The 6 th Int. Conf. on Hydroscience and Engineering (ICHE-2004), May 30-June 3, Brisbane, Australia 1 EFFECT OF MULTIPLE STEPS VERSUS SINGLE STEP ON THE HYDRAULIC PERFORMANCE OF RADIAL STILLING BASINS UNDER FREE HYDRAULIC A-JUMP CONDITIONS Abdel-Azim M. Negm 1 , Gamal M. Abdel-Aal 2 , Amany A. Habib 3 , and Talaat M. Owais 1 ABSTRACT Steps may be constructed in stilling basins based on land topography and design requirements. For the purpose of increasing the energy dissipation and reducing the length of hydraulic jump, multiple steps are used instead of single step. The effects of both single and multiple negative steps on the performance of radial stilling basins are investigated experimentally by analyzing large series of experimental data. The data are collected using a laboratory flume of relatively large dimensions. Both the dissipated energy and the length of jump are taken as indicators for the hydraulic performance of the basin under the effect of single and multiple steps. The proper number of steps and the their best location to improve the performance of the radial stilling basins are determined. An alternative solution is to use sloping negative step instead of sudden negative one. The effects of Different sloping negative steps on the energy dissipation and on the length of jump are also investigated experimentally. 1. INTRODUCTION One of the measure that used inside the stilling basin to control the hydraulic jump is the step. Previous investigations regarding the use of the negative step indicated that the use of the step in radial stilling basins increases the length of the free hydraulic jump and decreases the energy dissipation compared to the smooth stilling basin, Negm et al. (2003a,b,c), Abdel-Aal eta al. (2003) and Habib et al. (2003). Negm et al. (2003a), developed theoretical equations for depth ratio and for the energy loss ratio of the free hydraulic jumps formed in radial stilling basins containing negative step. Both of A and B jumps were considered. Empirical formula were developed for both the length and the depth ratios of the free hydraulic jumps. Recently, experimental investigations, Negm et al. (2003b,c) were conducted to study the effect of the negative step location on the basic characteristics of the hydraulic jump formed in the stilling basin. It was concluded that the length of jump was minimized and the energy loss is maximized compared to the no step case when the step is constructed at or beyond 50% of stilling basin downstream of the gate. Theoretical expressions for the depth ratio and the energy loss ratio of the hydraulic jump formed in stilling basins containing negative step and a continuous end sill were developed, Abdel-Aal et al. (2003). The effect of the end sill alone was also studied theoretically, Habib et al. (2003). Few studies dealing with the submerged hydraulic jump in radial stilling basins containing negative step were also conducted, Negm et al. (2002a,b). It should also be mentioned that the radial 1 Professor of Hydraulics, Dept. of Water & Water Structures Eng., Faculty of Engineering, Zagazig University, Zagazig, Egypt, E-mail: amnegm85@yahoo.com 2 Associate Professor, Dept. of Water & Water Structures Eng., Faculty of Engineering, Zagazig University, Zagazig, Egypt. 3 Assistant Professor, Dept. of Water & Water Structures Eng., Faculty of Engineering, Zagazig University, Zagazig, Egypt