parish, among other complications.
What to watch for: The outcome of further study. It remains disputed among experts what effect dredging might have and what the cost-benefit would be. Come December, some unknowns will be resolved when the Corps completes its study.
Congress authorizes dredging of Vermilion River Homeowners have demanded work on the river to remove build-up believed to have worsened the historic floods of 2016.
Sen. Bill Cassidy’s office said the Corps of Engineers will release a work plan later this week, which would be the first indication of a timeline for the Vermilion dredging project.