Hydrology

Major streams of the Appalachian Highlands

The hydrology of the Southern Appalachians is largely the story of the regions numerous rivers. Waters draining from the western side of the Appalachians eventually reach the Gulf of Mexico, while drainages on the eastern side end up in the Atlantic Ocean. Major Gulf drainages of the region drain to the Ohio River (New-Kanawha, Tennessee, and Cumberland river drainages) or to the Alabama-Apalachicola Rivers (Coosa-Tallapoosa, Chattahoochee river drainages). Atlantic slope drainages include those to the Chesapeake Bay (Potomac, Rapidan-Rappahannock, and James River drainages) and through the Carolinas (Roanoke, PeeDee, Santee-Cooper, and Savannah River drainages). The U.S. Geological Survey has developed a nationwide system of delineating drainages as hydrologic units that are commonly used to summarize information about watersheds.

Major rivers include the Tennessee, French Broad, Cumberland, Hiwassee, and Holston rivers.

Streams have influenced the topography differently in each province:

• Piedmont Province: In the foothill zone of the Piedmont of North Carolina and Virginia, northeast-flowing tributaries to the southeast-flowing master streams are long and subparallel, whereas opposing tributaries are short and irregular in direction. Small streams flow on saprolite, whereas larger streams flow on bedrock. Soil erosion in the Piedmont is among the severest in the nation.
• Blue Ridge Province: Streams in this province have etched out nonresistent rocks and shear zones to form trench valleys and intermountain basins.
• Ridge and Valley Province: Etching of nonresistant rock by streams has had a much stronger effect on topography here than in the Blue Ridge, owing to the much greater difference in the erodibility of bedrock in this Province. The New River cuts directly across the ridges of this Province, following a direction of flow it has had for hundreds of millions of years.
• Appalachian Plateau Province: The stream drainage pattern in this province generally is dendritic (i.e., random), owing to the subtety of bedrock structures here. However, bedrock control of drainage by fractures and folds occur in some places.