Open Channel Flow At High Velocities

One of the problems in the engineering design of chutes or steep spillway channels is the proper freeboard allowance to be made for the entrainment of air at high velocities. Calculations of the channel dimensions also must be modified with respect to the application of normal frictional resistance which is altered as the result of air entrainment. In all cases where water flowing in a steep chute is allowed to accelerate over a sufficient distance, air is mixed with the stream and the phenomenon of “white water” results. The same admixture of air with water can be observed in waterfalls or in natural stream channels where the velocity is sufficiently high to draw air into the water by its agitation.