Confluence of the Bhagirathi and Alaknanda Rivers to produce the Ganges at Devprayag, India
Confluence of the Bhagirathi and Alaknanda Rivers to produce the Ganges at Devprayag, India
The same confluence viewed from upstream at a different time; note the swirl of sediment from the Alaknanda.
The same confluence viewed from upstream at a different time; note the swirl of sediment from the Alaknanda.

In geography, a confluence (also: conflux) occurs where two or more flowing bodies of water join together 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.

Scientific study of confluences

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]

River confluence flow zones

Hydrodynamic features of a river/flume confluence can be separated into six identifiable distinct zones, also called confluence flow zones.
Hydrodynamic features of a river/flume confluence can be separated into six identifiable distinct zones, also called confluence flow zones.

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

  1. Stagnation zone
  2. Flow deflection zone
  3. Flow separation zone / recirculation zone
  4. Maximum velocity zone
  5. Flow recovery zone
  6. Shear layers

Confluences and mankind

The fountain at Point State Park in Pittsburgh, at the apex of the confluence of the Allegheny (top) and the Monongahela
The fountain at Point State Park in Pittsburgh, at the apex of the confluence of the Allegheny (top) and the Monongahela

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.[8] Pre-Christian Slavic peoples chose confluences as the sites for fortified triangular temples, where they practiced human sacrifice and other sacred rites.[9] In Hinduism, the confluence of two sacred rivers often is a pilgrimage site for ritual bathing.[10] In Pittsburgh, a number of adherents to Mayanism consider their city's confluence to be sacred.[11]

Notable confluences

The White Nile and Blue Nile merge at Khartoum; April 2013 satellite view
The White Nile and Blue Nile merge at Khartoum; April 2013 satellite view

Africa

Asia

The Nam Khan flows into the Mekong at Luang Prabang in Laos
The Nam Khan flows into the Mekong at Luang Prabang in Laos
The confluence of the Jialing and the Yangtze in Chongqing. The Yangtze flows left to right across the bottom of the image.
The confluence of the Jialing and the Yangtze in Chongqing. The Yangtze flows left to right across the bottom of the image.

Australia

Europe

The Seine becomes a single channel at the west end of the Île de la Cité in Paris. The Pont Neuf can be seen.
The Seine becomes a single channel at the west end of the Île de la Cité in Paris. The Pont Neuf can be seen.

Seine

The Mosel flows into the Rhine at Koblenz.
The Mosel flows into the Rhine at Koblenz.

Rhine

Danube basin

The triple confluence in Passau; from left to right, the Inn, the Danube, and the Ilz.
The triple confluence in Passau; from left to right, the Inn, the Danube, and the Ilz.

Other

The confluence of the Sava into the Danube at Belgrade. Pictured from Belgrade Fortress, Serbia.
The confluence of the Sava into the Danube at Belgrade. Pictured from Belgrade Fortress, Serbia.

North America

The confluence of the Allegheny and Monongahela at Pittsburgh, forming the Ohio
The confluence of the Allegheny and Monongahela at Pittsburgh, forming the Ohio
The Ohio flows into the Mississippi at Cairo.
The Ohio flows into the Mississippi at Cairo.
The Rideau Falls in Ottawa, where the Rideau River tumbles into Ottawa River at its mouth.
The Rideau Falls in Ottawa, where the Rideau River tumbles into Ottawa River at its mouth.

Mississippi basin

Atlantic watersheds

Pacific watersheds

The confluence of the Rio Negro (black) and the Rio Solimões (turbid) near Manaus, Brazil.
The confluence of the Rio Negro (black) and the Rio Solimões (turbid) near Manaus, Brazil.

South America

Confluences of two waterways

Confluence of canalsThis simplified diagram shows how a section of the Industrial Canal in New Orleans also serves as the channel for the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet Canal. At the bottom, a portion of the Intracoastal is also shown to be "confluent" with the Mississippi River.
Confluence of canals
This simplified diagram shows how a section of the Industrial Canal in New Orleans also serves as the channel for the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet Canal. At the bottom, a portion of the Intracoastal is also shown to be "confluent" with the Mississippi River.

