Study on Sediment Transport Process on Permeable Bed

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In order to predict the alluvial phenomenon in the natural rivers with the permeable boundaries and seepage flow, it is necessary to establish a model to describe non-equilibrium sediment transport process on a permeable bed, of which constituent elements are sediment pick-up rate and step length. In this study, it is intended to propose a reasonable formula to estimate the pick-up rate of sand particles on a permeable bed with steady transpiration velocity and to verify the derived formula experimentally. As for the step length, firstly the experimental research is intended, and based on its information, a reasonable way of estimating the step length is proposed.Incipient motion and transport of a sand particle affected by transpiration velocity has been theoretically analyzed. Meanwhile, a devised experiment has been carried out in laboratory flume to obtain the experimental data in good accuracy, by making use of a video film analyzing system. The obtained results of this study will … More be available for analyses of various kinds of fluvial process in rivers.Next, in order to make the above mentioned model exact the flow structure has been examined. When the seepage flow in the highly permeable porous medium is accompanied with the flow over it, the interaction between surface flow and seepage flow cannot be neglected. In case of high permeability, Darcy law for seepage flow is not necessarily applicable because of the predominance of non-linearity term. This non-linearity makes the propagation of the pressure fluctuation inherent to the free surface flow into the inside of the porous medium and the subsequent fluctuation of seepage flow velocity anisotropic, and the subsequent appearance of apparent Reynolds stress plays a role of appreciable momentum exchange. Namely seepage flow is affected by the drag of the faster free usrface flow. In this part of this study. a physical modelling of this mechanism is formulated to evaluate the induced seepage velocity, and the effect on the sediment transport process is examined. The theoretical results are verified by flume experiments. Less