New report shows increasing flood risk in Delaware

Portions of Cupola Park in Millsboro were flooded during Hurricane Sandy in 2012. Delaware State News/Glenn Rolfe

Rapid runoff from inland storms, the rising sea level and Atlantic Ocean surge spurred by tidal events and major weather makers all put Delaware on the map for flood risk.

That risk is even greater than what’s documented in current Federal Emergency Management Agency flood mapping, according to a recent report issued by the First Street Foundation, a nonprofit research and technology group working to define America’s growing flood dangers.

First Street Foundation’s data, based on decades of peer-reviewed research, shows that 29,084 properties (20.1%) in Sussex County are designated at risk of flooding from a major storm, as opposed to 21,689 (15%) currently marked that way through FEMA mapping.

For Kent County, First Street’s data is 4,584 properties, or 5.6%, at risk, as opposed to FEMA’s 3,083 (3.8%).

Nationwide, First Street’s flood model identifies 14.6 million properties with the same level of risk. That’s 70% more than the 8.7 million that FEMA classifies as having substantial risk or within “special flood hazard areas.”

Why the disparities?

“In environmental engineering, there is a concept called ‘stationarity,’ which assumes that today is going to be like yesterday, and tomorrow is going to be like yesterday,” said Dr. Ed Kearns, First Street Foundation’s chief data officer. “This concept used to work, but with a changing environment, it’s a poor assumption, and no longer does. FEMA’s method assumes stationarity; First Street’s does not.”

Delaware’s Department of Natural Resources and Environmental Control works in partnership with FEMA in mapping. The joint venture, called the “cooperating technical partnership,” began in 2003.

DNREC officials addressed the difference in the mapping approaches.

“The First Street Foundation, my understanding, is that they set out to try to come up with a system to estimate flood risk at properties all over the country,” said Gina Tonn, an engineer with DNREC.

“They had a number of experts on flood risk develop models that account for a number of different types of flooding and then recently put out a report and like a webtool that gives a flood risk score on individual properties. There are big differences with their approach to FEMA’s mapping approach. They are tackling the whole country at once, kind of applying the same mapping to the entire country,” she said.

“FEMA’s mapping approach tends to be more localized. FEMA gives more to us through this cooperating technical partnership to use our local knowledge to improve maps where needs are identified. There is a lot of localized information going into FEMA’s mapping process that likely is not a part of the First Street Foundation process,” said Ms. Tonn.

Mike Powell, an environmental scientist with DNREC, said First Street’s numbers could be helpful, depending on where you live.

“I think the First Street Foundation using data in those areas can show a property risk factor that may be very beneficial compared to the very crude FEMA maps that exist in those counties or watersheds,” he said.

“But in Delaware, the FEMA maps tend to be quite a bit more sophisticated. So, there are differences when you compare the First Street Foundation risk analysis to FEMA’s risk analysis, depending on what part of the country you are in and whether you are in a watershed or coastal area that FEMA has really studied in detail.”

Find your flood risk

In creating its Flood Factor model — accessible at floodfactor.com — First Street Foundation used rainfall and federal elevation data coupled with coastal flooding estimates from hurricanes. Results were checked against a national database of flood claims and historic flood paths.

First Street’s Flood Factor site offers informative interactive maps and webtools. By ZIP code, they feature:

• Summary, which identifies areas with increasing risk and projects predicted change in the number of at-risk properties in the next 30 years.

• Score Map, which shows a property’s comprehensive flood risk, ranging from 1 (low) to 10 (high).

• Historic Flooding, which includes various storm events that significantly impacted that area.

• Flood Risk Explorer, which tabulates the chance of flooding and water depth.

Portions of Oak Orchard experience flooding during a coastal storm event. Submitted photo

• Environmental Changes. A warmer atmosphere also means warmer oceans, which can intensify flooding from hurricanes and offshore storms. Sea level rise also increases coastal flood risks, as there’s more water available when high tides and coastal storms cause flooding.

• Community Solutions. Open spaces, marshes/wetlands, beach dunes and re-nourishment, rain gardens and bioswales are among community solutions to help protect areas from flooding.

First Street’s Flood Factor also offers risk reducers, such as zoning, building codes, evacuation plans, risk communication, levees/floodwalls and natural storage.

By the numbers

Not surprisingly, flood risk in Delaware is more prominent in Sussex County because of its low-lying coastal area and inland bays.
Flood Factor’s interactive webtool offers pinpoint detail. With a street address and ZIP code, property owners can instantly find projected flood risk.

In the Bethany Beach/19930 ZIP code, approximately 2,135 properties are already at risk. Within 30 years, some 2,186 – or 99% of the total 2,208 — will be at risk, according to Flood Factor data.

For nearby Ocean View (19970 ZIP code), Flood Factor shows approximately 3,114 properties already at risk, with 5,300 projected at risk within three decades.

Flood Factor’s assessment of a property in the 500 block of North Bradford Street in Seaford is “minimal flood factor. … Although flood risks across the country are changing because of the environment, this property is unlikely to flood over the next 30 years.”

