To investigate the shrinking behavior of peat soils associated with drainage, we used undisturbed rectangular parallelepiped shape peat specimens to observe changes of height, vertical strain distributions, matric potential distributions and drainage. Volumetric water content distribution data derived from matric potential distributions and soil water retention curves were applied to estimate the change of vertical stress distribution. Further to investigate the shrinking-swelling behavior of peat soils as a result of repetitive drainage and water supply terms, we analyzed the shrinking-swelling behavior of rectangular parallelepiped shape specimens. Resulting from the increase of vertical stress caused by the loss of buoyancy, three stages of peat soil shrinkage were observed;(1) an abrupt shrinkage according to drainage from macro pores, (2) a moderate shrinkage according to drainage from micro pores, (3) a slow, long term shrinkage due to the decrease of air-filled porosity and solid phase volume without drainage. Differences in bulk densities, pore-size distributions, the degree of saturation and suction force of pore water resulted in the difference in shrinking behaviors of peat soils under unsaturated conditions. We inferred that peat soil swelling above water table resulted from decreasing of suction force with capillary water uptake. We could observe irreversible shrinkage due to residual strain during long term shrinking behaviors of peat soils according to repetitions of water level changes.

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The compression characteristics of remolded clay can be expressed by the compression index C'_c which is obtained from the e-log p curve of the consolidation test and the coefficient of volume compressibility m'_v. So far, the compression index equations have been proposed by many researchers using initial void ratio e₀ which is one of the factors of condition of soil, or liquid limit W_L which is one of the factors of type of soil. In this paper, introducing the initial porosity n₀ (=100e₀/(1+e₀)) in which e₀ is normalized by (1+e₀), C'_c and m_v' equations were expressed as a function of n₀ only.

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Based on the relationships of both compression index C'_c and coefficient of volume compressibility m'_v for remolded clays versus initial porosity n₀ the relationships of C_c, and m_v for undisturbed Ariake clay versus n₀ were obtained taking sensitivity ratio S_t which is a factor of structure of clay, into account. Assuming that C_c-C'_c andm_v-m'_v relationships were expressed as C_c= K_cC'_c and m_v= K_mm'_v, K_c was expressed as K_c= S_t^0.22, while K_m was expressed as K_m=1.1 for clays with various sensitivity ratios.

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A series of laboratory model tests were carried out to study the uplift behavior of shallow buried pipe in dense sand. The results of these model tests to assess the response of buried pipes to upward pipe movements were presented. Tests were performed by measuring uplift load-displacement of pipe, soil pressure distribution around pipe and observing slip surface using the model pipe diameter of 260mm with shallow depth of cover (less than two times the pipe diameter D). Slip surface were observed using thin horizontal colored sand layers placed in the sand mass. The results indicate that the experimental data agree well with several analytical models. Then the paper presented the results that were conducted to investigate the suitable protection for uplifting of shallow pipe. The results suggested that the uplift resistance could be increased significantly by the incorporation of geogrids and crushed gravels for backfill materials.

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Sufficiency of irrigation water and reuse of return flow from agricultural land, in the Kino River Basin in the central part of Japan were quantitatively analyzed, using the Basin Hydrological Model developed by the authors. The results with respect to irrigation water sufficiency showed that:(1) lower sufficiency was found during the dry years in the mid-stream region, where 20 % of the total area was paddy fields irrigated from small streams or ponds; and (2) the sufficiency was higher in the downstream regions, where paddy fields were irrigated from the sufficient and stable river water, despite that the paddy area was larger than in the mid-stream regions. The results with respect to reuse of return flow helped to prove that:(1) in the lower regions, larger contribution of the return flow from the upper regions to the water diverted from the main river was ascertained throughout the irrigation period;(2) irrigation stage and rainfall distribution affected contribution pattern of return flow; and (3) irrigationwater in the downstream regions was largely dependent on the agricultural return flow from the upper regions.

