A method to estimate an ultimate bearing capacity, R_u, of timber piles driven in medium to very soft clay (whose N-value ranges between 0 and 8) is investigated. Firstly, as the skin friction and the end resistance composing R_u are uniquely dependent on the undrained shear strength of clay, c_u, a linear relationship between the N-value and c_u is proposed on the basis of statistical analysis of the unconfined compression test results. Then the values of R_u are calculated by the bearing capacity formula of pile using the N-c_u relationship proposed, and are compared with the second-limit-resistances measured in the static axial compressive load tests of a single pile, with the result that some 90% of estimation accuracy is found. As the timber pile tapers to the lower end, its ultimate bearing capacity becomes larger than that calculated using the sectional diameter of the lower end of pile. Taking this taper of timber pile into account the values of R_u are newly calculated and compared accurately with the second-limit-resistances. The above discussion leads to the conclusion that the N-c_u relationship proposed is effectively practical and accurate in estimating R_u of timber piles driven in medium to very soft clay. It's also particularly stated that a special effect of taper should be included into the calculation of R_u of timber piles.

Unsaturated hydraulic properties of the surface crust were estimated by the evaporation method. Two undisturbed soils, a subsoil sample and a layered sample consisting of crusted layer and subsoil, were obtained from a sandy loam field, and evaporation experiments were carried out in a laboratory. Observed pressure heads and cumulative evaporation amounts were inversely analyzed to predict soil water retention curves and unsaturated hydraulic conductivities. At first, hydraulic properties of the non-crusted layer were obtained from the inverse analysis for the subsoil sample. Subsequently, hydraulic properties of the surface crust were estimated by inversely analyzing the layered sample with the assumption that hydraulic properties of the subsoil are known. The crusted layer had smaller saturated water content, lower air-entry pressure head, and lower hydraulic conductivity in high pressure head range than non-crusted layer, corresponding to the predominance of smaller pores. It was indicated that the evaporation method is a promising approach for estimating hydraulic properties of a crusted layer in relatively lower pressure head ranges.

Elasto-plastic analysis methods for saturated and unsaturated soils that can account for temperature effects have not been well established. The main objective of this study was to develop a numerical method for elasto-plastic analysis of saturated and unsaturated soils that can consider the temperature dependence and to validate the model. A model with a new material parameter accounting for such temperature dependence observed in the results of isotropic consolidation tests of unsaturated soils was coupled with the existing saturated and unsaturated elasto-plastic model. Triaxial compression tests conducted under different temperatures for silt with different densities (loosely and densely packed) were simulated using the proposed coupled model. As for the loosely packed specimen, the model reproduced well that the strength of the critical state was not affected by temperature. As for the densely packed specimen, while it was simulated that the shear strength became smaller at higher temperature, there were discrepancies between observed and simulated values. Although the smaller volumetric strain (i.e., expansion) at higher temperatures was well simulated, the simulation overestimated that at lower temperature. It could be corrected at some extent with the introduction of the shear band concept.

In inland valleys of Ghana, it is necessary to develop low-cost irrigation facilities that can be constructed, maintained, and sustainably managed with the technological know-how of local farmers. For this purpose, we developed a reinforcement technology for irrigation facilities at paddy fields such as the levees and irrigation canals by implementation of planting works. The soil hardness greatly fluctuated within 7.3 - 27.8 mm in the facilities with no vegetation, and the soil water content varied widely from 4.3 to 37.1% regardless of the presence or absence of vegetation depending on the plant species. In addition, the irrigation facilities with implemented planting work showed significantly greater resistance to slaking collapse than those without vegetation in both cases of flooding and inundation. It was demonstrated that the vegetation would reinforce the irrigation facilities in the mechanical properties of the civil engineering structure to prevent slaking collapse. Moreover, in ascending order of the collapse grade, the root fresh weights of 4.71 g in Chrysopogon aciculatus, 2.07 g in Stenotaphrum secundatum and 2.05 g in Cynodon dactylon were included in test samples. The root weight was indicated the possibility to become quantitative estimation for resistance to slaking collapse.

