Experimental Study of the Coefficient of Discharge for Porous Stepped Spillways

Porous stepped spillways are environmentally friendly hydraulic structures that manage the flow in open channels. This study aimed to investigate experimentally the discharge coefficient on porous and impermeable spillways. Six physical models of porous and impermeable spillways were utilized with three downstream slopes of 1:1, 1:2, and 1:3. Dimensional analysis was used to obtain the significant parameters that dominate the flow over stepped spillways. The results indicated that an increase in the porosity of the spillway leads to a reduction in the head above the spillway at the upstream side. Moreover, the discharge coefficient increased with the increase in porosity and the downstream slope. The average discharge coefficient values increased by 20% when the porosity rose from 0.00 to 0.42. Also, the average discharge coefficient values increased by 22% when the downstream slope increased from 1:3 to 1:1. Furthermore, the impact of porosity on the discharge coefficient reduced with increasing the (H/L), and the curves tended to converge. Three relationships were developed to predict the discharge coefficient for general, porous, and impermeable stepped spillways. The developed relationships can estimate (Cd) with high accuracy. The determination coefficient (R²) was 0.927, 0.984, and 0.992 respectively. Moreover, the root means square error (RMSE) was 0.032, 0.012, and 0.008 respectively. Further, the relative error percentage (RE%) was 3.17%, 1,14%, and 0.892% respectively.