Experimental Investigation of Chute Bed Roughness Height Effects on Energy Dissipation

Chute spillways are widely used hydraulic structures in dams, where effective energy dissipation is essential to reduce downstream scour and minimize the required dimensions of stilling basins. This study investigates the influence of chute bed roughness height on energy dissipation using physical model experiments. Two chute slopes (25° and 35°) and four uniform roughness sizes (3.38, 7.0, 12.7, and 38.1 mm) were tested under discharges ranging from 4 to 40 L/s, yielding a total of 80 runs. Results show that roughened beds dissipated 7–38% more energy compared with smooth beds. Energy dissipation per unit length of spillway and relative dissipation to upstream energy increased by 60% and 78%, respectively. Larger roughness elements enhanced turbulence and shear stresses, while steeper slopes and higher discharges reduced effectiveness. A threshold behavior was observed, indicating that roughness elements below a critical size contributed little to energy loss. Regression analysis produced predictive equations with high accuracy (R² up to 0.95), providing reliable tools for estimating energy dissipation in roughened chutes. The findings highlight the importance of selecting appropriate roughness dimensions and chute slopes to optimize hydraulic efficiency and reduce construction costs. This research contributes to improved design of energy dissipation systems in spillways and chute structures.