Effect of surface roughness on mass transfer at the sediment-water interface

A general model which predicts oxygen flux at the sediment-water interface is proposed. This theoretical model is divided into two parts: one is for mass transfer in the boundary layer based on Dade (1993), the other oxygen kinetics model in the sediment developed by Nakamura and Stefan (1994). According to this model, oxygen flux is described as a function of DO concentration in the bulk water, the shear velocity, Schmidt number, equivalent sand roughness, volumetric consumption rate of oxygen in the sediment, and apparent diffusion coefficient. Experiments were performed with a rectangular, closed flume in which flow velocity can be controlled. Rectangular roughness elements were put on this flume floor, to investigate the effect of surface roughness. Both theoretical predictions and experimental results showed that oxygen flux at the sediment-water interface had a maximum value at a buffer region between smooth and complete rough surfaces.