View source for Drainage divide

{{Short description|Elevated terrain that separates neighbouring drainage basins}}
{{Redirect|Height of land}}
[[File:Europäische Wasserscheiden.png|thumb|300px|Major drainage divides (yellow and red ridgelines<ref name="RndmHse1">{{cite web|access-date=7 September 2013|publisher=Random House Inc.|title=ridgeline. Dictionary.com|edition=Dictionary.com Unabridged
|url=http://dictionary.reference.com/browse/ridgeline?s=t }}</ref>) and [[drainage basin]]s (green regions) in Europe]]
A '''drainage divide''', '''water divide''', '''ridgeline''',<ref name="RndmHse1"/> '''watershed''', '''water parting''' or '''height of land''' is elevated [[terrain]] that separates neighboring [[drainage basin]]s. On rugged land, the divide lies along topographical [[ridge]]s, and may be in the form of a single range of [[hill]]s or [[mountain]]s, known as a '''dividing range'''. On flat terrain, especially where the ground is [[marsh]]y, the divide may be difficult to discern.
A [[triple divide]] is a point, often a [[summit]], where three drainage basins meet. A ''valley floor divide'' is a low drainage divide that runs across a [[valley]], sometimes created by [[Deposition (geology)|deposition]] or [[stream capture]]. Major divides separating rivers that drain to different seas or oceans are [[continental divide]]s.
The term ''height of land'' is used in Canada and the United States to refer to a drainage divide.<ref>{{Cite encyclopedia|author=Colombo, John Robert|date=16 December 2013|title=Height of land|encyclopedia=The Canadian Encyclopedia|url=http://www.thecanadianencyclopedia.ca/en/article/height-of-land/|archive-url=https://web.archive.org/web/20140620162213/http://www.thecanadianencyclopedia.ca/en/article/height-of-land/|archive-date=20 June 2014|url-status=live}}</ref> It is frequently used in border descriptions, which are set according to the "doctrine of [[natural boundaries]]".<ref>{{Cite book|author=Dikshit, Ramesh Dutta|year=1999|title=Political Geography: the Spatiality of Politics|edition=3rd|publisher=McGraw-Hill|location=New Delhi|page=70|isbn=978-0-07-463578-0}}</ref> In [[glacier|glaciated]] areas it often refers to a low point on a divide where it is possible to [[portage]] a canoe from one river system to another.<ref>{{Cite encyclopedia|author=Decker, Jody F.|year=2011|title=Portages|editor1-link=David J. Wishart|editor=Wishart, David J.|encyclopedia=Encyclopedia of the Great Plains|url=http://plainshumanities.unl.edu/encyclopedia/doc/egp.tra.025}}</ref>
==Types==
[[File:Schuylkill-Lehigh River Drainage Divides USGS, Hazelton-Mauch Chunk & Mountain Quads, NW+NE-4.jpg|thumb|[[United States Geological Survey|USGS]] map of Schuylkill-Lehigh River drainage divides]]
[[File:Minor drainage divide south of Buckeye Arizona aerial.jpg|thumb|A minor drainage divide south of [[Buckeye, Arizona]]. Both branches flow to the [[Gila River]].]]
Drainage divides can be divided into three types:<ref>{{cite web |title=Divide |url=https://www.nationalgeographic.org/encyclopedia/divide/ |website=Resource Library |publisher=National Geographic Society |access-date=3 April 2022}}</ref>
*[[Continental divides]] in which waters on each side flow to different oceans, such as the [[Continental Divide of the Americas]] and the [[Congo-Nile Divide]].<ref>{{cite web |title=Congo-Nile Divide Landscape |url=https://albertinerift.wcs.org/Wild-Places/Congo-Nile-Divide.aspx |website=Albertine Rift |publisher=Wildlife conservation Society |access-date=3 April 2022}}</ref>
*Major drainage divides in which waters on each side of the divide never meet but flow into the same ocean, such as the divide between the [[Yellow River]] basin and the [[Yangtze River|Yangtze]]. Another, more subtle example is the Schuylkill-Lehigh divide at [[Pisgah Mountain]] in Pennsylvania in which two minor creeks divide to flow and grow east and west respectively joining the [[Lehigh River]] and [[Delaware River]] or the [[Susquehanna River]] and [[Potomac River]], with each tributary complex having separate outlets into the Atlantic.
*Minor drainage divides in which waters are originally separate but eventually join at a river confluence, such as the [[Mississippi River]] and the [[Missouri River]] drainage divides.
==Valley-floor divides==
[[File:Figure of a drainage basin.svg|thumb|440x440px|Labeled figure of a drainage basin.]]
