High-Tide Flooding On The Rise, Especially Along The East Coast, Forecasters Warn

Jul 10, 2019
Originally published on July 10, 2019 9:48 pm

Sea levels are rising, and that is sending more ocean water into streets, sewers and homes. For people who live and work in coastal communities, that means more otherwise-sunny days disrupted by flooding.

"Really the future is now in terms of sea level rise impacts," says William Sweet, an oceanographer for the National Oceanic and Atmospheric Administration. Average sea levels have already started rising as a result of global climate change. "The ocean is at the brim. It's clogging storm water systems and it's spilling into streets."

For the last five years, Sweet and a team of forecasters at NOAA have been tracking the number of so-called high-tide flood days in coastal cities, in order to help local officials understand trends and plan ahead. Their latest report, released today, finds that the number of high-tide flood days is rising significantly in more than 40 coastal communities.

"Flood risk is not the same everywhere," says Sweet. "There are a lot of wet spots emerging, and they're getting worse, deeper, more widespread at a fairly rapid clip."

While West Coast and Gulf Coast cities including San Diego, Seattle, Galveston and Houston are being affected, the biggest increases in flood risk are concentrated on the East Coast.

In 2018, 12 communities broke or tied their previous records for the number of days with high-tide flooding, some with more than 20 days of storm-free flooding, according to the report. All were on the Eastern seaboard, from Massachusetts down to Florida.

"The East Coast has a very highly populated, developed coastline that has experienced relatively high rates of sea level rise over the last several decades," says Sweet.

"It has a very active coastline: the water moves when the winds or the ocean currents change," he says. "All of this is creating a situation where high-tide flooding — which is a direct result of sea level rise — is becoming apparent and more problematic throughout the coast."

That has local officials and urban planners rethinking how they engineer the those communities, budget for flooding and communicate flood risk to their residents.

In Annapolis, Md., where high-tide flooding is quickly becoming a chronic problem, the city plans to upgrade storm drains, raise roads and install pumps to keep low-lying areas dry. A study published earlier this year estimated high-tide flooding in one part of the city in 2017 cost businesses about $100,000 in lost revenue.

Police closed Dock Street in downtown Annapolis, Md., in 2017 after ocean water flooded in during a high tide.
Brian Witte / AP

The government in nearby Baltimore, Md., has joined cities in Florida and Texas in issuing flood-proofing guidance for residents living in areas prone to invasion by ocean water.

In Charleston, S.C., rising seas have combined with more extreme rain events — a phenomenon also exacerbated by climate change — to create a chronic flooding problem in the city, which sits on a low-lying peninsula.

"The entire peninsula is really affected," says Katie McKain, Charleston's director of sustainability. She says in the summer, flooding is often forecast once a week, which means it's a big part of what her office is dealing with on a daily basis. Every time there's possible flooding, public alerts need to be sent out and the police department has to close roads that are underwater.

"It's difficult," she says of the chronic road closures. "Having the personnel to do it is a challenge."

"We're planning for 2-3 feet of sea level rise over the next 50 years," says McKain. "It's just something we're getting ingrained in everyone's heads."

The city is also thinking long-term about how to adapt to future tidal flooding. Charleston's chief resilience officer, Mark Wilbert, has brought in engineers and planners from the Netherlands to help develop new infrastructure. The city is upgrading some sewers, installing valves to help keep out ocean water during particularly high tides.

Wilbert says NOAA and National Weather Service reports, such as the one published today, are some of the most important forecasting tools available to his team. He needs to know how many days of tidal flooding to expect next year, and how the trend is changing in the coming decades.

"That's really about budgeting," he says. "We're going to have to respond to each of these, [and] we're going to need resources to meet what the expected demand will be."

Boston, Mass., which experienced a whopping 19 high-tide flood days last year, has been struggling to keep up with the risks posed by rising seas. Much of the city was built on earthfill more than 100 years ago.

"At the time they were filled, sea level rise wasn't something that anyone contemplated," says Stephanie Kruel, an environmental planner at the Boston engineering firm VHB. She says the city's commercial and financial districts and "even city hall itself is very low lying."

Boston has a sweeping plan to raise roads and expand waterfront parks to help keep the water out. Kruel says Boston is also in the midst of updating its zoning laws to require new buildings in low-lying areas to have raised first floors.

