Misplaced Pages

#366633

83-625: A creek in North America and elsewhere, such as Australia, is a stream that is usually smaller than a river. In the British Isles it is a small tidal inlet . Creek may also refer to: Stream 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

166-403: A bed armor layer, and other depositional features, plus well defined banks due to bank erosion, are good identifiers when assessing for perennial streams. Particle size will help identify a perennial stream. Perennial streams cut through the soil profile, which removes fine and small particles. By assessing areas for relatively coarse material left behind in the stream bed and finer sediments along

249-575: A confined channel and is free to spread out and infiltrate the surface. This reduces the carrying capacity of the flow and results in deposition of sediments. The flow can take the form of infrequent debris flows or one or more ephemeral or perennial streams. Alluvial fans are common in the geologic record , such as in the Triassic basins of eastern North America and the New Red Sandstone of south Devon . Such fan deposits likely contain

332-658: A continuous aquatic habitat until they reach maturity. Crayfish and other crustaceans , snails , bivalves (clams), and aquatic worms also indicate the stream is perennial. These require a persistent aquatic environment for survival. Fish and amphibians are secondary indicators in assessment of a perennial stream because some fish and amphibians can inhabit areas without persistent water regime. When assessing for fish, all available habitat should be assessed: pools, riffles, root clumps and other obstructions. Fish will seek cover if alerted to human presence, but should be easily observed in perennial streams. Amphibians also indicate

415-470: A continuous or intermittent stream. The same non-perennial channel might change characteristics from intermittent to ephemeral over its course. Washes can fill up quickly during rains, and there may be a sudden torrent of water after a thunderstorm begins upstream, such as during monsoonal conditions. In the United States, an intermittent or seasonal stream is one that only flows for part of

498-615: 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. A creek ( / k r iː k / ) or crick ( / k r ɪ k / ): 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

581-558: A debris flow can come to a halt while still on moderately tilted ground. The flow then becomes consolidated under its own weight. Debris flow fans occur in all climates but are more common where the source rock is mudstone or matrix-rich saprolite rather than coarser, more permeable regolith . The abundance of fine-grained sediments encourages the initial hillslope failure and subsequent cohesive flow of debris. Saturation of clay-rich colluvium by locally intense thunderstorms initiates slope failure. The resulting debris flow travels down

664-422: A drainage network. Although each tributary has its own source, international practice is to take the source farthest from the river mouth as the source of the entire river system, from which the most extended length of the river measured as the starting point is taken as the length of the whole river system, and that furthest starting point is conventionally taken as the source of the whole river system. For example,

747-514: A hiatus of 70,000 to 80,000 years between the old and new fans, with evidence of tectonic tilting at 45,000 years ago and an end to fan deposition 20,000 years ago. Both the hiatus and the more recent end to fan deposition are thought to be connected to periods of enhanced southwest monsoon precipitation. Climate has also influenced fan formation in Death Valley , California , US, where dating of beds suggests that peaks of fan deposition during

830-664: A lag of gravel deposits that have the appearance of a network of braided streams. Where the flow is more continuous, as with spring snow melt, incised-channel flow in channels 1–4 meters (3–10 ft) high takes place in a network of braided streams. Such alluvial fans tend to have a shallower slope but can become enormous. The Kosi and other fans along the Himalaya mountain front in the Indo-Gangetic plain are examples of gigantic stream-flow-dominated alluvial fans, sometimes described as megafans . Here, continued movement on

913-540: A larger stream. Common terms for individual river distributaries in English-speaking countries are arm and channel . There are a number of regional names for a stream. 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

SECTION 10

#1732765616367

996-443: A million people were rendered homeless, about a thousand lost their lives and thousands of hectares of crops were destroyed. Buried alluvial fans are sometimes found at the margins of petroleum basins. Debris flow fans make poor petroleum reservoirs, but fluvial fans are potentially significant reservoirs. Though fluvial fans are typically of poorer quality than reservoirs closer to the basin center, due to their complex structure,

