n hassanpour - University of Tabriz, Tabriz, Iran
a abbaspour - University of Tabriz, Tabriz, Iran
a hosszadeh dalir - University of Tabriz, Tabriz, Iran
d Farsadizadeh - University of Tabriz, Tabriz, Iran

The gradually expanding stilling basin is attractive to the designer due to its compatibility with a large range of upstream and downstream sections, and to having a small sequent depth ratio and the hydraulic jump length. However, the hydraulic jump in such stilling basins often encounters instability and symmetrical flow problems. In the present study, the effect of divergence ratio and the height of roughness elements in improving the hydraulic jump characteristics such as the length and roller length of the hydraulic jump and the relative energy loss was investigated in a gradually stilling basin. Also with the experimental data, empirical formulae were developed to express the hydraulic jump characteristics relating to the roughness elements height and divergence ratio of the wall. The results showed that the length and roller length of the hydraulic jump on a gradual expansion basin with the rough bed were appreciably smaller than that of the corresponding hydraulic jump in a rectangular basin with the smooth and rough bed. It was also found that the roughness elements could considerably improve the general conditions of the expanding hydraulic jump and could stabilize the position of this type of the hydraulic jump.

Expansion stilling basin, Hydraulic jump, Roughness elements, Roller length