In order to promote the conversion of paddy fields to dry farmlands by improving water drainage, understanding the mechanism of drying cracks in clayey soils has been demanded. In this paper, the drying process of saturated soil in a container was analyzed over time using the digital image correlation (DIC) method, which can measure the displacement and strain of the soil surface over an area. We applied the DIC method to investigate the growth mechanism of crack widths, which greatly affect hydraulic properties. The displacement analysis showed that the crack widths resulted from increases in the distance between neighboring crack blocks. Furthermore, the principal strain analysis suggested that the substantial shrinkage of the surrounding crack block might make the crack blocks shrink due to evaporation from the soil surface. In addition, the formation of the crack block released the constraint between the container and soil particles, and the constraint direction became only the inner direction of the crack block, which caused the drying shrinkage in the direction of the crack block contraction.

In lowland peat areas of Hokkaido, the number of malfunctions on rice paddy irrigation pipelines, such as misalignment and leakage, has recently been increasing due to peat subsidence. However, the quantitative evaluations of the behaviour of the pipeline after construction have not been well explored. In this study, focusing on irrigation pipelines placed in Shinotsu Peatland, central Hokkaido, changes in the vertical alignment of pipelines after a couple of decades from the construction and their cause were examined. The average amount of subsidence of the pipelines was ca.20 cm after approximately 20 years of the initial construction. The subsidence was relatively uniform in the section without any special construction conditions such as intersection with road or junction to aqueduct bridge. On the other hand, the subsidence of the pipelines occurred unevenly at the intersection with the road where the vertical load was high and at the junction to the aqueduct bridge where the pipeline was fixed to a firm pile foundation. Uneven subsidence may damage the joints of the pipes and some of the observed misalignment excessed the allowance designated by the design criteria. Thus, the risk of incidence such as leakage may increase at those sections. Therefore, continuous observation and measures against uneven subsidence of pipelines are strongly required.

Vertical earth pressure behavior and shear band propagation on cyclic loading mode in a trap door part were compared with experimental results obtained for monotonic loading mode. For the taper loading mode, the peak minimum value and residual value in the active side were larger than the values of monotonic loading mode, and the peak maximum value in the passive side was equal to that of value of monotonic loading mode and the residual value was smaller than the value of monotonic loading mode. For cyclic loading mode in constant displacement, the gradient in a loop shape of vertical earth pressure ratio (σ_v/σ_v(0)) became small as constant displacement became large and σ_v/σ_v(0) tended to be the maximum value around constant displacement ±0.7 mm. Also, the shear band inside the extensive arch-shape in an active state and that outside the extensive fan-shape in a passive state on cyclic loading mode developed upper direction alternately resembling a deer horn.

We investigated the effects of residual chlorine on fish and shellfish in channel that receive chlorine-treated water from sewage treatment facilities. At the treated water inflow point, the residual chlorine concentration showed 0.1 to 0.2 mg/L, and even at a point 500 m downstream, it showed 0.03 mg/L. No negative effect of the inflow of treated water was found on the distribution of fish. In addition, no inhibition of the movement of Gnathopogon elongatus due to the high-concentration chlorine zone. On the other hand, it became clear that shellfish are strongly affected by residual chlorine. Numbers of individuals of live shells of Semisulcospira spp., Corbicula spp. and Sinotaia quadrata histrica at the downstream from the treated water inflow point was less than at the upstream. Live Unionidae were able to find at the only upstream from the treated water inflow point.

Shear bond strength between inorganic repair material and concrete with different conditions of carbonation and surface roughness were evaluated. It was confirmed that shear bond strength increased with an increase in roughness of concrete surface. The relationship between shear bond strength and arithmetical mean roughness of specimens with carbonated concrete was almost identical with that of specimens with non-carbonated concrete. These results lead to the conclusion that carbonation of concrete doesn't influence shear bond strength to inorganic repair material. On the other hand, specimens with mortar with very smooth surface prepared according to JIS R 5201 showed lower shear bond strength than that of specimens with carbonated or non-carbonated concrete. Therefore, it is reasonable to evaluate shear bond strength using specimens made of above-mentioned mortar or concrete with smooth surface to avoid overestimations.

In the 2018 Hokkaido Iburi East Earthquake, large diameter pipeline was severely damaged by large seismic ground motions. Seismic countermeasures such as selection of backfill material, high degree of compaction, and anti-floating measures were carried out in the district where the soft ground along the pipeline was deeply deposited. However, pipe detachment and flotation occurred in many places. Especially at the bend pipe, the joint detachment was caused by the large deformation of backfill ground and pipe.

