Polyethylene reinforced with short glass fiber pipes (hereinafter referred to as PE-GF pipes), which is applied to agricultural pipelines, has lower ductility than polyethylene pipe, and it is necessary to understand the bending performance limits for ground followability in the longitudinal direction. In this paper, focusing on the allowable radius of curvature of PE-GF pipe having electrofusion joint (hereinafter referred to as EF joint), horizontal bending tests using real scale pipes were conducted to investigate the bending limit performance and the ultimate bending limit of EF joints. The result showed that in the gently curved pipeline where the radius of curvature of the pipeline in the longitudinal direction is 20 times the outside diameter of the pipe, no fracture points appeared at butt fusion joints and EF joints, and no significant changes were observed in the circumferential cross section of the pipe. There indicate that there is little change in the cross-sectional area of water flow. In addition, we confirmed that it is reasonable to set the allowable radius of curvature of the PE-GF pipe having EF joint in the longitudinal direction to 60 times the outside diameter of the pipe.

The corrosion of an agricultural steel sheet pile is evaluated by its plate thickness, which is one of the useful parameters for corroded condition of in-service structures. By the authors, results of this paper lead to development of estimation method for plate thickness in service steel sheet pile, which is based on non-contact detection. In this study, experiments and one-dimensional heat conduction analysis was conducted by model steel plates, which was set to several experimental conditions in different thickness of model steel plates. The heat flex in steel sheet pile is affected by its thickness. The one-dimensional heat conduction model is used by two layers of corroded steel specimens simulating steel sheet piles and glass beads simulating back soil. As a result, from the viewpoint of heat flux, it is confirmed that the thinner the plate thickness of the steel material, the larger the heat flux per unit width that contributes to the temperature rise. Therefore, the largely temperature rise is detected in thinner the plate thickness condition, and a negative correlation is obtained between the plate thickness and the amount of temperature change.

In this study, we attempted to verify the effect of installing rubber poles at regular intervals along the edge of a road bordering an irrigation canal to deter pedestrians from approaching the canal. Further, the optimal installation intervals were examined. A questionnaire survey conducted among village residents (where experiments were performed) demonstrated that the alerting effect was exceptionally high when the interval between the poles was 2-3 m. The distance from the edge of the road to the position of pedestrians was greater with statistical significance when the interval between the poles was 3 m in comparison to when no poles were present along the road. The distance from the edge of the waterway to the position of pedestrian traffic increased significantly. In addition, it was found that the around the road influences the line of movement of pedestrians. Thus, it is essential to understand the line of movement when installing fall prevention measures.

In recent years, many small earth dams have been retrofitted because of deterioration. The phreatic lines in small earth dams with sloping cores are geometrically calculated with the sectional shape of embankment, the water elevation and the permeability of soil materials in the current design. However, there is possibility that actual phreatic lines and calculated ones are different because of the assumption that the foundation ground is impermeable. In this study, the problems of the calculation method for phreatic line in the current design have been organized based on the results of FEM analysis. As a result, it was found that when the permeability of the sloping core is low, the phreatic line calculated by the design calculation is on the dangerous side, and that the seepage flow of the foundation soil affects the phreatic line. To solve these two problems, we proposed methods to reduce the calculation error of the current design by using functions that include the permeability of each embankment material and to obtain results that are closer to the actual phreatic lines.

To understand the effects of short-time fluctuation of water demand in paddy fields on water requirement to an irrigation canal, field measurements were conducted in a paddy block that takes water from the same irrigation canal (ditch). Half-day fluctuation of the number of irrigated paddy fields and total irrigation water amount to the paddy fields in the paddy block were determined. The results indicated that the water demand (total irrigation water amount) for the paddy fields showed random large short-time fluctuations (0 to 2.5 times of the unit water requirement in this study), with its maximum value far exceeding the unit water requirement unless water resources are limited. Therefore, to adequately meet current and future water demands in paddy fields in Japan, the design discharge of irrigation canal must be greater than the unit water requirement, and supply of a large amount of delivery water requirement is essential in an open channel irrigation system. This fact suggests that delivery water requirement in open channel irrigation systems should be understood as water requirement to allow irrigation under short-time fluctuations in water demand in paddy fields.

Accurate estimates of annual or seasonal riverine constituent loads, which is the terrestrial mass flux conveyed through rivers, are essential to water pollution control measures and watershed mass studies. An unbiased estimate of river load and its confidence interval can be calculated based on the Horvitz-Thompson (HT) estimator. However, the HT estimator may fail to provide precise load estimates based on low-frequency water quality (WQ) monitoring data such as monthly routine samples employed in WQ monitoring in Japanese public waters. In this study, the authors calculated unbiased estimates and those confidence intervals of decadal averages of annual river loads based on long-term (decadal) low-frequency (monthly) monitoring data at the Yamasaki station in Hyogo prefecture, Japan, located in the upper watershed of Ibo river. The results also showed that a traditional rating curve method tends to provide biased load estimates, whereas a simple average estimate can be used for unbiased load estimation.