1079-439: A minimum, major structural flood control measures are required to mitigate risk, and in some cases, the only alternative is to restrict development on the fan surface. Such measures can be politically controversial, particularly since the hazard is not obvious to property owners. In the United States, areas at risk of alluvial fan flooding are marked as Zone AO on flood insurance rate maps . Alluvial fan flooding commonly takes

1162-409: A part of the fan with a steeper gradient, where deposition resumes. As a result, normally only part of the fan is active at any particular time, and the bypassed areas may undergo soil formation or erosion. Alluvial fans can be dominated by debris flows ( debris flow fans ) or stream flow ( fluvial fans ). Which kind of fan is formed is controlled by climate, tectonics , and the type of bedrock in

1245-404: A path into mines or other underground chambers. According to official U.S. definitions, the channels of intermittent streams are well-defined, as opposed to ephemeral streams, which may or may not have a defined channel, and rely mainly on storm runoff, as their aquatic bed is above the water table . An ephemeral stream does not have the biological, hydrological, and physical characteristics of

1328-412: A perennial stream and include tadpoles , frogs , salamanders , and newts . These amphibians can be found in stream channels, along stream banks, and even under rocks. Frogs and tadpoles usually inhabit shallow and slow moving waters near the sides of stream banks. Frogs will typically jump into water when alerted to human presence. Well defined river beds composed of riffles, pools, runs, gravel bars,

1411-483: A perennial stream, fine sediment may cling to riparian plant stems and tree trunks. Organic debris drift lines or piles may be found within the active overbank area after recent high flow. Streams, headwaters, and streams flowing only part of the year provide many benefits upstream and downstream. They defend against floods, remove contaminants, recycle nutrients that are potentially dangerous as well as provide food and habitat for many forms of fish. Such streams also play

1494-406: A slow-moving wetted channel or stagnant area. This is evidence that iron-oxidizing bacteria are present, indicating persistent expression of oxygen-depleted ground water. In a forested area, leaf and needle litter in the stream channel is an additional indicator. Accumulation of leaf litter does not occur in perennial streams since such material is continuously flushed. In the adjacent overbank of

1577-486: A stream as intermittent, "showing interruptions in time or space". Generally, streams that flow only during and immediately after precipitation are termed ephemeral . There is no clear demarcation between surface runoff and an ephemeral stream, and some ephemeral streams can be classed as intermittent—flow all but disappearing in the normal course of seasons but ample flow (backups) restoring stream presence — such circumstances are documented when stream beds have opened up

1660-424: 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

1743-473: A streamflow-dominated alluvial fan shows nearly the same depositional facies as ordinary fluvial environments, so that identification of ancient alluvial fans must be based on radial paleomorphology in a piedmont setting. Alluvial fans are characteristic of mountainous terrain in arid to semiarid climates , but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation. They have also been found on other bodies of

SECTION 20

#1732765616367

1826-524: 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

1909-564: A vital role in preserving our drinking water quality and supply, ensuring a steady flow of water to surface waters and helping to restore deep aquifers. The extent of land basin drained by a stream is termed its drainage basin (also known in North America as the watershed and, in British English, as a catchment). A basin may also be composed of smaller basins. For instance, the Continental Divide in North America divides

1992-419: A water content between 40 and 80 weight percent. Floods may transition to hyperconcentrated flows as they entrain sediments, while debris flows may become hyperconcentrated flows if they are diluted by water. Because flooding on alluvial fans carries large quantities of sediment, channels can rapidly become blocked, creating great uncertainty about flow paths that magnifies the dangers. Alluvial fan flooding in

2075-435: 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

2158-525: Is an accumulation of sediments that fans out from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment . This accumulation is shaped like a section of a shallow cone , with its apex at the source of sediments. Alluvial fans vary greatly in size, from only a few meters across at the base to as much as 150 kilometers across, with a slope of 1.5 to 25 degrees. Some giant alluvial fans have areas of almost 20,000 square kilometres (7,700 sq mi). The slope measured from