In the present study, two-dimensional Finite Element Method (FEM) analysis was conducted for the purpose of clarify the behavior of bend pipe and the effect of mechanical properties of backfill material of the Apporo pipeline in Hokkaido during the earthquake. Through the FEM analysis, the proposed elasto-plastic dynamic analysis which can represent the reduction of strength for backfill material during earthquake exhibited the satisfactory predictions of the movement of bend pipe. The results of analysis and the damaged bend pipe movement at site were discussed considering the soil pipe interaction.

Agricultural pipelines in peat grounds are susceptible to disconnected joint dues, water leakage, and cuts in the pipes owing to pipe flattening or uneven settlement. An effective measure for such pipelines involves integrating joints by electrofusion even under uneven settlement and the use of polyethylene pipes with ground followability in the pipe longitudinal direction. Such pipes include those made of polyethylene reinforced with short glass fiber pipes (hereafter referred to as PE-GF pipes), which can be designed with smaller thickness as the rigidity along the pipe circumferential direction is higher than that of a polyethylene pipe, and have often been the object of application studies concerned with cost reduction. However, as the PE-GF pipes are reinforced with short glass fibers, their flexural performance limits must be ascertained for followability in the pipe longitudinal direction. Therefore, horizontal flexural testing was performed in this study under conditions where actual pipelines were arranged in the ground to confirm their deformation characteristics. Consequently, it was found that the allowable radius of curvature in the pipe longitudinal direction is 60D, where D is the outer diameter of the pipe.

The aim of this study is to evaluate the soil water movement in a crop field where ridge shape was changed and suggest optimal methods for soil water measurement and analysis to quantify the water consumption. Field measurement was performed and a numerical model was developed using HYDRUS 2D/3D to evaluate the soil water movement at a welsh onion field with ridging cultivation. The computing domain was changed in four stages with ridging. Simulated result using inverse solution for soil hydraulic properties had good agreement with measurement and indicated that the soil moisture content at the soil layer which was generated by ridging was relatively low after precipitation. There was little different between soil moisture contents simulated under ridging and non-ridging scenarios. The water consumption estimated using the results from ridging and non-ridging scenarios had good agreement with measurement.

The detection of material damage is most important issue for maintenance and management of in-service concrete structures. In recent years, concrete damage is quantitatively evaluated by relation between newly development parameters and mechanical properties. By the author, damage evaluation parameters for concrete is developed by using acoustic emission (AE) method based on stress field. The AE is one of the useful methods for detection of elastic waves in stress field. In this study, damage evaluation of in-service concrete road wall is conducted by AE energy parameters analysis in core test. Testing structure is appeared to accumulation of cracking damage. The detected AE is compared to mechanical properties. Thus, the detected AE waves are closely associated with damage accumulation. This phenomenon is indexed by the detection of high energy AE at the initial loading stage, which is closely related to the strain energy calculated from the stress-strain curve. Therefore, the degrees of damage in concrete samples are quantitatively evaluated by AE energy parameter, even when the initial mechanical properties of concrete structure at the time of construction are unknown.

Engineering and biological removal techniques of heavy metals in contaminated farmlands are sometimes unfeasible because of high cost and low efficiency on a large scale. Thus, the immobilization of metals in soils to prevent toxic metal uptake into crops using organic amendments has gained prominence. However, it is unclear which property of organic amendments influences heavy metal immobilization. We observed the chemical forms of Cu, Cd, and Pb through soil batch tests to elucidate the factors of immobilization using cow manure, poultry manure, and rice straw, including composting for 1 or 3 months (CM, PM, RS₀, RS₁, and RS₃, respectively). The results from the experiments showed that CM had a high immobilization effect due to high cation exchange capacity and the mechanism of immobilization varies according to heavy metals. Furthermore, PM can promote the mobility of the three heavy metals, likely due to the heavy metal and dissolved organic matter complex. Based on the chemical forms, it is determined that composting promotes the immobilization effect of Cu in dune sand.

