Effect of the chute bed roughness height on the B-jump characteristics

Rock and gabion types of chute structures are used in many natural and artificial channels. The excess kinetic energy downstream of this structure is dissipated through hydraulic Jump. One type of the hydraulic jump is the B-jump. A B-jump is defined as the jump having the toe section located on a positively sloping upstream channel and the roller length end on a downstream horizontal channel. Determination of hydraulic jump characteristics such as the sequent depth ratio, jump length and roller length which occur at the roughened bed chute can help to design a safe and economic stilling basin. In this study, to estimate sequent depth ratio on the rough bed, using Buckingham theorem and incomplete self similarity theory a general non-dimensional relation was developed. Also general equations were developed for estimating jump and roller lengths. Then tests were conducted for a wide range of relative roughness, flow discharge and Froude numbers. The results showed that relative roughness could reduce the sequent depth ratio, jump length and roller length.