A soil physicochemical survey was conducted on soybean fields converted from clayey paddy fields in the western part of Hokkaido. A cylinder infiltrometer method was used as a simple method for the evaluation of soil physics. The soil chemistry of the surveyed fields was within the range of the soil diagnosis criterion, but there was a tendency for many of the fields to show poor soil physics below the shallow topsoil. When the basic intake rate (I_b) measured in the surveyed fields was less than 100 mm･h^-1, grain yield per plant was affected and the grain yield per square meter was less than 300 g･m^-2, although there was no relationship to planting density. Analyzing the relationship between I_b and soil physical properties using quantification theory type II, it was found that a soil structure that was underdeveloped and had few cracks and pores reduced the I_b to less than 100 mm･h^-1, and the yield of soybeans was consequently lowered. On the basis of these results, we concluded that the cylinder infiltrometer method that reflects the soil status in terms of the presence cracks and pores can be applied for evaluation of soil physical properties in fields under soybean cultivation that were converted from clayey paddy fields, with an I_b of 100 mm･h^-1 or more indicating an improvement in the index value of the soil physical properties.

Field demonstration tests of the bio-pile and land-farming purification methods for remediating petroleum contamination were performed using the Kunigami-maji soil which broadly exposed on surface of the northern half of Okinawa Island. These methods involve the addition of phosphorus and nitrogen compounds or Ryukyu limestone particles to petroleum-contaminated soil. Both methods were found to be effective. The addition of Ryukyu limestone particles shortened the time needed for Total Petroleum Hydrocarbons (TPH) degradation to begin. Land-farming purification with no artificial air supply proved effective for the remediation of petroleum-contaminated Kunigami-maji soil. The lowered water content and pH neutralization may encourage the activation of petroleum-degrading microbes. In practical use, the relationship between petroleum odor and TPH concentration should be investigated with a pilot test on site. This pilot test determines the required period for purification from the TPH removal rate. The field demonstration tests discussed in this study give reference data gathered with nourishment and different of purification-promoting mthods.

To establish a method for monitoring soil moisture and salinity levels in reclaimed agricultural fields, the apparent permittivity (ε) of clayey soil sampled from Isahaya reclaimed land was determined by conducting drainage experiments in the laboratory under different moisture and salinity levels. The daily variations in ε and bulk electrical conductivity (σ_b) during the summer season were monitored by employing time domain transmissiometry (TDT) sensors horizontally installed at five different depths, and volumetric water content (θ), matric potential (ψ_m), soil-water electrical conductivity (σ_w), and osmotic potential (ψ_o) were then estimated based on the both ε and σ_b. The values of θ, ψ_m, σ_w, and ψ_o at different depths above 30 cm were successfully estimated and their corresponding variations during the entire summer season were established. However, values of the aforementioned parameters could not be easily estimated at depths below 30 cm owing to inadequate data regarding ε vs. θ. Hence, the proposed method can aid in conducting coupled field monitoring of θ, ψ_m, σ_w, and ψ_o for clayey soils.

This study investigated the dynamics of submerged weeds caused natural disturbance in the river ecosystem, for 11 years from 2004 at Maekawa river of the class B river of South Okayama. Vallisneria asiatica and Potamogeton malaianus were dominant in 2004, and the Sparganium japonicum formed community like a long belt. Vallisneria asiatica community spread in the whole area in 2006, and particle size composition of the bottom increased fine sand, and the species composition simplified. Sparganium japonicum community disappeared by competition with Vallisneria asiatica community in 2007. Potamogeton malaianus community gradually decreased by competition with the Vallisneria asiatica community from 2008, too. However, Vallisneria asiatica community washed away by the net storm rain more than 100 mm of 2011 and 2013, and changed particle size composition of bottom. At the same time, it promoted the new distribution of Potamogeton malaianus and the species composition of submerged weeds diversified.

