New flood maps show what goes under when the District gets wet
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What would it take to flood the National Mall, Ronald Reagan National Airport or Joint Base Anacostia-Bolling? According to the first interactive flood maps of their kind, recently released for the Washington, D.C. region: a lot, a little less than a lot and not much, respectively.
The new digital maps, available online, allow officials and members of the public to see which areas are most likely to flood during high-water events along the Potomac and Anacostia rivers and to plan accordingly. How to make the most of the maps will be the subject of a public webinar at 6 p.m. on Tuesday evening (dial-in information available here).
“The maps will assist local officials, emergency managers and the general public in making decisions before and during a flood about evacuations, road closures and moving vehicles to higher ground,” said Stacey Underwood, Silver Jackets Team coordinator with the U.S. Army Corps of Engineers.
The Silver Jackets Team, which oversaw the maps’ creation, is made up of local and federal agency staffers involved in flood mitigation and storm response.
The maps reflect the extent and depth of a freshwater flood on the Potomac, which could swell from rains far upriver as well as from local storms. They also predict impacts of a tidal flood on both the Potomac and Anacostia rivers.
The mapped area extends from Fletcher’s Cove in Northwest Washington 14 miles down the Potomac to the mouth of Broad Creek near Fort Hunt, VA. To the east, the map covers 10 miles of the Anacostia, from New York Avenue to its confluence with the Potomac.
The interactive screens cover three different reaches of the rivers. One focuses on an upper portion of the Potomac, including part of Arlington and Georgetown; another, on the lower part of the river, which includes Virginia’s flood-prone city of Alexandria and Bolling Air Force Base and residential areas in Maryland.
A third screen focuses on the Anacostia and its confluence with the Potomac. It includes several notable landmarks and assets: parts of Arlington and Fort Myer in Virginia, the National Mall and Washington Navy Yard in the District and Anacostia Naval Station in Maryland.
“As someone who spent many childhood weekends playing along these riverbanks, I've looked forward to the day when residents could have a sense of what areas will flood when the river overflows its banks,” said Peter Ahnert, hydrologist in charge at the National Weather Service Middle Atlantic River Forecast Center, in a press release.
Residents can use the map to see just how much of the river would need to rise for their properties to flood in the future. They also can use a “current forecast” viewing option to see how the river is projected to rise in real time during a storm.
But officials charged with preparing cities and facilities for such events might get the most use out of the new mapping tool. Even “near” or “minor” flooding would put portions of the Anacostia Naval Station under one to two feet of water, according to the maps. A major flood like the one caused by Tropical Storm Isabel in 2003 — which sent a storm surge eight feet above normal tide into the District’s southwest waterfront area — would flood the Washington Navy Yard and a handful of national parks along the rivers.
The makers of the maps consider their release this year timely, because it’s been 80 years since the Potomac River flood of 1936, one of the worst inundations on record for the District. The map shows the region what would be underwater today if the river rose again to its record crest of just over 11 feet.
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