Little Falls Watershed

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The Little Falls Watershed and Minnehaha Branch

The Little Falls watershed is one of the County's most urban stream systems, with part of its drainage from the northwest portion of the District of Columbia. This watershed contains some of the oldest developed areas of the County. There are several historic elements in the watershed such as Battery Bailey (a landmark fortification from the Civil War), the route of the old trolley line, the Washington Aqueduct, and the C&O Canal, all of which have played a role in shaping the watershed's landscape.

Most of the development in this watershed occurred prior to today's requirements for natural stream buffer, wetland, and floodplain protection, and for stormwater runoff controls. The original drainage pattern of Little Falls has been extensively altered, with much of the original headwaters and tributaries enclosed in storm drain pipes or channelized. What remains of the headwaters now receives drainage from highly impervious areas in the Bethesda Central Business District and Friendship Heights. Channelized and piped areas throughout the watershed deliver flows into downstream channels at accelerated velocities and often with very high temperatures after flowing through open concrete channels or across paved surfaces warmed by the summer sun. These stormflows seriously impact the remaining natural channels downstream.

Several catastrophic pollution events have also influenced watershed conditions, including a large oil spill which ignited and burned for two days in 1959 (melting the Massachusetts Ave. Bridge), chlorine discharges associated with treatment of drinking water supplies, chronic sewer line problems, and an underground oil leak which was discovered and repaired over the last two years. As a consequence of inadequately controlled runoff and periodic pollution events, stream resource conditions are poor, with the exception of the lower reach of Little Falls below MacArthur Blvd. A study conducted in 1976 found no life in Little Falls (Dietermann, 1976). In 1994, Maryland Biological Stream Survey monitoring found American eel, longnose dace, river chub and redbreast sunfish in the lower mainstem below MacArthur Blvd. Above Massachusetts Ave., only three individuals of the very pollution tolerant blacknose dace were found. Macroinvertebrate species found above MacArthur are all pollution tolerant. Below MacArthur Blvd., the macroinvertebrate population is somewhat more diverse, however, the number of individuals, or abundance, remains low. The biological community in Little Falls will be re-examined in 1999 as part of the County's rotating watershed monitoring program. Only recently can it be said with any level of confidence that some major water pollution impacts have been corrected. Sources of apparent illicit discharges throughout the watershed are currently being investigated and, once determined, will be stopped.

Due to the highly developed nature of the watershed, few site opportunities exist to add remedial stormwater controls. Possible incremental restorations are being studied that could improve conditions, particularly water quality, to help restore a more stable aquatic community. Now that water pollution impacts are being better managed, biological resources in this watershed may very well be on the verge of a turn-around, particularly in the lower mainstem where habitat conditions can still support an aquatic community. The best opportunities for restoring a more balanced aquatic community are in the reaches from Massachusetts Ave. downstream to the Potomac River because this area still contains stream habitat capable of supporting fish, aquatic insects, and other aquatic organisms. The high population density and many recreational opportunities, including the extensive trail system and linkage to the National C&O Canal Park, make this area a potential showcase of our ability to blend urban life with the natural environment.

Little Falls Biological Stream Condition, Habitat Conditions, and Watershed Management Category

Subwatershed/

Stream Condition
Habitat Condition
Primary Factors Affecting Stream Condition
Unique or Special Chacteritics and Management Category

Willet Branch
POOR Overall
70% of stream channel is enclosed in storm drains or lined with a concrete ditch. High velocity uncontrolled runoff a major impact which will be difficult to mitigate due to limited sites available for new stormwater controls.
The Capital Crescent Trail and Hiker/Biker Trail make this one of the most visited stream valley areas in the County; however, few residents even know the stream is running right alongside them.

Urban Watershed Management Area

Upper Mainstem
FAIR Overall, except POOR in channelized sections
Forested riparian buffer through Town of Somerset and the Town's efforts to stabilize and improve habitat conditions has helped to maintain habitat conditions. Chronic pollution sources from storm drain outfalls are being addressed and water quality impacts should be improving.

