Stream orders

Abstract

The streams in a drainage basin can be assigned orders (e.g., see Leopold et al., 1964). This can be done in several ways. (a) Horton orders:Horton (1945) originally developed the notion of stream orders. First-order streams are those which have no tributaries, second-order streams are those which receive as tributaries only streams of the first order, etc. However, the main stream is denoted by the same order number all the way to its headwaters, and hence one of the first-order streams (normally either the longest or the one which seems the most direct upstream continuation of the main stream) has to be renumbered as second order. The renumbering procedure is repeated with higher-order streams, so that the Nth order stream extends headward to the begining of the longest tributary. Thus, as a stream-order map is prepared, one of the lower-order streams is renumbered every time two channels of equal order join one another. ...