In just six years, estimates of the cost of damage storm surges could cause to coastal communities in Louisiana have doubled, thanks to climate change and other factors, according to a new study from the Coastal Protection and Restoration Authority.
Worst-case numbers, which measure what would happen if no additional mitigation efforts were pursued, estimate annual damages in these areas at $5.5 billion from 2023, up from $2.7 billion. estimated in 2017.
The data also shows that floodwater flooding created by a hurricane with a 1% chance of occurring each year, the so-called 100-year storm, is expected to reach higher levels over the next 50 years. as global warming increases flood heights. and storm intensities.
This map shows the water levels of a 1% hurricane surge event, caused by a so-called 100-year storm in 2073, if no further coastal restoration…
The estimates were developed as starting points to use in determining which new projects should be included in the 2023 update to the state’s $50 billion, 50-year Master Plan for Coastal Restoration and Disaster Risk Reduction. hurricane, said Stuart Brown, who is overseeing the rewrite of the master plan for the authority.
Coastal Authority Chairman Chip Kline was quick to point out to members of the authority’s board of directors on Wednesday that officials already have plans to add a variety of risk reduction projects to the plan that would reduce the total potential damage. The master plan will then be presented to the state legislature next year for approval.
However, the estimates come after consecutive years of nearly unprecedented damage totals, resulting from both storm surge flooding and hurricane damage.
Tropical cyclone damage in Louisiana in 2020 totaled between $20 billion and $50 billion, according to the National Oceanic and Atmospheric Administration. This count included the effects of hurricanes Laura, Beta, Delta and Zeta.
Damage from two storms in 2021 – Tropical Storm Claudette and Hurricane Ida – totaled between $50 billion and $100 billion.
“Yes, there will still be quite a bit of risk living on the Louisiana coast,” Brown said.
10 communities most at risk
Brown said the expected annual damage in 10 areas along the coast represents 50% of the total for 2023’s worst cases, with the towns of Slidell, Eden Isles and Pearl River leading the way with annual damage estimated at $845 million. .
Fifth on this list is the potential damage of $234 million per year to the communities of Mandeville, Covington, Madisonville and Abita Springs.
The projects already under consideration for these communities in St. Tammany Parish, if added to the master plan, could, however, significantly reduce this damage. The Army Corps of Engineers has proposed a combination of $4.1 billion in hazard reduction projects at St. Tammany that could be submitted to Congress for authorization and potential future funding in early 2023.
The tentatively selected plan includes building a 16.3-mile U-shaped combination of levees and flood walls in the Slidell area and raising more than 6,600 homes up to 13 feet to meet to future 100-year flood levels. It also includes flood protection for over 1,850 non-residential structures and improved drainage along Bayou Patassat and Mile Branch.
Meanwhile, damages of $294 million a year expected for Destrehan, New Sarpy and Norco could be reduced by a $1.2 billion Corps proposal to maintain New York area hurricane levees. Orleans on the eastern shore at 100-year levels between 2023 and 2073.
Anticipated damages of $271 million a year to the communities of Luling and Boutte could be reduced by a $1.6 billion Upper Barataria hurricane risk reduction dyke, a project pending authorization and funding from Congress.
The Morgan City and Berwick areas, which are expected to suffer $245 million in annual damages, and New Iberia, which could suffer $156 million in damages annually, could see their damages reduced somewhat by the Corps’ proposal. of $1.3 billion. South-Central Coastal Risk Reduction Project.
This project recommends raising 1,790 residences up to 13 feet above the ground and protecting approximately 400 non-residential structures from flooding. The plan is still open for public comment before final approval by Corps leadership; it must then be submitted to Congress for authorization and funding.
And the Houma area is estimated to suffer $189 million in damage annually, but that number is expected to drop as additional segments of the levee system from Morganza to Gulf are completed. The 2021 infrastructure bill included $379 million for the Corps for its 65% share of the $3 billion, 92-mile project. A portion of the $106 million per year in damages for the Larose area is also expected to be reduced by improvements to the Morganza levee system.
Less clear, however, are the chances of reducing the expected $165 million in damages per year for the Lafitte, Jean Lafitte and Barataria communities, which were devastated by the surge of Hurricane Ida in 2021. Officials from the have lobbied the Corps to come up with an increased risk reduction plan, but for now, planned state-funded levee improvements in the area are limited to heights designed solely to reduce flooding in the aftermath of a 50-year overvoltage.
The $139 million in expected damage to communities in Vermilion Parish could be reduced by its inclusion in the Southwest Louisiana Hurricane Risk Reduction Project, which also includes Calcasieu and Cameron Parishes. . The $1.5 billion project, already authorized by Congress, received $120 million from a 2022 infrastructure vote to raise about 600 homes. Plans call for eventually raising a total of 3,462 homes. The project also includes a number of coastal restoration elements, some of which have already been completed.
State officials point out that many coastal restoration projects, including the use of pipeline-displaced sediment to create new wetlands in places where it will provide additional protection for levees, will also help lower sea levels. surge over the next 50 years.
Models based on a variety of factors
The model used to develop the authority’s risk estimates uses estimates of future damage to structures and their contents; non-structural assets, including roads, vehicles and crops; lost wages, sales and rent during repairs or reconstruction; travel costs related to temporary relocations; and debris cleanup and landscaping costs.
To determine when and where this damage will occur, the authority uses a separate set of models that measure wave height plus wave and other flood attributes. The surge models are calibrated by running “synthetic storms” that mimic tropical systems of varying sizes and intensities, ranging from those with a 20% chance of occurring each year to those with only 0.01 % chance, often called so-called Storms from 5 years to 1000 years.
Officials also use the models to show the water heights that would be created by a hurricane surge event with a 1% chance of occurring within a year, the so-called 100-year storm.
Surge models have undergone significant adjustments since they were last used for the 2017 master plan update, Brown said, including new information on changes in land height and water depth along on the side. Modelers also increased the number of “synthetic storms” – storm simulations run at different angles and strengths at different locations along the coast to 645, up from 446 synthetic storms used in the 2017 update.
Modeling of “future without action” flood risk and associated damage is used as a benchmark in conducting a review of new projects, with each project being connected to models to see how well they reduce risk and at what cost. As the best projects are identified, they are then dropped into the models in groups to determine how well they work together and what the final risk reduction will look like.
Brown said those results should be available by September, in the form of similar maps of potential flooding over the next five decades and expected risk reductions as the projects are completed.
Formal public hearings on the rewrite of the master plan will be scheduled after its planned release in January 2023. A final version of the plan will be presented to the Legislative Assembly later in the year.