Abstract
Mass transfer mechanism in porous riverbed was investigated using chloride tracer method and a hotfilm anemometer in two experimental open channels which have porous media composed of 1.9cm and 4.08cm diameter ceramic ball respectively. Water depth to particle diameter ratio was about 1.7 and surface flow mean velocity was 3.9cm/s-42cm/s.
Flow over porous riverbed was found to have very high turbulent intensity near porous boundary, which was about 20% of surface flow mean velocity in all hydraulic conditions. Values of vertical-direction diffusion coefficient in porous media increased with increasing surface flow mean velocity, and were found to have the distribution pattern in porous media which shows linear decrease with depth. Observed values of diffusion coefficient near porous boundary satisfied the theoretical relationship between diffusion coefficient and turbulent intensity.
