Design of Stilling Basin with Stepped End Sill

Stilling basins are frequently used to dissipate excess flow energy at downstream of hydraulic structures such as spillways which may otherwise cause excess scouring in the river bed and hence may lead to failure of the hydraulic structure itself. Thus, design of stilling basin is an important technical and economical activity. In the design of stilling basin, length and geometry is very important as it affects the formation of hydraulic jump, and hence the energy dissipation. In this study, the impact of end sill in thestilling basin is studied through the model study of Siahbisheh Dam spillway in Iran. A stepped spillway with 1.5 m width and a stilling basin at the downstream of the stepped chute were constructed to evaluate stilling basin performance. Four stepped end sills were tested at three different locations of 2.3, 2.4, and 2.8 m from the beginning of the stilling basin. Various flow characteristics were studied for three different discharges. Five different cross sections were considered in the stilling basin to investigate forced hydraulic jump properties. Hydraulic characteristics of forced hydraulic jump by various aspects of stepped end sill have been compared with classical hydraulic jump characteristics. Further, the best design combination has been suggested on the basis of hydraulic characteristics of the jump under variable conditions

Keywords:

Stilling Basin , Energy Dissipation , Hydraulic Jump , Length of Jump