Nation's capital sinking into the sea, study says

Adam Silverman | The Burlington (Vt.) Free Press

To some, the results of a study that concludes the District of Columbia is sinking is a physical manifestation of the political environment in the nation's capital.

But new research from the U.S. Geological Survey and the University of Vermont shows that the land in the district — where the Lincoln Memorial was built on silt dredged from the Potomac River — is expected to fall 6 inches or more during the next 100 years, raising flood fears and adding to worries about the effect of rising sea levels on low-lying cities across the USA.

"It's ironic that the nation's capital, the place least responsive to the dangers of climate change, is sitting in one of the worst spots it could be," Paul Bierman, a geologist at the University of Vermont in Burlington and senior author of a new paper about Washington's descent, said in a statement. "Will the Congress just sit there with their feet getting ever wetter?"

The scientists made no attempt to predict that.

"This falling land will exacerbate the flooding that the nation's capital faces from rising ocean waters due to a warming climate and melting ice sheets — accelerating the threat to the region's monuments, roads, wildlife refuges and military installations," University of Vermont researchers said in releasing the findings Tuesday. The paper was published online this week in the journal GSA Today.

Washington was founded July 16, 1790, near the confluence of the Potomac and Anacostia rivers. Although long-told tales of the region say the city named after George Washington was built on a swamp, the story is little more than urban legend, according to a 2014 essay by city historian Don Hawkins in The Washington Post.

But the study indicates that Washington is likely to become a lot wetter by 2100.

Study results confirm a long-held hypothesis, said Ben DeJong, the report's lead author. He researched land and sea around the Chesapeake Bay while a doctoral student at the University of Vermont with support from the U.S. Geological Survey.

Tide gauges in the Chesapeake Bay have shown for 60 years that sea level "is rising at twice the global average rate and faster than elsewhere on the East Coast." The hypothesis: Land in the Chesapeake region that had been pushed up by the weight of a prehistoric ice sheet has been settling down again since the ice sheet melted some 20,000 years ago.

To prove the theory, scientists drilled extensively in Maryland's coastal plain — 70 boreholes, some as deep as 100 feet, in and around the Blackwater National Wildlife Refuge on the Chesapeake Bay's eastern shore.

Then DeJong and the research team "examined layers of sediment in these deep cores, using a suite of techniques to calculate the age of the sand, other rocks, and organic matter in each layer," the University of Vermont said.

Finally, geologists combined the data with maps to create detailed, three-dimensional portraits of the Chesapeake Bay region during periods that stretched back several million years. The data overall convinced the scientists their model is bullet proof.

The sinking, known as subsidence, is just beginning geologically speaking and "will last for millennia," the university said.

A sinking capital on a river that is influenced by the tides could be problematic enough, but climate change adds to the concerns. The Intergovernmental Panel on Climate Change predicts a rise in global sea level of 1 to 3 feet by 2100 because of global warming, the University of Vermont noted.

Southeastern Virginia, especially around Norfolk and Hampton where the federal government has naval and Air Force bases, has one of the highest rates of relative sea-level rise on the Atlantic Coast precisely because of the combination of subsidence and sea-level rise, U.S. Geological Survey scientists said have said previously.

"Right now is the time to start making preparations," DeJong said. "Six extra inches of water really matters in this part of the world."

Participating in the study were scientists from the U.S. Geological Survey, the University of Vermont, Utah State University, Berkeley Geochronology Center in California and Imperial College in London.

Cities most at risk

A 2013 World Bank study says five of the top 10 cities worldwide at greatest monetary risk of storm damage from rising sea levels and subsidence are on the East Coast and don't include Washington.

1. Guangzhou, China

2. Miami

3. New York

4. New Orleans

5. Mumbai, India

6. Nagoya, Japan

7. Tampa

8. Boston

9. Shenzhen, China

10. Osaka, Japan

Source: World Bank