Stream Gradient


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stream gradient

[′strēm ‚grād·ē·ənt]
(geology)
The angle, measured in the direction of flow, between the water surface (for large streams) or the channel flow (for small streams) and the horizontal. Also known as stream slope.

Stream Gradient

 

the difference in water-surface elevations measured at the source and at the mouth of a stream or at the ends of a section of a stream. The stream gradient of a section divided by the length of that section is called the slope. The gradient of a section of a stream is usually calculated for 1 km of the channel. This gradient amounts to several cm per km for typical streams on level ground and to several m per km for mountain streams.


Stream Gradient

 

(or stream slope). For a given stretch of a stream, the gradient is the ratio of the drop the stream undergoes and the length of the stretch. A stream gradient may be expressed in terms of the number of units of vertical distance per hundred units of horizontal distance or per thousand units of horizontal distance. In the former case the term “percent grade” is sometimes used.

The gradient of a stream generally decreases from the source to the mouth. In some cases, however, the gradient may vary in a different way as a result of the special nature of the topography or the rocks and soils through which the channel runs. Streams in mountain regions may undergo considerable drops over short distances; rapids and races may be observed in such cases. The gradients of individual stretches of a stream are determined from the water level during a period of a low, steady flow rate. The overall gradient of a stream is found by averaging the gradients of the individual stretches.

Occasionally the water surface of a stream may exhibit what may be called a transverse gradient, or transverse slope—that is, the surface from one side to the other may not be level. Such a gradient may be produced by various factors, including wind and the shape of the channel. At a bend, for example, the water surface may be higher at the convex bank.

References in periodicals archive ?
Occupancy 1 Stream No Stream width, stream i depth, stream gradient, bank slope, bare soil (%), elevation, riparian zone width, litter cover (%), abundance of: Aspen, Alder, Cottonwood, Willow, Lodgepole pine, Jeffrey pine, Fire, Dogwood, Grasses/ forbs 1 Stream No Slope of river bank, 2 percent understory cover 2 m high at 10 m from water, percent understory cover 2 m high at 15 in from water, percent understory cover 1 m high at 10 m & 15 m from water, percent canopy cover, river depth, river width 1 Stream No Vegetation classes: 3 Tamarix, Pluchea, Prosopis-Acacia, Baccharis-Salix, shrub, sparse, nonvegetation, wetland 9 Stream No Percent canopy cover of: 4 all tree species 10-15 m tall, Salicaceae spp.
The qualitative habitat variables include the following categories; substrate types, instream cover, channel morphology, riparian quality/bank erosion, pool/glide and riffle/run quality, and local stream gradient. Each qualitative habitat category is ranked by a series of categories representing varying states of stream habitat condition.
Variables used in the model include: stream gradient, average water fluctuation (m), % canopy closure, % trees in the 2.5-15.2 cm diameter at breast height (dbh) class, % shrub cover, shrub height, and woody species composition within 200 m of the stream.
As part of this natural stream channel design approach, a spreadsheet routine has been developed that provides a basis for the spacing and sizing of pools and steps, depending mainly on stream gradient. This again stems from the geometric relationships between step height and step length observed in natural step-pool streams.
In their undisturbed state, alluvial river systems of the northern Rocky Mountains often follow an alternating pattern of confined and unconfined valley segments as they move down the stream gradient. Stream reaches within unconfined valley segments have an additional alternating pattern of downwelling and upwelling vertical exchange of water and materials between the hyporheic zone and surface stream.
In warmwater Wisconsin streams, Lyons (1996) found that basin area and stream gradient influenced patterns of fish assemblages.
The spacing of grade control structures will vary depending on stream gradient, streambed erodibility, and variations in bed and bank conditions influencing constructability.
(4) Stream gradient - the average slope (in meters per kilometer) along the water course between a lake and its next lake.
The high degree of intercorrelation among physical and chemical variables in our data, while collectively defining a composite stream gradient related to stream order, also hampers modeling efforts to predict fish community response to specific forms of habitat change.
Where stream gradient is low, duration of inundation is long, and fine sediment and organic matter are abundant, anoxia may influence vegetation zonation more than any other environmental factor (Wharton et al.
This model states that the detachment limited channels do not observe continuous coverage of sediments, even at low flow because of equal stream gradients for erosion and uplift (see Figure 2).
These projects involve rural and urban watershed conditions, headwater and larger streams, and a range of stream gradients. The project sites include various floodplain conditions, including riparian wetlands, stormwater retention cells, and vegetated buffers.