Complex free-surface flows in the vicinity of an obstacle placed on the floor of a channel to generate a surface wave has been studied experimentally and numerically. The numerical method examined is the simplified MAC method of Hirt & Nichol with the volume of fraction(VOF) method of treating the free surface. This calculation method used with a third-order upwind differencing scheme gives results that agree very well with experiments for not too large waves with relatively small velocities. The experiments show that as the flow volume and the velocity increase, the disturbances appear on the free surface with significant air entrainment. The present calculation method, although does not reproduce the detailes of the experiment exactly, shows appearance similar disturbances.

To understand the detailed processes of rainfall infiltration into 2-layered ground, the lab-scale experiments were conducted by using sand and decomposed granite. And the two phase flow and the saturated-unsaturated seepage analysis were carried out to reproduce the experiments, and compared results of these analysis methods. In the experiments, when the surface layer has low permeability, pore pressure increased as soon as the rainfall was started. On the other hand, in the case of reverse layer system, pore pressure increased after the wetting front reached the sensors. It seemed to be no influence of pore air, but the two phase flow analysis reproduced the experimental results better and the results of the analysis showed the increasing of the pore air pressure obviously.

Flow structure and the criteria for formation of intake vortices have been studied experimentally and numerically. A particular emphasis is placed on the influence of the inflow property such as shear and nonuniformity on the flow pattern and formation of intake vortex . In the experiment, it is verified that when the inflow contains vorticity or circulation, an intake ' vortex can form . Computational study is made to see if the highly three-dimensional and vortical flow in the intake bay can be predicted. Although there still is a limitation as to the grid density that can be handled with present-day work stations, and intense line vortex cannot be predicted, weak recirculation of the flow can be aptly predicted by the present method.

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