Home | Session 4 | Rivers Pg 1, 2, 3, 4, 5, 6

Rivers

Presented by Ellen Metzger
San Jose State University and BAESI

D. Controls on Stream Flow

1. Slope or gradient
   
   Definition: Difference in elevation between two points along a stream divided by the distance between them measured along the stream.
   
   If a stream drops by 500 feet over a distance of 2 miles, what is its gradient in feet per mile?
   
   In general, if the river's slope increases, velocity also increases, as do the river's capacity to erode and transport sediment. When a stream's gradient lessens (as when it flows from mountain to valley), it drops its sediment.
   
   
2. Volume of Flow (Discharge)
   
   Discharge is the volume of water flowing past a given point in a given time. Discharge is measured in cubic feet per second (cfs) or cubic meters per second and is related to water velocity and cross sectional area.
   
   
3. Channel shape
   
   Where a river is deep, less water comes into contact with the streambed, there is less friction, and the velocity increases. In a shallow river, much of the water is in contact with the streambed, there is more friction, and the river slows down.
   
   
4. Channel roughness
   
   The presence of lots of boulders and other obstacles causes a river to slow down.

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updated March 4, 2002

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