Is it finally time to plan the future withdrawal of homes and businesses from the parts of Delaware’s coastal strip that are the most vulnerable to chronic flooding from sea-level rise and the bigger storms coming with climate change? The State of Delaware thinks so.
In its new Climate Action Plan, the state’s Department of Natural Resources and Environmental Control says the state should begin to plan for moving people and infrastructure out of harm’s way as the ocean rises.
The latest warning follows a DNREC projection in 2011 that between 8 and 11 percent of the state’s land will be permanently inundated by the end of the current century. It was a startling forecast that has been echoed in the aggregate by other reputable predictions, and is now being seen locally by plans to raise roads and bridges from the most vulnerable areas.
In about 2017, the agency updated its inundation maps, adding one-foot increments which increased the maps’ usefulness. Those maps are now available for download on DNREC’s Flood Planning Tool but the agency did not refresh the 2011 analysis. It plans to update the maps again with new and better elevation data but does not expect them to be published for another year or more.
“Our goal in mapping projected sea-level rise is to create the most accurate maps using the best available data that is appropriate for stakeholders to make decisions at the spatial scale of individual properties,” said Jesse Hayden, DNREC’s Coastal Programs administrator, in a statement.
Although DNREC did not update its inundation analysis for the new report, it stands by the prediction it made 15 years ago, and urges state, county and local planners to plan for a watery future.
The new report calls on officials to “prepare a multi-decadal strategy for potential strategic retreat from areas highly vulnerable to persistent and repetitive flooding.”
The costs of raising buildings and roads in the face of rising flood waters are high and time-consuming, and that must be weighed against the alternative of moving away from the most vulnerable areas, the report said.
“While these efforts may effectively reduce risks, the long-term sustainability must be weighed in comparison to other solutions – like creating long-term plans to potentially move development and infrastructure out of harm’s way,” it said.
The report called for public education on the concept of strategic retreat, and a statewide resilience plan on how to adapt to rising seas and protect communities “including options for strategic retreat from high-risk areas.”
Even people who reject the idea of retreat from flood-prone areas should elevate their homes and build with flood-resistant materials, the report said.
Underlying DNREC’s advocacy for retreat is its new forecast for future sea-level rise, which sounds a dire warning for the approximately 10 percent of the state that is 10 feet or less above current sea level.
In the current decade, the number of days in which flooding at Lewes, for example, has increased to almost 41 days a year from about six days a year in the 1980s when measured by a “minor flood” threshold set by the National Weather Service.
At Reedy Point in New Castle County, site of the other tide gauge evaluated by the report, the number of “minor flood” days has increased to 23 from about two over the same period, the report said.
By the end of the century, both communities will see a “minor flood” almost every day under an intermediate projection for sea-level rise, the report says. It says high tides alone are already nearing the “minor flood” level, and that flooding may be worsened by weather patterns including spring tides and full moons.
‘There are many low-lying vulnerable communities and roads that begin to flood before the NWS minor threshold is reached at either gauge,” the report says. “The persistence of minor flooding without significant need from weather systems puts Delaware as transitioning into a new flood regime.”
That outlook, the report says, should underpin smart climate planning, building and maintaining coastal protections, developing infrastructure and managing farms and natural resources in a way that equals preparation for more extreme flooding events such as hurricanes or nor’easters.
“I don’t see the evacuation, that’s hard to do. What I advocate is an engineering approach. I don’t know anyone who is calling for a retreat or resettlement of a town along the Delaware Bay.Dr. Jerry Kauffman, director of the University of Delaware’s Water Resources Center,
By the end of the century, seas at the Delaware coast are expected to rise by 1.9 feet to 6.7 feet from 2000 levels, in line with DNREC’s earlier forecasts. As with previous forecasts, the rise will reflect human-caused climate change, increased in Delaware and other mid-Atlantic states by land sinking.
For now, the 2011 analysis remains relevant to showing planners and the public how Delaware will be affected by future flooding, said Susan Love, administrator in DNREC’s Sustainability and Climate Section.
“The 2011 analysis … allowed us to understand broadly which resources were the most potentially impacted and where those impacts occur. It has been very valuable in understanding the statewide scale and scope of vulnerability, which was its intent,” Love said in a statement.
While DNREC is calling for retreat planning, a more realistic option for people and businesses in flood-prone areas would be more adaptation – such as elevating buildings and roads, argued Dr. Jerry Kauffman, director of the University of Delaware’s Water Resources Center, and a contributor to the report.
“I don’t see the evacuation, that’s hard to do,” Kauffman said. “What I advocate is an engineering approach. I don’t know anyone who is calling for a retreat or resettlement of a town along the Delaware Bay. What can be done is to harden things and make them higher.”
For example, Delaware’s Department of Transportation has begun raising bridges and roadways over four creeks along Route 9 because of their vulnerability to flooding. They include the replacement of Bridge 1-305, which, along with three other bridges are in poor to fair condition, “falls within areas that are frequently flooded during higher tidal events,” DelDOT said on its website.
While Kauffman argues that retreat would be hard to achieve statewide, the town of Glenville in New Castle County suggests that it might be possible. The town was permanently evacuated and its homes bought out by the state and the county after extensive flooding brought by two hurricanes in 2003 and 2004. Almost 200 homes were damaged or destroyed, and ultimately purchased by the governments, while around 1,000 people were relocated to safer areas, Kauffman said. The flooding there was classified as a 1 in 500-year event, according to an account by the Federal Emergency Management Agency.
Since the remnants of Tropical Storm Ida caused significant flooding in the US northeast in September 2021, Delaware has escaped major weather events, leading some people to underestimate the danger of rising seas and bigger storms, Kauffman warned.
“We’re just in between floods so this is the time to plan,” he said. “A period of tranquility sets in and persuades people to think that everything is fine. But there will be another flood, that’s for certain.”
