ABSTRACT
Streamwise ridges in open-channel flows induce secondary currents which alter the flow structure relative to the scenario with no ridges on the bed. We investigate the effects of ridge spacing, cross-section, surface roughness, and relative submergence on the hydraulic resistance in open-channel flows. Our results show that at small ridge spacing, the hydraulic resistance is reduced by up to 32% relative to a prediction based on the divided channel method. As the ridge spacing increased, the hydraulic resistance is amplified by up to 35% before reducing again and matching that of a case with no ridges. For comparable ridge spacings and flow depths, the hydraulic resistance over square ridges was less than that over triangular ridges. Increasing the ridge surface roughness increased the hydraulic resistance relative to the smooth ridge scenarios. Interestingly, the streamwise ridges were observed to suppress the water surface fluctuations relative to a case with no ridges.
