In geography, a confluence (also: conflux) occurs where two or more watercourses join to form a single channel. [1] A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); or where two streams meet to become the source of a river of a new name (such as the confluence of the Monongahela and Allegheny rivers at Pittsburgh, forming the Ohio); or where two separated channels of a river (forming a river island) rejoin at the downstream end.
Confluences are studied in a variety of sciences. Hydrology studies the characteristic flow patterns of confluences and how they give rise to patterns of erosion, bars, and scour pools. [2] The water flows and their consequences are often studied with mathematical models. [3] Confluences are relevant to the distribution of living organisms (i.e., ecology) as well; "the general pattern [downstream of confluences] of increasing stream flow and decreasing slopes drives a corresponding shift in habitat characteristics." [4]
Another science relevant to the study of confluences is chemistry, because sometimes the mixing of the waters of two streams triggers a chemical reaction, particularly in a polluted stream. The United States Geological Survey gives an example: "chemical changes occur when a stream contaminated with acid mine drainage combines with a stream with near-neutral pH water; these reactions happen very rapidly and influence the subsequent transport of metals downstream of the mixing zone." [5]
A natural phenomenon at confluences that is obvious even to casual observers is a difference in color between the two streams; see images in this article for several examples. According to Lynch, "the color of each river is determined by many things: type and amount of vegetation in the watershed, geological properties, dissolved chemicals, sediments and biologic content – usually algae." Lynch also notes that color differences can persist for miles downstream before they finally blend completely. [6]
Hydrodynamic behaviour of flow in a confluence can be divided into six distinct features [7] which are commonly called confluence flow zones (CFZ). These include
The broader field of engineering encompasses a vast assortment of subjects which concern confluences.
In Hydraulic civil engineering, where two or more underground culverted / artificially buried watercourses intersect, great attention should be paid to the hydrodynamic aspects of the system to ensure the longevity and efficiency of the structure. [8]
Engineers have to design these systems whilst considering a list of factors that ensure the discharge point is structurally stable to support the receiving structure in the face of the weakness formed by the discharge point due to the lack of material. [9] [10] The velocities and hydraulic efficiencies should be meticulously calculated and can be altered by integrating different combinations of geometries, components such a gradients, cascades and an adequate junction angle which is sympathetic to the direction of the watercourse’s flow to minimise turbulent flow, maximise evacuation velocity and to ultimately maximise hydraulic efficiency. [11]
Since rivers often serve as political boundaries, confluences sometimes demarcate three abutting political entities, such as nations, states, or provinces, forming a tripoint. Various examples are found in the list below.
A number of major cities, such as Chongqing, St. Louis, and Khartoum, arose at confluences; further examples appear in the list. Within a city, a confluence often forms a visually prominent point, so that confluences are sometimes chosen as the site of prominent public buildings or monuments, as in Koblenz, Lyon, and Winnipeg. Cities also often build parks at confluences, sometimes as projects of municipal improvement, as at Portland and Pittsburgh. In other cases, a confluence is an industrial site, as in Philadelphia or Mannheim. Often a confluence lies in the shared floodplain of the two rivers and nothing is built on it, for example at Manaus, described below.
One other way that confluences may be exploited by humans is as sacred places in religions. Rogers suggests that for the ancient peoples of the Iron Age in northwest Europe, watery locations were often sacred, especially sources and confluences. [12] Pre-Christian Slavic peoples chose confluences as the sites for fortified triangular temples, where they practiced human sacrifice and other sacred rites. [13] In Hinduism, the confluence of two sacred rivers often is a pilgrimage site for ritual bathing. [14] In Pittsburgh, a number of adherents to Mayanism consider their city's confluence to be sacred. [15]
Mississippi basin
Atlantic watersheds
Pacific watersheds
Occasionally, "confluence" is used to describe the meeting of tidal or other non-riverine bodies of water, such as two canals [26] or a canal and a lake. [27] A one-mile (1.6 km) portion of the Industrial Canal in New Orleans accommodates the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet Canal; therefore those three waterways are confluent there.
The term confluence can also apply to the process of merging or flowing together of other substance. [28] For example, it may refer to the merger of the flow of two glaciers. [29]
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The Mississippi River is the primary river, and second-longest river, of the largest drainage basin in the United States. From its traditional source of Lake Itasca in northern Minnesota, it flows generally south for 2,340 miles (3,766 km) to the Mississippi River Delta in the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains all or parts of 32 U.S. states and two Canadian provinces between the Rocky and Appalachian mountains. The main stem is entirely within the United States; the total drainage basin is 1,151,000 sq mi (2,980,000 km2), of which only about one percent is in Canada. The Mississippi ranks as the thirteenth-largest river by discharge in the world. The river either borders or passes through the states of Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.