Occasionally "confluence" is used to describe the meeting of tidal or other non-riverine bodies of water, such as two canals[21] or a canal and a lake.[22] 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 also applies to the merger of the flow of two glaciers.[23]

See also

Notes

  1. ^ "Conflux – Definition of conflux by Merriam-Webster". merriam-webster.com.
  2. ^ A widely cited work is James L. Best (1986) The morphology of river channel confluences. Progress in Physical Geography 10:157–174. For work citing Best, see [1].
  3. ^ A recent contribution with review of earlier work is Laurent Schindfessel, Stéphan Creëlle and Tom De Mulder (2015) "Flow patterns in an open channel confluence with increasingly dominant tributary inflow," Water 7: 4724–4751; available on line.
  4. ^ Quoted from Beechie et al. (2012), who cite earlier work. Tim Beechie, John S. Richardson, Angela M. Gurnell, and Junjiro Negishi (2012) "Watershed processes, human impacts, and process-based restoration." In Philip Roni and Tim Beechie (eds.) (2012) Stream and Watershed Restoration: A Guide to Restoring Riverine Processes and Habitats, John Wiley & Sons. Excerpts available on line at Google Books.
  5. ^ U.S. Geological Survey, "How do contaminants mix at the confluence of two streams?", on line at [2].
  6. ^ David Lynch (2014) "The Confluence of Rivers"; Earth Science Picture of the Day, at [3].
  7. ^ Best, James L. (1987). "Flow Dynamics at River Channel Confluences: Implications for Sediment Transport and Bed Morphology". Recent Developments in Fluvial Sedimentology. pp. 27–35. doi:10.2110/pec.87.39.0027. ISBN 978-0-918985-67-5.
  8. ^ Rogers, Adam (2011) Late Roman Towns in Britain: Rethinking Change and Decline. Cambridge: Cambridge University Press, p. 42. Excerpts available on line at Google Books.
  9. ^ Gasparini, Evel (n.d.) "Slavic religion", in Encyclopedia Britannica, on line edition: [4]
  10. ^ Source: Letizia (2017), who writes, "as rivers are considered holy entities, at the meeting of two streams the 'sacredness' of the first river add to that of the second one. The confluence seems to have a sort of 'additive fame' ... because it gives pilgrims the chance to bathe in two rivers at the same time."
  11. ^ Ann Rodgers, "So how did the Point get on a Mayan calendar?", Pittsburgh Post-Gazette, June 22, 2008. On line at [5].
  12. ^ See reporting in the New York Times ([6]) and The Atlantic ([7]).
  13. ^ The incorporation of invisible rivers into confluences elsewhere in the subcontinent is documented by Letizia (2017).
  14. ^ "Karad Tourism | Top Tourist Places to Visit in Karad Area | Travel Guide". www.gruhkhoj.com. Retrieved 2019-10-14.
  15. ^ See New Straits Times, August 28, 2017, 'Najib launches River of Life, Blue Pool projects", at [8].
  16. ^ See Bruno Maçães, "Signs and Symbols on the Sino-Russian Border", published in The Diplomat. On line at [9].
  17. ^ See Andrea Schulte-Peevers, Kerry Christiani, Marc Di Duca, Catherine Le Nevez, Tom Masters, Ryan Ver Berkmoes, and Benedict Walker (2016) Lonely Planet Germany, Lonely Planet Publishing. Excerpts posted on line at Google Books: [10]
  18. ^ Kogovšek, Janja; Petrič, Metka; Zupan Hajna, Nadja; Pipan, Tanja. "Planinska jama" [Planina Cave]. In Šmid Hribar, Mateja; Golež, Gregor; Podjed, Dan; Kladnik, Drago; Erhartič, Bojan; Pavlin, Primož; Ines, Jerele (eds.). Enciklopedija naravne in kulturne dediščine na Slovenskem [Encyclopedia of Natural and Cultural Heritage in Slovenia] (in Slovenian). Archived from the original on 19 April 2012. Retrieved 17 May 2012.
  19. ^ "Southampton | city and unitary authority, England, United Kingdom".
  20. ^ "Caronoco: confluencia de los rios Caroní y Orinoco". Parques Nacionales Venezuela. Retrieved 4 March 2019.
  21. ^ The U.S. Army Corps of Engineers refers to the confluence of the Assawoman Canal with the Bethany Loop Canal in Delaware. See: "CENAP-OP-R-Quarterly Report, 2004-05-12". Philadelphia Engineer District. Archived from the original on 2004-10-17. Retrieved 2006-03-11.
  22. ^ Engineers in New Orleans refer to the confluence of the 17th Street Canal and Lake Pontchartrain. See: "Interim Closure Structure at 17th St. Canal". Task Force Guardian. Archived from the original on 2006-06-25. Retrieved 2006-03-11.
  23. ^ Vladimir Kotlyakov and Anna Komarova (2006) Elsevier's Dictionary of Geography: in English, Russian, French, Spanish and German. Elsevier. Passage cited may be accessed on Google Books.

References