A stream is a continuous body of surface water flowing within the bed and banks of a channel. The channel is a watercourse, although the watercourse may be seasonally or periodically dry. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. A long, large stream is usually called a river, while a smaller, less voluminous, and more intermittent stream is known as a creek or tributary, among other names.
The flow of a stream is controlled by three inputs – surface runoff (from precipitation or meltwater), daylighted subterranean water, and surface groundwater (spring water). The surface and subterranean water are highly variable between periods of rainfall. Groundwater, on the other hand, has a relatively constant input and is controlled more by long-term patterns of precipitation. The stream encompasses surface, subsurface and groundwater fluxes that respond to geological, geomorphological, hydrological and biotic controls.Alexander, L. C., Autrey, B., DeMeester, J., Fritz, K. M., Golden, H. E., Goodrich, D. C., ... & McManus, M. G. (2015). Connectivity of streams and wetlands to downstream waters: review and synthesis of the scientific evidence (Vol. 475). EPA/600/R-14.
Streams are important as conduits in the water cycle, instruments in groundwater recharge, and corridors for fish and wildlife migration. The biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity. The study of streams and waterways in general is known as surface hydrology and is a core element of environmental geography."What is hydrology and what do hydrologists do?" U.S. Geological Survey (USGS). Atlanta, GA. 2009-05-13.
Types
Brook A brook is a stream smaller than a creek, especially one that is fed by a spring or seep. It is usually small and easily forded. A brook is characterised by its shallowness.
Creek A creek () or crick (): In Australia, Canada, New Zealand and the United States, a (narrow) stream that is smaller than a river; a minor tributary of a river; a brook. Sometimes navigable by water craft and may be intermittent. In the United Kingdom, India, and parts of Maryland, New England,Spruce Creek Association. Kittery, ME. "About the Spruce Creek Watershed." Accessed 2010-10-02. a tidal inlet, typically in a salt marsh or mangrove swamp, or between enclosed and drained former salt marshes or swamps (e.g. Portsbridge Creek separating Portsea Island from the mainland). In these cases, the "stream" is the tidal stream, the course of the seawater through the creek channel at low and high tide.
In hydrography, gut is a small creek; this is seen in proper names in eastern North America from the Mid-Atlantic states (for instance, The Gut in Pennsylvania, Ash Gut in Delaware, and other streams) down into the Caribbean (for instance, Guinea Gut, Fish Bay Gut, Cob Gut, Battery Gut and other rivers and streams in the United States Virgin Islands, in Jamaica (Sandy Gut, Bens Gut River, White Gut River), and in many streams and creeks of the Dutch Caribbean).
River A river is a large natural stream that is much wider and deeper than a creek and not easily fordable, and may be a navigable waterway.
Runnel The linear channel between the parallel ridges or bars on a shoreline beach or river floodplain, or between a bar and the shore. Also called a swale.
Tributary A tributary is a contributory stream to a larger stream, or a stream which does not reach a static body of water such as a lake, bay or ocean but joins another river (a parent river). Sometimes also called a branch or fork.Bisson, Peter and Wondzell, Steven. "Olympic Experimental State Forest Synthesis of Riparian Research and Monitoring" , United States Forest Service, p. 15 (December 1, 2009).
Distributary A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel, and the phenomenon is known as river bifurcation. Distributaries are common features of river deltas, and are often found where a valleyed stream enters wide flatlands or approaches the coastal plains around a lake or an ocean. They can also occur inland, on alluvial fans, or where a tributary stream bifurcates as it nears its confluence with a larger stream. Common terms for individual river distributaries in English-speaking countries are arm and channel.
Other names There are a number of regional names for a stream.
Northern America Branch is used to name streams in Maryland, Virginia and much of the United States. Creek is common throughout the United States, as well as Australia. Falls is also used to name streams in Maryland, for streams/rivers which have waterfalls on them, even if such falls only have a small vertical drop. Little Gunpowder Falls, Gwynns Falls, and the Jones Falls are actually rivers named in this manner, unique to Maryland. Kill in New York, Pennsylvania, Delaware, and New Jersey comes from a Dutch language word meaning "riverbed" or "water channel", and can also be used for the UK meaning of 'creek'. Run in Ohio, Maryland, Michigan, New Jersey, Pennsylvania, Virginia, or West Virginia can be the name of a stream. Run in Florida is the name given to streams coming out of small natural springs. River is used for streams from larger springs like the Silver River and Rainbow River. Stream and brook are used in Midwestern states, Mid-Atlantic states, and New England. Gut is sometimes used for a small creek, from the Mid-Atlantic states down into the Caribbean (see above).
