Courtesy of The Fairfax Journal, February 20, 2001
© 2001 The Journal Newspapers

The decline, according to the report, has shown a significant relationship between declining stream quality and an increase in the region's impenetrable surfaces, such as roads, rooftops, paved parking lots, curbs and gutters causing rain runoff.

While officials cannot predict how much degradation is the result of the so-called concrete boom, the study finds a linear trend between increased development and lowered stream quality.

For instance, Difficult Run has the largest watershed in Fairfax County, covering a 58-square-mile area, including Reston, Vienna, Fairfax City, Wolf Trap Farm Park and parts of Tysons Corner. Where the levels of impenetrable surfaces occupy more than 20 percent or more in places like Reston and Wolf Trap, the stream's health drops to poor and very poor.

The report finds that the headwaters of Accotink Creek originate in the urban and highly developed areas of Vienna and Fairfax City and pass through levels of impenetrable surface greater than 25 percent. Rankings across this subwatershed are consistently poor.

Research presented on watershed management at proceedings of the American Water Resources Association since 1979 indicates at levels of 10 to 20 percent of impervious surface cover, quality of plant and animal life and stream conditions are "significantly diminished."

Using a scale of poor, very poor, fair, good and excellent to judge overall stream conditions, county officials and citizen volunteers sampled 114 in Fairfax County and 25 in Prince William and reported nearly half of the Fairfax County's streams are in poor condition, a third are in fair condition, while less than a third are ranked as good or excellent.

Fairfax County has 850 miles of streams spread over 30 watersheds feeding the Potomac River. About 60 percent of the land is developed; 40 percent is dedicated to parks and open space.

As a result, the study's authors, comprising officials representing Fairfax County's Stormwater Planning Division and citizen volunteers from environmental groups such as the Audubon Society and the Izaak Walton League of America, have devised management strategies to be used by county planners when evaluating future development in the county.

They have identified three regions: Watershed Protection areas, where impervious levels are fair, or good; Watershed Level Restoration I Area, where impervious levels are generally fair; and Watershed Level Restoration II Area, where impervious levels are consistently poor.

In the first category, study authors recommend that planners ensure stream conditions are maintained, while in the second category, careful monitoring is highly recommended. In the third category, the authors recommend active measures such as stormwater management strategies, targeted restoration activities and increased dialogue with the development community.

Fred Rose, chief of the county's stormwater management branch, was responsible for spearheading the stream study.

"This study is a prelude to getting detailed information about the county's watershed management plans," Rose said.

To underscore the importance of streamwater protection, Rose said he had requested Fairfax County Executive Anthony Griffin to include $1 million to fund future stream protection studies.