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This paper evaluated the effect of particle size and localisation on trap-door problem. The tests were performed using the glass beads having two kinds of particle diameters of 0.2mm and 0.4mm. The testing beds were prepared by pluviation air and were two layers that were changed the heights and particle sizes of upper and lower layer. The height of testing bed was 20cm and width of trap-door was 10cm, and the tests were conducted 8 kinds of testing beds. The tests were observed a relationship between the earth pressure and displacement and propagation of shear band. The width of shear bands were 20times the mean grain diameter regardless of heights and particle sizes of lower and upper layers. The peak earth pressures differed according to be the heights and particle sizes of lower and upper layers, and the case of this phenomenon was considered to be a difference of progressive failure and zone of localisation.

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In the Lower Syr Darya region of the Aral Sea Basin, secondary salinization of irrigated lands has been a crucial problem. To clarify the mechanism of secondary salinization, studies on water balance were carried out in an irrigation block where a rice-based cropping system has been practiced. Results of on-site studies are summarized as follows. 1) The amount of water supplied to a block is dependent not so much upon the crop water requirement as upon the conveyance capacity of the canal system. 2) The conveyance losses in a distribution canal were estimated at around 5.8% km^-1. 3) The performance of land-leveling was extremely low in rice plots. Since the ponding depth is managed based on the highest portion of a plot, this brings about deep water which leads to wastage of irrigation water and salt accumulation. 4) The average for unavoidable losses of evapotranspiration and deep percolation in rice fields throughout the cropping season was estimated at about 9.3 mm d^-1. A large portion of water introduced to rice fields, excluding unavoidable losses, tends to be released into field drains.

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The prevention of reddish soil loss in Kunigami Maaji areas is very important in environmental conservationfor the coral reef region in Okinawa, Japan. In this paper, the mechanical properties and erosion loss characteristics of cement-stabilized soil were investigated in order to provide material for soil structures such as embankment. Erosion tests for stabilized soils were carried out in field to examine the effects of cement content on soil loss. The stabilized soils having cement contents more than 2.5% were significant for preventing soil loss. For clarifying out the mechanical properties of cement-stabilized soil, soil compaction tests, slaking tests, unconfined compression tests and CBR tests were carried out. Furthermore, from the results obtained the effects of cement content and drying-wetting on those properties were discussed. Cement treatment is a useful method to improve those mechanical properties and control the soil loss in surface layer of soil structures.

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Using soil, crop and climate data from three agro-ecological zones of Ghana and rainfall-runoff coefficients from Niger, the authors, show by computer simulation, that tank irrigation offers a sustainable alternative to rainfed agriculture in Ghana. Water balance of rainwater catchment apron, water storage tank and a 350 m²-cultivated field is simultaneously carried out bounded by the condition that the tank does not empty during the period of simulation. Suitable apron areas are determined for three crops grown under different climates with sprinkler and drip irrigation. Results indicate that drip irrigation economises on apron area by as much as 41% in the case of citrus, 22%for Tomato and 28% for maize compared to sprinkler. Optimum tank capacities are also economised by over 40%. This is attributed to reduced field evapotranspiration under drip irrigation. Irrigation type makes little difference to apron area under moist conditiOns, because then, drip behaves similarly to sprinkler irrigation. Small tank capacities produce excessive tank overflows which, are aggravated in sprinkler irrigation. Low rainfall years also force the system to have large apron areas that cause excessive overflow in good rainfall years.

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In this study, we statistically discussed the possibility to classify rice varieties using the ground data of multiangular spectral reflectance data out of rice plant canopy. We grew fourteen varieties of rice in the experimental rice paddy field where environmental conditions like soil, nutrition, water supply and local climate were expected to be homogeneous, and then we measured the value of the spectral reflectance at multiangulars of each rice canopy. Reflectance data were collected from 400nm to 850nm in every 1nm. And we measured the spectral reflectance at the off nadir angle of 45 degrees, 30 degrees, 15 degrees in the direction of the backward scattering and the forward scattering in the principalplane, and at the same angle of the principal plane in the orthogonal plane.
The reflectance data of the green band (550nm-560nm), the visible red band (675nm-685nm) and the near infrared band (745nm-749nm) at every measuring angle were computed for each rice variety. And then, the unpaired t-tests were done between one pair of means of rice varieties at every measuring angle.
As a result of this test, the number of pairs of rice varieties which can be statistically distinguished using multianglar spectral reflectance data increased more than that just using the spectral reflectance data at the nadir angle. It became clearer that the difference of spectral reflectance measured from the rice canopies at multiangulars is statistically significant.

