Water quality of underground dams that people on Miyako Island in Okinawa have been using as drinking water reaches the limit value of 300mgL^-1, which is the national standard decided as a hard water quality. The pellet (a grain of calcium carbonate) is produced at about 4.8t per day in the process of decreasing the hard water underground on the island; equivalent to 1, 750t a year. This pellet is a porous material and has not a little effect on air and water cleaning. A basic experiment was conducted to control the red soil run-off, which is a big problem in Okinawa. New experimental equipment which is able to get arbitrary permeability by inserting the pellet produced on the island inside a pipe as an absorption material was developed. The experiments are done by changing the thickness of the pellet and velocity of permeability under pouring 1, 500 mgL^-1 turbid water including lower 74μm particles of red soil into a transparent cylinder pipe 10 cm in diameter and 30, 40, 50 cm in height. As a result of the experiments, it was proved that the level of control of the red soil run-off is increased when the velocity of permeability is slow (under 1.0×10^-2 cm·s^-1) and the thickness of the pellet in the cylinder pipe is increased (not less than 50 cm).

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This study dealt with the changes in soil and nutrient losses with selective erosion. Slope model experiments were conducted under the artificial rainfall simulator. The soils were filled in plots of 8 degrees and compacted with different dry density. Two types of simulated rainfall were supplied in erosion experiments; one is for 240 minutes under the intensity of around 25mm/h, the other for 120 minutes under the intensity of around 60mm/h. Surface runoff, soil loss, total nitrogen and phosphorus in suspension and supernatant, particle size distribution of soils lost were measured.
In this study, it was observed that the mean particle diameter (D₅₀) increased with time in selective erosion process. On the basis of the calculation of ER (enrichment ratio) and the analysis of soil particle size distribution, it became clear that the nutrient concentration in lost soils decreased with the increase in the mean particle diameter (D₅₀). From these results; it became clear that the nitrogen and phosphorus losses accompanied with soil erosion were strongly influenced by ER and particle size distribution of soils lost.

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In the paddy field with gravel and sand subsoil that was low groundwater level, the plane changes in concentrations of oxygen and carbon dioxide were investigated over 2 years. The soil air was sampled from the subsoil in about 50cm depth at 1, 5, 10 and 15m from the levee to the center. Those points situated one line and three lines were investigated in this paddy field.
Following results were obtained. Those oxygen concentrations at each point gradually decreased in irrigation period and the lowest concentration were observed in early September. In non-irrigation period, those concentrations increased, and eventually reached the atomospheric level. On the other hand, the carbon dioxide concentrations in the subsoil increased gradually in irrigation period and the highest concentration were observed in early September. In non-irrigation period, those concentrations decreased. This tendency of changes in carbon dioxide was in inverse relation to that in oxygen. These annual changes in concentrations of two parameters were recognized. As the distance from the levee increased, the oxygen concentration tend to be lower and those carbon dioxide concentrations higher. The total concentrations of oxygen and carbon dioxide became nearly equal to 21% at each sampling point.

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High-swelling montmorillonite shows abnormally large viscosity in comparison with low-swelling kaolinite, but the mechanism for causing such difference has not been clarified. The viscosity of dilute suspension of montmorillonite and kaolinite was measured precisely by using an Ostwald viscometer, and the effect of mineral species on the viscosity was discussed.
The limiting viscosity [η], which is a hydrodynamic interaction between particle and solvent, reflected the effectof the shapeof the particle;in addition, the change in [η] with salt concentration was dependent only on the thickness of the diffuse double layer, regardless of the differences in the electric charges of the clay minerals. The hydrodynamic interaction caused by the interparticles collision was discussed by using the Huggins's coefficient, k. According to Einstein's and Batchelor's viscosity formula, the k of the rigid body-sphere particle was roughly equal to 1, as was k of the clay minerals. This result seems to be valid for kaolinite, since the particles are thick and firm. However, behavior of montmorillonite particles, which has a sheet-like shape and a flexible structure, was also close to that of the rigid body particle. Furthermore, because increment of viscosity caused by the interparticles collision is almost equal to the square of the limiting viscosity, the hydrodynamic interaction is dependent only on the shape of the particle, and not affected by type of clay minerals.

