We investigated the overwintering habitats and environments of the endangered Tokyo daruma pond frog, Pelophylax porosus porosus, in the paddy of multiple areas. The frogs overwintered underground in every district. Overwintering habitats differed among areas; frogs overwintered in paddy fields in areas where paddy fields were dominated, whereas they chose different fields in areas with mixed fields. The frogs avoided wet fields and overwintered on adjacent ridges and slopes. There was no significant difference in the soil moisture content (volume water content) of the different areas in which frogs over wintered. Moreover, when the wintering and non-wintering environments of the same paddy field were compared, the soil water content during wintering was significantly lower. These results suggest that the frogs avoid overwintering in fields with high soil moisture and prefer dry soil habitats.

To evaluate the impact-abrasion resistance of materials subjected to intense water flow, such as in drop structures, headworks or aprons, we prototyped an impact-test setup that allowed a steel ball to drop freely from a height of 1 m onto the surface of a 150 mm side cubic concrete specimen. Comparative tests were conducted using steel balls of two different weights (1,041.7 g and 439.5 g). Two specimen inclination angles (10° and 20°) were chosen. The dependence of specimen-surface wear, on ball weight and inclination angle, was evaluated. The results showed that the heavier the steel ball, the more the specimen wore. Furthermore, it was found that the influence of the specimen inclination angle could be practically ignored when the compressive strength of concrete was 40 N/mm² or more. However, when comparing the maximum wear depths from tests using steel balls of different weights and diameters, it is necessary to consider the influence of additional parameters such as steel ball volume and weight per unit area.

The storage structure and processes for generating surface runoff of a distributed water circulation model were modified to improve short-term runoff simulation and evaluate flood control potentials of agricultural facilities. The application of the original and updated models to two (small and large) floods in the Yagisawa reservoir catchment improved the NSE score from 0.889 to 0.956 and relative error of peak inflow from 20.9% to 8.7%. The results of applying the updated model to nine agricultural reservoir catchments showed that the NSE scores for medium to large floods in each catchment were greater than 0.696, except for one small (5.1 km²) catchment. The updated model was able to simulate the short-term runoff from the onset to peak in the medium to large floods. The updated model can be used to evaluate the effectiveness of flood control operations in agricultural facilities and other flood response measures on a catchment scale.

Simulated discharges with and without prior release were compared to evaluate the reduction of peak discharge (peak cut ratios) at reservoirs and downstream points. Peak cut ratios were characterized based on two indices: storage volume prepared by prior release divided by reservoir catchment area (normalized storage) and ratio of catchment area at downstream points to that of the reservoir (reservoir areal ratio). The peak cut effects at reservoirs increased sigmoidally as the normalized storage increased. The peak cut effects at downstream points declined approximately linearly as the reservoir areal ratio decreased. Based on these two relationships, the flood control effects for any agricultural reservoirs can be estimated based on normalized storage and reservoir areal ratios.

In this study, biochar was made from three different raw materials (rice husk, rice straw, and bagasse) at different pyrolysis temperatures and time, and its properties and effect of biochar on the growth of salt-tolerant crop (Sesbania cannabina) when applied to saline soil (EC_e = 0 dS/m, 4.0 dS/m, 8.0 dS/m) were determined. Pyrolysis temperatures of 250°C to 300°C were suitable for carbonization, and yields (ratio of mass after carbonization to mass before carbonization) decreased with increasing pyrolysis time. The content of water-soluble ions tended to increase with higher temperatures and longer time. In the Sesbania cannabina cultivation test, rice husk biochar and rice straw biochar application significantly increased dry matter weight compared to the control and bagasse biochar application at a soil salinity of EC_e = 8.0 dS/m. The cultivation tests using rice husk biochar and rice straw biochar prepared under different carbonization conditions showed no significant differences in dry matter weight, suggesting that the application of biochar using a simple method, in which the material is packed in a pail and heated from the outside by a fire, is the most suitable for Sesbania cannabina cultivation in saline soils.

