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Flood Control Mechanism on Public View

New Alexandria remains a flood-prone area.

Those who suffered some of the worst devastation from Hurricane Isabel two years ago were treated to a first-hand look at some of the control measures in place to regulate not only tropical storms but also plain old heavy rainfall.

That was the impetus behind last Saturday's Open House at the Belle View/New Alexandria Stormwater Pumping Station. "This is a community outreach and education program to tell the community what protection they have and what they don't have," said Don Lacquement, Fairfax County Stormwater Planning Division.

"These people (residents of New Alexandria) live in a floodplain. This is their chance to see the inner working of the Stormwater Pump Station and Tide Gate and how the system is designed to give some protection in potential flooding situations," Lacquement said.

Joining him were Craig M. Thomas, environmental protection specialist, U.S. Army Corps of Engineers, and Kathryn Moore, an engineer with Fairfax County. Located just behind the Belle View Shopping Center, 13th and I streets, the pump station and a smaller flood-gate facility several blocks closer to the river serve as control mechanisms to deal with slow or fast rising waters.

"We are involved in this effort in response to the county. We have an existing study ongoing with the county that takes into account 100 different scenarios dealing with everything from hurricanes to large rain storms," said Thomas.

"Our study is limited to the Belle Haven watershed. It also offers general recommendations as to what the county can do to alleviate or help flooding situations," he said.

PART OF THE CORPS' study involves updating the floodplain map not only as it applies to major storms, such as hurricanes, but also the impact of heavy rain storms. Titled "Flood Inundation Areas by Elevation," the map, on display at the open house, identified those areas most vulnerable to flooding under various scenarios.

"This station is built over a large holding tank that goes down 13 feet below sea level. When it rains, water enters the holding tank and is then released into the river," Moore explained to the area residents attending the public education session.

This is accomplished by four large pumps that automatically go into operation depending on the demand of water volume. "At a certain level, pump number one turns on and, as the demand increases, the other three pumps come on accordingly," Moore said.

"Everything is automatic. No one needs to be here at the station. If there is a power loss, there is also an automatic generator that activates to operate the pumps," she said. "The system is checked out daily."

Each Tide Gate operates according to the water level, according to Lacquement. "If it senses a water level of four feet, it closes automatically. It will back flood water of up to eight feet above mean sea level," he said.

The smaller station's tide gate will automatically close when it senses a high tide or a storm surge, according to the engineers. "There are two vulnerable areas in New Alexandria of 40 and 50 acres each," Lacquement said.

THE JOINT STUDY by the Corps and Fairfax County "will determine the floodplain limits for various frequencies of flooding, taking into account overland flooding within the Belle Haven watershed along with tidal and non-tidal flooding influences of the Potomac River." Results will hopefully lead to a plan for future flood-control improvements, according to Thomas.

Due to the severe flood of the New Alexandria area during Hurricane Isabel, it was determined that the existing hydraulic models for the area do not take into account the time factor when overland flooding and tidal-backwater flooding occur simultaneously. The new modeling and mapping "will enhance the county's ability to prepare for future flooding events" due from either tropical storms or heavy rainfall in a short period of time.

Scheduled for completion by the end of next month, the study encompasses the following: data collection, watershed reconnaissance, hydraulic analysis and floodplain mapping, and flood damage reduction recommendations. It will all be detailed in a report to be prepared for the county by the corps.

"This is the first step in what we hope will be a continuing partnership between Fairfax County and the Corps of Engineers to reduce the risk of flooding for residents in the floodplain. It is important to understand that the recommendations the Corps is providing as a part of this study will not be detailed designs or a single recommended solution. They will be more general recommendations about feasible alternatives to reduce damages from flooding," Lacquement said.

"THESE RECOMMENDATIONS will be the basis for the corps' cost-benefit analysis. This will determine whether or not the corps believes the project warrants federal funding. It is our hope that the results will show that this area qualifies for additional federal funding. The existing facilities provide a measure of protection for the most vulnerable areas. The question is what additional measures are feasible and whether the county will be able to work with the corps as partners in addressing these concerns," he said.