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 as streamlets, brooks or creeks.
The flow of a stream is controlled by three inputs – surface runoff (from precipitation or meltwater), daylighted subterranean water, and surfaced 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.
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 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, 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.
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.
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 and Virginia. 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 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.