We investigated effects of poultry manure biochar application on wheat production and soil chemical properties, compared with fused phosphate application, for an Andisol with P₂O₅ and Zn deficiency. Soil soluble Zn and Cu with poultry manure biochar application were significantly higher than that with application of fused phosphate. Soil pH and available P₂O₅ were not significantly different between fused phosphate treatment and poultry manure biochar treatment. These results suggest that those have similar ability of soil acid neutralization and P₂O₅ storage to soils. Therefore, poultry manure biochar can be viable as an amendment for not only soil carbon sequestration but also storages of P₂O₅ and micronutrients to soils. However, losing the balance of soil exchangeable base composition with heavy application of poultry manure biochar should be noted.

We developed a rotary underwater abrasion tester that can be applied to high strength concrete materials with a large coarse aggregate. In this study, firstly, we experimentally investigated the test conditions under which the developed tester can generate stable flow and large abrasion action. The results confirmed that (1) a stable water flow can be generated when the initial water level is 40 cm and rotational speed is 70 rpm and (2) a large abrasive force was generated by using an abrasive material in the shape of a prism with a length of 19 mm, width of 19 mm, and height of 20 mm. Secondly, we performed an accelerated abrasion test for concrete and mortar and confirmed the characteristics of abrasion on the specimens. The results indicated that, when dissimilar materials are adjacent to each other, the downstream specimen, where the materials are switched, is affected by the dissimilar materials. Conversely, it was confirmed that a longer flow distance of the same material was effective in reducing the effect of the dissimilar materials.

In this study, we developed a model for estimating the protein content of rice from UAV images of large size paddy fields. The correlation between the protein content and the vegetation indices was examined, and the GNDVI at 38 days after heading showed the highest correlation coefficient. A simple linear regression analysis using the GNDVI at 38 days after heading showed good estimation accuracy. The protein content estimation map created using the estimation model showed that the protein content differed depending on the plot before land readjustment and was higher in the banking part than in the cutting part. As well as the protein content, the amount of available soil nitrogen was higher in the banking part than in the cutting part. These results suggest that the protein content difference in these fields was caused by the spatial difference in the amount of available nitrogen due to land readjustment. In addition, it was suggested that the unevenness of the protein content due to the farmland consolidation influence could be observed by using UAV.

Six combinations of drainage equipment for paddy fields dam were prepared to evaluate the peak cut functions of discharge from paddy. First, a hydraulic experiment using artificial channels was conducted to determine the flow coefficient in each device used to calculate discharge. Next, paddy models which can simulate water balance on paddy field were built and set the determined flow coefficient for each device. The discharge and water depth of paddy models were calculated using generated rainfall with nine different rainfall scales ranging from 100 to 500 mm/3d. As a result, all devices effected a peak cut function on discharge from the paddy field, at the same time, the peak water depth on the paddy was increased. The characteristics of the effect are dependent on the type of device. The peak cut effect using a “function-integrated” device was maximized at 100-150 mm, and the effect of a “function-independent” device was maximized at 300 mm. Simultaneously, the device of function-integrated type required time decreasing water depth until initial condition compare with the device of another type. To structure a sustainable framework for paddy field dam activity, it is important to assume the target rainfall scale for disaster prevention, understand the characteristics of the devices, and the conditions of paddy fields in the area, and then consider in advance how to install them.

High turbidity water that followed huge landslides in the upper area of the Tedori River in 2015 brought out the serious problems of sedimentation in paddy fields and bed of the river. Groundwater level in the alluvial fan area increasingly lowered just after the occurrence of turbid water and it had continued for several years. Therefore, a conceptual and lumped hydrologic model was developed to evaluate the impacts of turbid water on groundwater level. At first, the model parameters were determined using the data of 2002-2010. The calculated groundwater level coincided almost with the measured one and validity of the hydrologic model was proved. In the next step, the model was applied to the years of 2011-2020 to verify the model performance and investigate the impacts of turbid water. As a result, great difference between the measured and calculated level was found just after the occurrence of turbid water in 2015 and it continued for several years, while the both levels showed similar fluctuation in 2011-2014 before the occurrence. The great difference indicates the possibility of impacts of turbid water on groundwater and it is considered that the lowering of groundwater level was caused by decrease in paddy filed percolation and seepage from river due to sedimentation of soil particles.

