irginia is a well-watered state receiving approximately one meter (39 inches) of precipitation per year. Much of this water runs off into streams and rivers, while the rest returns as groundwater.
Most of Virginias rivers rise in the mountains and flow east-southeast to the Atlantic Ocean or west-southwest into the Tennessee and Ohio River basins. The character of Virginias streams is a direct reflection of the geologic and physiographic province over which they flow. Valley and Ridge streams flow briskly down linear valleys between parallel ridges. Northern Blue Ridge streams fall rapidly from ridge crests to the low country on either side of the range. Only the Potomac, James, and Roanoke Rivers breach the Blue Ridge. Streams meander across the Piedmont with low to moderate gradients, but drop swiftly to the Coastal Plain in the Fall Zone. On the Coastal Plain streams have low gradients and become wide estuaries as they approach the Chesapeake Bay.