A numerical simulation model has been developed for computing the behavior of drift wood and its dam up process due to jamming between and/or in front of the houses when drift wood debouches into horizontally two-dimensional flow field. The calculation is accomplished by an interacting combination of Eulerian fluid and Lagragian drift wood equations, in which a turbulent diffusivity and rotational angular velocity of the drift wood are stochastically given. The positions, rotational angles in a group of drift wood, and time change of the number of dammed up drift wood in the experiments are well explained by the calculation.