The Illinois River is a principal tributary of the Mississippi River at approximately 273 miles (439 km) in length. Located in the U.S. state of Illinois, the river has a drainage basin of 28,756.6 square miles (74,479 km2). The Illinois River begins with the confluence of the Des Plaines and Kankakee rivers in the Chicago metropolitan area, and it generally flows to the southwest across Illinois, until it empties into the Mississippi near Grafton, Illinois. Its drainage basin extends into southeastern Wisconsin, northwestern Indiana, and a very small area of southwestern Michigan in addition to central Illinois. Along its shores are several river ports, including Peoria, Illinois. Historic and recreation areas on the river include Starved Rock, and the internationally important wetlands of the Emiquon Complex and Dixon Waterfowl Refuge.
The River Tame is a river in the West Midlands of England, and one of the principal tributaries of the River Trent. The Tame is about 95 km (59 mi) long from the source at Oldbury to its confluence with the Trent near Alrewas, but the main river length of the entire catchment, i.e. the Tame and its main tributaries, is about 285 km (177 mi).
The River Blackwater is a tributary of the Loddon in England and sub-tributary of the Thames. It rises at two springs in Rowhill Nature Reserve between Aldershot, Hampshire and Farnham, Surrey. It curves a course north then west to join the Loddon in Swallowfield civil parish, central Berkshire. Part of the river splits Hampshire from Surrey; a smaller part does so as to Hampshire and Berkshire.
The Hutchinson River is a 10 mile-long (16 km) freshwater stream located in the New York City borough of the Bronx and Southern Westchester County, New York, United States. It forms on the New Rochelle–Scarsdale municipal line off Brookline Road in the latter community and flows south, draining a 19.4-square-mile (50 km2) area. It continues to serve as New Rochelle's city line with Eastchester; further downstream; its lower reaches divide Mount Vernon and Pelham until it enters the Bronx and empties into Long Island Sound's Eastchester Bay.
Frankford Creek is a minor tributary of the Delaware River in southeast Pennsylvania. It derived its name from today's Frankford, Philadelphia neighborhood.
The Sulm is a river in the Heilbronn district of Baden-Württemberg, Germany. It is an unnavigable right tributary of the Neckar. It rises in the Löwenstein Mountains and after 26.3 kilometres (16.3 mi) distance and 315 metres (1,033 ft) elevation drop flows into the Neckar at Bad Friedrichshall, near Untereisesheim and Neckarsulm. Its valley together with its tributary valleys is also known as the Weinsberg Valley, after Weinsberg, which is located there. The medieval region of Sulmgau, as well as the city of Neckarsulm, were named for it. The upper valley of the Sulm is a protected area.
River bifurcation occurs when a river flowing in a single channel separates into two or more separate streams which then continue downstream. Some rivers form complex networks of distributaries, typically in their deltas. If the streams eventually merge again or empty into the same body of water, then the bifurcation forms a river island.
Loantaka Brook is a tributary of the Passaic River in New Jersey in the United States.
Wheeling Creek is a tributary of the Ohio River, 25 miles (40 km) long, in the northern panhandle of West Virginia, with a watershed extending into southwestern Pennsylvania. Via the Ohio River, it is part of the watershed of the Mississippi River, draining an area of approximately 300 square miles (780 km2) on the unglaciated portion of the Allegheny Plateau. It flows into the Ohio River in downtown Wheeling, just downstream of Ohio's Wheeling Creek on the opposite bank. A variant name is Big Wheeling Creek. According to the French explorer Pierre Joseph Céloron de Blainville, the native name of the stream is the Kanououara River, as was inscribed on the lead plate buried at the mouth by the Ohio River in 1749.
Highland Creek is a river in the Scarborough district of Toronto, Ontario, emptying into Lake Ontario at the eastern end of the Scarborough Bluffs. It is home to several species of fish including trout, carp, bass and salmon. It is a meandering river which, like most rivers in Toronto, travels through a glacial ravine formed after the last Ice Age. The Highland Creek watershed, including tributaries, is almost entirely contained within Scarborough.
A river is a natural flowing watercourse, usually a freshwater stream, flowing on the Earth's land surface or inside caves towards another waterbody at a lower elevation, such as an ocean, sea, bay, lake, wetland, or another river. In some cases, a river flows into the ground or becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to by names such as creek, brook, and rivulet. There are no official definitions for these various generic terms for a watercourse as applied to geographic features, although in some countries or communities, a stream is customarily referred to by one of these names as determined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and Northeast England, and "beck" in Northern England. Sometimes a river is defined as being larger than a creek, but not always; the language is vague.
