The annual maximum series (AMS) method is generally applied to estimate the return level of extreme rainfall. The sample size, however, is so small that the estimated return level and return period are strongly fluctuated even when just one or a few extreme-size minima or maxima are included by change in a target duration for the analysis. That often disturbs correct estimation of secular change in return level and return period of rainfall. In this study, we estimated the secular change in the return level and that in return period of daily rainfall in Japan by applying the metastatistical extreme value (MEV) distribution to daily rainfall data. The results showed that the estimated 100-year daily rainfall by applying the MEV distribution showed similarly increasing trend nationwide as when the annual maximum method was applied. In addition, compared with the AMS method, the fluctuation range of the estimated values was suppressed, and the trend of annual change was shown more clearly.

Shear and pull-off bond strengths between inorganic repair material and concrete were evaluated with different conditions of water-cement ratio, surface roughness and curing. Both bond strengths increased with an increase in strength of concrete. It was confirmed that, when concrete had identical strength but different microstructure, specimens with concrete having porous microstructure showed larger shear and pull-off bond strengths than that with dense microstructure. It supposed that, in the case of concrete having porous microstructure, bonding interface between concrete and inorganic material was formed by penetration of primer or polymer cement mortar into concrete resulting in larger bond strength. On the other hand, surface roughness of concrete improved significantly shear bond strength, but not improved pull-off bond strength. There results indicate that surface roughness influences differently on bond strength depending on a direction of stress.

Grey-headed lapwings are wild birds that nest in paddy fields and are closely associated with agriculture, but farming activities have been reported to be the main cause of their breeding failures. With the increasing development of water facilities and the shift to early crop rice, elucidating the impact of different crop calendars for rice cultivation on their breeding is important in order to achieve a symbiotic relationship between Grey-headed lapwings and agriculture. This study focused on Hatsushimo, a late rice crop variety grown in Gifu Prefecture. We investigated the breeding status of Grey-headed lapwings between study sites with different crop rice calendars in Gifu Prefecture to clarify the effect of changes in crop calendars for rice cultivation on their reproduction. The results showed that late rice production varieties created a favorable environment for Grey-headed lapwings breeding lasted longer. And, that production less affected to their breeding by farming activities than the other areas. The results of this study indicate that a local rice calendar considering the life histories of paddy creatures could achieve symbiosis.

We employed the COsmic-ray Soil Moisture Observing System (COSMOS) to monitor temporal changes in epithermal neutron count in reclaimed farmland characterized by high levels of clay deposits. The number of epithermal neutrons was corrected for atmospheric pressure, absolute humidity, and background neutron count hourly. The corrected hourly count of epithermal neutrons (N) showed substantial variability and no discernible correlation with the volumetric water content (θ) measured by time-domain transmission (TDT) sensors at three different depths (5 cm, 15 cm, and 25 cm) in proximity to COSMOS. However, the daily mean of N exhibited a clear negative association with θ at a depth of 5 cm. These findings suggest that COSMOS can effectively monitor changes in mean θ in surface soils of reclaimed agricultural land with high levels of clay and a tendency to retain high soil moisture conditions.

The fertilizer components and salinity of sediments (fish feces, leftovers, etc.) collected from aquaculture tanks, where saltwater fish are raised, were investigated for application to farmlands. The sedimentation solids were acidic at pH 4.9, and the C/N ratio was lower than those of cattle manure and swine manure. Total nitrogen and phosphate were higher than those of cattle manure and swine manure, but potassium was much lower than those of cattle manure and swine manure. The content of heavy metals in the sedimentation solids was well below the allowable amount for sludge fertilizer. The sedimentation solids contained high concentrations of chloride (Cl^-) and sodium (Na⁺) ions. The origin of the Cl^- and Na⁺ was thought to be due to seawater in the sedimentation solids. Since commercial compost made from cattle manure contained about 1.82% Cl^- and 0.57% Na⁺ in dry matter, it was considered that the sedimentation solids would not be a problem in application to agricultural land if the Cl^- and Na⁺ contents were similar or lower.

A survey of rice yield components was conducted in 2019 in several paddy fields where agrivoltaic systems were implemented in Marugame City, Kagawa Prefecture. Cnaphalocrocis medinalis (a type of pest) infestation was observed in all paddies except for Paddy b. Under the panels of the Paddy b, yield, number of rice ears, ripening rate, number of seeds per ear and thousand-grain weight were 54%, 64%, 86%, 98% and 99% respectively, compared to outside of the panels. However, there were no statistically significant differences among the factors other than yield. In 2020, a detailed distribution survey of rice ear numbers was conducted in Paddy b. The results revealed that the number of ears varied by more than 50 ears/m² within the rows under the panels, while the number of ears outside the panels increased as the rows moved away from the panels. It has been revealed that variations in rice growth occur depending on the location, both within and outside the panels, due to the continuous movement of panel shadows caused by the changing inclination of the sun based on seasons and time.

A method for calculating the uncertainty of estimates of the riverine constituent loads, which comprise a major part of the material supply from the terrestrial area to the receiving waters, has not been established. In this paper, we propose the bias-corrected regression estimator that combines the Horvitz-Thompson estimator with the rating curve method as an asymptotically unbiased and precise river load estimator based on a small-size sample. In addition, confidence intervals for the proposed estimator are also proposed as a precise confidence interval. The central 95% confidence interval of annual river load by the proposed method was evaluated in terms of the bracketing probability of the true value and the width of the confidence interval, using monthly routine sampling strategy based on 173 daily water quality data sets from nine watersheds in the United States. The results demonstrate that the proposed method can provide more precise intervals, with appropriate coverage of the true loads, than the previously proposed interval based on the bootstrap-t intervals of the log-transformed Horvitz-Thompson estimator.