2241-438: Is approximately in equilibrium with erosion, so the river annually carries some 100 million cubic meters (3.5 × 10 ^  cu ft) of sediment as it exits the mountains. Deposition of this magnitude over millions of years is more than sufficient to account for the megafan. In North America , streams flowing into California's Central Valley have deposited smaller but still extensive alluvial fans, such as that of

2324-432: Is described as fanglomerate . Stream flow deposits tend to be sheetlike, better sorted than debris flow deposits, and sometimes show well-developed sedimentary structures such as cross-bedding. These are more prevalent in the medial and distal fan. In the distal fan, where channels are very shallow and braided, stream flow deposits consist of sandy interbeds with planar and trough slanted stratification. The medial fan of

2407-568: Is located adjacent to low-relief terrain. In Nepal , the Koshi River has built a megafan covering some 15,000 km (5,800 sq mi) below its exit from Himalayan foothills onto the nearly level plains where the river traverses into India before joining the Ganges . Along the upper Koshi tributaries, tectonic forces elevate the Himalayas several millimeters annually. Uplift

2490-438: Is most likely composed of round grains of water ice or solid organic compounds about two centimeters in diameter. Alluvial fans are the most important groundwater reservoirs in many regions. Many urban, industrial, and agricultural areas are located on alluvial fans, including the conurbations of Los Angeles, California ; Salt Lake City, Utah ; and Denver, Colorado , in the western United States, and in many other parts of

2573-425: Is sometimes termed a "young" or "immature" stream, and the later state a "mature" or "old" stream. Meanders are looping changes of direction of a stream caused by the erosion and deposition of bank materials. These are typically serpentine in form. Typically, over time the meanders gradually migrate downstream. If some resistant material slows or stops the downstream movement of a meander, a stream may erode through

Creek - Misplaced Pages Continue

2656-456: Is usually called a creek and marked on topographic maps with a solid blue line. There are five generic classifications: "Macroinvertebrate" refers to easily seen invertebrates , larger than 0.5 mm, found in stream and river bottoms. Macroinvertebrates are larval stages of most aquatic insects and their presence is a good indicator that the stream is perennial. Larvae of caddisflies , mayflies , stoneflies , and damselflies require

2739-625: The Apennine Mountains of Italy have resulted in repeated loss of life. A flood on 1 October 1581 at Piedimonte Matese resulted in the loss of 400 lives. Loss of life from alluvial fan floods continued into the 19th century, and the hazard of alluvial fan flooding remains a concern in Italy. On January 1, 1934, record rainfall in a recently burned area of the San Gabriel Mountains , California , caused severe flooding of

2822-737: The Kings River flowing out of the Sierra Nevada . Like the Himalayan megafans, these are streamflow-dominated fans. Alluvial fans are also found on Mars . Unlike alluvial fans on Earth, those on Mars are rarely associated with tectonic processes, but are much more common on crater rims. The crater rim alluvial fans appear to have been deposited by sheetflow rather than debris flows. Three alluvial fans have been found in Saheki Crater . These fans confirmed past fluvial flow on

2905-518: The Main Boundary Thrust over the last ten million years has focused the drainage of 750 kilometres (470 miles) of mountain frontage into just three enormous fans. Alluvial fans are common in the geologic record, but may have been particularly important before the evolution of land plants in the mid-Paleozoic. They are characteristic of fault-bounded basins and can be 5,000 meters (16,000 ft) or thicker due to tectonic subsidence of

2988-678: The Solar System . Alluvial fans are built in response to erosion induced by tectonic uplift . The upwards coarsening of the beds making up the fan reflects cycles of erosion in the highlands that feed sediments to the fan. However, climate and changes in base level may be as important as tectonic uplift. For example, alluvial fans in the Himalayas show older fans entrenched and overlain by younger fans. The younger fans, in turn, are cut by deep incised valleys showing two terrace levels. Dating via optically stimulated luminescence suggests

