In hydrography, a tributary (or tributary) is a natural watercourse that pours its waters into another major one. Man-made canals are usually excluded from the list of tributaries of a river. The place where two or more streams meet and join their waters is called confluence. The terms tributary and confluence also apply, by extension, to glaciers.
The descriptive terms right tributary and left tributary are always applied from the perspective of those who observe the river with their back to its origin, looking in the direction of the current, in the same way as the denomination of the banks (in this regard the terms right hydrographic and left hydrographic are used ).
The opposite of tributary is effluent (or distributary), a watercourse (natural or artificial) that moves away from the main river discharging part of its flow. A watercourse that feeds a lake is generally called a tributary.
In many cases at the confluence it is clear which watercourse is the main river and which tributary, as one of the two is much longer and has a greater flow. However, there are other cases in which a watercourse of shorter length or flow than the watercourse considered tributary is considered to be the main river; this is the case, for example, of the confluence between the Po and the Tanaro (the Tanaro, considered a tributary, is longer, at the confluence point, than the Po into which it flows), the confluence of the Ob 'and Irtyš rivers in Siberia (the river Irtyš, considered a tributary, is longer than the Ob 'into which it flows) and the confluence between Volga and Kama in European Russia (the Kama, considered a tributary, is longer, at the confluence point, than the Volga into which it flows ).
In orography the tributaries are ordered starting from those closest to the source of the river to which they are tributary to those closest to the mouth. Using graph theory one can examine the arrangement of tributaries in hierarchies with elements of the first, second, third order, and so on. The territory that is drained by a river and by the network of its tributaries of each order constitutes a hydrographic basin.
Wiktionary contains the dictionary lemma «affluent»
Wikimedia Commons contains images or other files on tributary
affluènte, on Treccani.it - Online Encyclopedias, Institute of the Italian Encyclopedia.
(EN) Affluent, in Encyclopedia Britannica, Encyclopædia Britannica, Inc.