Drainage divide

Last updated November 12, 2023

A drainage divide, water divide, ridgeline,^[1]watershed, water parting or height of land is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridges, and may be in the form of a single range of hills or mountains, known as a dividing range. On flat terrain, especially where the ground is marshy, 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 or stream capture. Major divides separating rivers that drain to different seas or oceans are continental divides.

The term height of land is used in Canada and the United States to refer to a drainage divide.^[2] It is frequently used in border descriptions, which are set according to the "doctrine of natural boundaries".^[3] In 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.^[4]

Types

Drainage divides can be divided into three types:^[5]

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.^[6]
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. 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

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.^[7]

Examples include the Kartitsch Saddle in the 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.

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, 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 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 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.^[8] 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.^[9]

Portages and canals

Drainage divides hinder waterway navigation. In pre-industrial times, water divides were crossed at portages. Later, canals 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.^[10]

Related Research Articles

The Casiquiare river is a distributary of the upper Orinoco flowing southward into the Rio Negro, in Venezuela, South America. As such, it forms a unique natural canal between the Orinoco and Amazon river systems. It is the world's largest river of the kind that links two major river systems, a so-called bifurcation. The area forms a water divide, more dramatically at regional flood stage.

<span class="mw-page-title-main">Continental Divide of the Americas</span> Principal hydrological divide of North and South America

The Continental Divide of the Americas is the principal, and largely mountainous, hydrological divide of the Americas. The Continental Divide extends from the Bering Strait to the Strait of Magellan, and separates the watersheds that drain into the Pacific Ocean from those river systems that drain into the Atlantic and Arctic Ocean, including those that drain into the Gulf of Mexico, the Caribbean Sea, and Hudson Bay.

A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, the drainage divide, made up of a succession of elevated features, such as ridges and hills. A basin may consist of smaller basins that merge at river confluences, forming a hierarchical pattern.

An endorheic basin is a drainage basin that normally retains water and allows no outflow to other, external bodies of water ; instead, the water drainage flows into permanent and seasonal lakes and swamps that equilibrate through evaporation. Endorheic basins also are called closed basins, terminal basins, and internal drainage systems.

<span class="mw-page-title-main">Pigeon River (Minnesota–Ontario)</span> River in Minnesota and Ontario, Canada and United States

The Pigeon River forms part of the Canada–United States border between the state of Minnesota and the province of Ontario, west of Lake Superior. In pre-industrial times, the river was a waterway of great importance for transportation and the fur trade.

<span class="mw-page-title-main">Eastern Continental Divide</span> Hydrological divide in eastern North America

The Eastern Continental Divide, Eastern Divide or Appalachian Divide is a hydrological divide in eastern North America that separates the easterly Atlantic Seaboard watershed from the westerly Gulf of Mexico watershed. The divide nearly spans the United States from south of Lake Ontario through the Florida peninsula, and consists of raised terrain including the Appalachian Mountains to the north, the southern Piedmont Plateau and lowland ridges in the Atlantic Coastal Plain to the south. Water including rainfall and snowfall, lakes, streams and rivers on the eastern/southern side of the divide drains to the Atlantic Ocean; water on the western/northern side of the divide drains to the Gulf of Mexico. The ECD is one of six continental hydrological divides of North America which define several drainage basins, each of which drains to a particular body of water.

<span class="mw-page-title-main">Little Conemaugh River</span> River in the U.S. state of Pennsylvania

The Little Conemaugh River is a tributary of the Conemaugh River, approximately 30 miles (48 km) long, in western Pennsylvania in the United States.

The main European watershed is the drainage divide ("watershed") which separates the basins of the rivers that empty into the Atlantic Ocean, the North Sea and the Baltic Sea from those that feed the Mediterranean Sea, the Adriatic Sea and the Black Sea. It stretches from the tip of the Iberian Peninsula at Gibraltar in the southwest to the endorheic basin of the Caspian Sea in Russia in the northeast.

The Chicago Portage was an ancient portage that connected the Great Lakes waterway system with the Mississippi River system. Connecting these two great water trails meant comparatively easy access from the mouth of the St Lawrence River on the Atlantic Ocean to the Rocky Mountains, and the Gulf of Mexico. The approximately six-mile link had been used by Native Americans for thousands of years during the Pre-Columbian era for travel and trade.

<span class="mw-page-title-main">River bifurcation</span> The forking of a river into its distributaries

River bifurcation occurs when a river flowing in a single stream 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.

<span class="mw-page-title-main">Laurentian Divide</span> Hydrological divide in North America

The Laurentian Divide also called the Northern Divide and locally the height of land, is a continental divide in central North America that separates the Hudson Bay watershed to the north from the Gulf of Mexico watershed to the south and the Great Lakes-St. Lawrence watershed to the southeast.

<span class="mw-page-title-main">Height of Land Portage</span> Historic site in Minnesota / Thunder Bay District, Ontario

Height of Land Portage is a portage along the historic Boundary Waters route between Canada and the United States. Located at the border of the Canadian province of Ontario and the U.S. state of Minnesota, the path is a relatively easy crossing of the Laurentian Divide separating the Hudson Bay and Great Lakes-St. Lawrence watersheds.

The Traverse Gap is an ancient river channel occupied by Lake Traverse, Big Stone Lake and the valley connecting them at Browns Valley, Minnesota. It is located on the border of the U.S. states of Minnesota and South Dakota. Traverse Gap has an unusual distinction for a valley: it is crossed by a continental divide, and in some floods water has flowed across that divide from one drainage basin to the other. Before the Anglo-American Convention of 1818 it marked the border between British territory in the north and U.S. – or earlier, French – territory in the south.