3071-691: The Tombigbee River basin. Continuing in this vein, a component of the Mississippi River basin is the Ohio River basin, which in turn includes the Kentucky River basin, and so forth. Stream crossings are where streams are crossed by roads , pipelines , railways , or any other thing which might restrict the flow of the stream in ordinary or flood conditions. Any structure over or in a stream which results in limitations on

3154-698: The Valles Marineris canyon system. These provide evidence of the existence and nature of faulting in this region of Mars. Alluvial fans have been observed by the Cassini-Huygens mission on Titan using the Cassini orbiter's synthetic aperture radar instrument. These fans are more common in the drier mid-latitudes at the end of methane/ethane rivers where it is thought that frequent wetting and drying occur due to precipitation, much like arid fans on Earth. Radar imaging suggests that fan material

3237-480: The velocity of the stream. A perennial stream is one which flows continuously all year. Some perennial streams may only have continuous flow in segments of its stream bed year round during years of normal rainfall. Blue-line streams are perennial streams and are marked on topographic maps with a solid blue line. The word "perennial" from the 1640s, meaning "evergreen," is established in Latin perennis, keeping

3320-704: 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 ). 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 . The linear channel between

3403-604: The alluvial fan on which the towns of Montrose and Glendale were built. The floods caused significant loss of life and property. The Koshi River in India has built up a megafan where it exits the Himalayas onto the Ganges plain . The river has a history of frequently and capriciously changing its course, so that it has been called the Sorrow of Bihar for contributing disproportionately to India's death tolls in flooding. These exceed those of all countries except Bangladesh . Over

Creek - Misplaced Pages Continue

3486-409: The apex is generally concave, with the steepest slope near the apex (the proximal fan or fanhead ) and becoming less steep further out (the medial fan or midfan ) and shallowing at the edges of the fan (the distal fan or outer fan ). Sieve deposits , which are lobes of coarse gravel, may be present on the proximal fan. The sediments in an alluvial fan are usually coarse and poorly sorted, with

3569-431: The area feeding the flow onto the fan. Debris flow fans receive most of their sediments in the form of debris flows. Debris flows are slurry-like mixtures of water and particles of all sizes, from clay to boulders, that resemble wet concrete . They are characterized by having a yield strength, meaning that they are highly viscous at low flow velocities but become less viscous as the flow velocity increases. This means that

3652-533: 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

3735-525: 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. Typically, streams are said to have a particular elevation profile , beginning 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

3818-597: The base stage of erosion. The scientists have offered a way based on data to define the origin of the lake. A classified sample was the one measured by the Chinese researchers from the University of Chinese Academy of Sciences. As an essential symbol of the river formation environment, the river source needs an objective and straightforward and effective method of judging . A calculation model of river source catchment area based on critical support flow (CSD) proposed, and

3901-768: The basin and uplift of the mountain front. Most are red from hematite produced by diagenetic alteration of iron-rich minerals in a shallow, oxidizing environment. Examples of paleofans include the Triassic basins of eastern North America and the New Red Sandstone of south Devon, the Devonian Hornelen Basin of Norway, and the Devonian- Carboniferous in the Gaspé Peninsula of Canada. Such fan deposit likely contain

3984-478: The bottom. Multiple braided streams are usually present and active during water flows. Phreatophytes (plants with long tap roots capable of reaching a deep water table ) are sometimes found in sinuous lines radiating from arid climate fan toes. These fan-toe phreatophyte strips trace buried channels of coarse sediments from the fan that have interfingered with impermeable playa sediments. Alluvial fans also develop in wetter climates when high-relief terrain