The Smestow Brook, sometimes called the River Smestow, is a small river that plays an important part in the drainage of Wolverhampton, South Staffordshire, and parts of Dudley in the United Kingdom, and has contributed to the industrial development of the Black Country. It is the most important tributary of the River Stour, Worcestershire and part of the River Severn catchment.
The Anyangcheon is a river in Gyeonggi-do and Seoul, South Korea. It has its source on the slopes of Mount Gwanggyo in the city of Uiwang and flows north, through the city of Gunpo, where a major cleanup operation saw several species of birds return to the area in 2005. Here, though, the water table remains depleted. The river then flows through Anyang City, where it is met by its major tributary, the Hakuicheon stream. From here, it loops around to the west before continuing north to the border with Gwangmyeong City. As the river passes to the west of Mount Gwanak, it forms the border between Gwangmyeong and Seoul, where it is lined on the Gwangmyeong side with rape fields and cherry blossom trees. After the stream is joined near Guil Station from the west by the Mokgamcheon stream, which forms another border between Gwangmyeong and Seoul, it is then totally within the capital. Here, it is also joined from the east by the Dorimcheon and passes through a conservation zone for migratory birds which was established after a 2005 cleanup operation, whereafter it joins the Han. Most of the length of the river has a path alongside providing easy access, the only parts without this lying in Uiwang. Seoul City Council has embarked on a programme of exclusive cycle path creation alongside its waterways, including the Anyangcheon, to be completed in 2010.
The Sheldrake River is a freshwater stream located in Southern Westchester County, New York. The river forms in White Plains and flows six miles (9.7 km) south until it joins the Mamaroneck River. Approximately 1.58 miles (2.54 km) of the Sheldrake River flow through Scarsdale, 2.13 miles (3.43 km) through New Rochelle and two miles (3.2 km) through the Town of Mamaroneck.
Lucky Run is a tributary of Keyser Creek in Lackawanna County, Pennsylvania, in the United States. It is approximately 2.4 miles (3.9 km) long and flows through Ransom Township and Scranton. The watershed of the creek has an area of 1.66 square miles (4.3 km2). It is considered to be a Coldwater Fishery and contains trout. However, it loses flow to underground mine pools. Land uses in its watershed include forests, open space, and industrial land. A county park known as McDade Park is in the stream's vicinity.
Leach Creek is a tributary of Leggetts Creek in Lackawanna County, Pennsylvania, in the United States. It is approximately 1.9 miles (3.1 km) long and flows through Scranton. The watershed of the creek has an area of 2.55 square miles (6.6 km2). The creek loses substantial amounts of water to underground mine pools. The creek is in the Coal Region and has been channelized and/or culvertized in some reaches. It flows alongside Pennsylvania Route 307 for a substantial part of its length. The creek has a riparian buffer in its upper and middle reaches, but various invasive plants grow along its banks in its lower reaches.
Eddy Creek is a tributary of the Lackawanna River in Lackawanna County, Pennsylvania, in the United States. It is approximately 5.7 miles (9.2 km) long and flows through Olyphant and Throop. The watershed of the creek has an area of 7.53 square miles (19.5 km2). The creek experiences serious flow loss and is considered to be impaired. It has a natural channel in some reaches, but its channel disappears in other reaches. Rock formations in the creek's vicinity include the Catskill Formation and the Llewellyn Formation. The creek is a second-order stream.
Benson Hollow is a tributary of Bowman Creek in Wyoming County, Pennsylvania, in the United States. It is approximately 0.9 miles (1.4 km) long and flows through Eaton Township. The watershed of the stream has an area of 1.82 square miles (4.7 km2). Benson Hollow is a first-order stream and is not designated as an impaired waterbody. The surficial geology in its vicinity consists of Wisconsinan Outwash, alluvium, Wisconsinan Till, bedrock, and a lake. The stream's watershed is designated as a High-Quality Coldwater Fishery and a Migratory Fishery.
Welton Beck is a small local stream which originates from Old Man's Head Spring in the west of Welton civil parish and flows eastwards through Welton and Dunholme in the West Lindsey district of Lincolnshire for approximately 10 km (6.2 mi) to a confluence with Barlings Eau near Reasby, which goes on to join the River Witham. The beck is fed from groundwater springs of the Lincolnshire limestone aquifer, with clear freshwater and aquatic plant growth typical of calcareous conditions. The channel of the beck has been largely modified from its original state, having been widened, straightened, and its course significantly altered.