Home  •   Search  •   Newsletter/Archive  •   Contact Us   

March 5, 2007

Dear Coalition Friends:

This article from the Northwest Current reports in greater detail on last month's hearing at the National Capital Planning Commission when the Flood and Stormwater report describing potentially disastrous impacts on the National Mall and adjacent areas, discussed in our last update, was presented to Commissioners. It bears reading to the end:

By ELIZABETH WIENER
Current Staff Writer

A draft report by the National Capital Planning Commission presents a disturbing picture of why areas of downtown Washington and the National Mall are prone to flooding, and it offers ominous warnings of future floods unless major improvements are made.

The report presented to the full commission last week was spurred by the disastrous and unexpected flood of June 2006, when heavy rains left parts of the Mall and Constitution Avenue under water and forced closure of several federal agencies and Smithsonian museums.

But neither the new report, nor an ongoing study by the General Services Administration, has pinpointed a precise cause. The flooding was worse than expected given the amount of rain -- just over seven inches in one day -- but the waters also retreated much more quickly than expected, the report says, and the Potomac River remained below flood stage during the entire storm.

It is clear the low-lying Mall and Federal Triangle area are prone to flooding because of their location at the confluence of two rivers and atop three major streams -- Tiber Creek, James Creek and Slash Run. The Mall itself was once underwater, and the water table under the White House lawn is only two feet beneath the surface.

Downtown D.C. has experienced major floods five times in the past 120 years, but last June's flood was particularly damaging, shutting down operations at the Internal Revenue Service headquarters and the Commerce Department, Justice Department and National Archives buildings. Some damage has still not been repaired.

But the report puts major blame not on the area's rivers and creeks, but on the city's antiquated storm-water system, with its combined sewage and storm-water pipes that spill over into the Potomac and Anacostia rivers in times of high flow. They may simply lack adequate capacity to serve the Federal Triangle area, the report says.

This so-called "urban drainage flooding," said Michelle Desiderio, a commission planner who prepared the report, has no simple or inexpensive remedy.

Combined sewers are common in older cities, dumping storm water into the sewage treatment system and overflow into the rivers. The D.C. Water and Sewer Authority is now working under a consent decree to build storage tunnels to hold the excess untreated water, but even that 20-year, $1.9 billion project will not solve the downtown area's capacity problems, the report says.

Even with other flood control improvements, "urban drainage flooding remains an unmitigated flooding risk," the report says, with downtown areas of the city "especially susceptible to interior flooding."

The report highlights a mystery of sorts. Desiderio said her research indicates that pumps in buildings in the Federal Triangle "routinely generate" huge amounts of water that must be carried off by the D.C. Water and Sewer Authority's already overloaded pipes -- "up to 2 million gallons of water a day, before the Ronald Reagan Building was built. How much of the flood was caused by this dewatering?" she asked.

But Mike McGill of the General Services Administration said he believes a separate storm-water pipe was installed in the 1990s specifically to serve the Federal Triangle. McGill said he is confident that pipe is connected and dumps overflow into the Potomac River. But it does not show up on maps used to prepare the planning commission's report.

A separate problem is the earthen levee installed along the north side of the Mall after the "Great Flood" of 1936. The levee was never completed, and the Corps now says it needs to make two permanent closures -- at 23rd Street and Fort McNair -- as well as improve a temporary barrier at 17th Street, to make the levee effective.

Bitten by its experience in New Orleans, according to Desiderio, the Corps now "won't certify the levee" as protecting areas outside the 100-year flood plain until those improvements are made.

The Corps estimates that a major flood in Washington could cause more than $200 million in damages if those improvements are not completed, but it has not yet been able to persuade Congress to appropriate the estimated $7 million needed to complete the levee work, Desiderio said.

John Parsons, a top planner for the National Park Service, said he remembers shoveling sand at 17th Street during last June's flood. He said the levee improvements are critical and that "$7 million is peanuts, and $7 million to the Corps should be our highest priority."

Long-term trends are also disturbing. The report says water levels in the Chesapeake Bay are expected to rise by a foot over the next 100 years and that maps of the 100-year flood plain around the Mall and downtown area may no longer be accurate.

Desiderio quoted a forecast by Smithsonian scientists that a 1-foot rise in the water level of the Potomac River combined with a major storm surge "would make the Jefferson Memorial an island and flood the National Mall up to the Reflecting Pool."

New construction on the Mall and its environs is also creating more impervious surface and reducing the bare land and vegetation that absorb rainfall and storm-water runoff, the report says.

One map in the report is labeled "Areas of Residual Flooding," and it shows low-lying spots particularly prone to floods. Commission member Herbert Ames pointed out a large patch on the map near the site of the proposed new underground visitors center for the Vietnam Veterans Memorial.

"How close is that to the visitors center?" Ames asked.

"It's on top of it," Desiderio replied.

Yet "we have close to a congressional mandate to build there," Ames sputtered. "In private business, it would be absolutely crazy to build an underground center in a flood plain."

The new report says flooding in Washington's monumental core poses a risk to "national cultural and historic resources, a financial risk for property damage, and a security risk given the concentration of key federal functions."

But the solutions listed are vague: increased scrutiny of projects built near or within the floodplain, innovative storm-water management techniques and better cooperation between the myriad federal and local agencies that bear responsibility for flood control.

Back to the top

Copyright © 2004 National Coalition to Save Our Mall Inc. All Rights Reserved