4067-423: The coarsest sediments found on the proximal fan. When there is enough space in the alluvial plain for all of the sediment deposits to fan out without contacting other valley walls or rivers, an unconfined alluvial fan develops. Unconfined alluvial fans allow sediments to naturally fan out, and the shape of the fan is not influenced by other topological features. When the alluvial plain is more restricted, so that

4150-420: The fan comes into contact with topographic barriers, a confined fan is formed. Wave or channel erosion of the edge of the fan ( lateral erosion ) sometimes produces a "toe-trimmed" fan, in which the edge of the fan is marked by a small escarpment. Toe-trimmed fans may record climate changes or tectonic processes, and the process of lateral erosion may enhance the aquifer or petroleum reservoir potential of

4233-400: The fan. Toe-trimmed fans on the planet Mars provide evidence of past river systems. When numerous rivers and streams exit a mountain front onto a plain, the fans can combine to form a continuous apron. This is referred to as a bajada or piedmont alluvial plain . Alluvial fans usually form where a confined feeder channel exits a mountain front or a glacier margin. As the flow exits

SECTION 50

#1732765616367

4316-745: The fan: Finer sediments are deposited at the edge of the fan, but as the fan continues to grow, increasingly coarse sediments are deposited on top of the earlier, less coarse sediments. However, a few fans show normal grading indicating inactivity or even fan retreat, so that increasingly fine sediments are deposited on earlier coarser sediments. Normal or reverse grading sequences can be hundreds to thousands of meters in thickness. Depositional facies that have been reported for alluvial fans include debris flows, sheet floods and upper regime stream floods, sieve deposits, and braided stream flows, each leaving their own characteristic sediment deposits that can be identified by geologists. Debris flow deposits are common in

4399-516: The feeder channel and onto the surface of the fan. Debris flow fans have a network of mostly inactive distributary channels in the upper fan that gives way to mid- to lower-level lobes. The channels tend to be filled by subsequent cohesive debris flows. Usually only one lobe is active at a time, and inactive lobes may develop desert varnish or develop a soil profile from eolian dust deposition, on time scales of 1,000 to 10,000 years. Because of their high viscosity, debris flows tend to be confined to

4482-554: The feeder channel onto the fan surface, it is able to spread out into wide, shallow channels or to infiltrate the surface. This reduces the carrying power of the flow and results in deposition of sediments. Flow in the proximal fan, where the slope is steepest, is usually confined to a single channel (a fanhead trench ), which may be up to 30 meters (100 ft) deep. This channel is subject to blockage by accumulated sediments or debris flows , which causes flow to periodically break out of its old channel ( nodal avulsion ) and shift to

4565-400: The feeder channel. This results in sheetfloods on the alluvial fan, where sediment-laden water leaves its channel confines and spreads across the fan surface. These may include hyperconcentrated flows containing 20% to 45% sediments, which are intermediate between sheetfloods having 20% or less of sediments and debris flows with more than 45% sediments. As the flood recedes, it often leaves

4648-707: The flow is reduced to a trickle or less. Typically torrents have Apennine rather than Alpine sources, and in the summer they are fed by little precipitation and no melting snow. In this case the maximum discharge will be during the spring and autumn. An intermittent stream can also be called a winterbourne in Britain, a wadi in the Arabic -speaking world or torrente or rambla (this last one from arabic origin) in Spain and Latin America. In Australia, an intermittent stream

4731-447: 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

4814-530: The form of short (several hours) but energetic flash floods that occur with little or no warning. They typically result from heavy and prolonged rainfall, and are characterized by high velocities and capacity for sediment transport. Flows cover the range from floods through hyperconcentrated flows to debris flows, depending on the volume of sediments in the flow. Debris flows resemble freshly poured concrete, consisting mostly of coarse debris. Hyperconcentrated flows are intermediate between floods and debris flows, with

