Since most Sabo facilities like check dams and channel works are more or less at the site of natural beauty, planning and design of environmental free facility is coming very important recent years. Under this condition, landscape planning is adopted in many cases especially for the ones at national park. In order to accomplish landscape planning that has the aim of natural landscape conservation, however, consideration on “sensescape” including “smellscape” as well as “soundscape” is needed. In mountatinous area in which Sabo Works are necessary, smellscape is mainly consists of forest fragrance. Hence, to conserve the smellscape is simply conserve or restore the forest around the facilities. On the other hand, to conserved soundscape means design of falling water sound or sound of the flow over them.
In this study, the focus is put on this soundscape, and its basic characteristics is studied here using sound power spectrum analysis. And the results insist that Sabo facilities have less “bland soundscape” than natural falls or torrents which have sound characteristic abounds in high frequency as well as 1/f fluctuation in their power spectrum, whereas stone made Sabo dams have bland sound similar to the natural ones.
Therefore the basic data for soundscape design of Sabo facilities for “bland soundscape” are gained in this study.

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Unsolved effects of soil depth and its non-uniform distribution on rain-induced landslides remain although soil depth is known to affect both the infiltration and the equilibrium forces in the critical shear zone. A series of laboratory experiments by a sloping flume packed a sandy soil placed under a rainfall simulator were conducted to elucidate the effects of soil thickness. Five kinds of soil depths of uniform distribution and two types of nonuniform layers were tested. The rainfall intensity was set at constant (110mm/h) in every experiment to eliminate the effects of rainfall intensity on landslide initiation. Initial soil wetness was also controlled at a constant level. Pore water pressures and the motion of sliding masses were observed.Numerical simulations, which were composed of a slope stability and a seepage model, were also tried. Initiation times of failures resulted in a liner relationship with soil depths in both the laboratory and numerical experiments of uniform soil layers. The penetration velocities of the wetting fronts were observed to be constant in every experiment of uniform soil layers. The saturated area simultaneously appeared over all the bottom boundary of the uniform depth slope. Contrary to this phenomenon, the wetting front reached shallower part at first, and the saturated area also sequentially appeared in the same place of heterogenous soil distributions. Because the velocities of wetting front were always constant as the same as the uniform soil layers, soil depth became essential to the time when the wetting fronts reached the bottom ends. Failures were initiated at the shallower parts of the slope where the saturated areas first appeared in the slope of uniform soil layers. The simulations' results by a limit equilibrium analysis combined with finite seepage model corresponded well to those of the laboratory experiments for the critical times of failure and locations of slip circles. These results show that soil depth and its non-uniformity strongly regulate both initiation times and locations of slope failures.

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In order to estimate the degree of influence of geomorphological factor on the occurrence of failure on mountain slope (hillside landslide) by a rainstorm, slope models with different geomorphological factors are assumed and landslide simulations on each slope model are carried out. This simulation is consists of two physical model: One is quasi-3 dimensional saturated-unsaturated seepage flow analysis, another is slope stability analysis for an infinite-length slope.
The results by these simulations show that soil layer depth, carvature of contour, hillside slope gradient give great influence to the duration from the start of rainfall to the occurrence of hillside landslide, and the ratio of the collapsed area to the catchment area.

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