While elevating buildings is relatively simple from a purely engineering standpoint, higher first floors create a variety of other urban design issues that planners like Kruel are thinking about.

For example, raised buildings need ramps or elevators for strollers and people who use wheelchairs. And raising a handful of buildings in a flood-prone neighborhood doesn't necessarily make the area less vulnerable overall.

"If one or two buildings are raised up high, that's great for them, but it doesn't really help the whole area," explains Kruel. For example, the road may remain at a lower elevation while buildings are raised, cutting people off inside their homes or businesses.

"What happens if a building becomes kind of 'islanded' by a flood, where the building itself is fine and it can recover quickly, but the whole area around it isn't prepared?" she points out. "You know, something is only as strong as its weakest link."

Sweet, of NOAA, says high-tide flood forecasting is a critical part of such long-term planning decisions. Reports like the one published today provide basic information to every coastal community, including smaller towns that may not have the engineering resources that major cities do.

"I live at the coast, I get it. It's a great place to live," says Sweet, who lives in Annapolis, Md. "It's just a hard thing to get right when the water levels keep moving. So that's what we're trying to do, is give communities the best information to make smart decisions."

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Flooding in coastal cities is happening more and more, and rainstorms aren't the only culprit. A new report out today says that means chronic flooding in many places. NPR's Rebecca Hersher explains.

REBECCA HERSHER, BYLINE: Charleston, S.C., is one of the dozens of coastal cities where high tides increasingly mean water in the streets.

KATIE MCKAIN: Yeah, there was one two weeks ago.

HERSHER: Katie McKain is the director of sustainability for the city of Charleston. She says between rising sea levels and more extreme rain - both driven by climate change - she deals with floods and the weather forecast all the time.

MCKAIN: At this time of year, it can easily be once a week or more.

HERSHER: It's expensive, it's time-consuming and it's only getting worse. High-tide flooding events in Charleston have more than doubled since 2000. And by 2030, the city is projected to experience 10 to 20 days a year of ocean flooding without any storm to cause it. That's according to an annual report on high-tide flooding from the National Oceanic and Atmospheric Administration.

Mark Wilbert is the resilience director for Charleston.

MARK WILBERT: I do think we're going to have to adapt. I think everybody up and down the coast is going to have to adapt.

HERSHER: Positions like Wilbert's are a relatively new part of city government. He started as resilience director a couple years ago, specifically because of flooding. He says forecasts like the one released today by NOAA are extremely important tools for local officials who are trying to plan city services.

WILBERT: That's really about budgeting because as we're going to have to respond to each of these, we're going to need, you know, resources to meet what the expected demand will be.

HERSHER: For example, the number of high-tide flood days affects how much money needs to be set aside for police, for sewer maintenance, for public education about how to prepare for floods. High-tide flooding can also hurt local economies. A study last year found that one sunny-day flood in Annapolis, Md., cost businesses about $100,000. The new NOAA report finds that Annapolis and nearby Baltimore and Washington, D.C., all set new records for high-tide flooding last year. And the trend is accelerating. The same is true to the South and Florida, along the Gulf Coast in cities like Houston and Galveston and to the North.

Stephanie Kruel is an environmental planner with the Boston engineering firm VHB. She says much of the city was built on dirt that was trucked in, mostly to fill marshy areas.

STEPHANIE KRUEL: At the time they were filled, sea level rise wasn't something that anybody contemplated, and so the areas that were filled were just a couple of feet above high tide.

HERSHER: But as sea levels have risen, tides have gotten higher. Today, Boston has about 20 days of high-tide flooding a year in major downtown areas.

KRUEL: We have a major commercial district, the downtown financial district. Even City Hall itself is very low-lying.

HERSHER: And then there's planning for the future. There is still demand for new office space and homes right on the water. To protect those areas, the city plans to upgrade stormwater systems and raise roads higher. Kruel says there's also a plan to require new buildings in low-lying areas to have elevated first floors, which seems straightforward, but higher first floors actually change a normal city street a lot. For one thing, buildings still need to be accessible to strollers and people in wheelchairs.

KRUEL: So now you have to deal with, you know, ramps or elevators or something like that.

HERSHER: It's an example of how cities are grappling with the basics of how they're built, and they're being forced to figure it out now, with ocean water already in the basement. Rebecca Hersher, NPR News. Transcript provided by NPR, Copyright NPR.