GEO 101 Lecture Notes - Lecture 26: Foreset Bed, Distributary, Oxbow Lake
24 Jun 2018
School
Department
Course
Professor
Sediment Load
The majority of a stream's sediment load is carried in solution (dissolved load) or in
suspension. The remainder is called the bed load.
Dissolved load.Earth material that has been dissolved into ions and carried in solution
is the dissolved load.It is usually contributed by groundwater. Common ions are
calcium, bicarbonate, potassium, sulfate, and chloride. These ions may react to form
new minerals if the proper chemical conditions are encountered during flow. Minerals
may also precipitate in trapped pools through evaporation.
Suspended load. The suspended load is the fine grained sediment that remains in the‐
water during transportation. For example, a flooding river is muddy and discolored from
the large amounts of sediment suspended in the water. The suspended load is
generally made up of lighter weight, finer grained particles such as silt and clay. Most of‐ ‐
the sediment in a stream is carried as suspended load. It does not contribute greatly to
stream erosion, since it is not in frictional contact with the stream bed.
Bed load. The heavier, coarser grained earth material that travels along the bottom of ‐
the stream is the bed load. Traction occurs when these fragments move along by
rolling and sliding. Turbulent or eddying currents can temporarily lift these larger grains
into the overlying flow of water—the grains advance by short jumps or skips until the
surge diminishes and then fall back to the bottom because of their greater weight. This
process is called saltation.
Capacity and competence. The maximum load of sediment that a stream can
transport is called its capacity. Capacity is directly proportional to the discharge: the
greater the amount of water flowing in the stream, the greater the amount of sediment it
can carry. A stream's competence is a measure of the largest sized particle it can ‐
transport; competence is directly proportional to a stream's velocity, which can vary
seasonally. Because of increased capacity and competence, a single flood event can
cause more erosion than a hundred years of standard flow.
Stream Deposition
A stream's sediment load is typically deposited, eroded, and redeposited many times in
a stream channel, especially during climatic variations such as flooding. Sediments are
deposited throughout the length of the stream as bars or floodplain deposits. At the
mouth of the stream, the sediments are usually deposited in alluvial fans or deltas,
which represent a lower energy, more “permanent” depositional environment that is less‐
susceptible to changes in the stream flow.
Bars. Bars form in the middle of the channel or along the banks of a stream at points
where the velocity decreases, resulting in the deposition of some of the sediment load.
Bars are ridges generally made up of gravel or sand sized particles. A subsequent ‐ ‐
flood event will erode bars, transport the sediments, and redeposit the material as a
new bar farther downstream.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The majority of a stream"s sediment load is carried in solution (dissolved load) or in suspension. Dissolved load. earth material that has been dissolved into ions and carried in solution is the dissolved load. it is usually contributed by groundwater. Common ions are calcium, bicarbonate, potassium, sulfate, and chloride. These ions may react to form new minerals if the proper chemical conditions are encountered during flow. Minerals may also precipitate in trapped pools through evaporation. The suspended load is the fine grained sediment that remains in the water during transportation. For example, a flooding river is muddy and discolored from the large amounts of sediment suspended in the water. The suspended load is generally made up of lighter weight, finer grained particles such as silt and clay. Most of the sediment in a stream is carried as suspended load. It does not contribute greatly to stream erosion, since it is not in frictional contact with the stream bed.