To recover the mechanical function of primary equipment such as pipelines and tunnels that have deteriorated with age, restorative technology has been created in which a multilayered structure is formed by installing a renewal pipe into an existing pipe and then pouring a fill material into the space between the renewal and existing pipe. Pipelines and tunnels with a large diameter that have undergone this type of restoration can experience sudden buckling. Therefore, clarifying the buckling mechanism and analyzing techniques for estimating buckling resistance have become pressing issues. This study conducted indoor buckling model tests to clarify the influence that fill material packing ratios have on the resistance to buckling. The experimental model was a 1/10^th scale model of the actual tunnel, and a circular test pipe with a 150-mm nominal diameter was used. The behavior of the renewal pipes on filling failure of the fill materials was analyzed. From the results, we suggested for method of estimating the buckling resistance threshold for renewal pipes installed in underground structures such as tunnels that experience external water pressure.

It is an important and urgent challenge to establish disaster prevention technologies for small earth dams for agriculture, as a defensive measure against damage from a large-scale earthquake such as a Nankai Trough Earthquake. A construction method utilizing steel sheet piles with excellent toughness has a track record of installation as an anti-earthquake measure for coastal levees, and the authors are examining adapting this method for reinforcement of small earth dams. As part of this study, the modeled small earth dams were subjected to permeation, excitation, and overtopping experiments, and as a result, it was determined that the conventional counterweight fill method has limited effectiveness as a measure to counter liquefaction of foundation ground occurring in the event of a large-scale earthquake because it is focused on sliding failures. On the other hand, it was confirmed that providing sheet piles in the body of a small earth dam is effective for reduction of disaster damage in the surrounding villages, because the sheet piles maintain the height of small earth dams and thus it is possible to suppress they breaks due to an earthquake or overtopping water.

In recent years, deterioration and damage of concrete structures have become obvious due to long-term use. It is necessary to detect the deterioration and damages easily and accurately. Identifying efflorescence is an important issue for maintaining RC slabs. In this study, we attempted to identify efflorescence using a decision tree, which is one of machine learning techniques, in reinforced concrete slabs of road bridge that constructed 50 years ago. Two feature values were set as explanatory variables: luminance value and pixel value after DoG (Difference of Gaussian) filter. As a result, the proposed method was higher than the Otsu method, which is one of discriminant analysis methods, in all indicators of accuracy, recall, precision, and F value. The three indicators of accuracy, recall, and F value were 0.8 or higher. These results suggest that the proposed method is useful for identifying efflorescence.

In recent years, the relationship between the long-term durability and accumulation of cracking damage in reinforced concrete agricultural infrastructure has been discussed as a technical problem. The purpose of this study is to experimentally investigate the relationship between the frequency response and the defects including cracking damage in a reinforced concrete surface layer, applying resonance vibration and X-ray computed tomography (CT) methods. Prior to the resonance vibration test, distribution of micro-cracks in testing samples were inspected by helical X-ray CT. Then, accelerated degraded samples were tested. Thus, the decrease tendency of the resonance frequency was confirmed in degraded samples. A relation between resonance vibration characteristics and defects is correlated, and the development of defects of reinforced concrete surface is detected by resonance vibration method.

We investigated sediment deposition in fish pool structures and particle size distributions of the deposited sediments as well as those from paddy fields and levees over a 3-year period after installation of the structures in an agricultural drainage channel in Matsusaka City, Mie Prefecture, Japan. Sediment deposited in the upstream fish pool structure amounted to 18%–39% of the pool volume per year, whereas that deposited in the downstream structure amounted to 11%–17% of the pool volume per year. The water depth in fish pool structures used as wintering habitat could potentially be maintained in the downstream structures by constructing those adjacent to the upstream structures or sedimentation pools. This in turn might result in a reduction in the required frequency of dredging by farmers. Pool volumes were already filled 23%–29% by sediment just after installation. Particle size distributions of the sediments in the upper fish pool structure and channel side levees were coarser than those of paddy field side levees and paddy fields. This may indicate that sediments in the fish pool were supplied from channel side levees during rain events. Therefore, promoting the growth of native vegetation cover along the levees at the end of land consolidation projects might be an effective method for reducing soil erosion and sediment deposition in the fish pool structures.

