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The Upper Potomac Direct is located in rural western Montgomery County, and includes the subwatersheds of Little Monocacy, Broad Run, and Horsepen Branch. Due to the generally well-drained underlying Triassic sandstone, the upland streams here tend to experience low baseflow during the summer months. The combined drainage area of these subwatersheds that lies within Montgomery County is approximately 60 square miles. The Upper Potomac Direct Pre-Assessment Report (46 pp, 7307 kb)
Little Monocacy
The Little Monocacy headwaters are located southwest of the town of Comus. The stream flows southwest approximately nine miles through predominately agricultural areas and enters the Potomac River just downstream from the mouth of the Monocacy River. Many of the headwater streams are well forested and there is very little imperviousness within the subwatershed. The lower section of the stream is a wide, rapidly flowing body of water. Deep pools and an abundance of riffles support a diverse cool water fish community.
Broad Run
The headwaters of Broad Run begin west of the Town of Poolesville, near the intersection of Wasche Road and West Hunter Road. The stream flows south through rolling hills for approximately eight miles before entering the Potomac River. Landuse has been historically agricultural in this area, and many small farms still actively cultivate crops or maintain livestock. A forested stream buffer provides protection along many stretches of Broad Run. The watershed has been designated part of the County's Agricultural Preserve, so land uses are not expected to change significantly.
Horsepen Branch
Horsepen Branch begins in an upland area south of the Town of Poolesville, near the intersection of Westerly Road and West Willard Road. The stream flows south, with one branch flowing through a large impoundment located on the Poolesville Public Golf Course. Further downstream, there is an abrupt transition in geology from the sandstone-based upland areas to the alluvial sediments of the Potomac River floodplain. The stream enters the McKee-Besher Wildlife Management Area, where manmade impoundments provide important wetland habitat for many kinds of wildlife. Due to the high botanical diversity and value to wildlife, these areas have been designated wetland areas of state concern. The reach in the most lower portion of the subwatershed is subject to backwater from the Potomac River during flooding, resulting in sedimentation and bank erosion problems. The stream temperature regimes in the lower section may also be influenced by the Potomac River, or by the two large impoundments in the watershed.
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