A perennial stream or perennial river is a stream or river (channel) that has continuous flow in parts of its bed all year round during years of normal rainfall. A stream is a body of Water with a current, confined within a bed and stream-banks "Riverine" redirects here For the use of that term in Maritime geography, see there "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral" channels that flow only for hours or days following rainfall. During unusually dry years, a normally perennial stream may cease flowing, becoming intermittent for days, weeks, or months depending on severity of the drought. The boundaries between perennial, intermittent, and ephemeral channels are indefinite, and subject to a variety of identification methods adopted by local governments, academics, and others with a need to classify stream-flow permanence.
As stream-flow decreases in dry weather, visible flow above the stream bed may not be readily evident, especially in streams with coarse substrate (gravel and rocks), where water is flowing beneath and between these particles (hyporheic flow). From a biological perspective, a stream may be considered flowing if sufficient water is available to support flow-dependent aquatic life, including fish and gill-breathing amphibians, benthic insects, crustaceans, and mollusks, many of which survive in shallow hyporheic flow beneath rocks or logs. This extreme low flow may not be detectable on typical USGS stream-flow gages, but is vital to stream ecology. [1]
See also
- winterbourne, a stream or river that flows only in winter. A winterbourne is a Stream or River that is dry through the Summer months Winter is one of the four Seasons of Temperate zones Calculated astronomically, it begins on the Solstice and ends on the Equinox
References
- ^ Definition of "Perennial Stream". Office of Surface Mining - US Department of the Interior. Retrieved on March 28, 2007. Events 37 - Roman Emperor Caligula accepts the titles of the Principate, entitled to him by the Senate. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
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