Hydraulic performance of an isolated strip roughness with varying heights on flow dynamics in open channels

ABSTRACT This study aims to investigate the effects of single-strip roughness at various heights on flow behavior under subcritical flow conditions. A series of experiments were conducted in a 4-m-long, 0.6-m-wide flume using five different heights of strip roughness elements (7, 9, 11, 13, and 15 cm) at Noshirvani University, Babol, Iran. The results indicate a significant correlation between the strip roughness height and downstream velocity, with average increases in the downstream velocity ranging from 21.39 to 58.28% across varying roughness heights. Moreover, the velocity–shear velocity ratio (u/u*) was found to increase with increasing roughness height, suggesting that roughness plays a crucial role in generating turbulence. The increased velocities downstream for higher roughness elements could have implications for sediment transport, as higher velocities can lead to increased sediment entrainment and transport. However, deceleration upstream may contribute to sediment deposition. Additionally, the study examines the relationship between relative water depth differences upstream and downstream concerning the upstream depth normalized by the strip roughness height. Energy loss coefficients were calculated, revealing that greater upstream flow depths led to a reduction in the relative impact of strip roughness on energy dissipation. These findings demonstrate that increased roughness heights consistently result in greater energy losses.