Habitat structure is thought to play an important role in the colonization of benthic assemblages.  Previous studies have suggested that more convex substrates tend to have higher species richness than less convex ones due to modified fine-flow patterns and increased benthic colonization.  However, the characteristics of fine flow patterns and their importance for benthic assemblages are less clearly understood.  The present study attempted to investigate the combined effects of substrate structure and velocity on benthic colonization.  The colonization rates of benthic animals were measured with a range of experimental substrate structures and velocity levels.  Circular flows in concavities were more common at higher velocities and larger opening widths.  Three types of benthic animals settled more on substrates with wider openings between convexities.  Caddisfly larvae showed a unimodal pattern of colonization with a peak at the velocity regime of 15-30cm/s.  Thus, the combination of substrate structure and velocity appears to induce micro flow variation that in turn would control the structure of benthos communities.