To evaluate the heterogeneity of soil physical properties in the field, the knowledge about the effect of sample size (ex. sample area, sample volume) on theoretical distributions of soil physical properties is very important. To study this, a pore structure model was proposed. In the model, pores were divided into two categories, that is, cylindrical macropores and pores in soil matrix. In each category, random variables were defined. Using these variables, the effects of sample area and suction on the theoretical distributions of five soil physical properties (bulk density, etc) were examined with probability theory. Combining the information about saturated hydraulic conductivity obtained in the previous study, the results were summarized as follows: 1) Theoretical distributions of saturated hydraulic conductivity, volume water percentage drained from saturation to a certain suction and volume water percentage drained between two suctions skewed to the right when both of the sample area and the suction were relatively small. And they fitted to normal distribution when either the sample area or the suction was relatively large. 2) Theoretical distributions of bulk density, water content by volume at a certain suction and water content by weight at a certain suction fitted to normal distribution regardless of the magnitude of the sample area and the suction.

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In the present study, selective erosion process during the rill formation was studied. Particle size of eroded soil from clay loam and sandy loam soil were investigated. The soils were uniformly packed into a wooden erosion box of 80cm in length, 30cm in width and 5cm in depth. Slope of the erosion box was 10° and the surface flows of 0.93cm³/(s ·cm) and 1.86cm³/(s·cm) per unit width of the erosion box were provided at the top of the slope for 10 minutes. Sediments were collected at 2 minute intervals. In particle analysis, sieve was used to separate the sand particles and a paper filter was used to separate silt and clay particles. Clay particles were eroded more in the initial interval in both soils with both surface flow rates. Transportation of sand particles was the greatest with the highest erosion rate, whereas silt did not show any remarkable change. In the clay loam soil, fraction of the eroded silt and clay particles were higher than that of present in the original soil. Sand fraction of the eroded soil was only higher than the original in the case of sandy loam soil with 1.86cm³/(s·cm) surface flow. Rills were developed over the soil surface when the ratio of sand fraction of the eroded soil to the original soil was found larger than 0.64.

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The pressure infiltrometer (PI) method has been widely used to determine the field-saturated hydraulic conductivity of soil, K_fs. An equation to calculate K_fs is derived from the theory of constant-head infiltration into soil from a single ring. In the present study, the theory to determine K_fs developed in the PI method is examined by field tests and numerical calculations. The sand soil is selected in the study. Both the infiltration rate into the soil, and water movement in the soil beneath the ring, are measured with time during the PI test. Numerical calculation based on the finite element method is employed to simulate the measured water movement in the soil using K_fs calculated by the equation of the PI method. Unsaturated properties of the soil are determined based on the data published in the previous studies and measured in the field test. A soil parameter α which describes an exponential relationship of unsaturated hydraulic conductivity with a pressure head is calculated from the unsaturated properties of the soil. There is fairly good agreement between measured and calculated mater movement in the soil, as well as infiltration rate into the soil. Another series of the PI tests is also conducted to measure α in the sand soil. From the test results, a new value of α at approximately 0.06cm^-1 is proposed for sand with very little fine soil particles.

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The buckling mechanism of arch type underground structures was studied by the model experiment and the finite element analysis. The infinitesimal deformation analysis considering only the material non-linearity could not predict the limit load and finite deformation analysis was indispensable. In the analysis, using internal friction angle of soil layer at interface element, collapse loads were evaluated excessively. Therefore, interfacial friction angle between soil layer and arch structure have to be taken into account in the analysis. The maximum shearing strain evaluated by finite deformation analysis, showed that shear band occurred from upper part to side part of the arch as well as image processing of model experiment.