A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not connected to the open sea. Every continent on earth except Antarctica has at least one continental drainage divide; islands, even small ones like Killiniq Island on the Labrador Sea in Canada, may also host part of a continental divide or have their own island-spanning divide. The endpoints of a continental divide may be coastlines of gulfs, seas or oceans, the boundary of an endorheic basin, or another continental divide. One case, the Great Basin Divide, is a closed loop around an endoreic basin. The endpoints where a continental divide meets the coast are not always definite since the exact border between adjacent bodies of water is usually not clearly defined. The International Hydrographic Organization's publication Limits of Oceans and Seas defines exact boundaries of oceans, but it is not universally recognized. Where a continental divide meets an endorheic basin, such as the Great Divide Basin of Wyoming, the continental divide splits and encircles the basin. Where two divides intersect, they form a triple divide, or a tripoint, a junction where three watersheds meet.

The East Savanna River is a small yet historic stream in Aitkin and Saint Louis counties in the U.S. state of Minnesota. With a total length of 15.3 miles (24.6 km), the river rises in Wolf Lake, a small body of water within a spruce bog in Savanna Portage State Park, and flows northeasterly to the Saint Louis River at Floodwood, whence its waters flow to Lake Superior through the Great Lakes and the Saint Lawrence River to the Atlantic Ocean. A few thousand years ago the East Savanna was part of the Mississippi River itself, originating in northeast Minnesota and flowing southwesterly to Big Sandy Lake, from which the great river drained down its present valley to the Gulf of Mexico.

<span class="mw-page-title-main">Bifurcation lake</span> Lake that flows into two drainage basins

A bifurcation lake is a lake that has outflows into two different drainage basins and thus the drainage divide cannot be defined exactly because it is situated in the middle of the lake.

Pisgah Mountain or Pisgah Ridge is a ridgeline running 12.5 miles (20.1 km) from Tamaqua to Jim Thorpe, Pennsylvania. It is oriented north-northeast to south-southwest, and its north-side valley is followed by U.S. Route 209 from river gap to river gap. The ridge is a succession of peaks exceeding 1,440 feet (438.9 m) rising 300 to 540 feet above the boroughs of Lansford, Coaldale, and Tamaqua in the Panther Creek valley. The highest point on Pisgah Mountain is at 1,611 feet (491 m) in the borough of Summit Hill, which sits atop the ridge. Near Summit Hill was the "Sharpe Mountain" (peak) where in 1791 Phillip Ginter is documented as having discovered anthracite, leading to the formation of the Lehigh Coal Mine Company. In 1818 the Lehigh Coal Company took over the mines, and the mining camp gradually became a settlement and grew into Summit Hill.

A triple divide or triple watershed is a point on Earth's surface where three drainage basins meet. A triple divide results from the intersection of two drainage divides. Triple divides range from prominent mountain peaks to minor side peaks, down to simple slope changes on a ridge which are otherwise unremarkable. The elevation of a triple divide can be thousands of meters to barely above sea level. Triple divides are a common hydrographic feature of any terrain that has rivers, streams and/or lakes.

The Saint Lawrence River Divide is a continental divide in central and eastern North America that separates the Great Lakes-St. Lawrence River Basin from the southerly Atlantic Ocean watersheds. Water, including rainfall and snowfall, lakes, rivers and streams, north and west of the divide, drains into the Gulf of St. Lawrence or the Labrador Sea; water south and east of the divide drains into the Atlantic Ocean or Gulf of Mexico. The divide is one of six continental divides in North America that demarcate several watersheds that flow to different gulfs, seas or oceans.

References

1 2 "ridgeline. Dictionary.com" (Dictionary.com Unabridged ed.). Random House Inc. Retrieved 7 September 2013.
↑ Colombo, John Robert (16 December 2013). "Height of land". The Canadian Encyclopedia. Archived from the original on 20 June 2014.
↑ Dikshit, Ramesh Dutta (1999). Political Geography: the Spatiality of Politics (3rd ed.). New Delhi: McGraw-Hill. p. 70. ISBN 978-0-07-463578-0.
↑ Decker, Jody F. (2011). "Portages". In Wishart, David J. (ed.). Encyclopedia of the Great Plains.
↑ "Divide". Resource Library. National Geographic Society. Retrieved 3 April 2022.
↑ "Congo-Nile Divide Landscape". Albertine Rift. Wildlife conservation Society. Retrieved 3 April 2022.
↑ Leser, Hartmut, ed. (2005). Wörterbuch Allgemeine Geographie, 13th ed., dtv, Munich, p. 935. ISBN 978-3-423-03422-7.
↑ Del Papa, Eugene M. (1975). "The Royal Proclamation of 1763: Its Effects Upon Virginia Land Companies". The Virginia Magazine of History and Biography. JSTOR. 83 (4): 406–411. JSTOR 4247979.
↑ McGrath, Patrick T. (1927). "The Labrador Boundary Decision". Geographical Review. 17 (4): 643–660. doi:10.2307/208004. ISSN 0016-7428. JSTOR 208004.
↑ Shelley, Fred M. (2013). Nation Shapes: The Story Behind the World's Borders. Santa Barbara, California: ABC-CLIO. pp. 173, 242. ISBN 978-1-61069-105-5.