The kinetic characteristics of the non-uniform bed load and its responses to the turbulence near the bed

Mingxiao Liu

Wednesday 1 july 2015

11:00 - 11:15h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 9A. Sediment - Transport

In order to study the impacts of the interactions between the coarse and fine particles on the non-uniform sediment transport, the real time simultaneous monitoring of the sediment delivery amount, grain composition and the fluctuating velocity near bed have been realized, based on the technologies of instantaneous bed load acquisition, image identification and Doppler velocity measurement, etc. For the non-uniform sediment with bimodal pattern, several sets of experiments on the bed load transport were conducted in water flume. The analysis indicated that the random fluctuation of the transport quantity of the bed load and the selection proportions of the coarse particles have some response relations with the velocity fluctuation caused by the turbulence burst near the bed. The fine particles in the bed load mostly kept on transporting during the process of experiment, however, the transport of the coarse particles were always paroxysmal, abiding by three modes: priming, triggering and breaking. If the differential of diameter between coarse and fine particles is obvious, the coarse particles transport may have an supernormal performance, which is contributed by the exciting, colliding and unbinding effects of the fine particles to the coarse particles. The structure of the particles composition plays an important role in the enforcement of the three models. It restricts the effect intensity of exciting and breaking of the fine particles on the coarse particles, which brings about a consequence that the transport rates of the total, fine and coarse show different variation trends respectively with the changing of the bed material composition. Such cognition may give some significance inspiration for the improvement of non-uniform sediment transport theory.