Bed Sediment Entrainment Function Based on Kinetic Theory

Bed sediment entrainment function is derived based on kinetic theory. The entrainment rate is expressed as an upward flux by integrating the particle velocity over all possible upward motions. The possibility of upward motion is determined by a sediment particle velocity distribution function, which is obtained by solving the Boltzmann equation instead of using a prior assumed distribution. External forces and turbulence intensity of the flow are shown to exert significant influences on the velocity distribution function and, in turn, the entrainment rate. Comparisons between available laboratory data and the entrainment function show that the calculated entrainment rates agree well with the observations. Applications of the entrainment function to the specification of the bottom boundary condition for convection-diffusion equation of suspended load are also presented, which show that the calculated concentration profiles are in good agreement with observations. The study also suggests that kinetic theory is a promising analytical approach for the study of sediment motion near a riverbed.