Watershed Restoration Area

Middle Mainstem
FAIR to POOR Overall
This section of the watershed has experienced the least amount of channel alteration and has a good riparian zone. Frequently occurring high storm flows continue to impact channel stability . Erosion and sediment deposition cause significant habitat impairment.
Both the Capital Crescent Trail and Little Falls Hiker/Biker Trail bring many visitors to this stream valley. During the Civil War, the view from Battery Bailey extended far into Virginia. Since then this stream valley has become reforested.

Watershed Restoration Area

Little Falls Mall Trib.
FAIR to POOR
This small tributary drains a very highly impervious area. The stream channel has been altered, is extremely incised, and has severe erosion problems.
This stream valley has a high quality forested buffer and provides a frequently used connection to the Capital Crescent Trail system. Restoring and protecting this area from further degradation is a top priority within the context of the Little Falls Restoration efforts.

Watershed Restoration Area

Lower Mainstem
GOOD to FAIR
The lower mainstem channel is naturally stabilized by rocky conditions and bedrock.

Embeddedness, channel stability, and riparian conditions are generally good.

Potential chlorine discharges.
This section of the watershed has the potential to support a higher quality biological community. Recent changes to discharge practices from the reservoir are expected to result in an improvement in the biological conditions in this area.

Watershed Restoration Area

Dalecarlia Trib.

(Preliminary)
FAIR

(Preliminary)
Alteration of the stream valley for the reservoir and lack of a riparian buffer influence conditions here.

Watershed Restoration Area

Spring Valley Trib.
FAIR
The majority of the drainage flows from highly urbanized areas in the District of Columbia. High level of channel alteration in the District and inadequate riparian buffer impair conditions.

Urban Watershed Management Area

Minnehaha Branch - FAIR (preliminary)
FAIR (preliminary)
Inadequate riparian buffer, uncontrolled runoff, and high imperviousness affect this tributary.
Extensive channel restoration was conducted after catastrophic erosion caused extensive damage to the stream below MacArthur Blvd.

Watershed Restoration Area

Little Falls Watershed Management Categories

The current management efforts in Little Falls include the development of the Little Falls Watershed Restoration Action Plan which is currently in progress, and ongoing discharge investigations and pollution prevention efforts. The Action Plan will incorporate the approaches outlined below, with more detailed implementation and benchmark components to help improve watershed conditions and biological resources in the watershed.

The overall management approach in the Little Falls watershed includes aggressive pollution prevention measures coupled with projects to stabilize and restore, where feasible, the areas of natural stream channel that still have the potential to support an aquatic community, albeit a hardy and pollution tolerant one.

The limiting factor on the level to which this stream system will support a more diverse aquatic community is our ability to mitigate the effects of uncontrolled stormwater runoff. Because the watershed is very nearly fully developed, there simply are very few places suitable for cost effective stormwater retrofit projects. Efforts will be focused on providing treatments to small areas where feasible, in order to create "refugia" where organisms can take shelter during storm events, and stabilizing other areas to help limit further erosion and channel downcutting. The continued downcutting of channels must be addressed to reduce ongoing infrastructure repair costs, such as exposed and damaged sewer lines and eroding park trails, and to lessen delivery of sediments downstream.

Urban Watershed Management Area

This management category includes Willet Branch and Spring Valley Tributary.

Watershed Management Strategy

Continue working with Clean Water Partners and expand program as feasible.
Continue Pipe Detectives stormdrain outfall monitoring.
Support cost-effective stormwater controls on redevelopment sites, particularly quality controls, in conjunction with watershed-wide facilities if determined to be feasible.

Watershed Restoration Area

This category includes the Upper Mainstem, Middle Mainstem, Dalecarlia subwatershed, Little Falls Mall Tributary, and the Lower Mainstem

Watershed Management Strategy

Continue efforts to identify and implement stream restoration opportunities, working with the Little Falls watershed advisory group, Town of Somerset, and private landowners. A state grant has been secured to implement stream restoration projects in the stream channels below Massachusetts Ave.
Continue working with Clean Water Partners and Pipe Detectives volunteers to identify and better manage storm drain discharges throughout the watershed.

Maps

Land Cover
Impervious Area
Stream Condition
Management Categories

Land Cover Graph

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