geography Geography (from Ancient Greek ; combining 'Earth' and 'write', literally 'Earth writing') is the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding o ...

, hydrography, and fluvial

geomorphology Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...

, a thalweg or talweg () is the line or curve of lowest

elevation The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotenti ...

within a

valley A valley is an elongated low area often running between hills or mountains and typically containing a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...

watercourse A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

. Normally only the horizontal position of the curve is considered (as viewed on a map); the corresponding vertical position is represented in a '' stream profile''. Under

international law International law, also known as public international law and the law of nations, is the set of Rule of law, rules, norms, Customary law, legal customs and standards that State (polity), states and other actors feel an obligation to, and generall ...

, a thalweg is instead taken to be the middle of the primary navigable channel of a

waterway A waterway is any Navigability, navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other ways. A first distinction is ...

which is the default legal presumption for the boundary between entities such as states. Thalwegs can have local proprietorial and administrative significance because their formerly somewhat shifting position, reliant on renewed soundings, now more fixed as described internationally, is part of centuries-old custom and practice in some jurisdictions. In some jurisdictions and between some states the median line (between banks) is the preferred boundary presumption as may extend from estuaries. Also being easy to map, drawing "turning points" are the solution for a few major rivers such as the St Lawrence River-Great Lakes system.

Etymology

The word '' thalweg'' is of 19th-century German origin. The German word (modern spelling ) is a compound noun that is built from the German elements (since Duden's orthography reform of 1901 written ) meaning 'valley' (cognate with ''dale'' in English), and , meaning 'way'. It means 'valley way' and is used, with its modern spelling , in daily German to describe a path or road which follows the bottom of a valley, or in geography with the more technical meaning also adopted by English.

Hydrology

hydrological Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...

and fluvial landforms, the thalweg is a line drawn to join the lowest points along the length of a

stream bed A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...

in its downward slope, defining its deepest channel. The thalweg thus marks the natural direction (the profile) of a watercourse. The term is sometimes used to refer to a subterranean stream that percolates under the surface and in the same general direction as the surface stream.

Bouldering of thalweg of non-canalised rivers

Slowing stream-bed erosion by bouldering a thalweg helps stabilize natural rivers' course and depth. Placing boulders along the thalweg helps to protect the channel's sedimentary erosion and deposit balance. In concurrence with this, doing so along an instream to form artificial sills helps to slow the sedimentary erosion and deposit of watercourses, while keeping the esteem (fishing, local wildlife, and recreation) and natural resources of the running water source intact. Placement of boulders along a thalweg and the creation of instream sills makes drying up rarer and less severe during late summer, and abates cases of severe sediment erosion and deposit in the spring and fall months when the flow rates are high, particularly if those rates have increased. Such partial infilling of a thalweg was prototyped in Meacham Creek in Umatilla, Oregon.

Thalweg principle

The ''thalweg principle'' (also known as the ''thalweg doctrine'' or the ''rule of thalweg'') is the legal principle that if the boundary between two political entities is stated to be a waterway without further description (''e.g.'', a median line, right bank, eastern shore, low-tide line, etc.), the boundary follows the thalweg of that watercourse. A thalweg is the center of the principal navigable channel of the waterway (which is presumed to be the deepest part). If there are multiple navigable channels in a river, the one principally used for downstream travel (likely having the strongest current) is used.A. Oye Cukwurah, ''The Settlement of Boundary Disputes in International Law'', Manchester University Press, 1967, pp. 51 ''ff.'' The definition has been used in specific descriptions as well. The

Treaty of Versailles The Treaty of Versailles was a peace treaty signed on 28 June 1919. As the most important treaty of World War I, it ended the state of war between Germany and most of the Allies of World War I, Allied Powers. It was signed in the Palace ...

, for example, specifies that "In the case of boundaries which are defined by a avigablewaterway" the boundary is to follow "the median line of the principal channel of navigation." The precise drawing of river boundaries has been important on countless occasions. Notable examples include the Shatt al-Arab between Iraq and Iran, the

Danube The Danube ( ; see also #Names and etymology, other names) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest sou ...

in central

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

( Croatia–Serbia border dispute), the Kasikili/Sedudu Island dispute between

Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

and

Botswana Botswana, officially the Republic of Botswana, is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory part of the Kalahari Desert. It is bordered by South Africa to the sou ...

(settled by the

International Court of Justice The International Court of Justice (ICJ; , CIJ), or colloquially the World Court, is the only international court that Adjudication, adjudicates general disputes between nations, and gives advisory opinions on International law, internation ...

in 1999), and the 2004 dispute settlement under the UN

Law of the Sea Law of the sea (or ocean law) is a body of international law governing the rights and duties of State (polity), states in Ocean, maritime environments. It concerns matters such as navigational rights, sea mineral claims, and coastal waters juris ...

concerning the offshore boundary between

Guyana Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...

and

Suriname Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...

, in which the thalweg of the Courantyne River played a role in the ruling. In the 20th century dispute between the USSR and China (PRC) over Zhenbao Island,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

held that the Thalweg principle supported their position. The doctrine is also applied to sub-national boundaries, such as those between American states.''E.g.'', ''New Jersey v. Delaware'', 291 U.S. 361, 78 L.Ed. 847, 54 S.Ct. 407 (1934).

References

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