It is desirable to conserve farmland in mountainous areas from the viewpoints of stable food supply and the fulfillment of multifunctional roles. However, it is difficult to conserve all farmland in these areas in a declining population, and there is a need for measures to rationally conserve each land through that separates farmland that should be conserved from other land. This study was to clarify the actual conditions and issues of establishment of conservation management area for environmental land consolidation project in hilled rural area that require setting conservation management areas. A questionnaire survey was conducted in 27 districts in Niigata Prefecture, which has the largest number of projects completed by FY2019, and the status of landowners and management methods in the conservation management areas was analyzed using land exchange plans and field interviews. The results revealed that almost all of the conservation management areas were set aside for land with unfavorable conditions, and that land exchange between production areas and conservation management areas was difficult because no one wanted to newly convert land to conservation management areas. In addition, as a method of establishing a rational conservation management areas, the paper discusses the usefulness of a method in which dispersed abandoned farmland is accumulated in a conservation management area as non setting substitute lots, and all landowners jointly acquire them as creating substitute lots.

This study analyses the historical background of the amendment of the Farmland Consolidation Act in Japan. Just in ten years following the establishment of the act, the principal objective of the act had been changed from the one to advance farmland adjustment projects to the one to drive irrigation and drainage projects. Referring to the fundamental role of agriculture to produce food, the study reveals the following points by considering the technical constraints and resource limitations in the Meiji era. Agricultural technology had not developed sufficiently to bring in mechanization, which would have enabled adjustment projects to amalgamate fragmented farmland and enlarge small-scale farming plots. The inefficient, feudal land-use system could not be modernized due to the seasonal labour intensity of paddy cultivation, to which farm households was only capable of supplying limited numbers of labours. Adjustments to the distorted shape of farmland would increase water usage in paddy fields, but the water resource was not developed sufficiently to enable farmland adjustment projects to modernize the feudal irrigation system, which had been developed under conditions of water scarcity. With these technical constraints and limited resources, agricultural output had to be increased without modernising the feudal production system. The Farmland Consolidation Act then shifted its objective, from farmland adjustment work to irrigation and drainage projects that would not affect the collective actions of an agrarian community.

The effect of silicate-based surface impregnations on the abrasion resistance of mortar was verified using a water jet abrasion test. Several mortar substrates with different water-cement ratios and fine aggregate contents were used in the experiment. The test time required for the specimens with and without impregnations to abrade by 1 mm was determined, and the ratio of these times was evaluated as the effect of the impregnations on abrasion resistance. In addition, the depth at which the abrasion resistance was improved by the impregnations was estimated from the relationship between the depth from the surface of the specimen and the abrasion rate. The results revealed that the effect of the impregnations on the abrasion resistance and reforming depth was greater when the water-cement ratio of the mortar substrate was higher and the amount of fine aggregate was lower. While the impregnations contributed to an improvement in abrasion resistance near the mortar surface, there were indications that they might also facilitate abrasion progression beyond a certain depth.

Geopolymers are composite hard materials made by mixing industrial by-products such as fly ash, steel making slags and garbage melting furnace slags as binders and alkaline liquid activators such as NaOH and sodium silicate as activator. The compressive strength of geopolymer q_u is considered as a function of w which is the weight ratio of activator and binder and η which is the weight ratio of liquid NaOH and sodium silicate. The maximum compressive strength q_umax was defined as the maximum value among the peak values of q_u which were obtained for various values of w and η. This research discussed the chemical and mechanical characteristics, and the prediction method for the q_umax by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) observation of binders.

Larger floods are causing overtopping failures of irrigation pond embankments due to insufficient storage or release capacity for the existing reservoirs. Among the traditional modifications and innovative designs for resolving this problem, an overtopping protection system is promising to be most applicable because it can effectively regulate or decrease the amount of soil erosion due to overtopping flow, and keep the soil embankment away any troublesome damage or breakage during the overtopping. Gabion mattresses, an assembly of mattress-shaped wire mesh frames packed with rock particles and placed on the embankment crest and downstream slope, are proposed for the overtopping protection of the irrigation pond embankment. Both their protective safety against soil erosion due to overtopping flow and their structural safety against slide failure along embankment surface are verified based on the hydraulic analysis of the overtopping flow and the stress deformation analysis of the gabion mattresses. The design procedures of the gabion anchors and the energy dissipator required to keep the gabion mattresses structurally safe are successfully provided.