4897-402: The form of stream flow rather than debris flows. They are less sharply distinguished from ordinary fluvial deposits than are debris flow fans. Fluvial fans occur where there is perennial, seasonal, or ephemeral stream flow that feeds a system of distributary channels on the fan. In arid or semiarid climates, deposition is dominated by infrequent but intense rainfall that produces flash floods in

4980-407: 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 . A brook is a stream smaller than

5063-532: The lake has significant feeder rivers. The Kagera River, which flows into Lake Victoria near Bukoba's Tanzanian town , is the longest feeder, though sources do not agree on which is the Kagera's longest tributary and therefore the Nile's most remote source itself. To qualify as a stream, a body of water must be either recurring or perennial. Recurring (intermittent) streams have water in the channel for at least part of

SECTION 60

#1732765616367

5146-617: The largest accumulations of gravel in the geologic record. Alluvial fans have also been found on Mars and Titan , showing that fluvial processes have occurred on other worlds. Some of the largest alluvial fans are found along the Himalaya mountain front on the Indo-Gangetic plain . A shift of the feeder channel (a nodal avulsion ) can lead to catastrophic flooding, as occurred on the Kosi River fan in 2008. An alluvial fan

5229-450: The largest accumulations of gravel in the geologic record. Several kinds of sediment deposits ( facies ) are found in alluvial fans. Alluvial fans are characterized by coarse sedimentation, though the sediments making up the fan become less coarse further from the apex. Gravels show well-developed imbrication with the pebbles dipping towards the apex. Fan deposits typically show well-developed reverse grading caused by outbuilding of

5312-411: The last 25,000 years occurred during times of rapid climate change, both from wet to dry and from dry to wet. Alluvial fans are often found in desert areas, which are subjected to periodic flash floods from nearby thunderstorms in local hills. The typical watercourse in an arid climate has a large, funnel-shaped basin at the top, leading to a narrow defile , which opens out into an alluvial fan at

5395-471: The last few hundred years, the river had generally shifted westward across its fan, and by 2008, the main river channel was located on the extreme western part of the megafan. In August 2008 , high monsoon flows breached the embankment of the Koshi River . This diverted most of the river into an unprotected ancient channel and flooded the central part of the megafan. This was an area with a high population density that had been stable for over 200 years. Over

5478-424: The likely flood path, the likelihood of abrupt deposition and erosion of sediments carried by the flood from upstream sources, and a combination of the availability of sediments and of the slope and topography of the fan that creates extraordinary hazards. These hazards cannot reliably be mitigated by elevation on fill (raising existing buildings up to a meter (three feet) and building new foundations beneath them ). At

5561-683: The mainly easterly-draining Atlantic Ocean and Arctic Ocean basins from the largely westerly-flowing Pacific Ocean basin. The Atlantic Ocean basin, however, may be further subdivided into the Atlantic Ocean and Gulf of Mexico drainages. (This delineation is termed the Eastern Continental Divide .) Similarly, the Gulf of Mexico basin may be divided into the Mississippi River basin and several smaller basins, such as

5644-412: The meaning as "everlasting all year round," per "over" plus annus "year." This has been proved since the 1670s by the "living years" in the sense of botany. The metaphorical sense of "enduring, eternal" originates from 1750. They are related to "perennial." See biennial for shifts in vowels. Perennial streams have one or more of these characteristics: Absence of such characteristics supports classifying

5727-640: The movement of fish or other ecological elements may be an issue. Alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment . They are characteristic of mountainous terrain in arid to semiarid climates , but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation . They range in area from less than 1 square kilometer (0.4 sq mi) to almost 20,000 square kilometers (7,700 sq mi). Alluvial fans typically form where flow emerges from

5810-453: The neck between two legs of a meander to become temporarily straighter, leaving behind an arc-shaped body of water termed an oxbow lake or bayou . A flood may also cause a meander to be cut through in this way. The stream load is defined as the solid matter carried by a stream. Streams can carry sediment, or alluvium. The amount of load it can carry (capacity) as well as the largest object it can carry (competence) are both dependent on

