Tributary

This article is about a lesser flow of water. For other uses, see Tributary (disambiguation). For other uses of Confluence (which redirects here), see Confluence (disambiguation).

Biała Lądecka, a right tributary of Nysa Kłodzka in Poland, located in the village of Bielice in Lower Silesia.

A tributary or affluent is a stream or river that flows into a main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the mainstem river serve to drain the surrounding drainage basin of its surface water and groundwater by leading the water out into an ocean or sea.

A confluence, where two or more bodies of water meet together, usually refers to the joining of tributaries.

Reciprocal to a tributary is a distributary, a river or stream that branches off from and flows away from the main stream. Distributaries are most often found in river deltas.

Terminology

The Pfinz, a right tributary of the Rhine, located in Baden-Württemberg.

Walton Creek, a small tributary of the Lochsa River in northeastern Idaho, flowing slightly upstream of its confluence with a larger stream.

'Right tributary' and 'left tributary' (or 'right-bank tributary' and 'left-bank tributary') are terms stating the orientation of the tributary relative to the flow of the mainstem river. These terms are defined from the perspective of looking downstream (in the direction the water current of the main stem is going).

Where tributaries have the same name as the river into which they feed, they are called forks. These are typically designated by compass direction. For example, the American River receives flow from its north, middle, and south forks.

Forks are sometimes designated as right or left. Here, the "handedness" is from the point of view of an observer facing upstream. For instance, Steer Creek has a left tributary which is called Right Fork Steer Creek.

Ordering and enumeration

Tributaries are sometimes listed starting with those nearest to the source of the river and ending with those to those nearest to the mouth of the river. The Strahler Stream Order examines the arrangement of tributaries in a hierarchy of first, second, third, and higher orders, with the first order tributary being typically the least in size. For example, a second order tributary would be the result of two or more first order tributaries combining to form the second order tributary.

Another method is to list tributaries from mouth to source, in the form of a tree structure, stored as a tree data structure.

In Norway, the river Glomma meets its main tributary Vorma.

See also

• Estuary