The U.S. Army Corps of Engineers (USACE) has approved a $1.3 billion effort in Louisiana 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.
The New Orleans Times-Picayune noted July 6 that Lt. Gen. Scott Spellman, chief of engineers with the USACE, said in a letter to Congress dated July 1 that the financial benefits of the South Central Coast flood risk reduction plan will result in an annual net minimization in flood damages of more than $14 million a year.
The strategy is designed to protect individual homes and businesses, rather than build additional levees, gates or other structures, according to Spellman.
Congress must still authorize the plan and fund it in future USACE budgets.
The South Central Coast flood risk reduction plan is aimed at buildings located in the 25-year floodplain within the three parishes, or structures that have a 4 percent 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. Highway 90 and the Gulf Intracoastal Waterway.
Included are homes and businesses in 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, according to the New Orleans news source.
The plan was fashioned to rely on voluntary participation by homeowners and businesses, the newspaper noted, and it will not include buyouts or relocations of existing properties, an alternative discarded by planners as too expensive.
Some Buildings to Be Raised to 13 Feet High
The USACE identified 1,790 residential structures whose living space would be elevated no higher than 13 ft. above ground level — a height that will allow floodwaters to flow in and out beneath each structure.
At that elevation, the Corps calculated that the interior of the building will have only a 0.25 percent, or 400-year, chance of flooding, according to its estimates. That is even less than the risk faced by buildings located behind the improved New Orleans area levee system, which is designed to protect against 1 percent 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 ft. above ground level, a measure the USACE describes as "dry floodproofing." This improvement method will help the buildings withstand a 37-year storm event, the Times-Picayune reported.
The Corps found 185 warehouses that would be eligible for "wet floodproofing," including renovations up to 12 ft. above ground level. Floodwaters could enter enclosed lower areas without causing severe damage, with the changes intended to ensure the buildings' structural stability. When upgraded using this measure, the USACE told the newspaper, each structure will be strengthened enough to withstand a 71-year storm event.
Some warehouses might require more renovations to ensure flood protection for materials inside their buildings, but that added 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 USACE to determine house raising and floodproofing requirements are based on what agency officials call an intermediate rate of relative sea level rise — the combination of water rising due to global warming and local ground subsidence rates — through 2075. By then, sea levels will be 1.8 ft. higher than they are today, according to engineering estimates.
The agency estimates the floodproofing will result in homeowners and business owners saving $45.1 million in flood costs each year, although area property damage totaling about $31 million will still occur, resulting in the $14 million a year in net savings. Per USACE rules, the program's financial benefits must outweigh its costs.
To be eligible for funding, a building will have had to exist before Congress authorizes the project.
Floodproofing Plan Cost Pared Down to Save Money
In approving the floodproofing plan for the three parishes, USACE officials rejected proposals to build new extensions of existing levees as well as new ring levees around small communities in the parishes, and a long levee south of U.S. 90. The agency did so because the expense of each proposal was more than the expected savings from reduced flood damage, and the levee work also would have required significant spending on projects to mitigate environmental damage resulting from their construction.
The Times-Picayune reported that as it is, the Corps' initial floodproofing program costs will total $914.8 million, with the federal government paying $594.6 million and Louisiana responsible for $320.2 million.
The state also would be on the hook for an estimated $382,000 a year in operation and maintenance costs for the program over 50 years, beginning in 2025, which brings the total price of the project to $1.3 billion.
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