The Arlington County Government Stream Inventory/Assessment
Survey performed during the spring and summer of 1999 documented the
physical conditions of all perennial streams (28.5 miles) in
Arlington County, Virginia. Documentation occurred through
employment of a field method of ecology known as the Rapid Stream
Assessment Technique (RSAT) modified by Environmental Systems
Analysis, Inc. (ESA) to provide County officials with baseline
information on stream health and management recommendations for
restoration. The assessment technique evaluated over 30 physical
stream conditions at observation points located at 400-foot
intervals (between 12 and 13 observation points per mile) and
wherever unique or hazardous conditions were apparent. Evaluation
categories included channel stability, channel scouring and
deposition, physical in-stream habitat, water quality, riparian
habitat condition, aesthetics and remoteness. Arlington County
officials participated in all aspects of fieldwork, which included
a training seminar consisting of stream surveying, assessment and
restoration techniques. A total of 321 stations were investigated
with 235 stations actually being read. The difference of 86
stations did not meet perennial stream riffle evaluation criteria.
Ground-truthing determined that those reading stations contained
extensive runs of stream without riffle (i.e. slackwater), or was
either piped (closed section), concrete lined open section,
ephemeral or intermittent (without base flow), tidal water,
stormwater management facilities or beaver impoundments.
Photographs and data sheets for each observation point and a
selection of baseline cross-section (trend analysis) and
macroinvertebrate monitoring stations were included in the full
report on file with the Arlington County, Department of
Environmental Services.
Streams within Arlington County have been greatly impacted by
urban/suburban development. The majority of streams have been
hardened with stone in areas where streambank erosion has been a
problem, reflected by high channel stability scores. Arlington
County streams however, consistently rated poorly for water
quality. Substrate fouling, which is a biological film or coating
of growth on the stream bottom fueled by excessive nutrient,
significantly degraded overall stream quality. The high level of
substrate fouling suggests dilute nutrients feeding/fueling the
blooms of algae growth. A cursory evaluation of fisheries and
macroinvertebrates and other ancillary indicators denotes only the
most hardy and pollution tolerant of species. It was determined
that with each measurable storm event, a toxic pulse of stormwater
is delivered to the receiving streams, which hinders habitat
suitability for the progression of sensitive species. All streams
were subject to flows of high volume and short duration, which
significantly alter their appearance, stability and biological
carrying capacity.
Stormwater best management practices are lacking throughout the
County. The majority of the urbanized county was developed many
years ago prior to the routine addition of water quality/quantity
controls in land development. The historic engineering mentality
was for providing safe conveyance through hardening of the
receiving streams and/or extensive piping. The majority of
Arlington County watersheds are built-out and fairly stable, with
channel forming flows having occurred many times over, and with
bank repair having been historically performed accordingly.
Overall, the best scores came from the streams in the north half
the county (significant natural rock outcropping, wide forested
buffers) and declined as the assessment proceeded south from
lower density residential to higher levels of imperviousness.
The final report included prioritized, specific and detailed
management recommendations in the form of stormwater best
management practices, retrofits, education and training programs,
riparian plantings and most importantly stream restoration
opportunities.
