the s-jump’s characteristics in the rough sudden expanding stilling basin

One way to dissipate energy is to use sudden expansion stilling basin structures downstream of spillway, gates and chute. the present study is aimed to study influences of shear stress caused by a rough bed on sjump’s characteristics in an expanding stilling basin. experiments were performed in a horizontal laboratory flume with a rectangular crosssection, a plexiglas wall and floor with an expanding ratio of 0.33, a froude number range of 5.38 to 10.78. the results showed that the shear stress of the rough bed in the expanded stilling basin was more than 13.5 times the shear stress of the prismatic stilling basin with a smooth bed. secondary depth and the length of the sjump on the rough bed have reduced to 20% and 16%, respectively. also s jump with rough beds reduces the secondary depth by about 58.5% compared to classical hydraulic jump. increased shear stress has a marginal impact on jump efficiency, so that the effect of expanding on jump efficiency is greater than the effect of increased shear stress. expanding stilling basins with a smooth and rough bed are moderate compared to prismatic basin. it can and increase the jump efficiency for smooth and rough bed by 23.5 and 28.7%, respectively.