Abstract
It is well known that sediments and seeds are deposited between roughness elements, which induces the development of thick growth of trees. So, it is important to reveal turbulence structure and its effect on capturing process of particles between roughness elements. In the present study, two kinds of laboratory flume experiments were conducted using hemisphere roughness elements. First, we measured the flow velocity within roughness layer using PIV. The roughness elements were made of hydrogel. The technique enabled us to reveal the mean-flow and turbulence within roughness layer. Then, river plant seeds are added to the flow and we tracked the motion of the seeds over the rough bed to investigate the mechanism that seeds are trapped between the roughness elements. The PIV results indicated that the vertical velocity is mostly negative between the roughness elements. We examined the effect of coherent motion on the mechanism that seeds emerge from the rough bed. The results revealed that in rough bed flow, the bursting event responsible for particle entrainment is sweep.
