Sligo Creek Watershed

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The Sligo Creek watershed, a tributary to the Northwest Branch of the Anacostia River, is one of the County's most urbanized watersheds. It is also the location of extensive efforts to restore an urban stream system and is notable for the success that is being achieved in controlling urban stormwater runoff and re-establishing a viable biological community. Until just recently, the only fish identified in Sligo Creek were blacknose dace, goldfish and creek chub - species that are highly tolerant of polluted urban conditions. External anomalies found in the fishes sampled, particularly the creek chub population, could be associated with environmental degradation such as chronic, sublethal exposure to contaminants or high levels of suspended solids. Many watershed residents are familiar with signs that used to be posted throughout the watershed, particularly in the lower reaches, warning of polluted water conditions.

Many high density commercial and residential areas are located within the Sligo Creek watershed, including the Wheaton Triangle area and part of the Wheaton Central Business District, large areas of Takoma Park, and much of downtown Silver Spring. These areas and surrounding residential neighborhoods developed rapidly during the 1950's and 60's, before today's environmental standards for stream valley protection and stormwater management. All that remains of Sligo's natural stream network are mainstems of streams with most feeder tributaries paved over and piped into storm drains. The remaining stream system has been heavily armored in many areas to reduce channel erosion. These alterations may improve bank stability, but provide limited habitat value. Areas that have not been armored exhibit varying degrees of bank instability and erosion problems due to uncontrolled stormflows. Efforts to restore the watershed have included an examination of methods to improve flow conditions so that stream channel restoration efforts can occur, rather than completely armoring the stream and displacing all natural habitat.

New runoff controls at the Wheaton Branch, the University Boulevard.. and Sligo Golf course retrofit ponds, and improvements to the aged and leaking sanitary sewers are bringing positive changes to the streams. Since completion of the Wheaton Branch pond and associated stream channel restoration, native fish have been transplanted from other similar watersheds in order to augment the recovery of fish populations in Sligo Creek. Existing downstream blockages restrict normal fish movement in Sligo Creek to some degree, preventing the natural re-establishment of a more diverse fish community. Biological monitoring conducted by the Interstate Commission on the Potomac River Basin (ICPRB) indicates that the number of native fish species re-established in the Upper Sligo Creek mainstem has increased from three in 1988 to eleven currently. This is extremely encouraging.

Despite the onslaught of urbanization, the Sligo Creek stream valley park system has preserved a riparian corridor which allows the protection and restoration of pockets of high quality stream habitat. Flow conditions and impaired habitat which have prevented a viable biological community from living in the watershed are being addressed through joint efforts by DEP, M-NCPPC, the ICPRB, and the Metropolitan Washington Council of Governments as part of the regional Anacostia Watershed Restoration Project. Community groups and schools frequently contribute to efforts to clean up streams throughout the watershed. The Sligo Creek stream valley is heavily used by local residents and visitors, and is one of the County's most important urban natural environments. The successes achieved thus far in Sligo Creek are setting the standard for other urban watersheds in and beyond our County, and reflect Montgomery County's emerging national leadership in stream restoration.

Sligo Creek Stream Condition, Habitat Conditions and Management Category Designation

Subwatershed/ Stream Condition
Habitat Condition
Primary Factors Affecting Stream Condition
Unique Characteristics and Management Designation

Wheaton Branch - FAIR

(preliminary)
GOOD
This tributary drains the Wheaton Central Business District and high imperviousness, channel alteration and urban pollutant loads heavily impact the stream system.

An innovative stormwater retrofit project on Dennis Ave. has improved conditions dramatically and allowed stream restoration to occur downstream despite highly urban conditions.
The Wheaton Branch stormwater retrofit project has been instrumental in achieving improvements in the biological community in Sligo Creek. Fish communities have been re-established, and downstream of the Wheaton Branch pond, in-stream habitat restoration, and riparian vernal pools and microhabitats supporting amphibians can be observed.

Watershed Restoration Area

Upper Sligo - POOR

(preliminary)
FAIR to GOOD Overall
High imperviousness from high density residential and commercial areas and channel alteration affect flow conditions and habitat. Embeddedness levels are particularly high and banks are unstable in areas.
A stormwater retrofit project has been undertaken at an existing pond above University Blvd. to improve runoff conditions from this part of the drainage.

Watershed Restoration Area

Middle Sligo - FAIR

(preliminary)
GOOD
Channel alteration and marginal riparian zone influence habitat conditions, as well as urban runoff conditions typical throughout the watershed. However, this section directly benefits from the upstream improvement in flow conditions associated with the retrofit pond on the Wheaton Branch tributary.
A highly successful habitat improvement project is located in this section just above Forest Glen Rd. A shallow marsh has been created to replace wetland habitat and treat small amounts of road runoff, while simultaneously preserving tree canopy.

Watershed Restoration Area

Lower Sligo - POOR

(preliminary)
GOOD Overall

Flora Lane Trib. FAIR
This section exhibits many of the same problems found throughout the watershed, particularly channel alteration and riparian zone impacts.
Several stormwater retrofit and stream restoration projects are currently being implemented in this section, including a pond on the Sligo Golf course which will improve runoff from the beltway and upstream development. A unique tributary is also found on the west side of the stream which, owing to discharge from an underground spring in a Metro tunnel, has a relatively cool, clean baseflow source. A structure has been placed in the top section of this tributary to by-pass stormflows around the tributary, creating a "refugia" for organisms to retreat to during stormflows. Watershed Restoration Area

Long Branch - POOR

(preliminary)
Reconnaissance indicated problems with sediment deposition and embeddedness

Watershed Restoration Area

Sligo Creek Watershed Management Category

Watershed Restoration Area

All of the Sligo Creek drainage area is designated as a Watershed Restoration Area. Efforts continue to implement phased retrofit projects throughout the watershed and activities are ongoing to monitor the success of fish re-introduction activities that have occurred over the last several years. Current monitoring results show that the re-established fish community is thriving and the first signs of successful reproduction are being seen in the 1996 data.

The Sligo Creek watershed has been targeted as an important part of the overall Anacostia watershed restoration effort and has been the focus of efforts to control urban pollutant loadings and restore habitat conditions where possible. Several unique opportunities existed within this watershed to modify two older flood control facilities and improve runoff controls in this heavily urbanized area. Stormwater flow control has been improved at these sites, and water quality controls are being added to reduce urban pollutant concentrations. The ability to achieve flow control has allowed successful stream restoration activities to occur in stream segments where it would otherwise have been infeasible due to very high runoff velocities.

Efforts to control urban runoff in this watershed are limited by the small number of feasible opportunities to modify old flow control structures, or establish new stormwater runoff controls at strategically located sites. Large areas of the watershed remain uncontrolled. To ensure lasting success in re-establishing a viable biological community, strong local stewardship of this watershed must become a central part of the daily activities of watershed residents and businesses.

Watershed Management Strategy

Implementation of a strong public education program to inform residents about watershed conditions, including pollution prevention education for residents and businesses.
Continued implementation of Capital Improvement Program Stormwater Retrofit and Stream Restoration activities.

Maps

Land Cover
Impervious Area
Stream Condition
Management Categories

Land Cover Graph

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