The vertical infiltration experiments was executed to understand quantitatively the processes of rainfall infiltration, groundwater runoff and ascent of the groundwater level. The transferal model of the storm water in the unsaturated soil was proposed based on the results of the experiments. The transferal conditions of the storm water was simulated by this model. Following matters were confirmed by this study. (1) The groundwater runoff and the suction come up to steady conditions at the sametime. The infiltration proceeds under equilibrium conditions. (2) As the unsaturated zone decreases, the ascent of the groundwater level grows faster. (3) It was shown that this model simulated accurately the results of the experiments. This model can be used as a part when a practical model to predict the occurrence sites of hillside landslides is built.
We have measured the imdact load on a dam when debris flow clash into it and simultaneously observed the behavior of head part of the flow in experiments, that have been performed with glass beads of 5mm in diameter, in an open channel of 7m in length and 150mm in width. When the velocity or debris flow is relatively low, the measured load can be explained as static load due to sediment of debris. When the velocity is relatively high, the measured load is greater than one of dynamic pressure of steady jet flow in same profile. In the case of latter, the measured load agree at each time with the load caused by the flow's momentum variation assessed from the observation. Then, a model has been proposed to evaluate the deformation of the flow and, in the result, load on the dam. In this model, the initial conditions (flow depth, bulk density) are expressed in functional relationships determined from the experiments, and the load can be estimated quantitatively. The profile of flow, the load on the dam, and their variation with time calculated by this model have proven to agree well with those observed or measured in experiments.
The method to determine the interval of the consolidation works built-in the channel work have been suggested in this paper. The consolidation works have the role of a stabilizer for a watercourse at the constructed place. Under a certain hydraulic condition, a water flow itself has a limited length to maintain the straight watercourse. The theory on the plan forms of free meander proposed by authors can calculate this limited length. In case of the rectangular channel, this limited length is l/B=(Φ·π) 2/3(B/h) -1/3 The equation has the same tendency to the investigation on the intervals of the already constructed consolidation works in Japan, on the whole. However, the intervals of the alreaby constructed consolidation works are generally longer than this equation.
Soil erosion is a major environmental problem in Fiji. The steepland topography and highly erosive rainfall contribute to high natural rates of soil erosion. Over the past 30-50 years a substantial area of stoping land has been brought into some farm of agricultural production. The impact of this extension of agriculture and increased logging of rainforests on erosion has been considerable but there is a lack of quantitative information on rates of erosion. The effects of erosion include land degradation and decreased productivity, sediment deposition in rivers with subsequent increase in flooding, and damage to coral reefs by transported sediment. Legislation exists for the control of land use and the encouragement of conservation but it has not been widely applied. Land tenure systems, increasing demands for cash income and the lack of strong political commitment to conservation are contributing to the continuing problem of soil erosion.