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Stream load is a geologic term referring to the solid matter carried by a stream (Strahler and Strahler, 2006).

Erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...

and bed

shear stress Shear stress, often denoted by (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...

continually remove mineral material from the bed and banks of the stream channel, adding this material to the regular flow of water. The amount of solid load that a stream can carry, or stream capacity, is measured in metric tons per day, passing a given location. Stream capacity is dependent upon the stream's

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

, the amount of water flow, and the gradation (because streams that occur on steeper slopes tend to have greater flow and velocity) (Strahler and Strahler, 2006).

Types of stream erosion

There are two main sources of stream erosion: hydraulic action and abrasion. All of the materials added to normal stream flow through these processes increase the overall stream load (Strahler and Strahler, 2006).

Hydraulic action

Hydraulic action describes the erosion caused by the dragging of water over the stream bed and bank. This dragging, coupled with the impact of small parties, easily loosens and erodes smaller

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Al ...

matter, such as

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classif ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel wh ...

and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...

(Mangelsdorf, 1990). One powerful example of hydraulic action is bank caving, which normally occurs when a stream loosens

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

and undercuts a bank. Consequently, large masses of sediment slump and collapse into the stream, adding significantly to the stream's load (Strahler and Strahler, 2006). The severity of hydraulic action increases with stream velocity and current stream load.

Abrasion

Abrasion occurs when larger rock particles roll and strike against bedrock walls, chipping and splintering particles and pieces of rock (Strahler and Strahler). As these cobbles and boulders roll across the stream bed, they continue to crush and grind the bedrock, producing an assortment of eroded rock sizes (Ritter, 2006). Again, the severity of this type of erosion is dependent upon stream velocity and stream load (i.e. the presence of larger rock particles)..

Types of stream load

Mineral materials of many different shapes and particle sizes erode and contribute to overall stream load. Differences in the size of those materials determine how they will be transported down stream. Stream load is broken into three types:

dissolved load Dissolved load is the portion of a stream's total sediment load that is carried in solution, especially ions from chemical weathering. It is a major contributor to the total amount of material removed from a river's drainage basin, along with su ...

suspended load The suspended load of a flow of fluid, such as a river, is the portion of its sediment uplifted by the fluid's flow in the process of sediment transportation. It is kept suspended by the fluid's turbulence. The suspended load generally consists ...

, and

bed load The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or saltating (ho ...

(Ritter, 2006).

Dissolved load

Dissolved matter is invisible, and is transported in the form of chemical

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

. All streams carry some type of dissolved load. This type of load can result from mineral alteration from chemical erosion, or may even be the result of groundwater seepage into the stream. Materials comprising the

have the smallest particle size of the three load types (Strahler and Strahler, 2006).

Suspended load

Suspended load The suspended load of a flow of fluid, such as a river, is the portion of its sediment uplifted by the fluid's flow in the process of sediment transportation. It is kept suspended by the fluid's turbulence. The suspended load generally consists ...

is composed of fine sediment particles suspended and transported through the stream. These materials are too large to be dissolved, but too small to lie on the bed of the stream (Mangelsdorf, 1990). Stream flow keeps these suspended materials, such as clay and silt, from settling on the stream bed. Suspended load is the result of material eroded by hydraulic action at the stream surface bordering the channel as well as erosion of the channel itself. Suspended load accounts for the largest majority of stream load (Strahler and Strahler, 2006).

Bed load

Bed load The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or saltating (ho ...

rolls slowly along the floor of the stream. These include the largest and heaviest materials in the stream, ranging from sand and gravel to cobbles and boulders. There are two main ways to transport bed load: traction and saltation. Traction describes the “scooting and rolling” of particles along the bed (Ritter, 2006). In stream load transport, saltation is a bounce-like movement, occurring when large particles are suspended in the stream for a short distance after which they fall to the bed, dislodging particles from the house. The dislodged particles move downstream a short distance where they fall to the bed, again loosening bed load particles upon impact (Ritter, 2006).

Flood and stream load

Floods A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study o ...

create a scenario in which stream flow and velocity are unusually high due to the drastic addition of water to a stream. These heightened characteristics increase both the potential of stream erosion and heavier stream load (Knighton, 1998). Flooded streams are often responsible for heavy sediment transportation and deposition downstream. Stream capacity is greatly increased during a flood (Knighton, 1998). During a flood, increased suspended load may be visible, giving the stream a muddy color.

References

*Knighton, David. (1998). ''Fluvial Forms & Processes: A New Perspective'', London: Arnold. *Mangelsdorf, J. et al. (1990). ''River Morphology: A Guide for Geoscientists and Engineers'', Berlin: Springer-Verlag. *Ritter, M.E. (2006). ''The Physical Environment: an Introduction to Physical Geography: The Geologic Work of Streams''. Visited: March 2, 2008. '' https://web.archive.org/web/20080516233555/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/icecap.html'' *Strahler, A. and A. Strahler. (2006). ''Introducing Physical Geography'', Boston: Wiley & Sons. Erosion