Bed Rugosity Determination for Critical Velocity Profile in Cohesionless Sediment Beds

Abstract: Experimental results performed in a glass rectangular channel, with a loose bed in the central part where simulations of initiation of non-cohesive sediment motion for different grain sizes were developed, are presented in this paper. The optical technique of Particle Tracking Velocimetry (PTV) was used with the main goal of determination of critical velocity profiles for sediment initiation of motion. The parameter ks known as bed rugosity is difficult to obtain. For conditions near bed motion initiation velocity profiles were obtained and they allowed us to define a value of ks related to a representative grain size of the bed. It was shown that this bed rugosity is greater than the mean size of the bed, and the relative bed rugosity decreases when mean diameter increases. This finding should be taken into account when applying the different formulas for critical velocity in the scientific literature.