Weathering and Landforms Topics

Streams (Part 3)


Drainage Basins

• A stream’s drainage basin is the area that the stream drains.  Drainage basins are separated by divides, the high places between basins. 

Image from College of William & Mary geology website, courtesy of C. M. Bailey

This map shows the drainage basins of Virginia’s major rivers.  Each drainage basin is separated from its neighbors by a divide or higher area. 

Drainage Systems

• Geologic structures typically control the shape of drainage systems.  Two common drainage system shapes are trellis and dendritic.  

Drainage systems
Left: trellis drainage; right: dendritic drainage (Images courtesy of American Electric Power)

Trellis drainage and dendritic drainage can be seen on these satellite images of western Virginia and southern West Virginia.  Trellis streams generally follow the trend of the long, parallel valleys in the Valley and Ridge.  Dendritic streams flow in irregular directions, forming a branching pattern in the Appalachian Plateaus.

Water Gaps

• Water gaps are steep-walled, narrow valleys cut through ridges by streams.  These gaps are common in the Appalachians.

Water Gaps
Spectacular water gaps exist throughout the Valley and Ridge.  These gaps are cut by the New River (left) and Little Walker Creek (right). (Left photograph courtesy of the Virginia Division of Geology and Mineral Resources; right photograph by Phyllis Newbill)