State and local officials are rejecting a new report that says coastal states including Delaware need to spend billions of dollars on thousands of miles of sea walls to defend themselves against projected sea-level rise by 2040.
Sea walls might work in some places but are not appropriate, the officials said, on a scale proposed in the recent report from the Center for Climate Integrity, a national nonprofit, which proposes the construction of some 50,000 miles of walls around the country, including an eye-popping 941 miles in Delaware at a cost of $9.4 billion.
Experts from the Department of Natural Resources and Environmental Control and the Delaware Geological Survey defended Delaware’s use of a variety of strategies and said they are being widely adopted as seas rise.
“The study’s approach of evaluating one uniform flood mitigation strategy is not a realistic coastal defense that would be implemented,” DNREC said in a statement, referring to the report, titled: “High Tide Tax: The Price to Protect Coastal Communities from Rising Seas”.
The department said sea walls are used in some urban locations to prevent flooding and erosion but they are “almost never” used over a large area because, in part, they are much more expensive than other kinds of coastal defense.
The current approach includes building and maintaining protective dunes to guard against storms and rising seas, DNREC said. It noted that coastal defenses are part of the state’s Climate and Energy Plan, which was funded in this year’s budget and will be developed over the next 12-15 months.
John Callahan, lead author of the Delaware Geological Survey’s latest study on sea-level rise, said the sea wall proposal ignores a range of other solutions that are being pursued by Delaware.
“In Delaware, using sea walls is only one strategy for protecting communities and resources from sea-level rise and coastal flooding,” he said.
Other techniques include raising structures, building up marshes and replenishing beaches, depending on what is appropriate for each location.
“Every case of implementing mitigation projects is based upon the specific location surroundings, cause of the flooding, owners of the properties involved, and other factors,” Callahan wrote in an email. “Many of the more natural strategies, as opposed to shoreline hardening, allows for natural migration of shorelines and marshes, protects existing habitats of flora and fauna while keeping their ecosystem services, and overall produces a more resilient system to storms.“
The projected cost of the proposed sea walls would exceed not only the entire state budget but would also be beyond the means of many coastal communities.
In Lewes, one of the most vulnerable cities to sea-level rise, officials have no plans to build sea walls but are curbing coastal development and taking other measures to reduce flooding, said Mayor Ted Becker.
The city is also defending itself by requiring that new structures are built with 18 inches of “freeboard” – the level of the bottom of a house above the ground – a requirement that was increased in 2015, Becker said.
Asked whether Lewes will be able to defend itself against higher seas in 2040, Becker said officials are looking at whether to require even more “freeboard” and more pervious surface around new buildings to allow storm water to drain naturally into the soil rather than running off to flood streets and homes.
“We’re working as diligently as we can to make sure we are capable of addressing sea-level rise as it occurs, and in a proactive manner,” he said.
Within the state, Sussex County would face the biggest bill, $4 billion, for building the projected sea walls, while the most expensive defenses among Delaware’s cities would be at Lewes, which would have to pay $286 million, the report said.
The cost estimates assume relatively low carbon-emission scenarios, with their resulting climate-change effects, as calculated by the Intergovernmental Panel on Climate Change.
Under the two lowest scenarios, the global mean sea level will likely rise 11-24 inches, and 14-28 inches, respectively, by 2100, said the report
But under the IPCC’s two higher scenarios — which the new report called “more plausible” given that most countries are not meeting the emissions cuts that scientists say are needed to avert the worst effects of climate change -- seas are projected to rise between 15 and 39 inches by the end of the century.
Still, the cost estimates are based on the two lower scenarios, combined with a one-year storm surge, in an effort to focus discussion on baseline costs for defending coastal communities rather than looking at the consequences of higher emissions levels, even if they are seen as more realistic, the report said.
In Delaware, state officials project a rise of 1.3 feet by 2050, according to a mid-range forecast by the state’s Sea Level Rise Technical Committee, in a 2017 report. The panel also presented high and low forecasts of 1.9 and 0.72 feet, respectively, by 2050, while predicting that waters could rise as much as five feet by the end of the century.
Richard Wiles, executive director of the Center for Climate Integrity, said the projected mileage of sea walls in coastal states was calculated by identifying areas that have infrastructure – usually roads – that would be flooded by 2040, based on sea-level rise forecasts, assuming one of the two lower scenarios for carbon emissions.
He called the projection a “very conservative approach” given that most resilience planners assume a longer timeline and a 100-year storm.
The sea wall cost estimates are based on national standards followed by engineers plus local estimates from sea wall construction companies, leading to per-foot cost estimates, the report said.
Critics of sea walls say they merely divert water to vulnerable coastal areas, and prevent the buildup of marshes that are an essential part of the coast’s natural response to rising seas.
Wiles, in an email, acknowledged that sea walls may not be appropriate in every location but argued that they represent a minimum investment, and are a consistent way of measuring the cost of defending the coast nationwide.
In light of the huge construction costs that could not be met by local or even state governments, the report says the fossil fuel industry should pay because it has spent decades making huge profits from products that it has long known were damaging to the environment.
“Failing to hold polluters to this basic responsibility would be to knowingly bankrupt hundreds of communities, standing idly by as they are slowly and inexorably swallowed up by the sea,” the report said.
Like other mid-Atlantic states, Delaware is particularly vulnerable to rising seas because its land is sinking at the same time as waters are rising, resulting in the local rate of sea level rise at about twice what it is globally.
Recognizing that, the state is building sea-level rise into its plans at every level, improving communication between government departments, expanding funding opportunities, and increasing regulatory flexibility, Callahan said.
He cited the recent rebuilding of Prime Hook National Wildlife Reserve which is no longer being flooded by ocean water because dunes have been widened, channels have been diverted, and vegetation has been regrown, giving the southern Delaware preserve a better chance of surviving a future of higher seas.
“All of these actions play a large role in reducing the impacts of coastal flooding and building resilience for the future,” he said.