In Rehoboth Beach, a property on Maryland Avenue is also designated “minimal flood factor,” although flood insurance is recommended.

As another example, in the Millsboro/19966 ZIP code area, 2,889 properties this year have a 0.2% chance of experiencing some sort of flooding, with the majority experiencing 1½ feet or less and 466 flooding 4 feet or higher. In 2050, the number of properties with flooding probability at 4 feet or more increase to 666 in the Millsboro ZIP code, according to Flood Factor.

Along the coast, Flood Factor’s Risk Explorer identifies 33 properties in the Rehoboth Beach/19971 ZIP code having a 0.2% likelihood of flooding this year. The number rises to 140 in 15 years and 247 in 30 years. There are two properties identified as having a 50% chance of being impacted by flooding this year.

Further inland, the Seaford area (19973), through which the Nanticoke River flows, is projected to increase from 2,076 properties now at flood risk to 2,180 within 30 years.

In the Georgetown/19947 zone, 1,080 properties presently have a slim risk of minimal flooding. That risk only increases to 1,172 within three decades. This year, 33 properties in Georgetown’s zone identified by Flood Factor as having a 1 in 5 chance of some water reaching the building, and in 15 years, the number with 20% risk ups to 36.

The report shows the Milford/19963 area is more prone to flooding. This year, 68 properties have a 20% chance of some degree of flooding and 14 have a 50% chance.

There is flooding history from storms. Based on re-created Flood Factor models, Milford was impacted by Hurricane Isabel’s storm surge in 2003 (51 properties), a nor’easter in November 2009 (six properties) and Hurricane Irene’s storm surge in 2011, which impacted 29 properties.

Report called ‘forward-looking’

Chris Bason, executive director of the Delaware Center for Inland Bays, considers First Street Foundation’s report and data very timely and beneficial.

“I think they did a good job of describing some things that most people, at like a basic level, kind of understand, which is that flooding is increasing, and it is going to continue to increase due to a few factors,” he said.

“What sets this study apart is (that) the process that FEMA uses to determine flood plains is sort of backwards-looking. It looks at what has happened in the past. Then, this process that this organization put together, they were forward-looking. They were incorporating the projections on climate change. That included increased sea levels, increased extreme rain events and, I believe, also storm intensity and how that interacts with sea level rise.”

Mr. Bason said First Street’s report “is interacting with another factor, which is Americans’ and Delawareans’ and new Delawareans’ desire to live as close to the water as possible.”

“It’s like two freight trains running at each other, in terms of what it can mean for damage to property and public safety in the future,” he said. “It is really important in Delaware, particularly Sussex County, because our elevation is so low. So much of our land is so close to sea level. The land itself is sinking, and the water is going up. That’s for sure.”

First Street Foundation’s report, developed by more than 80 of the world’s leading hydrologists, researchers and data scientists — including those from Columbia University, George Mason University, the Massachusetts Institute of Technology and Rutgers University — built model outputs incorporating data from FEMA, the U.S. Geological Survey, the National Oceanic and Atmospheric Administration and other governmental agencies.

Weathering the storm

In light of First Street Foundation’s report, Mr. Powell believes FEMA and DNREC have done their homework and that Delaware will weather the storm.

“I think it is safe to say that Delaware is in better shape with regard to the FEMA flood plain maps than a lot of states. For the most part in Delaware, for watersheds that are large enough to have a significant flood risk that has been done, that approach has been done,” he said.

“There are parts of the country, I believe, actually many parts of the country where large watersheds, watersheds that have plenty of size to create enough runoff to cause significant flooding, that have never been mapped to that level of detail (of the First Street report). In fact, they have never been mapped using that kind of rainfall runoff modeling approach. Or if they have, it has been a very rudimentary approach, because budgets just historically have not allowed FEMA to create detailed maps based on hydrologic models in some parts of the country.”

According to Ms. Tonn, flood maps are generally built based on hydrologic and hydraulic models.

“So, engineering models that kind of simulate how much water is flowing into a stream or a river … then what the flow rate is during the storm and then also taking into account the topography, the shape of the land and the stream that the water is flowing through, so that you can estimate a height of the floodwater,” she said.

“When you are talking about FEMA maps, you usually are talking about the 1% annual chance flood or the ‘100-year flood,’ as it is often called … estimating what the flow rate would be in that level of a storm and then figuring out how high the water level would get.”

FEMA’s flood insurance rate maps “are intended to be based on current conditions, because that is what they set flood insurance rates on. So, sea level rise is only really accounted for as it has happened so far,” said Ms. Tonn.

“Another thing to note is FEMA’s maps are kind of focused on certain types of flooding and may show flood risk in areas where FEMA hasn’t done any mapping. That would be a distinction between the two. They may be showing more properties at flood risk because they are looking at all properties across the country, and FEMA’s mapping doesn’t necessarily include at-risk areas. There is certain criteria that FEMA uses to decide where flood plain mapping is needed,” she added.