5893-596: The origin of the Nile River is the confluence of the White Nile and the Blue Nile, but the source of the whole river system is in its upper reaches. If there is no specific designation, "length of the Nile" refers to the "river length of the Nile system", rather than to the length of the Nile river from the point where it is formed by a confluence of tributaries. The Nile's source is often cited as Lake Victoria, but

5976-430: 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

6059-415: The parallel ridges or bars on a shoreline beach or river floodplain, or between a bar and the shore. Also called a swale . 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. A distributary , or a distributary channel ,

6142-722: The planet and further supported the theory that liquid water was once present in some form on the Martian surface. In addition, observations of fans in Gale crater made by satellites from orbit have now been confirmed by the discovery of fluvial sediments by the Curiosity rover . Alluvial fans in Holden crater have toe-trimmed profiles attributed to fluvial erosion. The few alluvial fans associated with tectonic processes include those at Coprates Chasma and Juventae Chasma, which are part of

6225-465: The proximal and medial fan even in a debris-flow-dominated alluvial fan, and streamfloods dominate the distal fan. However, some debris-flow-dominated fans in arid climates consist almost entirely of debris flows and lag gravels from eolian winnowing of debris flows, with no evidence of sheetflood or sieve deposits. Debris-flow-dominated fans tend to be steep and poorly vegetated. Fluvial fans (streamflow-dominated fans) receive most of their sediments in

6308-473: The proximal and medial fan. These deposits lack sedimentary structure, other than occasional reverse-graded bedding towards the base, and they are poorly sorted. The proximal fan may also include gravel lobes that have been interpreted as sieve deposits, where runoff rapidly infiltrates and leaves behind only the coarse material. However, the gravel lobes have also been interpreted as debris flow deposits. Conglomerate originating as debris flows on alluvial fans

6391-469: The relationship between CSA and CSD with a minimum catchment area established. Using the model for comparison in two basins in Tibet (Helongqu and Niyang River White Water), the results show that the critical support flow (Qc) of the housing dragon song is 0.0028 m /s. At the same time, the white water curvature is 0.0085 m /s. Besides, the critical support flow can vary with hydrologic climate conditions, and

6474-425: The side of the stream or within the floodplain will be a good indicator of persistent water regime. A perennial stream can be identified 48 hours after a storm. Direct storm runoff usually has ceased at this point. If a stream is still flowing and contributing inflow is not observed above the channel, the observed water is likely baseflow. Another perennial stream indication is an abundance of red rust material in

6557-655: The vital support flow Qc in wet areas (white water) is larger than in semi-arid regions (heap slot). The proposed critical support flow (CSD) concept and model method can be used to determine the hydrographic indicators of river sources in complex geographical areas, and it can also reflect the impact of hydrologic climate change on river recharge in different regions. The source of a river or stream (its point of origin) can consist of lakes, swamps, springs, or glaciers. A typical river has several tributaries; each of these may be made up of several other smaller tributaries, so that together this stream and all its tributaries are called

6640-512: 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

6723-574: The world. However, flooding on alluvial fans poses unique problems for disaster prevention and preparation. The beds of coarse sediments associated with alluvial fans form aquifers that are the most important groundwater reservoirs in many regions. These include both arid regions, such as Egypt or Iraq, and humid regions, such as central Europe or Taiwan. Alluvial fans are subject to infrequent but often very damaging flooding, whose unusual characteristics distinguish alluvial fan floods from ordinary riverbank flooding. These include great uncertainty in

6806-521: The year and is marked on topographic maps with a line of blue dashes and dots. A wash , desert wash, or arroyo is normally a dry streambed in the deserts of the American Southwest , which flows after sufficient rainfall. In Italy, an intermittent stream is termed a torrent ( Italian : torrente ). In full flood the stream may or may not be "torrential" in the dramatic sense of the word, but there will be one or more seasons in which

6889-402: 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. The gradient of

#366633