Stream Power

What is stream power? Why is it important?

The ability of a stream erode material from its bed and banks or deposit material on top of them is ultimately controlled by the available energy of the system balanced by the resistance of the bed and bank materials. The energy of a stream can be computed several ways, but a common and convenient way is stream power, which is based on the slope of a river and the amount of flow. So very small streams and very low gradient streams have less stream power than steep and/or big rivers. In any case, stream power can increase or decrease from one location to the next along a river. The resistance of the bed and bank material is related to the size of particles. Big boulders are more resistant to movement than sand and gravel, and bedrock is almost immobile over human timescales.

Two related but different metrics of stream power give slightly different insights on a river’s characteristics. Specific Stream Power tells us how much energy is acting on a single location of the river bed. It indicates how big a particle the river can move. So places with high specific stream power might move big boulders and places with low specific stream power may only be able to move gravel. The Total Stream Power indicates how much total sediment a river can move. So big, wide, low gradient rivers can carry an immense load of sediment (like many, many dump trucks of dirt each year) but perhaps only small particles of sand, silt, and clay. Yet a small, steep river might carry large particle like boulder but not be able to carry an immense load (only a few dump trucks worth of sediment each year). 

The stops on this tour show locations where stream power has been measured, and provide information on measurement results.