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Two experiments were conducted. Firstly, the quantity of Na⁺ and Cl^- contents in 5-day-old soybean roots were measured during the initial 9h when the roots were immersed in 50 mmol/l NaCl solution and 50 mmol/l NaCl solution with small amount of CaCl₂ (0.5, 1.0 and 2.0 mmol/l). Secondly, suction (20kPa) was applied to the cross section of detopped soybean roots and the exudation collected for 9h and the volume was measured.
The resulting, Na⁺ content in the roots immersed in 50 immol/l NaCl and 50 mmol/l NaCl + 0.5 mmol/l CaCl2 solution for 9h was about 58 μ molg^-1_F.W. and 20 μ molg^-1_F.W., respectively. This implies that Ca²⁺ controls the K channel of cell membranes in the roots. On the other hand. Ca²⁺ did not effect Cl^- content in the roots. In addition, exudation volume was controlled osmotic pressure gradient between solution contained in the roots and the outside solution, if Ca²⁺ could maintain the ion permeability of cell membrane under 50 mmol/l NaCl solution.

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To clarify the mechanism of secondary salinization, studies on water and salt behavior were conducted in an irrigation block where a rice-based cropping system has been practiced in the Lower Syr Darya river basin of Kazakhstan. Results are summarized as follows. 1) Due to excessive irrigation of rice fields with slightly saline river water, dissolved salts were deposited mainly in upland fields in the block and its periphery. Changes in salt accumulation rates were dependent upon the scale of annual changes in cropping patterns. 2) A remarkable finding was obtained on the salt behavior in saturated soil layers of rice fields. Salts from the deeper layer diffused upward in percolated water and thus increased soil water salinity in the shallow layer after the subsoil was saturated. This finding refutes the hypothesis that rice cultivation practiced in arid areas is effective for leaching salts already accumulated in the soil. 3) Because of the movement of percolated water from rice fields through underneath the field-drained bed, the rise of the groundwater table and the salt accumulation were accelerated in the adjacent upland fields. Thus, mixed cropping with rice and upland crops based on an eight-year crop rotation system in an irrigation block accelerates waterlogging and salt accumulation in upland fields.

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Although the empirical Topp's equation is widely used as a calibration curve of time domain reflectometry (TDR) method, it has been known that the equation is not valid for soils having higher organic matters content, mineral materials with high dielectric constant and clayey soils. The purpose of this study was to apply and examine the Maxwell-De Loor model and the semi-empirical mixing model (α model) to measured data of six textured soils (two Ando soils, Reddish-yellow soils, surface soil and subsoil of Brown forest soils, and Toyoura Sand) collected in Kyushu Island, Japan. Both models involve four components as solid phase, bound water, free water, and air, and are expected to have higher fitness of between volumetric water content (θ) and apparent dielectric constant (ε) than Topp's equation. Relations between θ and ε were measured using a small vessel with TDR probe of two parallel wave guides under a drying process of soil water. The results showed that empirical Topp's equation underestimates soil water content for mineral soils of low bulk densities. Since dielectric mixing models take into account of the effect of bulk density on θ-ε relation, they were more suitable than the Topp's equation for the soils used in this study. Judging from the fitness for wide range of soil water content, the third-degree polynomial regression curve and α model were superior to the Maxwell-De Loor model. However, the Maxwell-De Loor model was found to be so flexible because it reasonably predicted measured values for different types of soil without fitting parameters.

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The discharge velocity of the flow through rockfill increases nonlinearly with the hydraulic gradient applied. This relation has been described by a quadratic-or a power-type function. In the present paper the nonlinear property of the flow through rockfill is investigated on the basis of the laboratory one-dimensional permeability test using river gravel. The discharge velocity measured in the test in response to the applied hydraulic gradient are described by the quadratic-type head loss equation, that is the Forchheimer equation. The hydraulic mean radius is effectively introduced into the head loss equation to taking account of the effect of rock particle size and shape, and rockfill voids on the flow through rockfill. A special feature of the head loss equation determined is that it requires only one parameter, that is the hydraulic mean radius of rockfill to determine the head loss property of the flow. Water temperature of the flow is also effectively included into the head loss equation. The power-type head loss equation of the flow through rockfill, which has been determined not theoretically but experimentally, is compared with the head loss equation determined from the tests. Functional relationship of the coefficients included in the power-type equation with the hydraulic mean radius and the water temperature is obtained.

