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

一些学者指出了沙质潮滩地下水流动对前滨边坡稳定性和变形过程的重要性。然而，对冲积区输沙率影响的定量描述还没有得到充分的研究。本文通过分析坡面上和多孔介质内部的流场来评价入渗和出渗对泥沙输移的影响。第一年，用扩展的Dicker非恒定渗流理论分析了砂基中的瞬变渗流，模拟了启动波的渗流过程。用动边界处理的数值模型来描述启动波的运动。结果表明，砂质边坡上的波速受渗流的影响很小，即使施加的压力变化很不稳定，入渗速度也不会表现出非稳定的特性。其次，讨论了泥沙颗粒在启动波和渗流两种水流运动下的运动。推导了考虑入渗和出渗影响的临界牵引力和输沙率的解析表达式。第二年，为了提高速度场的精度，采用了解析的非线性波动理论。利用所获得的波动，基于运动方程跟踪放置在斜坡上的球形质点的运动。讨论了泥沙运动特征和泥沙输沙率。

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.