عنوان مقاله [English]
The most common way to dissipate the water kinetic energy at the downstream of weirs , gates at chutes is to use the hydraulic jump. Hydraulic jump is a phenomenon that alters the flow regime of the state of supercritical to the subcritical with dissipating much of the flow kinetic energy and to prevent possible downstream scour of the structure. Development of the downstream scour hole of the hydraulic jump stilling basins can cause failure of the structure itself , which has been the interest of the researchers in the past. The extension of new roughened bed basin is essential to pursue and complete what previous researchers concluded for these basins.Safe and an economical design of hydraulic structures, an estimation of the maximum scour depth, and to minimization the scour dimensions is the interest of the researchers. Therefore, in this study the effect of placing the six-legged concrete elements under different lengths was investigated investigated. Covering the river bed downstream of the spillways and gates with these roughened and permeable elements can decrease the stilling basin length and expected less scour depth. These elements are tight together and placed on the bed. The covered length of the bed is equal to the length of jump on these elements. However, there is possibility in which few rows of the downstream elements are escaped because of the edge failure and therefore the roughened bed length is shortened. The main purpose of this study was to see how much exactly would be the magnitude of downstream scour depth if the covered length is decreased. .