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A stream bed or streambed is the bottom of a stream or 
The nature of any stream bed is always a function of the flow dynamics and the local geologic materials, influenced by that flow. With small streams in mesophytic regions, the nature of the stream bed is strongly responsive to conditions of
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
(bathymetry
Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...
) or the physical confine of the normal water flow ( channel). The lateral confines or channel margins are known as the stream bank
A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets.
Because ...
s or river banks, during all but flood stage Flood stage is the water level or stage at which the surface of a body of water has risen to a sufficient level to cause sufficient inundation of areas that are not normally covered by water, causing an inconvenience or a threat to life and property ...
. Under certain conditions a river can branch from one stream bed to multiple stream beds. A flood
A flood is an overflow of water ( 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 of the discipline hydrol ...
occurs when a stream overflows its banks and flows onto its flood plain. As a general rule, the bed is the part of the channel up to the normal water line, and the banks are that part above the normal water line. However, because water flow varies, this differentiation is subject to local interpretation. Usually, the bed is kept clear of terrestrial vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characte ...
, whereas the banks are subjected to water flow only during unusual or perhaps infrequent high water stages and therefore might support vegetation some or much of the time.
The nature of any stream bed is always a function of the flow dynamics and the local geologic materials, influenced by that flow. With small streams in mesophytic regions, the nature of the stream bed is strongly responsive to conditions of precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
runoff. Where natural conditions of either grassland
A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...
or forest
A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
ameliorate peak flows, stream beds are stable, possibly rich, with organic matter and exhibit minimal scour. These streams support a rich biota. Where conditions produce unnatural levels of runoff, such as occurs below roads, the stream beds will exhibit a greater amount of scour, often down to bedrock and banks may be undercut. This process greatly increases watershed erosion and results in thinner soils, upslope from the stream bed, as the channel adjusts to the increase in flow. The stream bed is very complex in terms of erosion. 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 ...
is transported, eroded and deposited on the stream bed. The majority of sediment washed out in floods is "near-threshold" sediment that has been deposited during normal flow and only needs a slightly higher flow to become mobile again. This shows that the stream bed is left mostly unchanged in size and shape.
Beds are usually what would be left once a stream is no longer in existence; the beds are usually well preserved even if they get buried, because the walls and canyons made by the stream usually have hard walls, usually soft sand and debris fill the bed. Dry stream beds are also subject to becoming underground water pockets (buried stream beds only) and flooding by heavy rains and water rising from the ground and may sometimes be part of the rejuvenation of the stream.
See also
*Armor (hydrology)
In hydrology and geography, armor is the association of surface pebbles, rocks or boulders with stream beds or beaches. Most commonly hydrological armor occurs naturally; however, a man-made form is usually called riprap, when shorelines or str ...
* Benthic zone
* Hyporheic zone
The hyporheic zone is the region of sediment and porous space beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water. The flow dynamics and behavior in this zone (termed hyporheic flow or underflow) is re ...
* Thalweg
In geography and fluvial geomorphology, a thalweg or talweg () is the line of lowest elevation within a valley or watercourse.
Under international law, a thalweg is the middle of the primary navigable channel of a waterway that defines the boun ...
References
External links
* {{Authority control Water streams Fluvial landforms Limnology Riparian zone Freshwater ecology