This study evaluated the validity of the unbiased Horvitz-Thompson (HT) estimator and the precise bias-corrected regression estimator (BCRE) in estimating the annual river loads based on long-term monthly routine water quality monitoring data in public water bodies in Japan. The annual loads of total nitrogen and phosphorus in the upper Ibo River, Japan, were evaluated in this study. The daily concentration data in the upper Ibo River were synthesized using monthly data in the upper Ibo River and daily data in nine watersheds in the U.S. As a result, BCRE is recommended for both the annual river load estimate based on annual monitoring data and the average annual river load estimate based on 10-year monitoring data because the probabilities of the confidence intervals bracketing the true load value of the HT estimator tend to have significantly low values compared to the expected confidence level.

Hydraulic analysis of overtopping flow on rockfill gabion constructed along soil embankment slope of farm pond was developed, and its numerical accuracy was investigated by comparing with overtopping tests in laboratory water flume inclined 20 and 30 degrees of slope. During flood overtopping on the rockfill gabion, there appear both a flow seeping through the rockfill gabion and a flow running over the rockfill. Hydraulic behavior should be properly determined to design a mechanically stable rockfill structure during flood overtopping. A nonlinear FEM seepage analysis and a numerical integration method of the spatially varied flow equation along a large slope of flow were formulated to compute the hydraulics of flows through and over the rockfill gabion, respectively, then combined in an iterative solution technique to solve an exchange of flow mass through the top surface of the rockfill. The hydraulic analysis provides good comparisons of water profile and discharge velocity with those measured in the overtopping tests of the rockfill gabion packed with round cobbles 100 to 200 mm in diameter. A successive improvement of the combined hydraulic analysis is required so that the hydraulics of overtopping flow on the gabion mattresses, which may be the most promising overtopping protection for a farm pond embankment dam, will be properly evaluated.

This study clarified the feature by which project participants reached consensus on the land consolidation project of small-scale distributed orchard plots located on sloping land. In order to reach a consensus, it is necessary to solve the problems of economic loss due to cutting down harvestable trees, the long period of no income, consensus building in a wide area consisting of multiple small-scale plots and securing tenants for the farmland. We found that the dispersion of small-scale plots allowed for the diversification of revenue risks. Additionally, improving the farmland consolidation rate within the plots would likely increase labor productivity. Furthermore, we identified that small-scale decentralization has the merit of enabling flexible selection of project areas according to the situation and reducing the size of the unit of discussion for consensus building. Existing cultivators in the project area can facilitate the transition of agricultural land rights by bridging the gap between landowners who do not wish to continue cultivation and new, relatively young cultivators outside the project area who wish to expand their cultivation scale.

The flood analysis method and its conditions were verified by comparing inundation depth data obtained from flood traces followed by the failure of a small earthen dam on the hillside valley area. The analysis model incorporated the precipitation runoff process and the ground structures (e.g., buildings and drainage channels). The model simulation results were consistent with the inundation depth obtained from flood traces. Precipitation and buildings significantly affected the simulation results, with inundation depths underestimated by more than 20 cm if these factors were not considered. To estimate appropriate inundation depths, it was necessary to input precipitation after the dam breach and during the antecedent (during the flood concentration period).

Agricultural reservoirs were damaged by debris flow at torrential rain in Japan. In this study, the model experiment is conducted to evaluate the load against the embankment. Based on the actual damage case due to debris flow, the peak inflow of sand assumed debris flow is set in this experiment. The load against the embankment is measured under the different condition of distance from slope to embankment and the impounded water. The measured load and calculated fluid force are compared. As the result, acting load is reduced as the distance is large from embankment to slope due to the large volume of debris flow. Especially, the effect is large without water. The evaluation method of fluid force could be proposed for the embankment of the agricultural reservoir.

This study aims to construct the preference and non-preference evaluation structures, which consist of psychological-environment, judgement, and evaluation layer, of the maintenance participants for irrigation ponds, and to clarify those differences between the participants’ generation. Interview survey using the evaluation grid method was conducted in Namegawa town, Saitama prefecture, where many small valleys are formed in the Hiki Hills. As the results, the following items were extracted as the representative judgment items in evaluation structures: play, disaster prevention, landscape, illegal act, and water environments. Comparative analysis of evaluation structures showed that there were differences among generations in terms of the number of items, contents, and relationships between the layers. In particular, the number of items per person in the evaluation and the environment layer was significantly higher in the elderly group than in the mature group. These imply that the elderly participants evaluate the irrigation ponds from multiple perspectives and a wide spatial domain. The reason for such differences in evaluation structure was due to the influence of changes in their daily relationship with the Yatsu landscapes including irrigation ponds.

An accelerated carbonation test and a fracture test were carried out to investigate the change in fracture properties of mortar due to the carbonation. Fracture parameters such as a notch tensile strength and a fracture energy of the carbonated specimens with different water-cement ratios were measured under the different curing conditions. A compressive strength test and a flexural strength test were also conducted for the mortars. The results were compared with the test results of the air curing specimens of the same material age. As a result, the compressive strength of the mortars showed a tendency to increase due to the carbonation. The fracture energy of the carbonated mortars was equal to or higher than that of the air curing specimens. In addition, it was confirmed that the changes in the flexural strength and the notch tensile strength of the carbonated mortars indicated a different tendency by the difference in the water-cement ratio.

