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<br />HYDRAULICS OF STEEP-GRADIENT STREAMS <br /> <br />ABSTRACT <br /> <br /> <br />By Robert D. Jarrett <br /> <br />Existing guidel ines for the evaluation of the channel roughness of <br /> <br />00 <br />steep-gradient streams (slope greater than 0.2 ~epeen~) have been based <br />1\ <br /> <br />on insufficient data. Many of these steep-gradient streams also require <br /> <br />additional hydraul ic analysis. Onsite surveys and 75 measurements of <br /> <br />discharge were made on 21 steep-gradient streams for the purpose of <br /> <br />computing the Manning roughness coefficient, n, and to provide data on <br /> <br />the. hydraul ics of these streams. These data show that: (1) n varies <br /> <br /> <br />inversely with depth, (2) n varies directly with slope, (3) the vertical- <br /> <br />velocity distribution does not fit a logarithmic curve, and (4) streams <br /> <br />thought to be in the supercritical flow range were actually in the <br /> <br />subcritical range. <br /> <br />I <br />A simple and objective method was employed to develop an equation <br /> <br />for predicting the n of steep-gradient streams by using multiple-regression <br /> <br />techniques and measurements of the slope and hydraulic radius. The <br /> <br />average standard error of estimate of this prediction equation was <br /> <br />28 percent when tested with Colorado data. The equation was verified <br /> <br />using other data available for steep-gradient streams. Regime-flow <br /> <br />equations for velocity and discharge also were developed. <br /> <br />S' <br />