Lake Barcroft is a
manmade lake formed as a reservoir from
the stored water of the intersection of Holmes Run and Tripps Run.
The original dam that
created the reservoir was completed in
1915 by the Alexandria Water Company.
That dam was 400 feet wide with a spillway at
the top, 205 feet above
mean sea level. The
reservoir of 520 million
gallons and formed a lake of 115 acres.
In 1942, five-foot-high wooden gates were
installed at the top of the dam
and expanded the lake to 800 million gallons and 135 acres, near its
In the early 1950’s, the
reservoir, dam and 680 acres surrounding the lake were
purchased by a Boston developer. The lake ceased serving as a
and was converted to recreational use.
The Watershed Improvement
District (WID) was formed in 1973 in the wake of the destruction
of the Lake by the failure of the dam as a result of tropical
Storm Agnes in 1972. Today, the WID functions as a State Agency
to maintain and operate the dam, manage water quality of the
Lake, manage the discharges from the dam and maintain and
improve the environmental integrity of the watershed above
By law, the WID must
maintain the water level of the
Lake. The dam is
designed and operated
to maintain a nearly constant water level.
The Lake collects runoff from fourteen and
one-half square miles of
Fairfax County and the City of Falls Church.
The rain water arrives from Tripps Run and
Upper Holmes Run into the
lake. The dam is
not designed for nor is
it operated in a flood control capacity.
For whatever volume of water that flows into
the Lake from Upper Holmes
and Tripps Runs, an equal volume must flow out into Lower Holmes Run. The goal is to maintain
the Lake water level
between 208.5 to 209 feet above mean sea level.
Controlling the water
level is a 12 foot high by 151 foot wide bascule
gate that is continuously managed by a computer that responds to
storm water. As the
water enters, the
gate is automatically opened only by as much is necessary to pass an
volume of water downstream. The
and outflow are balanced and the reservoir level is maintained within
target range. The
gate is operated by
four hydraulic rams powered by computer controlled electric pumps. There is diesel powered
generators as first
back up and gasoline powered pumps if all else fails.
Because the Lake is a
free flowing body of water, it
supports a wide variety of plant and animal life.
There are over 22 varieties of fish known to
inhabit the lake. The
extent and variety
of both terrestrial and aquatic life attest to the overall health of
the Lake. Although
testing of the water
quality has been done, it is not done periodically unless there is some
indicated reason. The
Lake is considered
safe at most times for recreational activities.
After a major storm, runoff could make the
Lake undesirable for
the Lake is safe for
most activities, some people could be sensitive to dissolved impurities
water. The water is
not considered to be
drinkable. The fish
can be eaten
sparingly however there may be heavy metals in the water that would
the fish regularly undesirable. Most
the dissolved elements in the Lake come from highway run off and are
with automobile use.