Broad Run Watershed

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The Broad Run, Horsepen Branch and Western County Potomac Drainages

Broad Run Watershed

The Broad Run originates west of Poolesville near Wasche Road and West Hunter Road. Flowing south toward the Potomac River, it passes through a part of Montgomery County that has changed little in over one-hundred years. This region, a part of the County's agricultural preserve, is characterized by rolling hills and many forested stream buffer areas. The watershed has red Triassic sandstone, with soils that tend to be droughty; consequently, the Broad Run can have low base flows during the summer months.

County biologists monitored the Broad Run during the summer of 1996, above River Road. This part of the stream is in a wide forested stream valley, just downstream of the NIH Animal Center. Stream habitat was in good condition with stable overhanging banks providing excellent fish cover, frequent riffles, and stream base flow reaching both lower banks with little channel substrate exposed. Seventeen species of fish were found in the lower Broad Run including largemouth bass and five species of sunfish. A caddisfly (Ochrotrichia sp.) was found in this watershed that had not been identified elsewhere in the County through the County's stream monitoring program. If the identification is verified, it would add a new taxon to the County's list of benthic macroinvertebrates. Grab samples for water chemistry for pH, dissolved oxygen, conductivity, and water temperature were all within state standards.

Horsepen Branch

Horsepen Branch originates south of Poolesville near the intersection of Westerly Road and West Willard Road. Like Broad Run, Horsepen Branch is within the red Triassic sandstone geologic area rather unique to this part of the County. Horsepen Branch flows through the Poolesville Public Golf Course and onto the Izaak Walton League property where two tributaries join with the main stem. At River Road, the Horsepen Branch abruptly leaves the upland areas around Poolesville and enters the Potomac River floodplain. Above River Road, Horsepen Branch is a typical piedmont headwater stream with a series of pools and riffles along its length.

Below River Road, Horsepen Branch loses its stream gradient as it enters the Potomac River floodplain in the McKee-Besher Wildlife Management Area. Many areas of the stream within the WMA have been impounded to provide different types of wetland habitat for many kinds of wildlife. These wetland areas have been designated as wetlands of state concern because of their botanical diversity and value to wildlife.

The lower reaches are subject to Potomac River floodwaters that back water up the Horsepen Branch and cause bank erosion and sediment deposition into the stream. The temperature regime of the streams in the lower reaches of the Horsepen Branch may also be affected by the Potomac River. Another possible cause, or contributing factor to conditions in the lower reaches are the two large impoundments in the watershed.

Broad Run, Horsepen Branch and Cabin Branch/Chisel Branch, and Western County Potomac Tributaries Stream Condition and Habitat Conditions with Management Category Designation

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

DEP Baseline monitoring is scheduled to occur in 2000.

Broad Run - GOOD

(preliminary)
GOOD - (preliminary for upper reaches)
Agricultural land uses are widespread throughout the watershed, with buffers and forest cover increasing in downstream areas. The many farm ponds throughout the watershed and unforested riparian areas at the NIH facility may be affecting stream temperatures.
Broad Run has remained in essentially the same land use - open, rolling farmland - for over 100 years.

Agricultural Watershed Management Area

Horsepen Branch - FAIR (preliminary)
FAIR - (preliminary)
The lower reaches of this drainage are influenced by the Potomac River floodplain and are subject to backwater flooding. Instream fish and benthic habitat is scarce. Large impoundments are found in both the upper and lower areas of the watershed. The upper ponds provide irrigation water. The lower ponds were created to provide seasonal open water wetland areas.
The lower reaches of Horsepen Branch and adjoining drainages have an unusual delta-like drainage pattern formed by floodplain migration on the Potomac River. Wetlands of special state concern are found in the lower and are regionally renowned for their habitat value.

Agricultural Watershed Management Area

Cabin Branch/Chisel Branch and Potomac River Direct drainages below Horsepen Branch
No current data
Large lot residential areas interspersed among agricultural uses make up the predominant land use. The seasonally wet conditions on the floodplain support diverse wetland communities.
The McKee Besher Wildlife Management Area contains designated wetlands of special state concern for their unique natural heritage.

Agricultural Watershed Management Area

Wasche Rd. Trib. - lower - GOOD
GOOD
Agricultural land uses are widespread throughout watershed. Dickerson Conservation Park protects large forested area.

Agricultural Watershed Management Area

Wasche Rd. Trib. - upper - FAIR
GOOD
Riparian buffer area sparse.

Agricultural Watershed Management Area

Potomac River Direct drainages, between Little Monocacy and Broad Run
No current data
These numerous streams consist of small drainage areas which are heavily influenced by seasonal water table fluctuations due to their location on the Potomac floodplain. The small drainage areas associated with these tributaries makes them very sensitive to localized land use conditions

Agricultural Watershed Management Area

Broad Run, Horsepen Branch, Cabin Branch/Chisel Branch and Western County Potomac River Tributaries' Watershed Management Categories

Agricultural Watershed Management Area

All of these western County drainages are located in the Agricultural Reserve wedge, and agriculture remains the predominant land use. Several large institutional and recreational land uses are located in these watersheds, including the NIH Animal Research Center in Broad Run and the Poolesville Golf Course and Izaac Walton League in Horsepen Branch. In addition to the use of best management practices on the agricultural areas, good stewardship and stream valley conservation measures are highly recommended for these areas and for the large lot residential areas. The C&O Canal National Historic Park extends along the Potomac River.

Watershed Management Strategy

Complete monitoring of these watersheds in 2000 to allow more detailed targeting of specific problem areas.
The use of appropriate agricultural BMPs is highly recommended as well as efforts to improve riparian buffers throughout these drainage areas.

Maps

Land Cover
Impervious Area
Stream Condition
Management Categories

Land Cover Graph

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