the most interesting, and puzzling, sections of Burke's Spring Branch
lies between the outlet of the McLean Greens stormwater pond and
the confluence of the western and eastern forks of the Branch on
the Brooks Square stormwater easement.
This section begins with the pool
pictured below, approximately 10-12 feet in diameter, that forms
just below the stormwater pond outlet. While the surface of this
pool often looks quite still, there is, even in relatively dry periods,
a steady flow of water out of the pipe, and a corresponding flow
over a little waterfall at the downstream end of the pool.
Below this point, the stream proceeds
for several hundred feet, curving and alternating between riffles
and pools. As you can see from the picture below, the stream is
quite wide -- 3 feet or more -- in this section.
As it passes through the McLean Province
common land, the stream becomes more sinuous -- working its way
through a series of curves -- and, unless there has been recent
rain, the surface flow narrows considerably, following the deepest
part of the channel. The channel itself, however, remains quite
wide and deep, with evidence of erosion along the sides, and extensive
gravelly bars within the channel, both seen in the picture below.
After several such curves, the stream
becomes straighter for a section, before taking a final turn toward
the east. In periods of lower flow, this part of the stream is frequently
dry, even when there is a steady flow of water from the pond upstream.
This was the case in October of 2003, when all the pictures on this
page were taken; the final pool of water, nestled in a curve, is
shown below. It's not clear why this phenomenon occurs, but it's
clear that the water is going somewhere. The most likely explanation
seems to lie in the gravelly, sandy soil in this area, which may
allow the stream to duck underground, rejoining the Branch, or perhaps
Pimmit Run, by an unseen channel. As mentioned in the Friends of
Burke's Spring Branch's Dec. 2003 testimony
before the Fairfax County Environmental Quality Advisory Council,
this section caused some confusion during the Fairfax County perennial
survey, when teams working their way upstream encountered a dry
streambed just above the confluence of the two forks, and concluded
that they had reached the limits of the stream's perennial flow.
However, as is clear from the pictures on this page, the reach just
below the McLean Greens stormwater pond, as welll as the reaches
above and below Hutchison street, all fed by the flow from Burke's
Spring, can be quite full of water even when the reaches immediately
downstream are dry.