erodes, transports, and deposits sediments and sculpts landscapes.
are channels of water that drain the landscape. Stream runoff, water in motion over the land surface, is crucial for humans.
Earth is the only planet in the Solar System
with flowing water. Without flowing water, Earth might resemble Mars.
Streamflow is used for
drinking water, transportation, waste disposal, recreation, commerce, irrigation, and energy generation.
Velocity is not
uniform in a channel. Friction slows water along channel edges; water flows faster in the deeper center.
In curved channels, the maximum velocity is swept to
the outside curve, which is preferentially scoured and deepened.
is turbulent. It is chaotic and erratic, with abundant mixing via eddies, which scour sediment and bedrock.
Dissolved load consists of
ions from mineral weathering.
Suspended load is made of
fine particles (silt and clay) entrained in the flow.
Bed load is composed of
the larger particles that roll, slide, and bounce along the bed of the channel. Movement is called saltation.
Sediment transport changes with
discharge. During high discharge, cobbles and boulders that are stranded at low discharge may be mobile.
is the maximum grain size transported.
is the maximum load (coarse, fine, and dissolved material) transported by streamflow.
Competence decreases with
velocity. Sediment grains drop out and water sorts them by size.
Gravel settles in
the highest velocity setting (channels), sands are deposited in slightly lower velocity settings (point bars and levees), and the muds (silts and clays) settle in slack water.
2 main types of stream
- Single main channel - Sinuous ("wiggly") - Low competence, steady discharge
- Multiple channels - Straight - High competence, flashy discharge
How do the meanders form in a Meandering Stream?
Low-velocity, low-sediment streams form meanders. Meanders shift from side to side in a snaking motion. The current is faster at outside banks, which are eroded. Sediments get deposited in inside banks forming point bars. The bends grow closer and the point bars bigger.
During a major flood, the river cuts across the loop. The current is faster at outside banks, which are eroded. The abandoned loop remains as an oxbow lake.