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Bioventing, a popular method of vadose-zone remediation, is the technology where air or O₂ gas is put into the site contaminated by volatile organic compound (VOC), activates indigenous microorganisms, and promotes biodegradation. Various reports about bioventing applied to sand or sandy soil have been published, while few reports on bioventing were published for silty and clayey soils. The object of this study is to reveal the ability of pollutant removal in Japanese volcanic ash soil whose texture is silt loam. Pollutant removal ratios, total germ numbers and changes of O₂ and CO₂ concentrations were measured through batch test, and distributions of pollutant removal ratios and total germ numbers through column experiment.
There were almost the same microorganisms per lg dry soil in the samples of volcanic ash soil as in those of sand, pollutant removal ratios in volcanic ash soil was lower than those in sand because of the activity of microorganisms that we could know from the changes of O₂ and CO₂ concentrations. In the column experiment, more pollutant was removed at the inlet for air than at the outlet

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Micrometeorological features are significantly different among coast, plateau and basin areas in Higashimatsuura Peninsula, Saga, Japan, due to geophysical complexity. It is important to know the emerging time of the lowest air temperature to avoid frost hazard of crops. To the end, we investigated the characteristics of nocturnal air temperature in the peninsula basin in fall-winter season based on the data measured at different observation sites and at the fixed meteorological stations. The data analyses showed the lowest air temperature occurs before and after the midnight as well as early in the morning. It was demonstrated that the occurrence around midnight relates with the abrupt rise in air temperature after its reduction. The abrupt rise is the special phenomenon in the basin, and may be caused by the warm wind blow from the coast. Furthermore, the observation also clarified that the wind blow induces higher air temperature in the basin than in the upland.

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In this study, the three-dimensional stability analysis procedure, in which the residual factor was incorporated, was proposed.
The stability analysis for an application of the peak, fully softened or residual strengths obtained from the shear was pointed out that the factor of safety was overestimated or underestimated and might not be appropriate for the actual condition of landslides. In this analysis procedure, the average shear strength parameter acting along the slip surface was calculated and was verified to be smaller than the parameter calculated by the two-dimensional analysis, then each domain of both the peak and residual strengths mobilized at the slide could be expressed clearly on the whole slip surface area. This procedure will be helpful in effective control works for landslide.

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During drying process, soil water in liquid phase remains in the form of independent pendular ring at the contact point of soil particles. At this water content (film stage), water is in vapor, liquid and semi-solid phase. Semi-solid phased water adsorbs on the soil surface as film, and not able to move by pressure change. As far as continuous body, liquid phase water transmits pressure, and moves conform to Darcy's law. The other side, it is still not clear that the pressure transition and liquid water movement of pendular ring. Because most studies, which focused on unsaturated soil water movement, have been discussed energy state of water without proper physical analysis of the water phase. In this study, we measured the time series of water pressure and the diameter of pendular ring under the condition of various water levels in glass beads (diameter=24mm) media. Consequently, pendular ring in the film stage, 1) could not transmit pressure each other, 2) could not move by the change of water level, 3) decreased by the vapor diffusion, 4) could not represent the pressure value at the inspection plane, 5) does move with phase transition.

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The storage water suspended in a sedimentation tank for several days can be seen very often in the Kunigami Maaji area. These phenomena occur in cases where the effluence of muddy water from field is contaminated by chemical fertilizers, which makes it more difficult to remove the sediment of fine soil particles and exasperates the pollution of river and sea areas. In order to demonstrate the influence of chemical fertilizer extended to the long-term suspension phenomena, this research was conducted for the analysis of water-stable aggregates; testing of the settlement of muddy water contaminated and uncontaminated by chemical fertilizer; and for the analysis of the particle sizes of suspended soil. As a result, it was clarified that chemical fertilizers have the dispersion effect and the flocculation settling inhibitory effect, which become the reasons of long-term suspension. It was also clarified that phosphate components profoundly affect the dispersion and flocculation settling inhibitory effects.
In most cases of the water suspended in the Kunigami Maaji area in the Okinawa islands, the settling is inhibited by chemical fertilizers.

