The efficient operation of reservoirs relies on the effective release of water during flooding, requiring a good understanding of spillways and their hydraulics. A series of experiments was conducted in a laboratory flume on a stepped spillway model with moderate slope (26.68) for discharges up to 0.0121 m 3 /s. Using regular uniform horizontal steps of 5 cm height, then several new step configurations including inclined and horizontal curved steps with and without reflector blocks, the flow patterns were investigated. The energy losses over a horizontal stepped spillway were compared with those obtained in a number of similar, previous studies, and with the results obtained for the new step configurations. Good agreement was shown with previous results for horizontal steps, and the inclined and horizontal curved steps dissipated about twice as much energy as the horizontal steps. The results highlight the importance of considering a variety of step forms in spillway design where flows are unpredictable and energy dissipation is important.

A piano key weir (PKW) is a modified version of non-linear weirs and it can be obtained via amending the centerline length of the weir by small a small footprint. It is developed to increase the hydraulic performance of the linear weirs via increasing the pass discharge and the energy dissipation. A laboratory investigation is conducted on five physical PKW (Type A) models to investigate the effect of inlet to outlet width ratio (Wi/Wo) on the hydraulic performance of PKWs. The results showed that the (Wi/Wo) ratio has a predominant influence on the hydraulic performance of PKW. It was found out that the best hydraulic performance was obtained with Wi/Wo ratio equal to 1.25 among other investigated Wi/Wo ratios because the discharge coefficient was the highest for the given discharge and head. Further, the results revealed that the variation of Wi/Wo ratio from 1.25 had a negative impact on both discharge coefficient and efficiency. It was found out that the percentages of reduction in discharge coefficient when Wi/Wo=0.8, 1, 1.5 and 2 were 11%, 6, 2 and 8%, respectively in comparison with the Wi/Wo=1.25. Similarly, for these Wi/Wo ratios, the percentages of reduction in discharge decrease by 11%, 6.5%, 2.35 and 9%, respectively, relatively to Wi/Wo=1.25. The Linear regression equations coefficients for the PKW models were varied from 0.983 to 0.994 which means the performance of the models are good for the given Wi/Wo ratios.