A factor which occasionally affects stilling basin operation is the slope of the chute upstream from the basin. The foregoing experimentation was sufficiently extensive to shed some light on this factor. The tests showed that the slope of chute upstream from the stilling basin was unimportant, as far as jump performance was concerned, provided the velocity distribution in the jet entering the jump was reasonably uniform.
For steep chutes or short flat chutes, the velocity distribution can be considered normal. Difficulty is experienced, however, with long flat chutes where frictional resistance on the bottom and side walls is sufficient to produce a center velocity greatly exceeding that on the bottom or sides.
When this occurs, greater activity results in the center of the stilling basin than at the sides, producing an asymmetrical jump with strong side eddies. This same effect is also witnessed when the angle of divergence of a chute is too great for the water to follow properly. |