GeoClassroom Physical Geology Historical Geology Structure Lab

Physical Geology

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River and Streams

River Systems:

- 3 major subsystems:

Dynamics of river systems:

rivers are complex systems influenced by number of things, which are:

1) Discharge

- amount of water passing by a given point during a specific time interval
- measured in cubic meters/second
- flow of river comes from runoff and from groundwater seepage
- groundwater is most important factor in supplying rivers with water.

2) Velocity

- not uniform through a stream channel
- depends on shape and roughness of the channel
- steep gradients produces faster rates of flow, also the greater the volume of water, the faster the flow.
- on a curve, the fastest water is on the outside, where the water brushes up against the far bank, causing erosion (cut bank)
- on the inside, velocity is much reduced, allowing some sediment to be deposited, forming point bars.

3) Gradient

- steepest at the headwater in the collecting zone
- decreases as one travels to the mouth of the river, where the gradient is almost zero.
- forms a nice concave cross-sectional view of a typical river, from head to mouth.

4) Sediment load

- fine particles are moved in suspension, never toughing the ground (suspended load)
- coarse particles are moved by traction along the stream bed, jumping along (bed load)
- dissolved materials are carried along in solution (dissolved load)

5) Base level

- the lowest level to which a river can erode its channel
- its the elevation of the stream's mouth, where it enters an ocean, or lake, or another river.
- cannot erode below this level, or else the river stops flowing at that point, causing water and sediment to pool at that point, forming a lake.
- eventually, water would overflow the lake and coninue travelling to the mouth.


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