Hydraulics of High‐Gradient Streams

Abstract

Onsite surveys and 75 measurements of discharge were made on 21 high‐gradient streams (slopes greater than 0.002) for the purpose of computing the Manning roughness coefficient, n, and to provide data on the hydraulics of these streams. These data show that: (1) n varies inversely with depth; (2) n varies directly with slope; and (3) streams thought to be in the supercritical flow range were actually in the subcritical range. A simple and objective method was employed to develop an equation for predicting the n of high‐gradient streams by using multiple‐regression techniques and measurements of the slope and hydraulic radius. The average standard error of estimate of this prediction equation was 28% when tested with Colorado data. The equation was verified using other data available for high‐gradient streams. Regimeflow equations for velocity and discharge also were developed.