A valley-floor divide occurs on the bottom of a valley and arises as a result of subsequent depositions, such as [[scree]], in a valley through which a river originally flowed continuously.<ref>Leser, Hartmut, ed. (2005). ''Wörterbuch Allgemeine Geographie'', 13th ed., dtv, Munich, p. 935. {{ISBN|978-3-423-03422-7}}.</ref>
Examples include the [[Kartitsch Saddle]] in the [[Gail (river)|Gail]] valley in [[East Tyrol]], which forms the watershed between the [[Drau]] and the Gail, and the divides in the ''Toblacher Feld'' between [[Innichen]] and [[Toblach]] in [[Italy]], where the [[Drau]] empties into the [[Black Sea]] and the [[Rienz]] into the [[Adriatic Sea|Adriatic]].
Settlements are often built on valley-floor divides in the Alps. Examples are [[Eben im Pongau]], [[Kirchberg in Tirol]] and [[Waidring]] (In all of these, the village name indicates the pass and the watershed is even explicitly displayed in the coat of arms). Extremely low divides with heights of less than two metres are found on the [[North German Plain]] within the ''[[Urstromtäler]]'', for example, between [[Havel]] and [[Finow]] in the ''Eberswalde Urstromtal''. In marsh deltas such as the [[Okavango Delta|Okavango]], the largest drainage area on earth, or in large lakes areas, such as the [[Finnish Lakeland]], it is difficult to find a meaningful definition of a watershed.
A [[bifurcation (river)|bifurcation]] is where the watershed is effectively in a river bed, in a wetland, or underground. The largest watershed of this type is the bifurcation of the [[Orinoco]] in the north of [[South America]], whose main stream empties into the [[Caribbean]], but which also drains into the South Atlantic via the [[Casiquiare canal]] and [[Amazon River]].
==Political boundaries==
Since ridgelines are sometimes easy to see and agree about, drainage divides may form [[Border#Natural borders|natural borders]] defining political boundaries, as with the [[Royal Proclamation of 1763]] in British North America which coincided with the ridgeline of the [[Appalachian Mountains]] forming the Eastern Continental Divide that separated settled colonial lands in the east from Indian Territory to the west.<ref>{{cite journal |last1=Del Papa |first1=Eugene M. |title=The Royal Proclamation of 1763: Its Effects Upon Virginia Land Companies |journal=The Virginia Magazine of History and Biography |year=1975 |volume=83 |issue=4 |pages=406–411 |publisher=JSTOR |jstor=4247979 }}</ref> Another instance of a border matching a watershed in modern times involves the western border between [[Labrador]] and [[Quebec]], as arbitrated by the privy council in 1927.<ref name=":4">{{Cite journal|last=McGrath|first=Patrick T.|date=1927|title=The Labrador Boundary Decision|url=https://www.jstor.org/stable/208004|journal=Geographical Review|volume=17|issue=4|pages=643–660|doi=10.2307/208004|jstor=208004|bibcode=1927GeoRv..17..643M |issn=0016-7428}}</ref>
==Portages and canals==
Drainage divides hinder waterway [[navigation]]. In pre-industrial times, water divides were crossed at [[portage]]s. Later, [[canal]]s connected adjoining drainage basins; a key problem in such canals is ensuring a sufficient water supply. Important examples are the [[Chicago Portage]], connecting the Great Lakes and Mississippi by the [[Chicago Sanitary and Ship Canal]], and the [[Canal des Deux Mers]] in France, connecting the Atlantic and the Mediterranean. The name is enshrined at the [[Height of Land Portage]] on the route from the [[Great Lakes]] in the Atlantic drainage basin to the [[Hudson Bay drainage basin]].<ref>{{Cite book|author=Shelley, Fred M. |year=2013|title=Nation Shapes: The Story Behind the World's Borders|publisher=ABC-CLIO|location=Santa Barbara, California|pages=173, 242|isbn=978-1-61069-105-5}}</ref>
==See also==
{{Commons category|Drainage divides}}
*{{annotated link|List of watershed topics}}
*{{annotated link|River source}}
==References==
{{Reflist}}
==Further reading==
*{{cite book |last1=DeBarry |first1=Paul A. |title=Watersheds : processes, assessment, and management |date=2004 |publisher=Wiley |location=Hoboken, N.J. |isbn=978-0471264231}}
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{{DEFAULTSORT:Drainage Divide}}
[[Category:Drainage basins| ]]
[[Category:Drainage divides| ]]
[[Category:Freshwater ecology]]
[[Category:Geomorphology]]
[[Category:Hydrology]]
[[Category:Rivers]]
[[Category:Water and the environment]]
[[Category:Water streams]]