Derek Ross, head of museum construction, despaired as he stared into the colossal 80-foot pit where workers were digging out the basement for the new African American history museum. The huge excavators had broken into a hard clay soil that encased much of Tiber Creek, which was buried 150 years ago. Over the decades, the soil had formed a pressurized cushion around the underground aquifer that held up other buildings on the Mall. But now, it seemed in danger of collapsing.
The water was rushing out of the aquifer more quickly than it was being replenished by the creek. It was the same aquifer that flowed under the Washington Monument, a mere 800 feet away. Ross worried that if the cushion collapsed, the monument would shift or, worse, topple over. When he closed his eyes, he saw a giant sinkhole.
“I had a recurring dream that I’d walk to work one day and the Washington Monument wouldn’t be there.”
The work had to stop. Water pumps around the monument normally used to pull extra water out of the ground during rainstorms were reconfigured to force water back underground to refill the cushion. Piezometers were installed to measure the pressure and level of groundwater.
What excavators unearthed at the site of the African American museum in 2012 was not only the long-forgotten topography of the nation’s capital, but a subterranean geology that, two centuries later, determines the city’s vulnerability to catastrophic flooding as climate change intensifies storms, rainfall and sea-level rise.
At risk are the national treasures housed inside the Federal Triangle, the low-lying area between the White House and the Capitol, home to 39 critical government facilities, $14 billion in property and irreplaceable artifacts of America’s history.
Personal treasures and the homes and businesses of Washingtonians living atop historical, buried streams across the city, are regularly inundated with raw sewage and filthy water. Urban floods can be fatal, as in August when 10 dogs drowned inside a kennel on Rhode Island Avenue NE, a location with a decades-old flood history.
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