Experimental investigation of flow intensity effects on hydraulic resistance over discrete engineered roughness in supercritical open channels

ABSTRACT This study investigates the influence of flow intensity on drag characteristics in a supercritical open-channel flow featuring discrete wart-type roughness elements mounted along the channel wall. Experiments were conducted in a recirculating Plexiglas flume at 2% bed slope, with velocity measurements acquired using a Kenek VP3000 electromagnetic current meter across five longitudinal stations. Dimensional analysis reduced the governing parameter space to a functional dependence of the bed friction coefficient on the Froude number alone, following the elimination of Reynolds and Weber number effects under fully turbulent supercritical conditions. Results demonstrate that bed shear force increases monotonically with the Froude number, rising by approximately 19.6% as Fr advances from 1.680 to 2.038, consistent with inertia-dominated momentum transfer. In contrast, the bed friction coefficient exhibits remarkable stability, varying by less than 3.6% across the same range, indicating that resistance characteristics are governed primarily by element geometry rather than flow velocity. These findings provide quantitative experimental evidence that bed friction coefficient invariance persists under asymmetric, partially roughened boundary conditions, offering practical implications for hydraulic design and resistance modeling in engineered and natural channels.