According to the "top down" system devised by Strahler, rivers of the first order are the outermost tributaries. If two streams of the same order merge, the resulting stream is given a number that is one higher. If two rivers with different stream orders merge, the resulting stream is given the higher of the two numbers.
The Strahler order is designed to reflect the morphology of a catchment and forms the basis of important hydrographical indicators of its structure, such as its bifurcation ratio, drainage density and frequency. Its basis is the watershed line of the catchment. It is, however, scale-dependent. The larger the map scale, the more orders of stream may be revealed. A general lower boundary for the definition of a "stream" may be set by defining its width at the mouth or, referencing a map, by limiting its extent. The system itself is also applicable for other small-scale structures outside of hydrology.
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6 окт 2020