Ueno Hidesaburō's "Lecture of Land Consolidation" is highly regarded as the book that established agricultural engineering in the Japanese academic field. However, the methodology adopted in the book has been negatively evaluated as notional. Furthermore, Ueno aimed at the realization of agricultural land form according to the development of the associated farming methods. This important aspect of Ueno's work is often overlooked, and the evaluation of his work has thus become one-sided. Hence, in this paper, the author reevaluate Ueno's book based on his perspective, and describe his technical viewpoints. The author believe that if the said book is considered as a planning guideline for land remediation based on technical principles, it can offer novel perspectives regarding future agricultural engineering. Furthermore, in this paper the author clarify that Ueno did not have a broad perspective of engineering concepts and did not respond to technological development such as replotting of agricultural land and agricultural tool improvement necessary for realization of appropriate agricultural land forms, which could have influenced the conservativeness of subsequent agricultural engineering.

Fish habitat assessments in an agricultural irrigation system was performed based on community analysis using modified TWINSPAN and species-specific habitat models using random forests. The results were compared with respect to the consistency in habitat conditions suitable for a community and species. As a result, 6 fish communities and 10 indicator species were identified from the community analysis. Cluster-specific or species-specific habitat suitability was found to be similar among the fish species within the same cluster. Thus, it was revealed that community analysis together with physical habitat surveys is capable of assessing species-specific habitat suitability. Habitat models were more useful when assessing habitat suitability of generalist species when habitat assessment results of the two methods were different. This study establishes the effectiveness of community analysis as a basic tool for species-based habitat assessment. Furthermore, machine learning-based habitat models for a target species can inform studies involving detailed ecological characteristics and predicting species distribution patterns. Further work is needed to develop frameworks for environmental assessment which balance the productivity of an irrigation system and management actions for the conservation of aquatic ecosystems.

The maintenance of damaged irrigation tunnels has become a major social concern; and thus, evaluating the damage conditions of current tunnels is of crucial importance. Voids behind the tunnel lining may be created during or after construction by the conventional method, and these voids are the main factors in its failure. Hence, it is imperative to comprehend the behaviors of the ground, the tunnel lining and the voids. This paper presents model tests of the interacting behaviors between the ground and a tunnel lining with voids under loading conditions. The experimental results show that the longitudinal and lateral convergences are large in the case of a void of 90 degree angle. To investigate the local deformation and the damage pattern, the three-dimensional distinct element method is applied, incorporating the Concrete Particle Model, and the numerical results are compared with the experimental data. The comparison clarifies the qualitative evaluation of the deformation behavior of the tunnel in the model tests by the numerical method.

To compare the performance of time domain transmissiometry (TDT) with that of the widely used time domain reflectometry (TDR), we conducted drainage experiments on Toyoura sand, saturated with CaCl₂ solutions that had different levels of electrical conductivity. Both techniques were used under identical experimental conditions to evaluate the volumetric water content (θ), bulk electrical conductivity (σ_b), and soil-water electrical conductivity (σ_w). Because both methods are based on travel time analysis in the time domain, the accuracy of measurement of θ, σ_b, and σ_w in TDT was nearly identical to that in TDR.

Hydraulics of the flow through the gates focuses on the discharge evaluation. Theory of hydraulics shows that the discharge coefficient is written by using the contraction coefficient. However previous studies have not succeeded in quantitatively relate these coefficients by showing experimental data. The present paper is intended to relate the contraction and discharge coefficients using the experimental data in order to make clear this problem. It has been found that the contraction coefficient monotonously decreases with the increase of Reynolds number, and the functional form has been obtained. Also the effect of the energy loss through the gate to contracted cross-section is considered as the velocity coefficient found to be about 0.95, which is a little smaller than that of the flow through orifice of about 0.98. The discharge evaluation combining these results showed good agreement with previous experimental data obtained for wide range of hydraulic conditions.

