Parallel sluice gates are crucial components in hydraulic structures, offering cost-effective and operationally flexible solutions for flow control in wide channels. This laboratory investigation examines the effectiveness of different bed roughness configurations—specifically trapezoidal and cubic geometries—in mitigating local scour downstream of parallel sluice gates, a persistent challenge that threatens structural integrity. The study systematically evaluated scour parameters under varying flow conditions and gate configurations, employing both quantitative measurements and qualitative flow visualization techniques. Results demonstrate that trapezoidal roughness elements significantly outperform their cubic counterparts across all measured parameters. Specifically, trapezoidal configurations achieved reductions of 25.3% in Average scour depth, 22% in scour length, 30.5% in cross-sectional area, and 50% in scour volume, compared to modest reductions of 20%, 14.35%, 21.57%, and 34.7% respectively for cubic roughness elements. The flow expansion ratio (𝑒) emerged as a critical parameter, with optimal performance observed at e = 0.56 (two gates open). However, effectiveness significantly decreased at lower expansion ratios (e = 0.283, single gate open) due to asymmetric hydraulic jumps and reverse flow patterns. Analysis of Froude number (Fr) effects revealed that trapezoidal roughness maintains superior performance even under high Froude numbers (Fr > 5) during asymmetric flow conditions, while cubic roughness shows diminished effectiveness. These findings provide valuable insights for optimizing hydraulic structure design, emphasizing the superiority of trapezoidal bed roughness configurations for enhanced scour protection and system stability in irrigation and drainage applications.
Akbari et al. (Thu,) studied this question.