In recent years, the utilization of heat pumps that use surface water, which is included in the geothermal heat category, as a heat source has been promoted. Agricultural irrigation canals have been constructed throughout Japan, and agricultural water flowing through canals is expected to be a heat source/sink for heat pumps. In this study, experiment was conducted by installing a sheet type heat exchanger in a shallower depth irrigation canal. The heat exchange characteristics of the heat pump system, such as the quantity of heat (the amount of heat extracted in the heat exchanger) and the heat transfer coefficient (the ease of heat extraction), were evaluated. From the experimental results, it was found that the higher the water temperature in the irrigation canals, the higher the quantity of heat and Coefficient of Performance of the heat pump system (SCOP). It was shown that the heat in flowing water in an irrigation canal can be efficiently utilized by focusing on the flow velocity and water temperature when designing a heat pump system that uses the flowing water in the canals as a heat source/sink.

Solute transport phenomena in subsurface dam reservoirs are affected by cut-off walls, the hydraulic conductivity of the aquifer, and saltwater intrusion. This study conducted solute transport experiments on four types of model aquifers with different hydraulic conductivity distributions. Solute transport behavior was then quantified using image analysis. As a result of quantifying the solute transport routes against both the storage and saltwater obstruction dams and evaluating the refraction of solute transport route crossing the boundaries of layers with different hydraulic conductivity based on centroid locations of solutes, it was revealed that the ratio of the hydraulic conductivity corresponds to the refractive angle of solute transport route. Calculating the spread of solute as the spread of a concentration distribution led to a conclusion that the spread of concentration distribution of solute close to the groundwater table increased with the transport distance regardless of the presence or absence of saltwater wedges. Meanwhile, the spread in horizontal direction of solute in the deep aquifer was limited due to the effect of a cut-off wall. In addition, it was revealed that entropy can be used as the indicator of spread of concentration distribution during short transport distances.

Cement mortar subjected to freeze-thaw cycle action at an early age is expected to suffer serious physical damage, resulting in the cement mortar’s mechanical performance degradation. In this study, we examine the effects of rapidly repeated freeze-thaw cycles on 81 moulded cement mortar specimens of different mixed proportions at an early age by using destructive and non-destructive testing methods. Three mortar mixes with different water-cement ratios of 50%, 60%, and 70% were tested to compare the mechanical properties according to JIS R 5201. The test findings demonstrate that the 50% water-cement ratio of mix composition is highly advised due to its improved early-age strength following the freeze-thaw process. The freeze-thaw test against mortars also indicates a strong link between mix proportions, curing age, and frost durability. Furthermore, ultrasonic pulse velocity showed a high correlation with compressive strength for specimens not subjected to freeze-thaw cycle action. These highlights could provide a laboratory reference of theoretical values for early-age cement mortar on its mechanical properties and can also be applied to extend the strength-weakness theory of cement mortars subjected to freeze-thaw cycles.

In order to quantify the flood control potentials of agricultural reservoirs equipped with spillway gates, we evaluated the effects of prior release at the S dam to reduce peak discharge during floods (peak cut ratio) by applying constant-volume release operation. We found that the implementation of a constant-volume release operation could reduce peak discharge by up to 60.2% during a total rainfall event of 200 mm/d. Although the peak cut effect decreased as the total rainfall increased, it was obtained even in a heavy rainfall event of 350 mm/d. The application of a constant-volume release operation at the S dam did not have an adverse effect in the recovery of the reservoir storage level when it stored inflows at the recession stage of floods, under the condition with the total rainfall amount to initiate a prior release operation.

We examined applicability of carbon stock estimation factor and investigated characteristics of commercially available poultry manure-derived biochar as fertilizer with component analysis and pot cultivation tests. As a result, carbon content and 100-year residue rate of carbon in biochar which used to determine carbon storage effect were showed approximate value with default value that given by J-credit scheme and sufficiently usable to estimation. According to component analysis, there were variation in the amount of fertilizer element including calcium and micronutrient as well as phosphate solubility in poultry manure-derived biochar. These variations considered to be caused by feedstock and pyrolysis temperature, which is also conceivable that these factors are important to identify the features of commercially available poultry manure biochar. The komatsuna pot cultivation test revealed that, in condition of available phosphorus and soluble zinc deficiency in the soil, the poultry manure-derived biochar treatment showed same level dry weight as fast-acting phosphorus fertilizer and micronutrient contained in biochar was available for crop growth.

In a small forested catchment (12.14 ha), both periodic (every two days) and flow-proportional sampling (every five mm aliquot of cumulative discharge) of stream water quality were conducted in 2016 using autosamplers to estimate annual stream loads. Bulk deposition was also measured. A total of 16 water quality parameters were assessed, including soluble and particulate matter. The results of the load estimates still showed large uncertainties for particulate matter, such as several times of point estimates, even with a large number of flow-proportional samples of 183 elements per year, and an acceptably small uncertainty for soluble matter. Such large uncertainties found for particulate matter were attributed to erratic and irregular variations in water quality. For particulate matter, periodic sampling with a two-day interval did not to provide an uncertainty of acceptable magnitude.

In large-scale paddy field area of Japan that rely on irrigation from rivers, stratified water user organization based on rural villages has controlled the water distribution adjustment among water users. In recent years, large-scale farmers have replaced small-scale farmers who have accounted for most water users. Consequently, as water users have decreased and diversified, reconstruction of the system for water distribution adjustment is required. Therefore, in this study, after making clear the basic requirements for the system that have been shown in previous studies, we have qualitatively analyzed the system using a conceptual model for typical irrigation facilities corresponding to the increase in large-scale farmers. The following results were observed: (1) stratified water user organizations with water user groups at each farm ditch as basic units are recommended as the system, and (2) to encourage adherence to agreements through water distribution adjustments, land improvement districts, which have the highest authority in the stratified water user organization, should be given the authority of remote monitoring and control in ICT (Information and Communication Technology) water management.