A drainage divide, water divide, ridgeline,
watershed, water parting or height of land is elevated
terrain
Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word ...
that separates neighboring
drainage basin
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, ...
s. On rugged land, the divide lies along topographical
ridges, and may be in the form of a single range of
hill
A hill is a landform that extends above the surrounding terrain. It often has a distinct summit.
Terminology
The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not a ...
s or
mountain
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher ...
s, known as a dividing range. On flat terrain, especially where the ground is
marsh
A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found ...
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
Deposition may refer to:
* Deposition (law), taking testimony outside of court
* Deposition (politics), the removal of a person of authority from political power
* Deposition (university), a widespread initiation ritual for new students practiced f ...
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. It is frequently used in border descriptions, which are set according to the "doctrine of
natural boundaries". 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.
Types
Drainage divides can be divided into three types:
*
Continental divide in which waters on each side flow to different oceans, such as the
Congo-Nile Divide
The Congo-Nile Divide (or Nile Congo Watershed) is the continental divide that separates the drainage basins of the Nile and Congo rivers.
It is about long.
There are several geologically and geographically distinct sections between the point on ...
.
*Major drainage divide 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
Pisgah Mountain or Pisgah Ridge (on older USGS maps) is a ridgeline running from Tamaqua to Jim Thorpe, Pennsylvania (from the Little Schuylkill River water gap to the Lehigh River water gap). It is oriented north-northeast to south-southwe ...
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
The Susquehanna River (; Lenape: Siskëwahane) is a major river located in the Mid-Atlantic region of the United States, overlapping between the lower Northeast and the Upland South. At long, it is the longest river on the East Coast of the ...
and
Potomac River
The Potomac River () drains the Mid-Atlantic United States, flowing from the Potomac Highlands into Chesapeake Bay. It is long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map. Retrieved Augu ...
, with each tributary complex having separate outlets into the Atlantic.
*Minor drainage divide in which waters part but eventually rejoin at a river confluence, such as the
Mississippi River
The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...
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.
Examples include the
Kartitsch Saddle
Kartitsch is a municipality in the district of Lienz in the Austrian state of Tyrol.
Geography
Kartitsch lies on both sides of the Gail River, near its confluence with the Puster Valley. The municipal area of Kartitsch is bounded in the north o ...
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
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, where the
Drau empties into the
Black Sea
The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
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
Waidring is a municipality in the Kitzbühel district in the Austrian state of Tyrol located 20 km northeast of Kitzbühel and 9 km east of Kirchdorf in Tirol near the border with Salzburg
Salzburg (, ; literally "Salt-Castle"; bar ...
(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
Finnish Lakeland or Finnish lake district ( fi, Järvi-Suomi, "Lake Finland", sv, Insjöfinland) is the largest of the four landscape regions into which the geography of Finland is divided.
The hilly, forest-covered landscape of the lake pl ...
, 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
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
, whose main stream empties into the
Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean ...
, but which also drains into the South Atlantic via the
Casiquiare canal
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 ...
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
The Royal Proclamation of 1763 was issued by King George III on 7 October 1763. It followed the Treaty of Paris (1763), which formally ended the Seven Years' War and transferred French territory in North America to Great Britain. The Procla ...
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. Another instance of a border matching a watershed in modern times involves the western border between
Labrador
, nickname = "The Big Land"
, etymology =
, subdivision_type = Country
, subdivision_name = Canada
, subdivision_type1 = Province
, subdivision_name1 ...
and
Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
, as arbitrated by the privy council in 1927.
Portages and canals
Drainage divides hinder waterway
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation ...
. In pre-industrial times, water divides were crossed at
portages. Later,
canal
Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface f ...
s connected adjoining drainage basins; a key problem in such canals is ensuring a sufficient water supply. Important examples are the
Chicago Portage
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 Atl ...
, connecting the Great Lakes and Mississippi by the
Chicago Sanitary and Ship Canal
The Chicago Sanitary and Ship Canal, historically known as the Chicago Drainage Canal, is a canal system that connects the Chicago River to the Des Plaines River. It reverses the direction of the Main Stem and the South Branch of the Chicago R ...
, and the
Canal des Deux Mers
, canal_length=Canal du Midi Garonne Lateral Canal
, max_boat_length=
, max_boat_beam=
, present_owner=
, original_num_locks=
, current_num_locks=Canal du Midi 65 locks Garonne Lateral Canal 53 locks
, min_elev=
, max_elev=
, status=
, navigatio ...
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
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
in the Atlantic watershed to the
Hudson Bay watershed
The Hudson Bay drainage basin is the drainage basin in northern North America where surface water empties into Hudson Bay and adjoining waters. Spanning an area of about , the basin is almost totally in Canada (spanning parts of the Prairies, ce ...
.
See also
*
*
References
Further reading
*
{{DEFAULTSORT:Drainage Divide
Freshwater ecology
Geomorphology
Hydrology
Rivers
Water and the environment
Water streams