Earthquake ground motion is known to generate hydrodynamic pressure in irrigation pipelines. However, there are a few recorded observations of this phenomenon, so such hydrodynamic pressure is not well understood. We made continuous observations of earthquake acceleration and hydraulic pressure at irrigation pipelines in operation, and measured hydrodynamic pressure during 17 earthquakes with seismic intensities ranging from 2 to 4 on Japanese scale. This study reports on analyses based on the data obtained. (1) The maximum velocity of earthquake ground motion and the maximum hydrodynamic pressure during the earthquake have a linear relationship whose correlation coefficient exceeds 0.9. (2) The hydrodynamic pressure increases as a result of overlaps in the hydrodynamic pressures generated at several locations along the pipeline. (3) The maximum hydrodynamic pressure during an earthquake can be estimated using a theoretical equation analytically derived from the basic formula for hydrodynamic pressure, assuming sine waves as the input earthquake ground motion.

When corroded condition in service steel sheet piles of agricultural canals are evaluated by using visible image analysis, textural characteristics of an image of a corroded surface are important information. In this study, spatial distribution characteristics of corroded condition in steel sheet pile are evaluated by texture analysis using gray level co-occurrence matrix on visible images. It is revealed that, by utilizing saturation of analytical images the textural homogeneity of a new steel sheet pile is higher value than a corroded one. The textural homogeneity of an extremely corroded steel sheet pile which has pit corrosion is lowest value in analytical images. Considering the spatial anisotropy, the feature of linear corrosion in an early stage is detected by a difference of the homogeneity in the long length and the short one. The textural characteristics of non-corrosion, corrosion and pit corrosion could be quantitatively evaluated by focusing on the textural homogeneity and the spatial anisotropy.

The aim of this study is to evaluate the water consumption environment and upward water flux to the root zone in a green house. Field measurement was performed in a heated greenhouse where strawberry was cultivated. Potential evapotranspiration was calculated using measured meteorological data in the green house and modified data from the open field. The result indicated that the effect of a large difference between measured and modified air temperature on evapotranspiration was relatively small and it was important to determine solar radiation precisely for quantification of evapotranspiration. A numerical model was developed using HYDRUS 2D/3D to predict the soil water movement. The result indicated that there was a layer with relatively high soil moisture condition under the root zone in this field; however, there was little upward water flux from the layer with high soil moisture condition to the root zone.

We investigated the influence of different levels of connectivity between forest and paddy levees on soil animals and nutrient cycles in satoyama. Three study sites were selected on Sado Island, central Japan, each of which has experienced different modifications in the transitional zone between forest and paddy levees. Twelve belt transects were set from the forest to paddy levee. In each belt transect, we collected soil animals and measured the organic matter decomposition rate. Collected soil animals were classified based on different guilds and compared between study sites. The result indicated some differences in the functional group composition of soil animals and organic matter decomposition rate in the forest and paddy levees among the study sites. At the site with high landscape connectivity, high amount of litter and high organic matter decomposition rate were observed at the forest edge. On the other hand, at the site with low landscape connectivity, relatively low densities of predator, relatively high densities of decomposers and shredders, and high organic decomposition rate were observed at paddy levees. Thus, the results suggest that even when a forest and agricultural land are adjacent to each other, the ecological function of the forest edge differs owing to differences in landscape connectivity.

The authors, using the prototype biogas volume measuring device they developed, observed the dissolution of carbon dioxide (CO₂) in water; however, using the prototype, based on downward displacement of water, CO₂ dissolution lowered the height of the water column in the device and destabilized gas volume measurement.

