|The present study proposes a method to simulate the behavior of driftwood based on a convection-diffusion equation with erosion / deposition terms as well as with an accumulation term. The erosion and deposition rate of driftwood is formulated by using its similarity to the erosion and deposition of bed sediment; the rate is treated as the function of relative water depth and size of driftwood. The functional form illustrates that driftwood entrainment does not occur at depths any shallower than the threshold water depth, and the driftwood deposition does not occur at depths any deeper than the threshold water depth. The convection-diffusion equation of driftwood is solved numerically using equations for a depth averaged 2-D flow and a 2-D sediment transport process. The numerical results show that driftwood deposition and trap are simulated well, and that the flood flow is affected seriously by driftwood accumulation.