Section 319
NONPOINT SOURCE PROGRAM SOCGESS STORY
Stream Restoration Reduces Peak Storm Flow and Improves Aquatic Life
in Sligo Creek
A , . , , I , Stormwater runoff and extensive habitat destruction contributed to
VVaterDOay improved e|iminating aN but four of the most pollution-tolerantfish species
in Maryland's Sligo Creek, a tributary to the Anacostia River. The Maryland Department of the
Environment (MDE) added the Anacostia River (including the Sligo Creek subwatershed) to the state's
Clean Water Act (CWA) section 303(d) list of impaired waters in 2002 for biological impairment, as
measured by combined fish/benthic bioassessment. As a result of restoration efforts in the Sligo Creek
subwatershed, in-stream conditions improved, as measured by a shift in the fish Index of Biotic Integrity
(IBI) from a "poor" to a "fair" rating. Water quality improvements have contributed to progress in meeting
the Anacostia River's total maximum daily load (TMDL) limits for phosphorus, nitrogen and sediment.
Problem
The Sligo Creek subwatershed is home to 82,000
people. It encompasses 11.1 square miles of highly
developed land in Montgomery County, Maryland, a
northern suburb of Washington, DC (Figure 1). Sligo
Creek is one of 14 tributaries to the Anacostia River,
which flows into the Potomac River, which in turn
empties into the Chesapeake Bay.
Maryland has a narrative water quality standard for
freshwater benthic community health that guides
how the state assesses the designated use for
aquatic life. MDE evaluates fish and benthic IBI
data reported in the Maryland Biological Stream
Survey to assess CWA section 303(d) listings of
impaired waters. In 2000 only four fish species (all
extremely pollution-tolerant) were found in Sligo
Creek. Consequently, Sligo Creek received a rating
of "poor" on EPA's IBI for fish. MDE therefore added
the Anacostia River watershed assessment unit
(which includes Sligo Creek) to the state's 2002
CWA section 303(d) list for biological impairment.
The source of impairment was unknown.
In addition, MDE has listed the Anacostia water-
shed for the following impairments (with list-
ing years): nutrients (1996), sediments (1996),
fecal coliform bacteria-non-tidal waters (2002),
toxics-polychlorinated biphenyls (PCBs) (2002),
toxics-heptachlor epoxide (2002), fecal coliform
bacteria-tidal waters (2004), and debris/floatables/
trash (2006). TMDLs have been approved for biologi-
cal oxygen demand/dissolved oxygen, phosphorus,
nitrogen, sediments, fecal coliform, PCBs and trash.
•
S
Montgomery
County
Prince George's
County
District/
off
Columbia
Figure 1. Maryland's Sligo Creek subwatershed drains a
densely populated area near Washington, DC.
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Project Highlights
Efforts to address water quality and habitat prob-
lems in Sligo Creek began more than 20 years ago.
Since the enactment of the Anacostia Watershed
Restoration Agreement in 1987, an evolving inter-
jurisdictional blueprint has guided restoration efforts
across the Anacostia watershed, including Sligo
Creek. In 1989 Montgomery County embarked on an
ambitious effort to restore water quality and habitat
conditions in the creek.
In Phase I (1989), the county transformed a dry
stormwater pond that collects runoff from 805 acres
into a three-celled, extended-detention wet pond
with wetland plantings. The detention wet pond
improved appearance, provided fish and wildlife
habitat, and captured sediment and trash. Below
the pond, the county restored 1,000 linear feet of
downstream aquatic habitat by creating two vernal
pools for amphibian breeding habitat and repairing
1,200 feet of riparian stream corridor.
In Phase II (1992-1994), another stormwater pond
serving 434 acres was rebuilt as a two-celled,
extended-detention wet pond/marsh. Other proj-
ects included restoring 2.5 miles of aquatic habitat,
creating a quarter-acre marsh, replanting five acres
of forest, implementing 19 small physical aquatic
habitat improvement projects and reintroducing
native fish species.
In Phase III (1996), the county constructed a one-
acre detention wet pond at a Sligo Creek golf course
to capture stormwater runoff from 70 acres, includ-
ing a one-mile portion of Interstate 495.
In Phase IV (1999), the county created two
stormwater wetlands and conducted restoration
work in middle Sligo Creek to help return stream
segments to more natural conditions that support
aquatic life habitat needs (e.g., replacing straight-
line concrete channels and pipes with meandering
channels with varied stable bottom).
In Phase V (2005-2007),
the county installed low
impact development
(LID) stormwater man-
agement bioretention
systems (Figure 2). The
county also established
a new goal to improve
the fish IBI from "poor"
to "fair" through tar-
geted reintroduction of
native fish.
Phase VI (2010-present) involves implementing
numerous small restoration projects in a 45-acre
subwatershed, including integrating upland water-
shed source control measures, such as LID, with
stream/wetland restoration and vegetated control
practices (e.g., replacing mowed grass areas with
vegetation that has greater potential for stormwater
retention, infiltration and evapotranspiration).
Results
Phases I-V implemented stormwater management
practices on 1,425 acres (48 percent) of the upper
Sligo Creek subwatershed, resulting in a 41 percent
reduction in peak flow discharge. This has led to
improvements in water quality, streambed and bank
stability, and in-stream habitat. MDE indicates that
benthic macroinvertebrate populations have become
more abundant and diverse, helping to support
increased fish populations. Between 2000 and 2009,
IBI scores forfish throughout most of upper Sligo
Creek improved from "poor" to "fair" (Figure 3).
Monitoring data confirmed the presence of 14 natu-
rally sustaining fish species, including habitat special-
ists (species that prefer specific types of habitat).
Figure 2. LID project installed during
Phase V of the Sligo Creek restoration
effort.
Figure 3. Fish Index of Biotic Integrity scores for
Sligo Creek (2000-2009).
Partners and Funding
The Sligo Creek restoration effort is the result
of a cooperative partnership with Montgomery
County, MDE, Maryland National Park and Planning
Commission, Washington Metropolitan Council
of Governments, Interstate Commission on the
Potomac River Basin, U.S. Army Corps of Engineers
and U.S. Environmental Protection Agency.
Approximately $3 million (excluding monitoring
costs) has been invested in the upper Sligo Creek
restoration effort, including $1.8 million from the
Montgomery County capital budget, $1 million from
the MDE's Small Creeks and Estuaries Reserve cost
share program, and $256,000 from the U.S. Army
Corps of Engineers.
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-12-001J
May 2012
For additional information contact:
James George, PhD
Manager, Water Quality Protection
and Restoration Program
Maryland Department of Environment
410-537-3579 • jgeorge@mde.state.md.us
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