The prevention of suspended soil and eutrophic component runoff from an upland field has become important for water quality conservation. The purpose of this study was to find out inflow, outflow, and trap of suspended soil and eutrophic component in a sedimentation tank. For the purpose of this study, field observation was made using a real sedimentation tank in a small upland watershed to analyze water quality-concentration of suspended soil, nitrogen, and phosphorus-at the inlet and the outlet points of the sedimentation tank during a rainfall event. As a result, it was found that trap efficiency of suspended soil, total nitrogen, and total phosphorus was 70%, 87%, and 57%, respectively. High correlation between suspended soil and particulated eutrophic component was found to have contributed to the trap of eutrophic component. The research results indicate that a part of suspended soil, nitrogen, and phosphorus was trapped with the sedimentation tank.

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When partially saturated soils swell and their water content increases, its soil structures supported by negative pressure are destroyed causing volume compression (collapse) and/or volume expansion (swelling). On the other hand, though compaction controls of embankment are managed by D-value (=ρ_d/ρ_<dmax>), the relation among volume change due to submergence, D-value, and consolidation pressure for the dynamically compacted soil is not examined sufficiently. In this study, the volume change was tested with Fujinomori clay, decomposed granite soil and Daisen loam by using oedometers; and the effect of D-value, consolidation pressure and water content on the volume change was verified.

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We have developed the "infiltration trench" to prevent reddish soil runoff from upland fields. The infiltration trench is set up at the lower end of the slope and filled with wood chips. On the slope, the surface runoff water with suspended soil flows into the infiltration trench and filters through the soil. In this study, effects of the infiltration trench on the prevention of surface water and suspended sediment runoff was examined. The experiment was conducted under natural rainfall condition using two slopes (2.0-m width×12.0-m length) during 2007. One is the experimental slope with infiltration trench (0.6-m width×2.0-m length×1.0-m depth) and another is the control slope without infiltration trench. The following results were obtained; i) surface runoff water on the experimental slope was 90% less than that on the control slope in case of precipitation less than 50mm, and 60% less in case of precipitation of 200mm; ii) suspended soil runoff on the experimental slope was 80% less than that on the control slope in case of precipitation of 200mm; iii) although surface runoff water on the experimental slope was 50% less than that on the control slope, suspended sediment runoff on the experimental slope was 80% less than that on the control slope; iv) the permeability of the trench was not reduced during the seven months of research; v) correlation between the permeability at the start of a rainfall event and the amount of precipitation in the seven days before the rainfall event was high. From these results, the high efficiency of the infiltration trench for the prevention of reddish soil runoff was confirmed.

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An on-site experiment concerning pressure reduction in a pipeline system was conducted using a test pipeline located in Ohno Mountain in Kagoshima Prefecture. A conventional and a new type of automatic control valve were installed in the pipeline independently and in combination with a safety valve; and a comparative study of the pressure control behavior was conducted under four experimental conditions. The results were as follows: (1) The use of the conventional control valve caused pressures on both of its downstream and upstream sides when the terminal valve was briefly operated, inevitably causing a large increase in pressure which affected the entire system. (2) With the conventional control valve, it was necessary to use the safety valve to block the upsurge of the upstream and downstream pressures; and to control and set the pressure on the downstream side. Therefore, the performance of the pressure-reducing system depends entirely on the safety valve. (3) The new type of control valve is sensitive to increases in downstream-side pressure caused by closing the terminal valve. It fully closes in response to such increases, enabling the suppression of increases in downstream-side pressure. (4) Moreover, the new type of control valve closes quickly when the terminal valve is closed abruptly. This, in turn, causes a pressure increase on the upstream side of the control valve. Thus, it is necessary to have a safety valve fitted on the upstream side of the new type of control valve.

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Abrupt closure of a valve in a pipeline system brings about water hammer that may be harmful to the entire system. A pressure-reducing pipeline system is equipped with an automatic control valve, which can be used together with safety valves. Full-scale hydraulic experiments are conducted in a test pipeline located in Ohno Mountain, Kagoshima Prefecture, in order to investigate effects of different types of safety valves on reducing water hammer. The results were as follows: (1) When the water flow is abruptly stopped by closing a terminal valve in a pressure-reducing pipeline system, the secondary side pressure control mechanism of a conventional control valve may not be able to respond to the transmission speed of the water hammer pressure. In this case, the water hammer pressure invariably reaches the upstream end through the control valve and affects the entire pipeline. (2) By installing a new type of control valve, pressure rise is kept small on both the downstream side of the control valve and the terminal end, and static pressure can be insulated in a stable manner even when the terminal valve is closed for a short period of time. (3) When the closing duration of the terminal valve is short, pressure increment in upstream side of the new control valve becomes large, by transmitting the water hammer pressure that is created by the abrupt closing of the main disc of the control valve. (4) To control the water hammer pressure, both the new and conventional control valves require safety valves to be installed on both the upstream and downstream sides. As a countermeasure of water hammer using a safety valve, upstream safety valve is more important in a system with new control valve, and the downstream one is more important in a system with the conventional control valve. (5) Since the direct-loaded safety valve acts more quickly, it is highly efficient in suppressing the maximum pressure. However, as the valve closing time in the terminal end becomes shorter, the pilot-operated safety valve tends to show high pressure-suppressing capability by providing a high ejection flow volume.

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Although willows are generally believed to expand population through seed dispersal, there have been some incidents in which alternative method for expansion was clearly used. In this study, the authors aimed to understand a "seed-free" method of willows reproduction. Observations of two sample populations suggest that willows may reproduce and establish new populations in unoccupied sites through branch propagation, a clonal reproduction process by rooting of deposited branches. As we examined the environmental factors which allowed the new establishments and the vegetation growth, in those sites where accumulated gravel particles were relatively larger had higher number of individuals produced from deposited branches instead of growing from seed. In addition, large branches may have greater chances of survival which may also be an advantage for healthier growth with this type of reproduction. These results suggest that willows may be able to expand populations by branches floated from upstream.

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