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

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.

• 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

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