United Kingdom Allt is used in the Scottish Highlands. Beck is used in an area between Lincolnshire, County Durham and Cumbria which were areas once occupied by the Danes and Norwegians. Bourne or winterbourne is used in the chalk downland of southern England for ephemeral rivers. When permanent, they are chalk streams. Brook. Burn is used in Scotland and North East England. Gill or ghyll is seen in the north of England and Kent and Surrey influenced by Old Norse. The variant "ghyll" is used in the Lake District and appears to have been an invention of William Wordsworth. Nant is used in Wales. Rivulet is a term encountered in Victorian era publications. Syke is used in the Scottish Lowlands and Cumbria for a seasonal stream.
Related terminology
Bar A shoal that develops in a stream as sediment is deposited as the current slows or is impeded by wave action at the confluence. Bifurcation A fork into two or more streams. Channel A depression created by constant erosion that carries the stream's flow. Confluence The point at which the two streams merge. If the two tributaries are of approximately equal size, the confluence may be called a fork. Drainage basin (also known as a watershed in the United States) The area of land where water flows into a stream. A large drainage basin such as the Amazon River contains many smaller drainage basins. Floodplain Lands adjacent to the stream that are subject to flooding when a stream overflows its banks. Headwaters or source The part of a stream or river proximate to its source. The word is most commonly used in the plural where there is no single point source. Knickpoint The point on a stream's profile where a sudden change in stream gradient occurs. Mouth The point at which the stream discharges, possibly via an estuary or delta, into a static body of water such as a lake or ocean. Pool A segment where the water is deeper and slower moving. Rapids A very turbulent, fast-flowing, and of various depths, stretch of a stream or river. Riffle A segment of the flow which is shallower and turbulent but to lesser degree and without the vigor of a rapid.
River A large natural stream, which may be a waterway. Run A somewhat smoothly flowing segment of the stream. Spring The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can, especially with caves, flow aboveground for part of its course, and underground for part of its course. Stream bed The bottom of a stream. Stream corridor Stream, its floodplains, and the transitional upland fringe."Stream Corridor Structure" Adapted from Stream Corridor Restoration: Principles, Processes, and Practices Streamflow The water moving through a stream channel. Stream gauge A site along the route of a stream or river, used for reference marking or water monitoring. Thalweg The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. Watercourse The channel followed by a stream (a flowing body of water) or the stream itself. In the UK, some aspects of criminal law, such as the Rivers (Prevention of Pollution) Act 1951, specify that a watercourse includes those rivers which are dry for part of the year. In some jurisdictions, owners of land over which the water flows may have the legal right to use or retain some or much of that water. This right may extend to estuaries, rivers, streams, anabranches and canals. Waterfall or cascade The fall of water where the stream goes over a sudden drop called a knickpoint; some knickpoints are formed by erosion when water flows over an especially resistant stratum, followed by one less so. The stream expends kinetic energy as it flows over the knickpoint. Wetted perimeter The line on which the stream's surface meets the channel walls.
Sources
A stream's source depends on the surrounding landscape and its function within larger river networks. While perennial and intermittent streams are typically supplied by smaller upstream waters and groundwater, headwater and ephemeral streams often derive most of their water from precipitation in the form of rain and snow. Most of this precipitated water re-enters the atmosphere by evaporation from soil and water bodies, or by the evapotranspiration of plants. Some of the water proceeds to sink into the earth by infiltration and becomes groundwater, much of which eventually enters streams. Some precipitated water is temporarily locked up in snow fields and glaciers, to be released later by evaporation or melting. The rest of the water flows off the land as runoff, the proportion of which varies according to many factors, such as wind, humidity, vegetation, rock types, and relief. This runoff starts as a thin film called sheet wash, combined with a network of tiny rills, together constituting sheet runoff; when this water is concentrated in a channel, a stream has its birth. Some creeks may start from ponds or lakes.
The streams typically derive most of their water from rain and snow precipitation. Most of this water re-enters the atmosphere either by evaporation from soil and water bodies, or by plant evapotranspiration. By infiltration some of the water sinks into the earth and becomes groundwater, much of which eventually enters streams. Most precipitated water is partially bottled up by evaporation or freezing in snow fields and glaciers. The majority of the water flows as a runoff from the ground; the proportion of this varies depending on several factors, such as climate, temperature, vegetation, types of rock, and relief. This runoff begins as a thin layer called sheet wash, combined with a network of tiny rills, which together form the sheet runoff; when this water is focused in a channel, a stream is born. Some rivers and streams may begin from lakes or ponds.
Freshwater's primary sources are precipitation and mountain snowmelt. However, rivers typically originate in the highlands, and are slowly created by the erosion of mountain snowmelt into lakes or rivers. Rivers usually flow from their source topographically, and erode as they pass until they reach the base stage of erosion.