Effects of Boulder Arrangement on Flow Resistance Due to Macro-Scale Bed Roughness

Flow resistance in gravel-bed channels is not only affected by the shape and size of roughness elements, but also their arrangement on channel bed surface (position to flow streamlines, spacing between protrusion from bed). Many investigations proved that open can be obtained integrating power velocity profile. For a macro-scale condition, this study aims investigate effect different boulder arrangements resistance. First, for each arrangement, equation relating Γ function profile, Froude number, slope was calibrated using available measurements performed flume covered pebbles with “Random”, “Transversal stripe”, “Longitudinal stripe” arrangements. experimental datasets were divided consider effects concentration Ch. Moreover, relationship “Random” element lower than 48% tested literature coarse elements randomly arranged. Finally, law investigated imposing threshold. The results demonstrated (i) Darcy–Weisbach friction factor accurately estimated proposed equation, (ii) increases Ch low values (<48%) concentration, while it does depend high concentrations (≥48%), (iii) more evident concentrations.