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Posted at 11:43 AM ET, 11/01/2012

If Hurricane Sandy had come south: the dramatic storm surge scenario for Washington, D.C.


GIS inundation maps for different amounts of water level rise around the tidal basin in Washington, D.C. The water levels shown are 0.4 m (1.3 feet, top left), 1 m ( 3.2 feet, top right), 2.5 m (8.2 feet, bottom left) and 5 m (16 feet, bottom right) (Risk Analysis)
What if Hurricane Sandy, and its massive storm surge, had tracked 300 miles further south, making landfall near Virginia Beach instead of Atlantic City?

In such a scenario, assuming the storm continued tracking inland to the south, the storm’s wind and waves would have piled water into the Chesapeake Bay, forcing a massive surge up the Potomac River, inundating low lying areas of Washington, D.C.

A 2011 study in the journal Risk Analysis analyzed the impacts of rising water levels in Washington, D.C. painting a grim picture of the aftermath. The study focus was on scenarios of gradually rising sea levels from climate change over the course of decades to centuries but acknowledged a landfalling coastal storm could temporarily swamp portions of the city today, just as Sandy marooned parts of New York City.

Capital Weather Gang writer Andrew Freedman discussed the study’s results in a 2011 blog post, a portion of which I’ll republish here (refer to the top image for the accompanying illustration) - bold text indicates my added emphasis:

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For illustrative purposes, the study shows that with 5 meters, or 16 feet, of sea level rise, the National Gallery of Art, FBI, IRS, Department of Justice, Federal Trade Commission, and Department of Education would all be under water.

. . .

The study makes clear that even modest amounts of sea level rise would have negative impacts on the city:

At 0.1 m [ or 0.3 feet of sea level rise], the impact seems deceptively small. The city, however, would have to act. The city has the option to accommodate to the increasing levels by insulating buildings, the metro, and allowing some areas to flood.

As Washington, DC is an important political and cultural center of the United States, this option will inevitably cause damage, and leave the city vulnerable to further rises in SLR.

Protecting the city by building flood barriers might be a more practical solution. At the current predictions, the barriers do not have to be especially high to protect the city. As sea levels increase, they would have to be increased in height and reinforced. City planners should also consider SLR in defining or changing land use.

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Sandy probably wouldn’t have generated the worst case 5 meter or 16 foot surge [shown above, bottom right], but something more on the order of 8-10 feet - represented in the bottom left panel of the above image.

The District has some recent experience with a storm surge of this magnitude. In 2003, Hurricane Isabel pushed a 8 foot tidal surge up the Potomac - which is about half the height of the worst case scenario in the Risk Analysis study.

Capital Weather Gang’s Steve Tracton discussed some of the effects from Isabel in a retrospective in 2008:

“The flooding near my home from Isabel [in southwest D.C.] was quite impressive, as water overtopped the wall along Washington Channel onto, yes, Water Street, from just under I-395 southeast to the, yes, Titanic Memorial. The well known Washington D.C. Fish Market was inundated, and nearby underground parking garages were flooded with cars bobbing around like toy ducks in a bathtub.”

The National Weather Service provided the following summary of the effects in Virginia and Maryland:

In Old Town, Alexandria:

“Portions of King Street near the intersection of Union Street were under as much as 5 to 6 feet of water. The area is about two blocks from the Potomac River.”

In Annapolis (from Chesapeake Bay Surge):

“Flooding caused by Hurricane Isabel caused extensive damage at the Naval Academy in Annapolis, Md. Half the classrooms were unusable. Lab equipment, plumbing and ventilation systems were also damaged. Several buildings were sandbagged, but officials say they underestimated the storm. Some parts of campus were covered by eight feet of water.”

It’s not out of the question, under the right set of circumstances (a strong hurricane - category 3 or higher - making landfall south of Washington, and tracking to the northwest), a stronger storm could collide with the southern mid-Atlantic and generate a higher storm surge than Isabel (or a Sandy-like storm displaced to the south). The reality of such a possibility - along with the slowly creeping sea level rise from climate warming - should serve as a compelling call to action for local infrastructure planners.

Post script: The National Capital Planning Commission says construction of a National Mall Levee is in progress to protect that area from flooding. Related link: DC Levee Upgrade Races Against Climate Change

By  |  11:43 AM ET, 11/01/2012

Categories:  Latest, Floods, Tropical Weather

 
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