Stream


A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long, large streams are usually called rivers, while smaller, less voluminous and more intermittent streams are known, amongst others, as brook, creek, rivulet, rill, run, tributary, feeder, freshet, narrow river, and streamlet.
The flow of a stream is controlled by three inputs – surface runoff, daylighted subterranean water, and surfaced groundwater. 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.
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.

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 hydrography, gut is a small creek; this is seen in proper names in eastern North America from the Mid-Atlantic states down into the 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. Sometimes also called a branch or fork.

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

; 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: 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 turbulent, fast-flowing stretch of a stream or river.
; Riffle: A segment where the flow is shallower and more turbulent.
; 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.
; 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 or the stream itself. In the UK, some aspects of criminal law, such as the Rivers 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.

Characteristics

Ranking

To qualify as a stream, a body of water must be either recurring or perennial. Recurring streams have water in the channel for at least part of the year. A stream of the first order is a stream which does not have any other recurring or perennial stream feeding into it. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream. Streams of lower order joining a higher order stream do not change the order of the higher stream.

Gradient

The gradient of a stream is a critical factor in determining its character and is entirely determined by its base level of erosion. The base level of erosion is the point at which the stream either enters the ocean, a lake or pond, or enters a stretch in which it has a much lower gradient, and may be specifically applied to any particular stretch of a stream.
In geological terms, the stream will erode down through its bed to achieve the base level of erosion throughout its course. If this base level is low, then the stream will rapidly cut through underlying strata and have a steep gradient, and if the base level is relatively high, then the stream will form a flood plain and meander.

Profile

Typically, streams are said to have a particular elevation profile, also known as longitudinal profile or long profile. It begins at the source with steep gradients, no flood plain, and little shifting of channels, eventually evolving into streams with low gradients, wide flood plains, and extensive meanders. The initial stage is sometimes termed a "young" or "immature" stream, and the later state a "mature" or "old" stream. A stream cross profile is a cross section from bank to bank.