Stream gradient
Encyclopedia
Stream gradient is the grade (slope) measured by the ratio of drop in a stream
per unit distance, usually expressed as feet per mile
or metre
s per kilometre
.
of water
(i.e. more ability to erode); whereas a low gradient indicates a more nearly level stream bed
and sluggishly moving water, that may be able to carry only small amounts of very fine sediment
. High gradient streams tend to have steep, narrow V-shaped valley
s, and are referred to as young streams. Low gradient streams have wider and less rugged valley
s, with a tendency for the stream to meander
.
substrate will tend to have a steep gradient near its source, and a low gradient nearing zero as it reaches its base level
. Of course, a uniform substrate would be rare in nature; hard layers of rock
along the way may establish a temporary base level, followed by a high gradient, or even a waterfall
, as softer materials are encountered below the hard layer.
Human dam
s, glaciation, changes in sea level
, and many other factors can also change the "normal" or natural gradient pattern.
s, stream gradient can be easily approximated if the scale of the map and the contour intervals are known. Contour lines form a V-shape on the map, pointing upstream. By counting the number of lines that cross a certain segment of a stream, multiplying this by the contour interval, and dividing that quantity by the length of the stream segment you can determine the stream gradient.
Because stream gradient is customarily given in feet per 1000 feet, one should then measure the amount a stream segment rises and the length of the stream segment in feet, then multiply feet per foot gradient by 1000. For example, if one measures a scale mile along the stream length, and counts three contour lines crossed on a map with ten-foot contours, the gradient is approximately 5.7 feet per 1000 feet, a fairly steep gradient.
----
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
per unit distance, usually expressed as feet per mile
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
or metre
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...
s per kilometre
Kilometre
The kilometre is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in of a second...
.
Hydrology and geology
A high gradient indicates a steep slope and rapid flowVolumetric flow rate
The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...
of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
(i.e. more ability to erode); whereas a low gradient indicates a more nearly level stream bed
Stream bed
A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...
and sluggishly moving water, that may be able to carry only small amounts of very fine sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
. High gradient streams tend to have steep, narrow V-shaped valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
s, and are referred to as young streams. Low gradient streams have wider and less rugged valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
s, with a tendency for the stream to meander
Meander
A meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the...
.
Fluvial Erosion
A stream that flows upon a uniformly erodibleErosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
substrate will tend to have a steep gradient near its source, and a low gradient nearing zero as it reaches its base level
Base level
The base level of a river or stream is the lowest point to which it can flow, often referred to as the 'mouth' of the river. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams...
. Of course, a uniform substrate would be rare in nature; hard layers of rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
along the way may establish a temporary base level, followed by a high gradient, or even a waterfall
Waterfall
A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...
, as softer materials are encountered below the hard layer.
Human dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
s, glaciation, changes in sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, and many other factors can also change the "normal" or natural gradient pattern.
Topographic mapping
On topographic mapTopographic map
A topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features...
s, stream gradient can be easily approximated if the scale of the map and the contour intervals are known. Contour lines form a V-shape on the map, pointing upstream. By counting the number of lines that cross a certain segment of a stream, multiplying this by the contour interval, and dividing that quantity by the length of the stream segment you can determine the stream gradient.
Because stream gradient is customarily given in feet per 1000 feet, one should then measure the amount a stream segment rises and the length of the stream segment in feet, then multiply feet per foot gradient by 1000. For example, if one measures a scale mile along the stream length, and counts three contour lines crossed on a map with ten-foot contours, the gradient is approximately 5.7 feet per 1000 feet, a fairly steep gradient.
See also
- Channel typesChannel typesA wide variety of river and stream channel types exist in limnology. All these can be divided into two groups by using the water-flow gradient as either low gradient channels for streams or rivers with less than two percent flow gradient, or high gradient channels for those with greater than a 2%...
- Relief ratioRelief ratioThe relief ratio is a number calculated to describe the Grade of a river or stream.The calculation is just the difference in elevation between the river's source and the river's confluence or mouth divided by the total length of the river or stream. This gives the average drop in elevation per...
- RapidRapidA rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water velocity and turbulence. A rapid is a hydrological feature between a run and a cascade. A rapid is characterised by the river becoming shallower and having some rocks exposed above the...
s - Types of waterfall
----