Partnerships are productive

DNREC’s partnership with FEMA has provided “a great opportunity for us to steer flood risk mapping in Delaware more than we already had in the past,” Mr. Powell said.

“FEMA recognizes that state and even municipal and county entities are in a great position to know where flood risk mapping issues exist, and so they created this partnership opportunity,” he said.

“I would say before 2003, FEMA certainly consulted heavily with DNREC, but after 2003, FEMA has helped us actually do flood plain mapping for them in Delaware. Not all of it and not even most of it, but to a significant extent, we are producing flood plain maps that FEMA reviews and then adopts as their own official federal flood plain map. They still do their own flood plain mapping in Delaware and elsewhere, as well.

“As a general rule, FEMA tells us through their website, through their educational materials, that roughly 20% of flood insurance claims and flood-related disasters have occurred outside of mapped flood plains. So, it would make sense that FEMA recognizes that one-fifth of flood claims and disaster assistance are occurring outside of their mapped 1%, 100-year flood plain,” Mr. Powell said.

Development and risky business

“Where you get into an interesting management challenge is that these flood plain maps are not only used for insurance, they are also used for building and construction and development standards,” Mr. Powell said.

“So, the flood plain map that is probably accurate right now in Delaware along the coast is used to make decisions about buildings, about subdivision designs that will be around for many, many decades. And that is where the fact that the maps are not predicting future flood levels but rather current flood levels, it becomes problematic. You want your house that has a floor elevation of, let’s say, 10 feet above sea level because that is how you design it today. Well, you want that house to remain safe from flooding to a design standard throughout its lifetime.”

Because FEMA’s maps are current flood risk assessments, not future risk assessments, DNREC encourages communities to enact development standards that “require floor elevations to be 18 inches above the current flood level, which could do a pretty good job of ensuring that the building is 18 inches higher than the current predicted 1% flood level but also gets it some protection out into the future as those heights increase,” Mr. Powell said.

Mr. Bason said teamwork is necessary to keep residents, visitors and natural resources safe.

“There certainly is a policy element to ensure that people are safe and that the shared resources that we all rely on are protected. In Sussex County, our inland bays, our coast, our waters, drive the economy, especially in eastern Sussex,” he said.

“We’re very much a tourism-based, real estate-based economy. It’s all interrelated to these amazing natural resources we have. People are coming here for those resources and low taxes, and that’s the whole thing. So, we’ve got to protect it.”

Mr. Bason envisions a potential line of flood protection through Sussex County’s forthcoming ordinance update discussion on buffers.

“In terms of current events, the county is working on improving an ordinance it has for buffers between new development and wetlands and waters. It is stalled right now, because of the pandemic, but if the county were to adopt that ordinance, it would provide an additional buffer area between new residential subdivisions and our wetlands and our waters. So, it would add some protection,” Mr. Bason said.

“There is individual responsibility there. There is an educational component in there, as well, and studies like this do help.”

Money talks

In his long tenure with DNREC, Mr. Powell has seen several iterations of coastal flood studies in Delaware, done by FEMA with usually a lot of the modeling performed by the Army Corps of Engineers and with independent private engineering firms.

“And in the 30 years that I have worked for the department, we have had three major coastal flood studies. I don’t think FEMA has a plan to do a major coastal flood study once every 10 years, but that seems to be about how it is has worked out,” said Mr. Powell.

“So, the amount of sea level rise that happens in a 10-year period is relatively insignificant over a 10-year period. So, updating the FEMA maps every decade, the flood heights along the coast should reflect the current conditions,” he said.

Mr. Powell added that funding is needed.

A boat along Sussex County’s coastal area capsizes during a major storm event. Submitted photo

“I wish that funding levels were sufficient to have regularly scheduled flood map updates everywhere, but it is just not the world we live in. I would say that we are trying to be judicious with the available resources that we have. We are a prioritization process and a prioritization group comprised of DNREC, (the Delaware Department of Transportation), municipal officials, to help us identify areas where there are needs for improvements to the flood plain maps,” he said.

“We look at things like places where property owners or developers challenge the accuracy of the maps to FEMA, which is very frequent. Frequently, people will argue that the map is not accurate at their location, and FEMA will review information submitted by the property owner and change the map. If we see a cluster of those in a given area, we recognize that that watershed may have some flood mapping issues and try to be responsive to those areas. But there is no set schedule.”

Insurance market

Delaware, in 20 years from 1997 to 2016, had a 13% decrease in flood insurance claim costs, one of six states to experience a decrease, according to research analyst Adam Johnson for QuoteWizard, a Seattle-based insurance comparison website.

“It comes down to the severity of the flood events that have happened over the last 20 years,” Mr. Johnson said.

Run by FEMA, the National Flood Insurance Program is a special insurance policy that is outside of standard home insurance policy, covering flood damage. The number of households in Delaware with active NFIP policies was just over 26,786, or about 6.1%, seventh highest in the U.S., according to Mr. Johnson.

Delaware’s annual average flood insurance rate of $724 is the 15th least expensive in the nation. The national average is $699, according to QuoteWizard.