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WWRC 83-04
Two Approaches for Estimation of Manning's n in Mountain Streams


An analysis of roughness coefficients for mountain streams in the Rocky Mountain Region was conducted to devise an empirical method for determination of Manning's n. Two approaches were developed. One procedure utilizes a diagrammatic key approach based upon water surface slope and observable channel characteristics, while the other attempts to relate the time-of-travel velocity of a dye cloud through a stream reach to channel roughness. The conclusions drawn indicate that good potential exists for the use of the diagrammatic key approach. A second significant conclusion of the study is that the estimation of n for steep, rough, tributaries at low flow by means of published tables and/or photographic comparisons can lead to erroneous results.

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