There are three types of sediment
transportation correlating to streams. The first type of sediment
transportation is solution load. Solution load is dissolved rock carried in the
flowing water. The solution will also contain dissolved salts, calcium,
magnesium, and bicarbonate, minerals that have been dissolved from the bedrock.
This type of load tends to be higher in areas where bedrock is prone to
chemical weathering and where flow is derived from groundwater pathways.
The second type of sediment
transportation is suspended load. Suspended load contains finer sediment, mainly
clay and silt and fine sand and tiny rocks, suspended by turbulence in the flow
by a process called abrasion. A suspended load moves at the same velocity as
the flow of the stream. Stream capacity is the maximum load of sediment that a
stream can carry and the stream capacity increases with increasing flow
velocity. Naturally, streams that contain a greater slop have a greater flow
and velocity. Flooding and storms will increase the velocity of the water due
to the drastic addition of water to the stream. Stream competence is the
largest size material the stream can move. Slow moving streams are highly
depositional and are considered a low stream capacity; high velocity streams
that can move larger rocks are considered to have a high stream competence. Much
of a river’s load is carried in suspension.
The third type of sediment
transportation is bed load. Bed load contains courser sediment, mainly sand and
gravel, which is too heavy to be carried in suspension and will slide or roll
along the stream bed. The amount of bed load will depend on the force exerted by
the flow of water, the resisting force of the material in the bed, the climate,
the type of bedrock, and the season of the year. There are two ways of transporting bed loads:
traction and saltation. Traction is the scooting and rolling of particles along
the bed; saltation is a bouncing movement.
When
velocity and discharge decrease, the stream’s ability to move sediment will
decrease as well. There are two ways that sediment may deposit on a stream bed:
aggradation and bars. Aggradation may raise the elevation of the bed with the
accumulation of sediment. Bars are formed when deposits of sand or gravel
accumulate and the bars will separate the channel into smaller channels.
Sources:
http://www.classzone.com/vpg_ebooks/ml_earthscience_na/accessibility/ml_earthscience_na/page_284.pdf
