The numerical model was developed to calculate diffusive dissolved-oxygen (DO) transfer rate at the rough sediment surface, considering hydraulic conditions in the water and biochemical reactions in the sediment. Calculation results showed a characteristic tendency of the relationship between DO transfer rate and roughness Reynolds number (Re*). Namely, non-dimensionalized DO transfer rate (Stanton
number, St) had a maximum value in the transitional region of surface roughness, in which the mass flux was three-four times larger than that at the smooth surface. In the completely rough region (Re* > 100), St decreased gradually as Re* increases, which was due to the effects of viscous ponding in the cavity between the
roughness elements. Although this tendency was qualitatively the same as those of existing papers in the field of heat and mass transfer engineering, quantitative estimations of St values required consideration of biochemical reactions in the sediment and quantification of DO concentration at the sediment surface. The
reproducibility of the experimental results by the numerical analysis was significantly improved by quantitative formulation of the flushing frequency of water fragment in the cavity between roughness elements and considering non-steady variations in
diffusive transfer rate due to step changes in DO concentration in the flushed region.