Hillside landslides are triggered by increase of soil moisture and ground-water level during heavy rain and can be understood to be the transient process of the surface soil layer on the mountain slope. In this study, the vertical infiltration experiments were executed using a large scale undisturbed soil sample to understand quantitatively the process of rainfall infiltration and ground-water run-off. The vertical distribution of the saturated-unsaturated hydraulic properties of forest soils was determined based on the results of the experi-ments. It was found that the hydraulic properties of forest soils vary for difference of depth where soils exist. A two-dimensional saturated-unsaturated infiltration analysis and slope stability analysis were executed using these hydraulic properties. It was confirmed by these analysis that values of the hydraulic properties of forest soils, the hydraulic conductivity, K, -pressure head, ψ, relationship and the volumetric water content, θ, -ψ relationship of forest soils, influence sensitively not only to movement of ground-water level on mountain slopes but also to their stability.

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There are many landslide and landfalls in Nepal due to the geological, topographycal, climatological and human activities reasons. The authors have carried out the investigations to clarify the relationship between landslides, landfalls and geological, distributional characters. In addition, prevention methods of these natural hazards are surveyed with twenty (20) of roads from January to June, 1992. As a results of the survey, following items are confirmed. 1) Geological distribution of landslides and landfalls in Nepal are mainly occurring at Siwalik (Sw), Nuwakot (Nw) and Kathmandu (Ka) group. 2) Landslide and landfall in Nepal are categorized largely into five (5) types (A, B, C, D, E) . 3) Installation of Gabion Retaining Wall and Concrete Retaining Wall are most popular prevention methods in Nepal. However, these average of actual prevention ratio for each roads are not so effective due to shortage of the national budget.

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The authors discussed the research history of sediment production, storage and transport in Japan. The results are as follows;
1) There are a number of long-term geomorphological research projects for understanding sediment movement in river basins in the United States. In Japan, however, most studies focus on short-term episodic events as a means of protecting residential areas from natural disasters.
2) Based on a hierarchical concept of scientific stage (phenomenalization, substantialization, and essential' ization), laboratory work to understand the mechanism of erosion processes is close to the stage of essential-ization, while field work to clarify dynamic processes in a river basin is still at the stage of phenomenaliza-tion.
3) Direct application of theories developed in the laboratory to basin-scale field work may lead to misunderstanding of actual phenomena. Long-term monitoring systems are needed to substantiate phenom-ena in the field. The authors believe that geomorphological research of mountain streams will play an important role to develop basin-scale theories, and give us new perspectives for understanding sediment movement in a river basin.

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In rivers where frequent sediment discharge occurs, it is not easy to determine the appropriate type of fishway to be attached downward to a sabo's low drop structure: groundsills. It has been reported that some types of fishways are liable to be blocked by discharged sediment and hence dry up. Slit fishways were proposed to ensure a path for upstream bound fish, some of which are already in use. However, the problem with slit fishways is that water runs so swiftly that fish cannot travel upstream to reach to the drop structure. The effect of roughness elements for use in a slit fishway to decelerate the running water was tested using an experimental flume.
Through experiments, the effective shape of roughness element was found, and the optimum layout of the roughness elements in a slit fishway was determined.

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