Air Entrained in Flow along a Steep-Stepped Spillway: Data and Insights from a Hydraulic Model

Abstract

Data and insights are presented on air entrainment in a hydraulic model of the stepped spillway for Gross Dam, Colorado, soon to be the tallest stepped spillway in the United States. The spillway’s chute was steep (2.0V:1.0H) and curved, and converged about 20% from its top to its base width. Data show that streamwise values of air concentration and flow depth were practically constant near the chute’s end for the spillway’s design discharge. The chute’s planform curvature resulted in nonuniform flow depth across the chute; flow depth along the chute’s centerline was greater than flow depth at the sidewall but contained slightly less entrained air. At the end of the chute, the average air concentration (volumetric proportion of bulked flow) varied from about 0.55–0.61. The depth-averaged concentration of entrained air near the end of the chute decreased with increasing water discharge, and was less than the equilibrium value suggested by the literature. The chute’s converging sidewalls caused slight increases in flow depth and reductions in flow velocity near the sidewalls.