ABSTRACT
This study conducted the flume experiments and the numerical simulations to consider driftwood motions on movable channel bed. Diverse sand bars including an alternating bar and a mid-channel bar were considered. As for the computation, we used the 2D (two-dimensional) shallow water flow model, called Nays2DH of the iRIC software to simulate the flow phase. Nays2DH is a Eulerian model to calculate the water flow. We coupled a Lagrangian type driftwood model, which expresses the driftwood as connected spherical shaped particles. We considered the root wad effect by using a larger diameter for a particle at a head of driftwood. The anisotropic bed friction for wood motion was considered in the sliding/rolling motions dependent on the directions in trunkwise, streamwise and moving pass. The calculation for the changeable draft at each particle and projection area was considered by an angle between trunkwise and flow directions. We modified the model of wood collision acting on jam formation to be reproduced well in the simulations, and those results were compared. The results in the simulations and experiments showed that the change of the time interval of wood supply is responsible for the pattern of wood collision and the number of stored wood pieces. In addition, the refined model on wood collision showed more similar stored wood patterns than the previous collision model.