Because many farmland stone walls have recently collapsed due to frequent heavy rains, the need to clarify the mechanism of the collapse has become a pressing issue. However, most prior analytical studies on the stability of farmland stone walls focused on seismic damage, and studies that examined the damage caused by heavy rain are scarce. The present study simulated the collapse behavior of farmland stone walls due to the effect of pore water pressure by using the 3D-DEM-MPS method, while considering the solid–fluid interaction. In order to evaluate the effect of the pore water in the backfill behind the stone wall, a comparison between two cases was made: with and without pore water. In the latter case, the displacement of the backfill was small and the wall was stable. Contrastingly, in the former case, sliding failure easily occurred in the backfill even with only slight movement of the wall; this eventually caused the wall to collapse by the combined effect of the slip created between stone blocks and the increasing force imposed by the sliding backfill. This study successfully demonstrated that it is possible to reproduce the collapse behavior of farmland stone walls, caused by backfill soil saturation following heavy rain, using the 3D-DEM-MPS method.

In inland valleys of Ghana, where the development of paddy fields has been promoted, the earth canals and levees have not been functioning satisfactorily due to frequent heavy rainfall and poor maintenance. Thus, we have been working on the development of reinforcement technology by planting cover plants in the levees and irrigation canals. The above-ground part of cover plants is associated with the cover effect and the under-ground part is related to soil binding effect. The above-ground to under-ground ratio was 2.54 for Chrysopogon aciculatus, 4.17 for Cynodon dactylon, and 4.93 for Stenotaphrum secundatum. Based on the lowest ratio obtained for Chrysopogon aciculatus, it was verified that the development of under-ground part must be prioritized. The results of pull-out strength test revealed that the root system takes more than one year to develop in order to bind the soil. Measurements at 15 months after planting showed a significant difference between no planting work plot and planting work plots. Among the 3 plants, Chrysopogon aciculatus was the most superior and recorded the highest value of 410 N. Although the strength of soil binding per gram of root weight is weak, the dense growth of many roots enlarged the pull-out strength.

In designing and construction management for pipelines using flexible pipes, sectional deflection is controlled within the range which is specified by technical standard. To estimate the deflection, external earth pressure, weight of water in the pipe, and restraint by backfill soil are considered as loads and supports, but internal pressure during the operation of pipeline is not yet considered. Aiming the formulation of the elimination amount of deflection caused by internal pressure, frame analyses are conducted for oval pipes under internal pressure. Obtained displacements are formulated by multiple regression analyses and a differential equation between radius difference and internal pressure is derived. By integrating this equation an exponential function is obtained, which shows that the difference in radii exponentially reduces and approaches to zero according to the increase in internal pressure.

A marked and recapture survey was conducted to clarify the effectiveness as fish refuges during flooding of the fish pool structure and four confluence structures constructed in a drainage channel with a length of approximately 2,035 m as part of the land consolidation project. A total of 8.3% of the fish were recaptured after the flooding of water. The proportion of small individuals decreased in some fish species and sites after rainfall compared to before rainfall. In the case of Oryzias latipes, the peak of the length distribution at the time of recapture was larger than that at the time of marked release. Therefore, it was inferred that small individuals were swept away due to the increase in flow velocity associated with rainfall. In addition, individuals marked at upstream sites were recaptured at downstream sites. These indicating that the construction of multiple refuge sites on the same drainage line was effective in preventing runoff from the drainage channel during flooding.

This study aimed to develop a new method to control Egeria densa, which overgrows in agricultural irrigation canals. We conducted two experiments (one in the laboratory and one in the field), focused on changes in light conditions and the growth of E. densa. In the laboratory experiment, the maximum tensile load of the stems was significantly reduced when the light was shaded to about 20 μmol·m^-2·s^-1 (1,400 lx). We discovered that shading exerted a significant negative effect on the number of roots. Furthermore, in the field experiment, which was conducted in an actual agricultural canal, the maximum tensile load on stems was reduced in both the 85-90% and 95-98% shade plots. In particular, in the 95-98% shade plot, the tensile load was reduced to about half of that in the control plot (non-shade) during the high grow season from August to October.