Cattle raising method using grazing is useful for saving labor, maintaining abandoned land, and improving cattle health. Japanese brown cattle-Kochi, which are suitable for grazing, are breed in grassland in the campus of the Faculty of Agriculture and Marine Science, Kochi University from March to November every year. In this study, we developed a method for estimating dry grass weight (mean absolute error: 0.05 to 0.15 kg･m⁻²) that can be used over a long grazing period. By applying this method to satellite images taken in 2022 and 2023, we attempted to visualize and compare the dynamics of dry grass weight, and to extract issues or knowledges on grassland management. The results suggest that for improving the efficiency and effectiveness on grassland use, it is necessary to pay attention to grass cultivation before the grazing period, rotation planning of grassland fields based on the topographical and geographical characteristics of each field, and environmental design considering the behavioral characteristics of cattle.

We developed models of component technologies, namely irrigation pond networks and pipeline systems, and incorporated them into the DWCM-AgWU (Distributed Water Circulation Model with Agricultural Water Uses). Using the constructed model, we evaluated the effects of the irrigation pond and pipeline systems on changes in basin water management. As a result, a calculation method was proposed for estimating inflows and outflows of a single and/or a series of irrigation ponds, and the method was applied successfully to numerous irrigation pond systems of various sizes. As for a pipeline irrigation system, a method for introducing a demand-driven water conveyance structure was developed by integrating farmers’ operations for terminal irrigation facilities in irrigation areas. A model implementing the developed technologies was applied to an actual basin. The impact of irrigation ponds on river water use was then evaluated, and the amount of agricultural water saved was calculated by combining the developed pipeline model and ICT water management technology. In addition, the proposed component technologies and additional expansions of them could be used to assess the impact of the integration of irrigation ponds and the expansion of ICT water management on basin-wide water use, as well as to assess changes in runoff due to climate change.

The seismic performance assessment of major embankment dams against the mega-earthquake, indicated as Level 2 earthquake, has been consistently undertaken in Japan. In order to evaluate the seismic performance, the residual sliding displacement of the slopes or the settlement of the crest are commonly predicted upon the response acceleration computed by preceding dynamic response analysis employing the equivalent linear method. Nevertheless, this standardized approach sometimes encounters unacceptable results in practice. For example, the settlement is underestimated especially when vulnerable embankment dams with lower stiffness are subjected to intense seismic motion. This paper discusses the limitation of the above conventional approach to the seismic performance assessment and reveals that the difference in shear strength used for the dynamic response analysis and the computation of the sliding displacement plays an important role in evaluation of the residual deformation. In addition, the seismic response analysis with an elasto-perfectly plastic constitutive model can be a feasible approach to the computation of the residual deformation under severe earthquake loading.

The dynamics of substances in flooded water after soil disturbance caused by mechanical weeding in paddy fields are not fully understood. This study investigated the dynamics of dissolved inorganic phosphorus (DIP) released from soil to flood water due to soil disturbance in pots simulated paddy fields with soil managed with two different fertilizers, one chemical fertilizer and the other compost. The pots with soil managed with compost had an increase in DIP in flooded water as a result. It was considered that the increase in DIP in flooded water in the compost soil plots of the simulated paddy fields was influenced by the molar ratio of iron (II) to DIP released into the flooded water and pH of the flooded water.

Many existing fishways in Japan are based on pool and weir designs. Whereas effective for species such as ayu and salmon, they are not suitable for small-bodied gobies (Gymnogobius spp.) during their upstream migration. Therefore, to acquire knowledge for enhancing fishway functionality, we conduct experiments using a full-scale fishway model and wild gobies with an average standard body length of 3.9 cm during their upstream migration period. The overfall section of the weir is inclined at 45° and features a thickness of 30 cm. When the head difference among pools (Δh) is 10 cm, more than 90% of the gobies successfully migrated upstream in the overfall section. However, beyond 15 cm (Δh), the flow velocity at the entry from the pool's tranquil zone to the overfall jet is about 160 cm/s or greater. Under these conditions, many gobies exhibit disrupted postures during upstream migration, thus resulting in lower success rates.

The authors have been studying heat utilization by heat pumps for running water in irrigation canals, and in a previous report, they have shown that the higher the water temperature in the canal, the higher the heat exchange rate of the heat exchanger, the amount of heat exchanged by the heat pump, and the energy consumption efficiency (SCOP) of the heat pump system. The objective of this study is to construct a heat pump system that can handle the hydraulic conditions that may occur in irrigation canals. In this study, focusing on flow velocity and water depth, a full-scale model experiment was conducted using flowing water in a shallow canal with a water depth between 0.23 m and 0.50 m as a heat source, and the heat exchange characteristics of the heat exchanger and SCOP were evaluated. The experimental results showed that the heat transfer coefficient increased by approximately 5% for each 0.20 m･s^-1 increase in flow velocity under relatively high velocity conditions of 0.50-0.90 m･s^-1, that the heat transfer coefficient, quantity of heat and SCOP decreased when the heat exchanger was exposed to air, and that the quantity of heat were higher for parallel pipes.