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We have been studying runoff by applying a water quality tank model. Runoff water quality has been surveyed at a agricultural watershed for seven years. In this research, we propose the necessity to consider transformation within the runoff process, accumulation in the soil, denitrification in a paddy field, and the land use patterns of a watershed concerning nitrogen runoff. We made a water quality tank model which included all these items, and we compared the simulated results with observed data. The results established that it satisfied two of the values between calculated and observed which did not coincide well. Therefore, this model verified that we can efficiently use it to predict nitrogen runoff loads from a watershed. Moreover, we show that nitrogen runoff loads can be calculated from rainfall data and fertilizer amounts with this model. Hence, it is verified that this newly developed model can be used efficiently as an essential tool to manage the water quality at various watershed levels.

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Recently, Level Model is often used for the analysis of flow in nature. But, the usual Level Model method was employed in cases where water level changes in small range. It was caused because the level thickness of usual Level Model method depends on the change of water level.
In this paper, the Moving Boundary Technique was applied to the Level Model for analyzing flow with large water level change with small level thickness changes and examined its valicity. The wave propagation analysis was carried out for a numerical example and it was improved that the present method can calculate stably even if the water surface crosses the boundary of each level. The usual Level Model method was not capable of calculating the vertical velocity near the water surface with the present method.

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In order to examine the effect of the water content and density on the shear strength properties, drained shear tests were carried out on decomposed granite soil whose water content and density differ during compaction. As a result, the strength properties of the compacted decomposed granite soil are not effected by the water content. The cohesion is nearly 0 when ρ_d0>1.7 g/cm³ and increases as the dry density increases when ρ_d0<1.7 g/cm³. The internal friction angle increases lineally as the dry density increases. Correcting the dilatancy effect reduces the fixed strength coefficients. The higher the density of the sample, the bigger the correcting quantity becomes. In addition, the shear tests results for unsaturated soil shows that the application of suction influence the cohesion.

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This study was carried out to clarify the mechanism of water consumption and capillary supply in upland field reclaimed some years ago as agricultural land. Crops selected were watermelons, net melons, and sweet potatoes for the spring and summer, and radishes, champion turnips, and broccolies for autumn. The watermelon was cultivated in vinyl tunnel, net melon in mulch and tunnel of rain shield, and sweet potatoes in mulch. Capillary supply was determined based on difference between evapotranspiration and water consumption in the effective soil layer.
The results obtained are as follows. First, the soil texture was sand or sandy loam and readily available moisture was about 34-103mm. Secondly, soil moisture tension in the driest layers was pF2.90 in the spring and summer mulching cultivation and pF2.50-2.90 in autumn cultivation. Thirdly, consumption was found to be 1.1-7.9mm/d, and capillary supply from deep soil layer under 80cm to exceed 1-2mm/d during a drought.

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These day, Sewage treatment plants in rural area are being constructed in increasing numbers to protect water quality in public water body and to improve the living environment. On the other hand, amount of the sludge increases in proportion to the number of plant. Local authorities are burdened with the heavy expense of sludge disposal. Accordingly, three communities of Hiezu village, Daisen and Saihaku towns in Tottori Prefecture, started the study to construct the joint composting plant with the aim of recycling of the sludge to fields and to grow tulip by using the compost. In this paper, an attempt of construction of composting plant is described. There sults obtained from this study are summarized as follows.(1) In long term experiment using a small composting plant, temperature in the tank ranges from 60°C to 80°C, and the water content of the compost from 40% to 50%. These data prove the better curing.(2) The components of compost after secondary curing meet the recommended standards on the organic fertilizer.(3) The rice bran added to the sludge plays a big role in increase of potassium in the compost.

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