Therefore, the authors improved the device to avoid the influence of CO₂ dissolution on biogas volume measurement. The accuracy and precision of the improved device was verified by injecting simulated biogas into the device using syringes. The simulated biogases, CO₂ mixed with methane gas to 30, 50, 75 and 100% of the CO₂ concentration, were applied to the verification of the device. The results were a difference of -2.8 to 4.7 mL and a standard deviation of 0 to 3.0 mL. Lowering of the rates of water-column height were also measured and indicated correlative relationship with the CO₂ concentration, depending on Henry's law. The correlative relationship would be useful for monitoring biogas production.

In addition, 3 mol/L of sodium hydroxide solution was added to the water in the device after simulated biogas volume measurement. After the sodium hydroxide solution absorbed all the CO₂ in the simulated biogas, the gas volume was remeasured. The CO₂ concentrations calculated with volumes before and after sodium hydroxide solution addition were approximately 2% smaller than the accurate concentrations. The addition of a sodium hydroxide solution to the device gives approximate CO₂ concentrations for convenience of measurements and supports making a relational expression between CO₂ concentration and the lowering rates of water-column height.

This study aimed to develop a distributed rainfall-runoff model, which simultaneously overcomes the problems of the calculation time and the data scarcity in Southeast Asian watershed to quantitatively evaluate the future changes in rainfall-runoff processes under rural development and climate change. The distributed rainfall-runoff model representing a watershed as a square mesh aggregate was developed. The calculation time was reduced by scaling the mesh resolution in kilometers. Four tank models representing flow characteristics of paddy, upland field, urban and forest areas were incorporated into each mesh element of the distributed rainfall-runoff model to capture the runoff from different land utilizations. A watershed groundwater tank model covering the entire watershed was incorporated to represent the temporally stable base-flow component. Based on scenario analyses, future changes in rainfall-runoff processes with land use and rainfall changes were quantitatively evaluated not only using annual and peak runoff from the entire watershed but also changes in annual runoff and runoff patterns from each land utilization.

The required amount of irrigation water in paddy fields varies depending on the time of year, because water intake permitted from rivers for water rights is determined by period. Generally, water intake permitted for a period from soil puddling is the largest. Periods for soil puddling have been advanced on a trial basis in response to changes in farming programs. When the periods for soil puddling are advanced, surveys on how early soil puddling was actually done in paddy fields are performed. The purpose of this study was to clarify whether synthetic aperture radar (SAR) data from the Sentinel-1 satellite can be effectively used in such surveys. Accuracy in determining whether each paddy field was flooded on the satellite observation date using Sentinel-1 satellite data and paddy parcel boundary data was verified. The average pixel value (backscattering coefficient) of the SAR image was equal to or less than the threshold value used to determine whether a paddy field was flooded. Verification of accuracy was performed in survey areas where the ground surface was observed by both the Sentinel-1 satellite and the Sentinel-2 satellite on the same clear day (20 April 2018). In addition, highly accurate results were obtained by determining whether each paddy field was flooded using multispectral data of the Sentinel-2 satellite and paddy parcel boundary data as verification. Determination accuracy was 79.1% when the VV-polarized SAR image was used and 75.8% when the VH-polarized SAR image was used. Therefore, VV-polarized SAR images are more suitable than VH-polarized SAR images for determining whether paddy fields are flooded. In addition, Sentinel-1 satellite data can be used effectively in surveys.

Examination on applicability of sandblast method as alternative method for abrasion tester using water jet with sand and confirmation on usefulness of sandblast for evaluation method on abrasion resistance of material in general were subject of this study. Comparison experiment using mortar specimen with different particle size of fine aggregate was conducted. As a result, it was confirmed that abrasion mechanism of sandblast was changed with change of test time, sandblast in short test time could simulate selective abrasion like obtained from abrasion tester using water jet with sand. On the other hand, sandblast in long test time could simulate uniform abrasion like obtained from taber type abrasion tester. There is a possibility that evaluation on abrasion resistance by sandblast is equivalent to current quality evaluation of inorganic repairing material by abrasion tester using water jet with sand. But, it was established only under the following conditions: test time of sandblast is 10 seconds and particle size of fine aggregate is over 0.6 mm.