Impact of bed roughness configurations on flow dynamics and hydraulic resistance in open-channel flows

Bed roughness significantly influences open-channel flow dynamics, affecting velocity profiles, energy distribution, and hydraulic resistance in natural and engineered rivers. This study investigates the effects of four bed roughness configurations, smooth forward (S-FW), offset roughness (R-OFF), and forward-oriented roughness at 60° (R-FW60) and 90° (R-FW90), on flow characteristics in an experimental flume. Velocity measurements, energy calculations, spectral analysis, and statistical tests (ANOVA) were employed to quantify the impact of roughness on mean flow velocity, Chezy coefficient (C), energy dissipation, and turbulence. Results reveal that S-FW yields the highest mean velocity (1.1587 m/s) and C (51.62), indicating minimal resistance, while R-FW90 produces the lowest mean velocity (0.4422 m/s) and C (18.51), reflecting significant drag and turbulence. Energy profiles show pronounced dissipation near rougher beds, with R-FW90 exhibiting the lowest near-bed energy due to vortex shedding. Spectral analysis highlights amplified low-frequency velocity fluctuations in rougher configurations, particularly R-FW90. Linear mixed-effects modeling and post-hoc tests confirms significant velocity differences across configurations (p < 0.05). These findings offer insights for optimizing channel design, managing erosion, and enhancing flow efficiency in hydraulic engineering applications.