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Annapolis, Baltimore lead nation for rise in flooding events

Tuesday's flooding may have been extreme, but it wasn't unfamiliar for much of the region.

The low spots are well known: Compromise and Dock streets in Annapolis, Caroline and Thames streets in Fells Point. After a good rain and a high tide, they're under water.

For Maryland's two largest cities on the Chesapeake, flooding that once occurred just a day or two in any given year is increasingly common — more so than anywhere else in the country, according to a recent federal study.

So-called "nuisance" floods overwhelm storm drains 10 times as frequently as they did half a century ago — growing to nearly 40 days a year in the state capital and 13 days a year in Baltimore.

The data from the National Oceanic and Atmospheric Administration could boost pushes in Maryland and other coastal states to adapt to rising sea levels and sinking land, protecting businesses and historic sites from damage and losses. But many of those affected by flooding weren't surprised by the region's distinction, accepting most flooding events just as scientists described them — as nuisances.

"If it rains really hard and the wind's blowing just right, the street outside will flood and you'll have to close the club," said Stephen Olsen, an assistant manager at the Fleet Reserve Club on Compromise Street in Annapolis. "It's been doing it for years."

The NOAA study looked at data from 2007-2013 and compared it with data from 1957-1963, at tide gauges from Boston to Mayport, Fla., on the Atlantic coast; Key West, Fla., to Port Isabel, Texas, on the Gulf of Mexico; and Seattle to La Jolla, Calif., on the Pacific coast.

What qualifies as a "nuisance" flood varies from gauge to gauge, depending on the slope of shoreline and the presence of any man-made barriers. In parts of New York and New Jersey devastated by superstorm Sandy, for example, it takes a rise of nearly 20 inches above normal high tide levels to cause nuisance flooding. But in Annapolis, perhaps not coincidentally with its ranking, it only takes about half of that.

The researchers say it's because rising sea levels means it takes less rain and smaller tide surges to cause flooding.

"We're seeing a very drastic change in the frequency of these events," said William Sweet of NOAA, one of the authors of the study. "Any increase in the mean sea level is only going to increase the frequency and the severity."

NOAA's data shows mean sea level is rising by about three and a half millimeters each year in Annapolis, and slightly less, 3.25 millimeters, in Baltimore.

Other cities that have seen dramatic rises in flooding include Atlantic City and Sandy Hook in New Jersey; Philadelphia; Port Isabel, Texas; Charleston, S.C.; Washington, D.C.; San Francisco; and Norfolk, Va.

While some might question whether the results reflect better reporting of flood data and impacts, Sweet said it accounts for the effects of outlier storms, increases in impervious surfaces and any sinking or rising of shorelines.

"I think it's important for these communities to start looking at their current situations and ask, 'Can we really get a handle on the situation?' so at least they're ready and they're aware," Sweet said.

A report last year from a panel of scientists urged Maryland to plan for sea level rise of up to 2 feet in the next 40 years, prompting officials to urge coastal communities to adjust building codes and zoning.

In Annapolis, such efforts are underway. The Army Corps of Engineers visited historic sites in the city's downtown flood plain last week as it prepares a report evaluating vulnerabilities and suggesting protective measures, said Lisa Craig, the city's director of historic preservation.

"It's been visible to everyone," Craig said. "It's an issue that no one discounts."

City officials routinely deliver a flatbed truck full of sand for businesses along Dock Street to fill up bags before significant storms. An inflatable bladder wraps around Market House on City Dock to protect its shops.

Once or twice a year, the flooding laps on the doorsteps of Armadillo's, a restaurant and bar on Dock Street, manager John O'Leary said.

"We just kind of deal with it. It doesn't cause any structural damage typically," O'Leary said. "If it were to come up a few more inches each time, that would be different story."

But it does mean lost revenue for the restaurant and lost wages for its staff, he said.

In Fells Point, damaging floods have been limited to hurricanes like Isabel in 2003, but nuisance floods are more common — particularly this year. Rainfall at Baltimore-Washington International Thurgood Marshall Airport, the point of record for Baltimore, reached 8.6 inches in April, a tenth of an inch shy of a record dating to 1889.

Tuesday's rainfall of more than 6 inches at BWI was the second-heaviest single-day rainfall there on record. Rain is more than 10 inches above normal there so far this year.

Real estate agents at Re/MAX at the eastern terminus of Thames Street know not to park out front when a heavy rain coincides with a high tide, office manager Amy Wells said. But that doesn't mean they always remember.

"We've seen a lot of people just have to fish stuff out of their cars," as water creeps westward toward Wolfe Street, she said.

Still, to some, rare flood damage almost means little reason to prepare for the worst. Artist Robert McClintock has twice piled sand bags in front of his gallery at Thames and Ann streets only for water to stay well clear of the corner.

"It's never crested the sidewalk over there," said McClintock, gesturing toward the bulkhead across the street. "I'm debating whether I'll even do the sandbags again."

But the NOAA scientists are hoping those like McClintock change their minds.

"I wouldn't say it's a dire situation, but it's a situation that really needs to be watched," Sweet said. "We're trying to provide timely and accurate data for these communities to become as informed as possible."

sdance@baltsun.com

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