Comparison of Energy Dissipation by Double Horizontal Screen and Stilling Basins at Vertical Drop Downstream

The aim of this study was to evaluate and compare the double horizontal screens with four types of stilling basin (I, II, III and IV) at vertical drop downstream in terms of energy dissipation. A total of 140 different experiments were performed on a vertical drop equipped with double horizontal screens (with 40 and 50% porosity) at relative spaces of 0.25, 0.33 and 0.5 between the screens, and two drop height of 20 and 25 cm. The results showed that the relative spacing and porosity of the double horizontal screen do not have a significant effect on the residual energy and the relative depth of downstream, however, the length of drop stilling basin is decreased with increasing the relative spacing and porosity of screen. In compared to the stilling basins, the use of double horizontal screens reduced the length of drop stilling basin and the residual energy and relative depth of downstream is reduced by more than 35 and 49%, respectively.