This study clarifies the critical determinants of residents' preference for irrigation canals maintained by residents in Kora town, Shiga prefecture, Japan. The results of a questionnaire survey using an evaluation structure model indicated that the preference factors for irrigation canals were clean water, inhabitation of living things, and maintenance by residents. In particular, residents born locally preferred irrigation canals to be maintained strictly by the local residents. In contrast, the residents whose birthplaces were outside Kora town preferred irrigation canals with the inhabitation of living things, maintenance as open channels, sufficient water flow, and clean water. The preference for irrigation canals thus varied between residents with different birthplaces. It is important to maintain the preference of irrigation canals to ensure the local management of irrigation canals.

The non-farmland notification operation is a system in which the Agricultural Commission notifies the owners of devastated agricultural land (Class B), which is expected to be difficult to recycle, as non-farmland. If a non-farmland notification is issued in area of agricultural land (AL), the land is excluded from the AL. In this study, we investigated the factors hindering the operation of the non-farmland notification system in AL through a questionnaire survey of all 20 municipalities in Ehime Prefecture. As a result, it was found that the factors hindering the operation in Ehime Prefecture are 1. Complexity of administrative procedures arising from modern land use problems such as unknown landowners and undetermined land boundaries, 2. The need to take into consideration the maintenance of cooperative relationships between farmers and local governments due to the unclear criteria for B classification, 3. Difficulty for the government to provide management guidance to sloping farmland because it is excluded from blue land, and 4. Concern in utilizing sloped farmland for other uses.

This research aims at evaluating the effectiveness of the dual channel system by the numerical simulations for the improvement of irrigation water management. The study site is Toyogawa waterway district located in the eastern part of Aichi Prefecture. In this district, upstream excessive water withdrawals often caused water deficit problems at the downstream areas of the East Main Channel. The open channel system had some difficulties for the fair water distribution. In order to solve this problem, a supplemental pipeline is now under construction to support the open-type main channel. The numerical simulation showed that the open-and-closed dual channel system can respond quickly to the water demand, make easier the operation of farm ponds and regulation reservoirs, and consequently relieve water deficit problems.

It is well known that surface drainage has effects on sloped farm fields under non-tillage cropping systems; however, previous case studies have not considered the surface drainage effect of these field under tillage cropping systems yet. As for a direction of slope, some studies mainly investigated sloped farm fields which inclined to a drainage canal side (it is called as a sloped farm field inclined along a long-sided). There is a limit to extending the slope’s gradient because the difference in terms of flooding depth is larger when cultivating rice. If sloped farm fields inclined along a short-sided, the slope’s gradient was larger than when the sloped farm field inclined along the long-sided. Therefore, a short-sided two-way sloped field was here constructed using a GNSS-controlled land leveler, and its drainage effect was considered under flat ridge cropping. The result showed that, under this system, there was no effect of surface drainage on sloped field, and the effect on open ditch was larger. Therefore, when considering the introduction of a sloped field, it is essential to select appropriate cultivation methods, such as non-tillage cropping systems or techniques matching the direction of the ridge with the slope.

The groundwater of the Tedori River (Ishikawa Prefecture, Japan) alluvial fan area consists of seepage water from the ground surface and the river itself. We combined several tank models that, in turn, became distributed tank models for comprehensively understanding groundwater flow and analyzing its flow in the alluvial fan area. The alluvial fan area is divided into 13 blocks, and the river is divided into four blocks, considering the groundwater flows in an orthogonal direction toward the groundwater counter line. The seepage water from the ground surface is classified by land use (paddy field, residential land, others). The tank model was set at individual blocks. As a result, we quantified the seepage water and groundwater flow processes for each block and evaluated the impact of underflow water on the groundwater environment. This method is highly efficient for solving groundwater management problems in this area. This model would be utilized not only for groundwater management in the future but also for groundwater development by evaluating its effects on individual blocks.

As results of the questionnaires for all prefectures in Japan, a number of abolished works of small earth dams for irrigation had increased rapidly since the new law for small earth dams for irrigation was enacted, and it was likely that the abolished works would continue to be constructed in the future. Therefore, we classified abolished works by surveys systematically at 85 sites in 19 prefectures and indicated these characteristics. The three main abolished works of small earth dam for irrigation included open-cut, underdrainage and filling-up work, and there was also a combination work that combined them. Constructing settling basins in ponds to prevent sediment outflow during drainage, driftwood captures to do the blockade of underdrainage pipes and other devices, it became clear that each prefecture had performed creative ideas to abolish small earth dams for irrigation in spite of the lack of countermeasure works and design guidelines.