Posted on July 13, 2022
The U.S. Army Corps of Engineers has signed off on a $1.3 billion plan to elevate or floodproof 2,240 homes and businesses in Iberia, St. Martin and St. Mary parishes that are subject to storm surge flooding during tropical storms and hurricanes.
Lt. Gen. Scott Spellman, chief of engineers with the Corps, said in a letter to Congress Friday that the financial benefits of the South Central Coast flood risk reduction plan will result in an annual net reduction in flood damages of more than $14 million a year. That plan will protect individual homes and businesses, rather than build additional levees, gates or other structures, he said.
Congress must still authorize the plan and fund it in future Corps budgets.
The plan is aimed at buildings located in the 25-year floodplain in the three parishes, or buildings that have 4% chance of flooding every year from storm surges caused by a tropical system or by high water from some other weather event. Most of the properties are along or south of U.S. 90 and the Gulf Intracoastal Waterway.
Included are homes and businesses in parts of the communities of Delcambre, Emma, Avery Island, Lydia, Jeanerette, Glencoe, Cypremort Point, Charenton, Baldwin, Franklin, Centerville, Calumet, Avalon, Patterson, Idlewood, Bayou Vista, and Morgan City.
The plan will rely on voluntary participation by homeowners and businesses. It includes no buyouts or relocations of existing properties, an alternative discarded as too expensive.
Corps planners identified 1,790 residential structures whose living space would be elevated no greater than 13 feet above ground level, a height that will allow floodwaters to flow in and out beneath the home.
At that elevation, the interior of the building will have only a 0.25% or 400-year chance of flooding, according to Corps estimates. That’s even less than the risk faced by buildings located behind the improved New Orleans area levee system, which is designed to protect against 1% surge events, the so-called 100-year storm.
Another 265 non-residential structures — including 32 public buildings — would be renovated to make walls, doors, windows and other openings impermeable to water rising to up to 3 feet above ground level, a measure the Corps describes as “dry floodproofing.” The improvements will help the buildings withstand a 37-year storm event.
And 185 warehouses would be eligible for “wet floodproofing,” including renovations up to 12 feet above ground level, to allow floodwaters to enter enclosed lower areas without causing significant damage, with the changes designed to ensure the buildings’ structural stability. That will alllow the buildings to withstand a 71-year storm event.
Some warehouses might require additional renovations to ensure flood protection for materials inside their buildings, but that additional cost will not be part of the grant program unless the state agrees to pay for it, according to the Corps plan.
The flood heights used by the Corps to determine house raising and floodproofing requirements are based on what officials call an intermediate rate of relative sea level rise — the combination of water rising because of global warming and local ground subsidence rates — through 2075. By then, sea levels will be 1.8 feet higher than they are today, according to Corps estimates.
The Corps estimates the floodproofing will result in $45.1 million in avoided flood damage each year. Still, about $31 million in flood damage in the area will still occur, resulting in the $14 million a year in net savings. That represents a 1.45 to 1 benefit to cost ratio for the project; per Corps rules, the financial benefits must outweigh the costs.
To be eligible for funding, a building will have had to exist before Congress authorizes the project.
In approving the floodproofing plan, Corps officials rejected proposals to build new extensions of existing levees in the three parishes, new ring levees around small communities in the parishes, and a long levee south of U.S. 90 through all three parishes. Those were rejected because their expenses were more than the expected savings from reduced flood damage, and because the levee projects also would have required significant spending on projects to mitigate environmental damage resulting from their construction.
The Corps estimates the initial floodproofing program’s costs to total $914.8 million, with the federal government paying $594.6 million and the state responsible for $320.2 million, or a 65%-35% federal-state split.
The state also would be responsible for an estimated $382,000 a year in operation and maintenance costs for the program for 50 years, beginning in 2025, which brings the total price of the project to $1.3 billion.