characteristics of s-jump on roughened bed stilling basin

formation of hydraulic jump is necessary for dissipation of the excess kinetic energy downstream of spillways and gates. hydraulic jump stilling basins of sudden expansion are one of the energy dissipater structures which are used where the available tail water depth is less than the required sequent depths. in the present study to further reduce the hydraulic jump sequent depths ratio, a roughened bed type of stilling basins of sudden expansion is experi-mentally investigated. four different expansion ratios of 0.33, 0.5, 0.67 and 1 were studied under wide range of flow conditions, froude numbers between 2 and 10. results of the present study show that sequent depths ratio is 16-20 percent lower and the jump efficiency can increase 20 percent in comparison to the classical jump.