1 st International Conference of Civil Engineering Science, ICCES1, Vol. 1, 2003 EFFECT OF END SILL IN RADIAL BASIN ON CHARACTERISTICS OF FREE HYDRAAULIC JUMPS Abdel-Azim M. Negm, Gamal M. Aabdel-Aal, Amany A. Habib and T.M.Owais Dept. of Water & Water Structures Eng., Faculty of Engineering, Zagazig University, Zagazig, Egypt, E-mail: amnegm85@yahoo.com ABSTRACT The end sill may be used in stilling basin to produce double effect on the flow upstream the sill and downstream of it. Upstream of the end sill, the characteristics of the hydraulic jump may be affected. Downstream of the end sill, the scour hole may be formed away from the apron and also may be modified in its dimensions. In this paper, the effect of end sill on the characteristics of the free hydraulic jump formed upstream of the sill in a radial basin is investigated experimentally. Sills of different heights were tested under wide range of flow conditions. It was found that the basic characteristics of the free radial hydraulic jump formed upstream of end sill are function of the supercritical flow Froude number and the relative height of the sill. The experimental data was used to estimate the derived functional relationship using the dimensional analysis. The developed statistical model agreed well with the experimental data. Moreover, a theoretical model for the energy loss ratio through the jump was developed and found to be in good agreement with the experimental data. Keywords: Hydraulic jump, Empirical modeling, Stilling basin, Non-prismatic basins, Expanding channels, End sill, Experimental studies 1. INTRODUCTION Hydraulic jumps are advantageous for dissipating kinetic energy in stilling basins. It may be free or submerged depending on both the location and the initial depth of the jump relative to the gate. The different classifications of jumps were reported in Chow 1) . The hydraulic jump may be also formed in prismatic or in non-prismatic channels (diverging or sudden expanded), and may be forced or non-forced. Most of the studies on different types of hydraulic jump are presented in Hager 2) . Khalifa and McCorquodale 3) , studied the radial hydraulic jump occurs in stilling basins with diverging side-walls. They concluded that the sequent depth ratio of the radial jump is less than that of the rectangular jump, and the length of the radial hydraulic jump is about 70% of that of rectangular jump with the same flow conditions. Also, the energy loss in a radial hydraulic jump was 15% higher than that of the rectangular jump. According to the various methods used in practice, stilling basins were arranged in a variety of geometrical configurations. On the other hand, sills or blocks were used in stilling basins to increase the rate of energy dissipation and to reduce the bed velocity in the region of the hydraulic jump. Many studies had been conducted to investigate the effect of sills in rectangular basins. The effect of the sill on the jump characteristics depends on factors such as the sill configuration, sill location and sill spacing when more than one sill was used. Several investigations dealt with the effect of sill on the hydraulic jump characteristics when the sill was constructed beneath hydraulic jump such as Shukry 4) , Rajaratnam 5) , Ohtsu and Yasuda 6) , and Hager and Li 7) . Hager and Li gave one of these classifications of the forced hydraulic jump due to vertical sill. They classified the jump over vertical sill into A-jump, B- jump, minimum B-jump and C-jump. The A-jump was corresponding to the classical hydraulic jump, which was characterized by the maximum sequent depth ratio for the free jumps. They stated that, A-jump in which the jump characteristics are not influenced by the presence of sill (or weak effect are present) as the sill was found at the end of the surface roller and thus it was out side the effective zone for the sill to affect the jump flow. Other studies on the effect of vertical sill on the jump and different classification of