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A dragonfly, Gynacantha japonica often inhabits paddy fields and passes the winter at the egg stage in soil of paddy fields. It had been seen often, but a marked decrease in density has been reported. In this paper, dormancy and hatching conditions were studied in eggs of G japonica. Diapause eggs showed relatively high tolerance against drying condition, while post-diapause eggs in spring were sensitive to drying history. Hatching of the post-diapause eggs was promoted by receiving light stimulus under ponding condition. It was considered that changes in physical conditions, especially moisture condition, of paddy fields by farm land consolidation and increase in number of fallow paddy fields may result in decrease of number in G japonica.

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Although the soil compaction is essential process in civil engineering, the principal mechanisms still remain unresolved. To capture the mechanism of soil compaction from micro-mechanical viewpoint, the current paper describes a numerical model where both the adhesive force and the lubricative effect due to liquid bridges are incorporated into the two-dimensional DEM model. Behavior of the soil compacted at various water contents is numerically obtained by relating the water content to the interparticle force based on liquid bridge between particles. In addition, a macro-particle model is adopted to represent an angularity of particle due to its complicated shape. Numerical simulation of soil compaction test by the proposed model is carried out and the results are found to be in good agreement with the compaction curve obtained through usual experiments. Whereas the current model is devoid of the reference of the physical phenomenon like excess pore water pressure, the result, that the peak of the dry density is obtained in the course of increasing water content, shows possibility of re-create and reveal the mechanisms of soil compaction using DEM simulation.

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Irrigation and drainage facilities function as not only for farming but also for other functions, for example, the drainage of housing area and the leisure of residents. Such situation has caused serious problems in farmer's financing, as only farmers, not but other residents, pay the cost of the constructions, operations and maintenances for these facilities in Japan. So today it is very important to develop studies on a new cost allocation method in order to make use of multifunctionality of these facilities. So this paper focuses comparative study on cost allocation of governmental and non-governmental expenses between Japan and U.S.

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Irrigation districts manage most of irrigation and drainage facilities whose function is not only for farming but also for other functions, for example, the drainage of housing area and the leisure of residents. Such situation has caused serious problems in farmer's financing, as only farmers, not but other residents, pay the cost of the management for these facilities in Japan. So today it is very important to develop studies on a new beneficiary expences method in order to make use of multifunctionality of these facilities. So this paper focuses study on the beneficiaries and their cost allocation of irrigation districts in Japan and California state.

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Recently in Okinawa, red soil runoff becomes a remarkable problem, and suspended sediment movements (erosion, transportation, and sedimentation) have to be grasped for assessments of new land development plans or sustainable managements of agriculture. A purpose of this study is to grasp the suspended sediment movements from the results of multi-point simultaneous observation in the small agricultural basin. The time series of discharge and suspended sediment concentration were measured on several rainfall events and at proper intervals of time. The time series of measured values, the relation between discharge and suspended sediment runoff, soil particle size in runoff water, and amount of sedimentation in the settling basin were examined. The sediment balances were calculated from these time series of the data in each rainfall event. The sediment balances were explained with the land use distribution, the structure and the arrangement of settling basins, and scale of rainfall event. It was substantiated that the low canopy covered farm lands affect sediment yield, the structure and the arrangement of settling basins affect sedimentation, and these suspended sediment movements differ according to the scale of rainfall event.

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In Japan, most of irrigation and drainage facilities have been operated, maintained and managed by Land Improvement Districts (LIDs). Income of LIDs which has been spent for operation, maintenance and management (OMM) of irrigation and drainage facilities has depended on an annual membership fee. But OMM costs for their facilities have raised up due to urbanization and disadvantage of agricultural industry, so LIDs' budget has had latent deficit and LIDs have tried to get other various financial sources. In order to make clear how LIDs cover OMM cost, typical LIDs' revenues were investigated and analyzed. As the result, it's made clear that LIDs' OMM costs were covered by the categorized sources or decreased by the method as follows, 1) national or local government managed these facilities, 2) LIDs have some “exceptional” governmental subsidies, 3) additional income such as rental of land, charge to users for their drainage to LIDs' managed canals, 4) some mayors in command area would give some subsidies to a LID, 5) charge levied on withdrawal land.

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