The objective of this study is to evaluate the salt tolerance of Moringa oleifera Lam. in four different conditions of EC_e (Electrical conductivity of the saturated paste extract) (Control, 4, 8, and 16 dS/m) added with NaCl to paddy soils, with the aim of utilizing Moringa oleifera Lam. as a conversion crop in salinized paddy fields. The dry matter weight of above-ground parts, excluding roots, did not differ significantly among the four conditions. The highest height and dry matter weight were observed when the plants were grown at 4 dS/m. On the other hand, dry matter weight of roots grown in 8 dS/m and 16 dS/m soils and height in 16 dS/m soil were significantly lower than those in 4 dS/m soil. The Na content per gram of dry matter increased with increasing salinity. The results indicate that Moringa oleifera Lam. grows well when the salinity is less than 4 dS/m, but growth inhibition in the roots was observed when the salinity was 8 dS/m. At 16 dS/m salinity, there was a clear growth inhibition in height, total dry matter weight, and root dry matter weight compared to other conditions.

Appropriate management and maintenance of irrigation facilities and rural roads are required to maintain the performance, due to the decrepitation. Concrete materials are used in a lot of irrigation facilities and rural roads. Quantitative evaluation of damage in concrete materials is an important technical issue in the maintenance and management of them. In this study, Acoustic Emission (AE) measurement is introduced to the compressive test for concrete, and AE double logistic analysis is performed using the AE energy characteristics to attempt quantitative damage evaluation. A double logistic curve is fitted to the cumulative AE energy release rate, and the damage parameter is extracted. In addition, waveform discrimination is performed by random forest, which is one of the supervised machine learning methods. The AE energy emission characteristics for each type of waveform are compared to verify the applicability of the double logistic curve. As a result, the double logistic curve corresponded to the crack state, and the correlation between the damage parameter and the dynamic modulus of elasticity are confirmed.

In this study, we attempted to identify efflorescence using a digital iamge in reinforced concrete slabs of road bridge that constructed 50 years ago. Three feature values were set as explanatory variables: luminance value, pixel value after DoG (Difference of Gaussian) filter, and pixel value after the histogram equalization. The algorithm was decision tree or random forest. The proposed method has a 10% higher accuracy rate (accuracy rate: 95%) than Ohtsu method, which is a discriminant analysis method. More accurate detection of efflorescence can be achieved by the same amount of data for the presence and absence of efflorescence. The usefulness of the pixel values after histogram equalization is revealed by evaluating the importance of explanatory variables based on SHAP values. Therefore, the proposed method can contribute to the automatic detection of efflorescence in RC slabs of road bridges.

The internal temperature of concrete open channels is an important factor involved in the occurrence of frost damage. It is therefore essential to know this factor to predict deterioration of concrete open channels in cold, snowy regions. In this study, the thermal properties of surface coating materials used to repair frost damage were determined, and the internal temperatures of the side walls of surface-coated concrete open channels in cold, snowy regions were estimated using one-dimensional unsteady heat conduction analysis. The applicability of the estimation formula was verified by comparing the results obtained with the formula and the actually measured temperatures of specimens installed in a channel in use in Hokkaido. The results of the study show that the temperature inside the side walls of the surface-coated concrete open channel during the winter season from December to March can be estimated with an estimation accuracy of approximately ±1.5°C or less by one-dimensional unsteady heat conduction analysis using the surface of the concrete open channel side wall as the heat conduction boundary at the range from the surface to a depth of 50 mm.

In this study, irrigation ponds in seven communities located downstream of the Dainichigawa Dam (Minami-Awaji City, Hyogo Prefecture) were categorized according to their functions in the water use network within the irrigation ponds complex. As a result, the irrigation ponds were classified into six categories based on the source and destination of water intake and distribution. The largest number of irrigation ponds in this area are "water catchment type", which take water from surrounding mountains and rivers and distribute it to other ponds, even though the area is the beneficiary area of a dam. The analysis of the location characteristics of each type and the questionnaire survey on the actual management of irrigation ponds showed that the "water catchment type" tends to be found in small ponds located on a slope and relatively far from the dam. On the other hand, the "relay type" and "utilization type" ponds, which take water from other ponds, are large ponds located relatively close to the plain, and are more likely to be managed in a continuous systematic manner. It was also shown that the "water catchment type" and "relay/utilization type" differ in the implementation of water fall as a countermeasure against heavy rainfall, and in the content of maintenance required in the future.

