I. Drainage basins - differences in scale
A drainage basin can be defined as the land on which precipitation collects and runs off to a particular stream. A tiny tributary has its small drainage basin or watershed; a major river like the Mississippi may have a vast drainage basin comprised of the land drained by all its many tributaries and all of theirs and so on.
You should be able to approximate the boundaries of the drainage basin of any of the larger streams of Virginia. You should also be able to delineate more broadly defined drainage basins such as the Tennessee River Drainage Basin, the Chowan River Drainage Basin, the Chesapeake Bay Drainage Basin, and the Atlantic Slope.
II. Properties of selected streams and drainage systems in Virginia.
The Potomac River, usually considered one of the major rivers of Virginia, lies wholly outside the state's boundaries. In 1632, the King of England gave the Potomac to Lord Baltimore when he established the Maryland Colony. The terms of the royal grant remain valid today.
The source of the South Fork Potomac River does lie in Virginia, in Highland County. And a major tributary, the Shenandoah River also lies within Virginia's borders. The North Fork Shenandoah River displays 29 classic meanders as it flows between Edinburg and Strasburg, north of Massanutten Mountain. The South Fork has been contaminated with mercury, the result of a spill from a rayon plant on its tributary, the South River, in Waynesboro. The plant operated between 1929 and 1950, but mercury persists in the channel gravels of the South Fork.
The York River is a mere 34 miles long. On each of its major tributaries, the Mattaponi and the Pamunkey, are located Virginia's only two Indian reservations, lands set aside since Colonial times for the tribes whose names are those of the respective river.
James River drainage basin is the largest in Virginia, cutting across four of the five physiographic provinces. With such a large collection area, severe floods have occurred in downstream portions several times in the historic period. The James Basin is the site of several important Virginia ports, including the river ports of Richmond at the fall line of the James River and Hopewell at the fall line on the Appomattox and the sea Ports of Hampton Roads. Hopewell is home to a major chemical industry that produced roach and ant poisons (mirex). From 1966-75 the main ingredient, kepone, seeped into the James poisoning the river all the way downstream and into the Hampton Roads. The lower James was closed to commercial fishing and shellfishing until the early 1990s.
The Roanoke River experiences a name change midway along its course. From Smith Mountain Lake (created by a dam on the Roanoke) to the VA/NC border the river is called the Staunton. Upstream from this stretch and downstream from the state line, the river is known as the Roanoke.
The Roanoke river system is home to a great variety of native fishes, a number equaled on the east coast only by the Santee River in South Carolina. Headwater streams of the Roanoke and Dan (a major tributary) rivers have several rare and threatened fish species, including the officially listed Orangefin Madtom (Threatened) and the Roanoke Logperch (Endangered).
The Roanoke Drainage Basin is the most developed in the state, with many small, industrial cities within its borders. It is frequently subject to flooding and as result of the residences and businesses built on its floodplain, these floods often incur high costs in terms of property damage.
The New River is believed to be the oldest river on the continent and the second oldest in the world (The Nile is considered the oldest on the planet.). It is thought to predate the folding of the Ridge and Valley and thus cuts across the grain of the Alleghenies and the Valley of Virginia.
The New River was once part of the Teays River system which emptied into the Atlantic via the channel currently occupied by the St. Lawrence River. As ice sheets of the Pleistocene moved south across the North American continent the course of the Teays was blocked. Water was forced to flow along the edge of the ice age and the Ohio River formed, draining waters of the New River to the Mississippi and Gulf of Mexico.
Note: It is not strange for a river to flow northward--a peculiarity often erroneously applied to the New River. Many of the world's rivers flow north, including some its longest such as the Nile in Africa; the Yukon and Mackenzie in Canada and Alaska; and the Ob, the Lena, and the Yenisey in Russia. The Shenandoah also flows north.
The Blackwater, Nottoway, and Meherrin rivers are tributaries to the Chowan, which flows to Albemarle Sound, NC.
The Holston (North, Middle, and South forks), Clinch and Powell rivers are tributaries to the Tennessee River, which joins the Ohio just before that stream's confluence with the Mississippi. The Holston and Powell have been severely impacted by chemical pollution; the Holston by mercury contamination at Saltville and the Powell by acid mine drainage. The Clinch has also suffered from chemical spills and siltation, but still holds onto what is left of the rich fish and mollusk fauna of the upper Tennessee drainage.
II. Natural Lakes
There are only two natural lakes in Virginia. Most lakes around the world are the products of the continental glaciation that occurred during the Pleistocene. Myriad lakes occur in regions once covered by ice; ice-free areas--like Virginia--have very few.
Mountain Lake, on Salt Pond Mountain in Giles Co., appears to be the result of a landslide. It seems to have dried up shortly after its discovery in 1751. Salts precipitated out of the shrinking pond and formed a salt lick. A wetter climate returned in the 1800s and the modern lake was formed.
Lake Drummond lies in the midst of Great Dismal Swamp. It is likely the product a prolonged drought which permitted the peat of the swamp to dry out and become flammable. A lightening fire then burned out a shallow depression in the peat, which later filled to become a lake when the drought was over.
III. Chesapeake Bay
The Chesapeake Bay is the flooded valley of the ice age Susquehanna River and the largest estuary on the east coast of the US. There are several good sites on the web that deal with the physical characteristics, ecosystems, and problems of the Bay. Links are available on the home page for this course.
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Posted March 4, 1997 by SLW. Updated 2-19-99 by slw.