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The flow transmissibility of rockfill structures is investigated by using the water flume experiment and the numerical calculation. The Forchheimer equation which was determined on the basis of the one-dimensional permeability test is employed to describe the head loss property of the flow through the rockfill. A hydraulic mean radius of voids is effectively introduced into the head loss equation. Firstly the nonlinear numerical calculation based on the finite element method is developed. Numerical difficulty due to the nonlinear relation between the flow velocity and the applied hydraulic gradient is solved by introducing the method of successive approximation. Then the laboratory water flume experiments are conducted to examine the validity of the head loss equation of the rockfill as well as the numerical calculation. It is shown that the flow transmissibility of the rockfill structures can be well determined by the head loss equation with the hydraulic mean radius of voids. Lastly the stage-discharge rating curves of the throughflow dams are calculated to study the effect of the water temperature on the flow through the rockfill. It is found that the flow transmissibility of the rockfill structure is determined predominantly by the properties of the solid matrix of the rockfill.

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As a fundamental subject for introducing of direct sowing of rice crop (DS), the authors studied about the judgement process for the large-scale rice cropping farmers to introduce DS as the new technology.
For judging that DS should be introduce or not, the farmers consider as follows; 1) As a prerequisite, there must be the needs to introduce new technology for changing their agricultural management. And the farmers think of the needs of DS as the new technology if their income opportunity will be increased by labor force decreasing in spring season. This stage is named ‘idea stage’. 2) Considering the condition of their region, they judge that DS can be introduced there or not. This is named ‘possibility judging stage’. 3) They estimate the economical advantage or disadvantage of DS, especially the anxiety of remarkably decreasing of yield on DS, which is the biggest risk in DS, and which is caused by the technological immature of DS. And the farmers decide to introduce DS when they consider that the anxiety will be able to be avoided. This is named ‘economical estimating stage’.
Hence, for spreading DS, the most important thing that the farmers may be secure is the agricultural coaching facilities to avoid the anxiety of remarkably decreasing of yield on DS.

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This study aimed to investigate the exchange of nutrients at sediment-water interface and the contribution of nutrient release from sediments to water quality in irrigation ponds. Water quality and sediments of two irrigation ponds were studied in Kyotanabe City of Kyoto Prefecture. Release fluxes of nitrogen and phosphorus were measured by laboratory experiments. The investigation of sediments showed nitrogen in interstitial water primarily consisted of NH₄-N and Org-N. The laboratory studies presented release fluxes of NH₄-N in the eutrophic downstream irrigation pond increased in summer and at the beginning of fall. It was supposed that remarkable inorganization of detritus at sediment-water interface and direct release to overlying water led to the increase of the release flux. In both irrigation ponds T-N and T-P were released from sediments during the sediment investigation term as a whole. At least in the upstream irrigation pond, the contribution of NH₄-N release flux to NH₄-N concentration in pond was small which was estimated from the result of Principal Component Analysis.

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The purpose of this study is the increasing of water application efficiency and length of border strip of smallstrip border irrigation on sandy field. The basic experiment about the effect of closed-end condition and slope was done on sandy field in the Arid Land Research Center of Tottori University. The volume balance equation with a term for remaining water at strip-end, and water advance and recession equations with a slope gradient term were used for analysis. The calculated value of infiltration water profile was in good agreement with measured value. In the case of closed-end condition, water application efficiency and length of strip increased compared to open-end condition. In the case of slope condition, length of strip increased too. We investigated the application of closed-end and slope condition for the sandy fields of Mu Us shamo-desert. It is estimated that length of strip and water application efficiency under the present state can be improved with the result obtained.

