when is a new river named when two rivers join
Sometimes when two rivers join a river with a new name is formed and at other times this doesn't happen. For example the Barwon and Culgoa Rivers join to form the Darling River (in Australia) while the Darling River is a tributary of the Murray River (ie the Murray doesn't change its name after been joined by the Darling).
I wants to know if this is, as I suspect, an arbitary naming convention as for rivers versus creeks (e.g. the Thompson and Barcoo Rivers join to form Coppers Creek).
Solution 1:
Place-naming conventions, and systems for standardizing place-naming, vary from country to country, and within countries, from region to region, district to district, area to area.
Your suspicion that the names of stretches of rivers have been and continue to be arbitrarily decided is, more or less, correct. This is true whether or not a confluence is coincident with a change of name.
Australia's New South Wales, for example, frequently uses a dual naming convention:
There has been a move in recent years to recognise the validity of Indigenous names and to promote the investigation and official use of these names. In NSW the Geographical Names Board has established a dual naming sub-committee and dual naming guidelines.
These guidelines recognise the significance of Aboriginal culture by giving dual names to already named geographical features, such as, rivers, [and] creeks .... Local Indigenous communities and historical sources [are] consulted to ensure cultural accuracy; a dual name can be assigned only where there is strong evidence of a pre-existing Indigenous placename, and the proposal must have the support of the local community.
(From "Dual Naming", an article at Our Languages.)
Another article at the same source provides a summary of the place-naming process in Australia:
In Australia there are two systems of placenames; there is the introduced system of placenames that Europeans developed to refer to places, and the network of Indigenous placenames that Indigenous people use.
Colonists, explorers, settlers and surveyors through their renaming of the Australian landscape have often consulted Indigenous people and adopted Indigenous names. Indeed it has been estimated (albeit rather unreliably) in New South Wales that over 75% of the current names of settlements and geographical features, such as creeks and hills, are of Aboriginal origin (Kennedy and Kennedy 1989).
(From "Aboriginal Place Names", op. cit.)
The process of naming and renaming as languages and cultures intermingle applies equally to rivers, creeks, mountains, geopolitically defined areas, and other place-names. It is a process largely driven by historically established customs, with a more recent gloss of systematic standardization.
Some of the complexity of the process is emphasized by this excerpt from a "Domestic Names - Frequently Asked Questions" article published by the United States Board on Geographic Names:
- What is the difference between “mountain,” “hill,” and “peak”; “lake” and “pond”; or “river” and “creek”?
There are no official definitions for generic terms as applied to geographic features. Such definitions as exist derive from the particular needs and applications of organizations using them. The GNIS database utilizes 63 broad categories of feature types originally defined solely to facilitate retrieval of entries with similar characteristics from the database.
These categories generally accord with dictionary definitions, but not always or in all respects. The differences are thematic and highly perceptive. For example, a lake is classified in the GNIS as a “natural body of inland water,” a definition that may not apply in other contexts. We have found 54 other generic terms with characteristics similar to a lake, and all are classified as lake, including features called ponds. It might be generally agreed that a pond is smaller than a lake, but even this is not always true.
All “linear flowing bodies of water” are classified as streams in the GNIS. At least 121 other generic terms fit this broad category, including creeks and rivers. Observers might contend that a creek must flow into a river, but such hierarchies do not exist in the Nation's namescape. Near the USGS offices in Northern Virginia, Little River flows into Goose Creek. Many controversies exist, such as mountain and hill, which we call “summit” along with 194 generic terms with similar characteristics. Cities, towns and other entities with human habitation are classified as populated places.
The British Ordnance Survey once defined a mountain as having 1,000 feet of elevation and less was a hill, but the distinction was abandoned sometime in the 1920's. There was even a movie with this as its theme in the late 1990's - The Englishman That Went Up a Hill and Down a Mountain. The U.S. Board on Geographic Names once stated that the difference between a hill and a mountain in the U.S. was 1,000 feet of local relief, but even this was abandoned in the early 1970's. Broad agreement on such questions is essentially impossible, which is why there are no official feature classification standards.
(Emphasis mine. The "GNIS" is the "Geographic Names Information System", a database of information about place-names in the US.)
Also in the US, 'official' names (their assignment and application) are governed by this section of the US Administrative Code:
43 U.S. Code § 364 - Uniformity in geographic nomenclature and orthography; exercise of functions of Secretary of the Interior
The Secretary of the Interior, hereinafter called the Secretary, conjointly with the Board on Geographic Names, as hereinafter provided, shall provide for uniformity in geographic nomenclature and orthography throughout the Federal Government. The Secretary may exercise his functions through such officials as he may designate, except that such authority as relates to the final approval or review of actions of the Board on Geographic Names shall be exercised by him, or his Under or Assistant Secretaries.
(As published by the Legal Information Institute at Cornell University Law School.)
Similar administrative codes in other countries, and in states, provinces and regions within countries, provide standardization for 'official' names. As expressed by this excerpt from the website of the US Board of Geographic Names, such standardization resolves many thorny national and international problems:
The original program of names standardization addressed the complex issues of domestic geographic feature names during the surge of exploration, mining, and settlement of western territories after the American Civil War. Inconsistencies and contradictions among many names, spellings, and applications became a serious problem to surveyors, map makers, and scientists who required uniform, non-conflicting geographic nomenclature. President Benjamin Harrison signed an Executive Order establishing the Board and giving it authority to resolve unsettled geographic names questions. Decisions of the Board were accepted as binding by all departments and agencies of the Federal Government.
The Board gradually expanded its interests to include foreign names and other areas of interest to the United States, a process that accelerated during World War II. In 1947, the Board was recreated by Congress in Public_Law_80-242 . The usefulness of standardizing (not regulating) geographic names has been proven time and again, and today more than 50 nations have some type of national names authority. The United Nations stated that "the best method to achieve international standardization is through strong programs of national standardization." Numerous nations established policies relevant to toponomy (the study of names) in their respective countries.
So, where and why the name of a river ("linear flowing body of water") changes is largely a matter of historical custom, filtered in some cases through the comparatively recent advent of official standardization in the naming of geographical features.