In this study, we proposed a method to calculate an appropriate cost-share rate for people in urban areas for the operational costs of drainage in agricultural facilities. To calculate this rate, we used discharge hydrographs with function fitting for design rainfall, and specific discharges in consideration of the increases in peak discharges and reductions in the time length to the peak resulting from urbanization. The proposed method was applied to the management of Nishikanbara region, one of the largest rice-growing areas in Japan. As a result, we were able to arrive at the proposition of this methodology and values for calculating appropriate cost-share rates by the people of urban-areas. When the cost-share rates was set at 1.0 per unit area for agricultural lands, we estimated the cost-share rate for people in urban areas would be in the range of 2.10 to 3.43, with an average of 2.77. In addition, we clarified that the proposed method can be applied even when there are changes in land use such as a decrease in agricultural land areas or when urbanization progresses.

In the Kamikita district of Aomori prefecture, Andosols with good physical properties is widely distributed, and it is known as a major production area for root vegetables, such as Chinese-yam and burdock. In this study, we explored the soil physical and chemical properties in a planting trench formed using a trencher before the cultivation of Chinese-yam, with the goal of properly managing drainage in the Andosol upland field in Chinese-yam cropping. In addition, during the growing season of the Chinese-yam, seasonal changes of soil hardness distribution, variation per day of soil moisture and electrical conductivity at each depth were monitored, and the quality survey was conducted after observing the tuber of Chinese-yam at the harvest season. At depths of 10, 30 and 60 cm at the harvesting season (early-November), saturated hydraulic conductivity decreased and the dry density increased approximately 1.2 times compared with the middle of May. Moreover, saturated hydraulic conductivity decreased with increasing depth, while dry density increased. In addition, soil hardness at depths deeper than 30 cm increased over time. From the above, it was clarified that the physical properties of the planting trench changed significantly after a growing season of approximately half a year. Moisture saturation at depths of 30, 60, and 100 cm tends to increase, was suggested that soil water tends to accumulate at depths shallower than 95 cm. From the results of the soil moisture observations using FMS and quality survey of Chinese-yam during harvesting season, rots and deformation of the tuber in Chinese-yam were not observed even if exposed to excessive moisture for approximately three days during the thickening growth.

In the study area where regulating reservoirs are located between open-channel sections and pipeline sections, the authors evaluated how those reservoirs affect irrigation flexibility upstream from them as well as downstream. The local Land Improvement District (LID) reduces scheduled flow rate for the reservoirs' service areas and then redistributes the reduction to open-channel's areas. This increases the scheduled flow rate in the open-channel's areas up to around 20% compared with the overall mean, thus it can be interpreted that irrigation flexibility is improved there. In daily operations, the LID attempts to minimize inflow for one of those reservoirs so as to maximize the water availability upstream. And occasionally, the LID increases the inflow depending on the situation such as rapid drawdown of the reservoir. This operation strategy can additionally increase the irrigation flexibility throughout the district. With this strategy during periods when the water demand is highest, the reservoir was used to absorb temporal flow mismatches over 24 hours or more, unlike the general principle for regulating reservoirs.

In recent years, the relationship between the long-term durability and repair quality in corroded steel sheet pile revetments has been discussed as a technical problem. By the authors, development of steel sheet pile - concrete composite had been proposed. In this study, survey for detection of deformation characteristics were performed applying field survey in service repaired corroded steel sheet pile revetments which is treated by the panel coating method. Results of field survey, the exudation of groundwater and the cracks on the surface layer of the panel material were detected. It was clarified that in order to maintain and manage in service structure for protection of repaired part, it is necessary to consider the groundwater drainage and control of cracking damage in the actual environment.

Curve number method is a simple method to calculate direct runoff height from daily rainfall and curve number which is determined by soil conditions at the rainfall event. Simple modification methods are proposed by U.S. Department of Agriculture and researchers, as estimation accuracy is not good in some application conditions. Following methods adaptability for CN to an existing dugout in Northern region, Ghana are examined; a) a method to a use standard CN, b) a method to use the average CN, c) a method to consider an antecedent rainfall, d) a method to change an initial abstraction ratio. As a result, the reproducibility of direct runoff height of those methods is found out to be not good. Thus, CN value estimation models developed by multiple regression analysis using rainfall related data which can be easily obtained in Africa are examined. As a result, NSE (Nash-Sutcliffe efficiency) becomes 0.74 in case to use daily rainfall converted to natural logarithm, dry period and rainfall intensity as explanatory variables and the model is highly satisfactory.

