Potomac

Course

The Potomac River runs 405 mi (652 km) from Fairfax Stone Historical Monument State Park in West Virginia on the Allegheny Plateau to Point Lookout, Maryland, and drains 14,679 sq mi (38,020 km2). The length of the river from the junction of its North and South Branches to Point Lookout is 302 mi (486 km).

The river has two sources. The source of the North Branch is at the Fairfax Stone located at the junction of Grant, Tucker, and Preston counties in West Virginia. The source of the South Branch is located near Hightown in northern Highland County, Virginia. The river's two branches converge just east of Green Spring in Hampshire County, West Virginia, to form the Potomac.

Hydrology

An average of approximately 486 million US gallons (1,840,000 m3) of water is withdrawn daily from the Potomac in the Washington area for water supply, providing about 78 percent of the region's total water usage, this amount includes approximately 80 percent of the drinking water consumed by the region's estimated 6.1 million residents.

As a result of damaging floods in 1936 and 1937, the Army Corps of Engineers proposed the Potomac River basin reservoir projects, a series of dams that were intended to regulate the river and to provide a more reliable water supply. One dam was to be built at Little Falls, just north of Washington, backing its pool up to Great Falls. Just above Great Falls, the much larger Seneca Dam was proposed whose reservoir would extend to Harpers Ferry.

History

The river itself is at least 3.5 million years old, likely extending back ten to twenty million years before the present when the Atlantic Ocean lowered and exposed coastal sediments along the fall line. This included the area at Great Falls, which eroded into its present form during recent glaciation periods.

The stream gradient of the entire river is 0.14%, a drop of 930 m over 652 km.

The Potomac River has long been inhabited by Native Americans, including being the periphery of the Delaware Adena culture. Precontact, the region was governed by the Algonquian Piscataway confederacy and their allies as warfare in the region increased. This led to the formation of a more complex political system led by the Tayac with countless Werowances governing local affairs.