Experimental Analysis of Hydraulic Jump Roller Length in Compound Rectangular Channels with Uniform Bed Roughness under Zero Slope Conditions

This study investigates the behavior of hydraulic jumps in compound rectangular channels with uniformly roughened beds, a configuration common in natural and engineered open-channel systems but underexplored in existing literature. While traditional research has focused on smooth or partially rough beds in prismatic channels, this work addresses the gap by experimentally analyzing roller length variations in channels featuring both major and minor flow sections roughened with consistent plastic elements. Conducted in a horizontal, closed-circuit flume, the experiments varied bed roughness (ε = 0–12 mm) and Froude numbers (F₁ ≈ 2–9) to replicate realistic flow conditions. Dimensionless parameters were used to derive empirical correlations between roller length and relative bed roughness, showing a consistent inverse relationship. Statistical regression confirmed strong linear trends between relative roughness and derived model coefficients for both bed types, with high determination coefficients (R² > 0.97). The findings demonstrate that full-bed roughness significantly enhances energy dissipation by reducing roller length, offering practical design implications for more compact and efficient stilling basins in compound channels.