We made biochar samples from rice husk at four different pyrolysis temperatures and investigated effects of pyrolysis temperatures on elemental compositions, carbon degradation resistance, creation of cristobalite, which is carcinogen, and dissolution characteristics of organic and inorganic compositions to evaluate an applicability as a filter material in subsurface drainage systems. Estimated unmineralized carbon in soil after 100 years was about 40% for rice husk biochar at 400℃ to less than 10% for rice husk biochar at 700℃. Creation of cristobalite was not confirmed for pyrolysis by 700℃. With increasing pyrolysis temperature, dissolution of organic carbon was suppressed. On the other hand, with increasing pyrolysis temperature, potassium, which shows alkali metal, was accumulated, and it should be took careful for high pH in subsurface drainage water from rice husk derived biochar produced at high temperatures.

One of the inputs to the WEPP model for simulating soil erosion is the soil erodibility coefficients, which indicate the soil-specific susceptibility to erosion. Rill erodibility and critical shear stress are generally calculated using equations that use soil texture and organic matter content as variables, but these equations may not be applicable to Japanese soils. In this study, laboratory rill erosion tests, liquid plasticity limit tests, and particle size tests were conducted on 15 Japanese soils to propose alternative equations for the rill erodibility and critical shear stress. The results showed that the possible range of the soil erodibility coefficients depends on whether the soils are plastic or not, and that the non-plastic soils were more erodible than the plastic soils. For plastic soils, the rill erodibility was formulated using the plasticity index or sand content as variables, and the critical shear stress was generally positively correlated with clay content. On the other hand, for the non-plastic soils, there was a positive linear relationship between the rill erodibility and sand content, and the critical shear stress was generally constant.

In Japan, the number of farmers is decreasing. In response to the scarcity of agricultural workforce, farmlands are being accumulated among farmers to maintain the agricultural infrastructure. This approach is changing the structure of agriculture in Japan, but the current water supply plan does not consider the impact of this change in agricultural structure. This study was conducted to determine the influence of multiple rice varieties and the placement of rotation crop blocks on water allocation within a district in open canal district with a farmland accumulation rate of approximately 70%. It was found that the multiple-crop grouping by large-scale farming operations enabled a clear division of the timing of puddling for each small irrigation canal. Grouping of crop varieties by large scale farming enterprises is an effective method to reduce water shortage even under the situation where farmland will be further accumulated in the future. Furthermore, it is suggested that the arrangement of rotation crop block may lead to the decrease in the occurrence of water shortages.

The effect of surface impregnation may vary depending on the conditions of the applied substrate. In this study, we experimentally verified the effect of the moisture content of a substrate during its application on the scaling-suppression effect of impregnation. Specifically, the scaling-suppression effect of impregnation was compared for mortars with water content ratios of 0%, 4%, and 6% under each condition. Results show that when silane-based impregnation was applied, the scaling-suppression effect decreased at a water content ratio of 6%. However, when silicate- and silane-based impregnations were applied to the layers, the scaling-suppression effect decreased with the water content ratio of the substrate. These results indicate that the appropriate dry/moist conditions differ depending on the impregnation application pattern. However, even considering the performance degradation caused by the water-content state of substrate, the result shows that scaling was significantly suppressed by the application of impregnation compared with the case where impregnation was not applied.

Swimming experiments were conducted on wild 0+ Cottus reinii with an average standard body length of 2.5 cm. Our key findings are: 1) C. reinii exhibited repetitive behaviors of resting on the bottom and forward movement in running water. During forward locomotion, propulsion was achieved by laterally oscillating the body, using the caudal fin for thrust. While at rest on the substrate, they maintained their position by pressing their pectoral fins against it. 2) The flow velocity during measurement ranges from 20-60 cm/s, 95% of one swimming time from resting to resting were <1 s. The maximum swimming speed measured during this period was 100 cm/s. 3) The flow velocity enabling forward movement for C. reinii was estimated to be <70 cm/s. 4) Flow velocities of 50 cm/s resulted in 55% of C. reinii exhibiting forward movement ≥30 cm in running water. However, this percentage decreased to 17% under flow velocity conditions of 60 cm/s.