Cause of Alexandria Flood Detected

U.S. Army Corps Will Present Findings at Neighborhood Meeting

Decades of run-off from construction sites in Fairfax County, producing sediment that narrowed Cameron Run, was the primary cause of the June 2006 flood that inundated the Huntington neighborhood near Alexandria, the U.S. Army Corps of Engineers has found.

In a report to be issued at a neighborhood meeting tonight, the federal agency, which studied the flood at the county's request, listed several potential long-term solutions to prevent a recurrence: a flood wall, a levee, dredging, or buying out homeowners and helping them to relocate.

All would be expensive, time-consuming fixes, said Fairfax County Board Chairman Gerald E. Connolly (D). A flood wall could cost $35 million and take 5-to-7 years to build. Dredging would initially cost $17 million to $18 million and have to be repeated periodically.

"There are no easy solutions," he said.

These alternatives were spelled out in two other major flood control studies commissioned by the county in 1977 and 1982. They were not acted on, most likely because of their expense, county officials have said.

The flooding on June 25-26 seriously damaged more than half of the neighborhood's 311 homes and caused an estimated $10 million in losses -- making it one of the area's hardest hit. The foul, sewage-laden water rose to nearly 14 feet in some locations, the county estimates.

The Corps, which is scheduled to discuss its findings with residents at tonight's meeting, said that between 1965 and 1999, five to six feet of sediment had accumulated in Cameron Run, a tributary that drains a heavily developed 31.5 square mile portion of Fairfax County, including Tysons Corner, into the Potomac River.

"Channel sedimentation had a considerable impact to flood elevations in Huntington," the agency said in the executive summary of its lengthy report.

Sedimentation is caused when soil becomes exposed and loose as it does in construction sites. Rain picks up the particles and carries them into rivers and streams. It is a common problem in highly urbanized areas.

The engineers' report cited two other demonstrable but less significant factors contributing to the flood: disruption to the channel caused by the Woodrow Wilson Bridge construction project, and development within the floodplain -- principally Jones Point and the Huntington Metro station.

The agency specifically ruled out three scenarios that generated wide speculation as possible causes in the days immediately after the flood: a barge blocking the channel at the George Washington Memorial Parkway; a release of water from Lake Barcroft, which is upstream, and the Potomac River tide stages.