Laser Doppler anemometry (LDA) measurements in the fully developed turbulent flow through a one-sided rib-roughened square channel with a rib-height-to-channel-height ratio of k / H = 0.0667 and a rib-pitch-to-rib-height ratio of p / k = 9 were carried out at Reynolds numbers (based on the channel height H and the mean bulk velocity u B ) of Re H = 5.0 · 10 4 and 1.0 · 10 5 . Mean velocities, Reynolds normal, and shear stresses were determined. The first- and second-order statistical moments of the velocity differed slightly between both Reynolds numbers when normalized by the bulk velocity and the channel height. Deviations were attributed to a minor elongation increase in the large recirculation region behind the rib with increasing Reynolds numbers. The crucial role of turbulent diffusion was reflected in the non-coincidence of the maximum primary mean shear and the Reynolds normal stress as well as outward drifts of the Reynolds stress peaks along the rib crest. Turbulent diffusion contributed significantly to the turbulence kinetic energy ( TKE ) budget near the rib crest and within the separated shear layer, while mean convection made a remarkable contribution only at the rib leading edge. The detailed first- and second-order moments provide a basis for the validation of computational methods and turbulence models. Graphic abstract