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Abstract Spillways usually used for escaping water from the U.S. side, having a high-water level, to D.S. side, having a low water level in most of the diversion head structures through water streams. The D.S. of such spillways usually suffers from the destructive impacts of the generated kinetic energy of the flowing water, having a very high speed, which may cause cavitation in such spillways body. The present work is introducing some geometrical treatments on the D.S. side of the spillway body, aiming to increase its efficiency in dissipating the kinetic energy of the flowing water, having great potential energy, and improve the flowing water quality by increasing its dissolved oxygen content, through generating huge aeration at the flow in the D.S. side, also, to prevent cavitation, which may occur, and generated on the surface of the spillway body, and protecting its safety. Literature proved that the stepped spillway body is one of the most practicable trails done for achieving the above-mentioned goals. The experiments were carried out in the Irrigation and Hydraulic Laboratory, Faculty of Engineering, Assiut University, Assiut, Egypt, using 21 tested spillway models, including different types of steps, with different ratios between their height, and width, for reaching the most suitable number of steps, and the optimum relative ratio between their heights and width. The obtained optimum number, shapes, and relative dimensions of the tested steps were examined using the available laboratory discharges ranged from 2.52 l/sec, to 19.12 l/sec (Upstream Froude number ranges from 0.01 to 0.08), for studying their impacts on the water-energy dissipation, and dissolved oxygen content as a water quality indicator. Abstract (iii) The study proved that, the step height to step length ratio (h/l) equals 0.50, and step height to spillway height ratio (h/H) equals 0.20 are the optimum dimension for improving the water-energy dissipation and flow aeration. Also, the present study proved that the reverse inclined step and quarter circular end sill enhance the water-energy dissipation and flow aeration more than the straight steps, where the length of reverse step to the step length ratio (lr/l) equals 0.25 can be taken as the optimum ratio. Radius of end sill to step height ratio (r/h) equals 0.40 gives the maximum energy dissipation and maximum dissolved oxygen content compared to the other ratios |