Solution of the problem of determining the frictional losses in natural streams, usually depends on the judgment and experience of the engineer. A rational approach to this problem is offered iu this paper. Existing theory on friction in open channels is reviewed, and a logical derivation leads to the development of formulas and charts to determine the relationship between stage and discharge in a given reach of river. An interdependent treatment of the hydraulic characteristics of flow and the sedimentary characteristics of the stream is, presented. Friction losses due to grain roughness, channel irregularities, and other factors are studied and formulated, and suggestions are made for practical application of a proposed rational method of friction evaluation.