Anaerobic co-digestion experiments were conducted under six conditions in which mixing ratios of rural sewage sludge was set at 50% by weight, and the ratio of kitchen garbage and sudachi peel, a food waste with a relatively high C/N ratio of 36.1, was varied to understand the effect of the mixing ratio of sudachi peel on the stability of digestion. As a result, digestion proceeded stably when the ratio of sudachi peel was low, but when the ratio of sudachi peel was larger than 20%, the pH and gas production rate gradually dropped, indicating process failure. When urea was added to the feedstock material, digestion proceeded stably, indicating that the cause of process failure was nitrogen deficiency. The method of adding urea at the feedstock material stage of digestion not only improves the stability of digestion, but also increases the fertilizer value of the digestate and the efficiency of digestate application to the field due to the increased nitrogen concentration in the digestate.

This study analyzed expectation and anxiety of a farmer who has decided to adopt ICT on-farm irrigation devices by using a qualitative analysis method, SCAT. The farmer's expectations for ICT on-farm irrigation devices were clarified as follows: (1) remote operation of water management at home, (2) reduction of water management operation mistakes by visualizing data, (3) realization of optimal time water management in all fields, (4) labor saving for water management, and (5) reduction of labor cost required for water management. The farmer's anxieties were clarified as follows: (1) the need for continuous rotation irrigation, (2) theft, damage, and failure of ICT on-farm irrigation devices, (3) data transmission problems, (4) malfunction of ICT on-farm irrigation devices and smartphone, (5) difficulty in attaching and detaching ICT on-farm irrigation devices, and (6) maladaptation to complicated water management such as puddling and intermittent irrigation. It was also clarified that the farmer still feels the need to go around the rice fields to check the growth of rice, even with the adoption of ICT on-farm irrigation devices. Furthermore, the issues to be examined for these were considered.

This study aims to determine the evaluation structure model (ESM) of irrigation channels in Kora town in Shiga prefecture, where a land improvement project was implemented to enhance water environments. Based on residents’ preference/non-preference for irrigation channels, the ESM consisted of three psychological layers: determinants, judgements, and estimates. Results of the questionnaire identified 12 determinants: the existence of open channels, accessibility of water bodies, landscape structures, ratio of concrete revetment, flow rate, biodiversity, residential maintenance of irrigation channels, amount of garbage, cleanliness of water, amounts of sludge and algae, road width, and convenience during droughts. These determinants impact judgements in terms of multi-functional roles, coolness, safety, and measure of management, which in turn influence estimates such as emotion, need, convenience, and reassurance. The residents’ preference/non-preference for irrigation channels is hierarchically determined through the aforementioned psychological analyses.

We developed a method for monitoring riverine radiocaesium discharge following heavy rainfall using a waterproof NaI(Tl) scintillation detector system. The system continuously obtained gamma-ray spectra; peak radiocaesium counting rates declined following rainfall because of the shielding effect from the increased water volume, but spiked just after heavy rainfall, likely because of radiocaesium associated with muddy water runoff. The ratio between the two major peaks for radiocaesium and the relationship between fluctuations in region-of-interest channels and temperature were consistent with previous studies, validating the measurements. Additionally, we proposed a procedure using a smoothed second-order derivative filter to detect significant changes into increasing trends in peak counting rates. This procedure is applicable to real-time monitoring and will be improved by adjusting smoothing parameters and integrating water-quality indicators such as turbidity.

To support subsurface drainage planning using pipes in paddy fields, we have developed a method to determine the drainage quality for each paddy field using Sentinel-2 satellite data and GIS polygon data showing paddy field parcels. The areas of interest are paddy field parcel polygons where rice has been harvested and wheat has not been planted after harvesting rice. First, parcel polygons, whose parcel mean of image pixel values of the near-infrared band data is above a certain threshold value, are determined as not cultivated and are excluded. Next, the remaining parcel polygons, whose parcel mean of image pixel values of the short-wave infrared band data is less than a certain threshold, are determined to have bad drainage. The remaining parcels are determined to have good drainage. The results obtained using the Sentinel-2 satellite data taken on February 21, 2021 (6 days after heavy rain) were collated with visually interpreted results using the aerial photograph taken on February 20, 2021. The overall correct answer rate (area basis) obtained by assuming the latter judgement result as the true value was 84%. Since the developed method uses the dry and wet conditions of the paddy field soil surfaces as a judgment index, it has the disadvantage that the result is dependent on the number of days between heavy rain events and satellite observations.