Potomac

Potomac (pətō`mək), river, 285 mi (459 km) long, formed SE of Cumberland, Md., by the confluence of its North and South branches and flowing generally SE to Chesapeake Bay. It forms part of the boundary between Maryland and West Virginia and then separates Virginia from both Maryland and the District of Columbia. The upper course of the Potomac has cut several gaps across the parallel ridges of the Appalachian Mts.; the water gap at Harpers Ferry, W.Va., is the largest. The river passes over the Great Falls above Washington, D.C., where it is crossed by Arlington Memorial Bridge and others, and enters a tidal estuary below the city. It is navigable for large ships to Washington, D.C., and formerly many smaller boats went to Cumberland, Md., via the Chesapeake and Ohio Canal. Its principal tributary is the Shenandoah River, which it receives at Harpers Ferry. The river is noted for both its beauty and its historical associations. Mt. Vernon is on the Virginia shore below Washington, D.C.

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Potomac

a river in the E central US, rising in the Appalachian Mountains of West Virginia: flows northeast, then generally southeast to Chesapeake Bay. Length (from the confluence of headstreams): 462 km (287 miles)

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Potomac 

a river in the northeastern US. It is formed by the confluence of the North Potomac and South Potomac rivers, which originate in the Appalachians, and empties in a wide estuary into Chesapeake Bay of the Atlantic Ocean. Its length from the source of the South Potomac is 590 km (including the estuary, 780 km) and its drainage basin measures 37,500 sq. km. A major tributary is the Shenandoah, on the right.

The Potomac is fed by snow and rain. Its water level rises in winter and spring. The mean flow rate in the lower reaches is 315 cu m per sec. Sea vessels of average size can travel on the river as far as Washington, D.C. A navigable canal from Washington to Cumberland was constructed parallel to the Potomac’s channel, bypassing the rapids.