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In this research, the estimation method of the convective heat transfer coefficient of concrete was examined. The estimation method of the convective heat transfer coefficient was done by a back analytical technique which used the result of an easy temperature measurement in the construction site. First of all, the objective function in a back analytical technique was examined by using the measurement temperature in the RC box culvert. Next, the temperature measurement condition in the construction site was examined from the result of applying the objective function which had examined it to two kinds of concrete specimens with a different size. And, the temperature of the mass concrete of the same mixing as a concrete specimen was analyzed, and the effectiveness of the identification value of the convective heat transfer coefficient was verified. As a result of a series of research, the effectiveness of the estimation method of the convective heat transfer coefficient proposed by this research was able to be confirmed.

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For establishing a quick and accurate forecasting system for flood drainage in low-lying areas, it is necessary to progressively improve runoff forecasting precision. The choice of runoff model will influence runoff forecasting precision directly. This paper discussed three types of flood models: the Parallel Tank Model (PTM); the Series Tank Model (STM); and the Back-Water Tank Model (BWTM). Filtering forecast-systems were constructed and were operated on the Kalman Filter technique. Comparisons for forecasting the water level in a pump-station up to 3 hours ahead were performed using the floods of August, 1995 and June, 1978 in the Kyukiyamakawa, the Imai, and the Odoorikawa basin in Niigata Prefecture, Japan. The forecasting precision of each model was discussed for the complete flood hydrogragh and for the flood peak. The results show that the BWTM flood forecast accuracy was higher than that for the PTM and the STM, particularly for 3 hours ahead. Furthermore, in analyzing the structure of the models, the following result was obtained. The BWTM method can reflect the characteristics of drainage holdback correctly for flood drainage in a low-lying area. Using the BWTM method results in a high degree of forecasting accuracy. Also, the BWTM method has the function of change-over holdback, in the gravitational drainage application, which aids high accuracy.

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In the present study an intensive field survey was conducted to grasp the recent changes in actual irrigation water management induced by the on-going policy of water use reformation in China, taking two irrigation districts, Saho Dam in the Chanjiang basin and Jinghuiqu in the Huanghe basin, as example.
As the results, the following outputs were withdrawn: 1) The types of irrigation management, the types of water use and kinds of water charges to water users were clarified in the comparative manner of two irrigation districts; 2) It was observed that supplyoriented and bureaucratic water management was dominant; 3) The equity in water allocation was a main target of water management; 4) A water guard, guangshuiyuan, who is nominated as a personnel of irrigation water control in the administrative village, played a significant role in water management; and 5) The bureaucratic water management has a possibility of converting to the contracting water management except drought period.

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Generally the replanting method has been adopted for the preservation of slopes in reclaimed farmland in Japan. Improvement of technology for replanting on slopes made it possible in a short period to establish vegetation to the state as it had been originally planned regardless of condition of soil or climate. However, as a relatively low cost replanting method for reclaimed farmhands, seed spraying method using introduced species has been widely adopted.
In this experiment, we studied the state of how woody plants had been invaded on the slope for ten years since replanting. The experimented slope, where replanting was done by fertilizer spray method using introduced species in 1985, is fronting on the forest placed on the edge of the reclaimed farmland. Moreover, additional fertilizing experiment was done in part of the slope by fertilizer bag method same year of the replanting. The result of the research in 1995 showed that the experimented slope was changed to forest, and proved fertilizer bag method is effective for invasion of woody plants.

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In order to accumulate information necessary for management of water qualities in a canal, investigation was carried out for a period of seven years. Models for prediction of water qualities were also evaluated using results of the investigation. The investigated canal consisted of a pipeline, a tunnel and a regulating reservoir. Source of the water was a eutrophicated lake.
Substances concerned with eutrophication decreased their concentrations following flow of the water. Sections where the decrease was found and amounts of the decrease were different between each substance. A rate of the concentration at an end of the water line to at source of water, i.e., a reaching rate changed every year and differ from the all other substances. The reaching rate tended to increase year by year. Simple models requiring time of flow as predictor variables were built. These models simulated the concentration of substances well.

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