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

许多学者指出了桑迪潮汐海滩中地下水流对前滨边坡稳定和变形过程的重要性。然而，对冲刷带输沙率影响的定量描述还没有得到充分的研究。本文通过对坡面和多孔介质内部流场的分析，研究了入渗和出渗对泥沙输移的影响，并在第一年中，利用扩展的Dicker非稳定渗流理论，模拟了波浪爬高时的入渗过程，分析了入渗和出渗对泥沙输移的影响。对于爬高波运动的描述，采用了动边界处理的数值模型。结果表明，桑迪边坡上的波速受渗流的影响很小，即使施加的压力变化是高度不稳定的，渗透速度也没有表现出不稳定的特性。其次，讨论了由起动波引起的水流运动和由渗流引起的水流运动下泥沙颗粒的运动。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，第二年采用了解析的非线性波浪理论，以提高流速场的精度。利用所得到的波动，基于运动方程追踪放置在斜坡上的球形质点运动。讨论了泥沙运动和输沙率的特点。

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.