$1.7 billion and 50 years and we will be no safer. But if not done we will be in peril.
Soil subsidence and rising seas are expected to reduce the height of New Orleans area levees and floodwalls by almost 2 feet in the next half century. Just to keep up the current standard of protection, the Army Corps of Engineers now proposes to spend about $1.7 billion raising 99 miles of levees and building or replacing almost 4¼ miles of floodwalls. The estimate comes from two studies released Friday for the hurricane protection systems on both sides of the Mississippi River in the New Orleans area. It’s $1.5 billion less than the Corps first calculated in December 2019, when the agency proposed elevating 102 miles of levee and building or replacing 20 miles of floodwalls, mostly on the east bank. Still, it reflects the enormous public cost simply to maintain today’s level of risk reduction in the face of sinking land and human-caused climate change.nola.com
This was an expansive study covering this whole area and determining what was needed.
The studies cover most of New Orleans and parts of Jefferson, Plaquemines, St. Bernard and St. Charles parishes. They were authorized by Congress in 2018 amid concerns that subsidence and rising seas would make parts of the levee system – as early as 2023 – too low to be certified as meeting National Flood Insurance Program standards. The legislation also requires the federal government to pay 65 percent of the project’s cost.
This is a change in terminology as the 100 year storms now are normal occurrence.
The updated reports also adopt new Corps language defining what must be provided: protection against flooding caused by levee topping that has a 1% chance of occurring in any given year. Gone are past comparisons of that risk level to surge created by a “100-year storm,” or to past storms such as Katrina, the costliest hurricane in U.S. history. “This terminology is no longer used because it falsely conveys a sense of time and lowers public risk perceptions,” the report said. Instead, the 1% flood event in the Corps’ book now represents the chance that water topping the levees would violate the National Flood Insurance Program’s base flood elevation standards for construction inside the levee system. The insurance program still refers to as a 100-year event.
The state wanted a higher standard but that request was not accepted.
The revised reports also reject Louisiana’s request to increase the protection to a 0.5% level, which used to be equated to a 200-year event. Gov. John Bel Edwards and the Southeast Louisiana Flood Protection Authority-East sought the higher standard, saying 1% was not adequate. The Corps itself has rated the levee systems in the New Orleans area as “high risk”, its second-worst level, because of the billions of dollars in damage that a flood event greater than 1% would cause. The new reports say the added costs of 0.5% protection are not as economically beneficial as the 1% level. And they say Congress authorized only 1% protection level, based on flood insurance standards in place in 2005 when Katrina struck. The reports also say the Corps improvement plans take into account only the effects of topping, and did not consider other issues such as whether segments of the levee system could fail for other reasons.
The report gave specifics for both the East and West banks. For the East bank they noted these improvements.
The new east bank report calls for elevating the height of 50 miles of earthen levees in 10-year intervals over the next 50 years. Individual lifts would increase levee heights 1 to 3 feet each time, but not each levee segment would be included in the later years. There also would be a mile of floodwall replacement and almost 2¼ miles of new floodwall, some along the Mississippi River levee in an area where an earthen levee would not fit. The river levee improvement is aimed at reducing the chance that a combination of storm surge and high river water doesn’t top the levee. The project also calls for restoring foreshore protection – large rocks that reduce the size of waves – in Lake Pontchartrain as levee improvements are made. That might require dredging to allow barges carrying the rocks to reach the worksites. The east bank project would have a “first cost” of $1.1 billion, with a positive benefit-cost ratio of 7.3. Even with the improvements, the Corps estimates that flood damage from levee topping will average $53 million a year. Without the lifts, the estimate is $246 million a year. The Corps estimated the east bank project would result in 292 more jobs over 50 years, representing $1.1 billion in labor income, and $1.3 billion in gross regional product. The state would pay $387 million of the construction cost, and would be responsible for the $479,000 annual cost of operating and maintaining the improvements. The operation and maintenance costs likely would fall to the east bank levee authority, which is funded by property taxes in Jefferson, Orleans and St. Bernard parishes.
The improvements for the West bank include the following.
The west bank project calls for 49 miles of levee lifts, replacing 268 feet of floodwalls and building 1 mile of new floodwall. It also includes almost 5⅔ acres of new foreshore rock protection. Included in the levee lifts are 10 miles of Mississippi River levee, again to account for the potential combination of storm surge and a high river. The west bank earthen levees would see individual lifts of 1½ to 3½ feet over five decades, but each segment would be lifted only once or twice during that time. The project’s “first cost” estimate of $602 million would result in a benefit-cost ratio of 4.7. The Corps estimates the improvements would reduce west bank economic damage by $8 million a year, compared to $84 million without the improvements. The project is expected to result in 158 jobs, representing $609 million in labor income, and $702 million in gross regional product. The state’s share of the west bank construction costs would be $211 million, and operation and maintenance costs would be about $400,000 a year, likely picked up by the west bank levee authority.
The topography of the land will determine much of the work.
How much each levee segment will be raised will depend on local rates of soil compaction and underlying subsidence, combined with the effects of global warming-induced sea level rise. Across the entire system, the Corps estimates that the average combination of sea level rise and subsidence through 2078 will be 1¾ to 2 feet. More rapid subsidence rates will require more height in some locations and the repeated addition of clay to keep up. A Corps spokesman said the west bank project does not include elevating the western end of the west bank levee system even higher to take into account higher storm surge levels if the proposed Upper Barataria levee system is approved for construction. That levee is to run south from the western side of Davis Pond to Raceland, to protect parts of Ascension, Assumption, Jefferson, Lafourche, St. Charles, St. James and St. John the Baptist parishes. A decision on adding height to that part of the west bank levee won’t be made until the Upper Barataria levee is approved by the Corps and authorized by Congress, possibly by the end of this year.
- By mail – U.S. Army Corps of Engineers, New Orleans District, c/o Bradley Drouant, CEMVN-PMO-L, Room 361, 7400 Leake Ave., New Orleans 70118.
- By email – CEMVN-LPVGRR@usace.army.mil.
A lot of work, a lot of money and for what is needed.