Recently, buckwheat has started gaining focus as a novel item. However, buckwheat is susceptible to excess soil moisture stress and severe yield decrease in wet fields. Therefore, agricultural production corporations, cultivation farmers, and people concerned with buckwheat municipal cultivation require information regarding wet damage factors affecting buckwheat yield. Herein, the spatial distribution of buckwheat yield in Ugo, Akita Prefecture, was established. Further, we statistically analyzed the relation between buckwheat yield and wet damage factors, i.e., topography, soil, drainage channel and drainage pump maintenance, and underdrainage function. Results showed that buckwheat is cultivated where there is a high risk of wet damage, such as damp land, and underdrainage makes a low risk of wet damage on the low-level ground. Therefore, in Ugo town, the information on topography, drainage channel and drainage pump maintenance, and subsurface drainage function helps estimate the wet damage risk.

The distribution area of bamboo forests was databased using aerial photos as basic data for the management and effective utilization of bamboo forests. However, bamboo forests are expected to expand over the year, and a method to continuously monitor their expansion is required. Therefore, using Sentinel-2 satellite images, the classification tree (overall accuracy: 95%) was created using satellite image in the shortwave infrared band (spatial resolution: 20 m), which is reported to be effective for extracting bamboo forest. By applying this tree to satellite images taken in 2018 and 2021 and comparing the bamboo extraction results, we attempted to identify locations that bamboo forests might expand, and the expansion was confirmed in 61% of the sites surveyed. This result showed the usefulness of a simple method using a single band of satellite image to monitor the expansion of bamboo forests.

The target area of this research is one in which the irrigation starting date and planted rice varieties were determined for each paddy field using satellite data and paddy cultivation ledger data. Due to utilizing normalized difference vegetation index (NDVI) images for managing the cultivation of rice paddies, the relationship between NDVI obtained from Sentinel-2 satellite data on June 29 (before the heading stage date) or August 1 (after the heading stage date) in 2018 and the rice planting period (date of transplanting five days after the start of irrigation) for the paddy fields where Akitakomachi (early-maturing cultivar) or Koshihikari (medium-maturing cultivar) rice was transplanted. Field lot average values of the NDVI aggregated for each field were used for the analysis. In addition, relative evaluations were conducted of the rice yield and rice protein content for the paddy fields where Akitakomachi rice was transplanted from date No. 1 (April 6–8) to date No. 5 (April 26 to May 2) based on the analysis results. The relative evaluation of rice yield was performed using the field lot average NDVI on June 29, and the relative evaluation of the rice protein content was performed using the field lot average NDVI on August 1. Fields judged to have a high rice yield and high rice protein content in this evaluation are fields that should be considered for reducing the amount of additional fertilization and the timing of additional fertilization. Providing this information to farmers should be useful for their cultivation management in the next year.

This study clarifies factors determining residents' evacuation intention during irrigation pond disasters. First, an evacuation intention model is constructed, following which a questionnaire investigation is conducted at Rokujoin-naka, Asakuchi city, Okayama prefecture, using the evacuation intention model. The multiple linear regression analysis reveals that the factors strongly influencing evacuation intention are a positive attitude when called to evacuate, the perception that people around oneself also need to evacuate in times of disaster, thinking that one's home will be damaged if the irrigation pond collapse and a positive attitude to evacuate. Therefore, to encourage residents' evacuation intention when the irrigation pond is in danger of collapsing, calling for evacuation, fostering people who urge resident to evacuate and making resident aware of the risks of the irrigation pond collapsing using hazard map, etc. are important.

As the external environment surrounding rural areas becomes uncertain and complex, the importance of scenario planning, in which multiple futures are assumed, and countermeasures are considered, is increasing. However, a government-led scenario planning workshop (WS) requires a high level of scenario accuracy, and thus requires a complex process including preliminary surveys and the gathering of experts. Therefore, this study focused on the participants' learning effect of the scenario planning workshop and devised a scenario planning workshop method that can be held with a small number of participants without calling in experts or conducting preliminary surveys. A workshop with an ex-post questionnaire was conducted in a town in Kyoto Prefecture. The results showed learning effects on participants in (1) building preparedness through multiple depictions of the future, (2) updating participants' mental models, and (3) strengthening relationships among various stakeholders. Future issues to be addressed include the implementation of the WS with diverse participants, verification of the range of themes that can be discussed by rural residents, the provision of relevant information to participants to facilitate the extraction of keywords, and the shortening of times allowed for the WS.