Study on sediment transport mechanism in swash zone considering in- and ex-filtration effects of a foreshore sandy beach

一些学者指出了砂质潮滩地下水流动对前滩边坡稳定性和变形过程的重要性。然而，对冲积带输沙速率影响的定量描述还没有得到充分的研究。本研究通过分析坡面和多孔介质内部的流场，评价了入滤和出滤对泥沙输运的影响。本文首先通过对Dicker非定常渗流理论的扩展，分析了模拟升压波渗流过程的砂基瞬态入渗流。采用了移动边界处理的数值模型来描述助跑波的运动。结果表明，沙质边坡上的波速受渗流的影响较小，入渗速度不表现出非定常特性，尽管施加的压力变化是非定常的。其次，讨论了泥沙颗粒在上升波和渗流作用下的运动。导出了临界牵引力和输沙速率的解析表达式，包括滤入和滤出效应。在第二年，为了提高速度场的精度，采用了解析型非线性波动理论。利用获得的波动，根据运动方程跟踪放置在斜坡上的球形粒子的运动。讨论了泥沙运动的特征和由此产生的输沙率。

Several workers have pointed out the importance of the groundwater flow in a sandy tidal beach on stability and deformation processes of the foreshore slope. The quantitative descriptions of the effects on sediment transport rates in swash zone, however, have not been sufficiently studied. The present study has evaluated the in- and ex-filtration effects on the sediment transport by analyzing the flow fields both for on a slope and inside the porous medium.In the first year, a transient infiltration flow into a sand basement, which simulates percolation process of run-up waves, has been analyzed by expanding Dicker's unsteady seepage flow theory. For a description on the run-up wave motion, a numerical model with moving boundary treatment has been used. As a result, the wave velocities on a sandy slope are little affected by the seepage flow, and the infiltration velocities do not show unsteady properties even though the imposed pressure variations are highly unsteady. Next, motions of a sediment particle under both flow motions by run-up waves and by seepage flows are discussed. Analytical expressions on the critical tractive force and sediment transport rate including in- and ex-filtration effects have been derived.In the second year, an analytical non-linear wave theory has been adopted in order to improve accuracy on the velocity field compared to the first year. Using obtained wave motions, a spherical particle motion placed on a slope is traced based on the equation of motion. The characteristics of the sediment motions and resultant sediment transport rate have been discussed.