The purpose of this study is to investigate the trend of landslide movement and displacement characteristics of sliding surfaces at different depths for a landslide at Toromeki, Ehime prefecture, Japan. We utilized observation data of borehole inclinometers at the three boreholes and self-recorders of groundwater level, rain-gauge situated approximately 3 km from the landslide. For the borehole located at relatively high elevation, sliding surfaces were observed at depths of 1 to 4 m and 9 to 10 m. At relatively shallow sliding surface (i.e., depth of 1 to 4 m), displacement velocity increased during the spring, summer and fall months when precipitation was higher, whereas for depth of 9 to 10 m it increased only during the period when average daily precipitation exceeded 50 mm. On the other hand, for the lowest elevation borehole, there were two sliding surfaces at different depths, but none of them showed any response to rainfall. We also found that regardless of the borehole, the sliding surfaces at different depths displace in similar directions for the landslide.

Rockfill reinforced by wire mesh cover or steel mesh frame may be employed effectively as an overtopping protection of embankment dams. During flood overtopping on embankment dam, there appear a flow seeping through the rockfill and a flow running over the top surface of rockfill. As both flows hydraulically attack rock particles to make the rockfill structure unstable, hydraulic properties such as water profile, discharge velocity and hydraulic gradient of flow should be properly determined in order to design a mechanically stable rockfill structure during flood overtopping. A nonlinear seepage analysis using FEM and a numerical integration method of the spatially varied flow equation are formulated to compute the hydraulics of flows through and over the rockfill, respectively, then combined in an iterative solution technique to solve an exchange of flow mass through the top surface of the rockfill. A rectangular rockfill embankment packed coarse gravels and cobbles into being constructed in the laboratory water flume, the flow depth and the piezometric head as well as the flow discharge are measured during partial and complete overtopping. The flow analysis developed above provides good comparisons with the measurements in the laboratory water flume tests, and is shown to be effective for calculating the hydraulics of the overtopping flow on the rockfill.

This study evaluated the characteristics of annual river loads based on inter-annual rating curves as power-law relationships between annual specific discharge and annual specific loads. Relationships between two parameters of rating curves and land use ratio were investigated using long-term daily paired observations of water quality and discharge from nine watersheds in the United States with a variety of land use and area. The results suggested the quantitative relationship between two parameter values and land use ratio. Estimation of the inter-annual rating curve was also investigated based on long-term monthly random monitoring of water quality. Such low-frequency monitoring data can provide an accurate but imprecise estimates of inter-annual rating curves.

Steel sheet pile revetments have been widely used in agricultural canals in the low flatland areas with drainage fields. In service facilities, used for over 40 years, partial repair work is not feasible due to overall corrosion. A newly renewal method with long service life and decrease life-cycle cost is required. By the authors, the stainless-steel sheet pile is proposed, which has viewpoint of corrosion resistant and economical. In this study, detection of corrosion characteristics of made stainless-steel in an agricultural drainage field by coupon tests. Thus, the results of characteristics of stainless-steel in actual environments, the corrosion properties of the developed material are improved compared to conventional steel sheet pile materials. The stainless-steel material can be selected according to the service period by converting the corrosion allowance used in the design of steel sheet piles to cost.

Cracks are the major deterioration of concrete structures of agricultural irrigation facilities. Admixtures to suppress concrete cracks are expansive additives and shrinkage-reducing admixtures, and the crack-suppressing effects of each admixture have been clarified. However, the number of researches that clarified the effect of concrete crack suppression when several admixtures were combined has not been argued enough. In this study, the effect of suppressing cracking of the concrete mixed with the polypropylene short fibers, expansive additives, and shrinkage-reducing admixtures was evaluated quantitatively. Furthermore, the laboratory and the field tests verified the applicability to medium-flow concrete because there is concern that the addition of the polypropylene short fibers may reduce the workability of concrete. As a result, it was concluded that the medium-fluidity concrete mixed with the several admixtures proposed in this study has a high crack suppression and could be applied to agricultural irrigation facilities.

Annual river load is the total mass entering receiving water bodies through a river. High-flow water quality monitoring has often been used in conjunction with periodic water quality monitoring to accurately and precisely estimate annual river loads. In this study, using daily water quality and discharge data from nine watersheds for a total of 25 years with seven water quality parameters, the load estimator that can provide accurate and precise load estimates was investigated based on two sampling strategies; monthly random sampling with high-flow sampling (eight samples per year) and discrete flow-proportional sampling with a sample size of 12. As a result, the bias-corrected regression estimator can provide accurate and precise load estimates for the former sampling strategy and the Horvitz-Thompson estimator can do so for the latter sampling strategy. The estimator by the rating curve method had a tendency to produce biased load estimates for the former sampling strategy and greater uncertainties for the latter compared to the other two estimators.

A method to determine the modulus of deformation for horizontal direction required in the design of steel sheet pile using the horizontal specimen by unconfined compression test was invented, and the modulus of deformation obtained from the normal test using the vertical specimen and borehole horizontal load test were compared. It was shown that a specimen with a diameter of 35 mm and a height of 63 mm can be made by utilizing the usual method of trimming out a specimen from a thin-wall sampling of soil material. From the results of the unconfined compression test using horizontal and vertical specimens, a significant difference in unconfined compression strength by the soil anisotropy was observed, but a significant difference in modulus of deformation was not observed. The modulus of deformation obtained from the borehole horizontal loading test was about 1/5 small value of the average modules of deformation obtained from the unconfined compression test using the horizontal specimen.

Several irrigation tunnels are damaged due to the application of plastic earth pressure for a long period and deformation progresses as time passes. In order to consider the maintenance for these damaged irrigation tunnels, evaluating the damage conditions, such as the convergence of the tunnel lining and cracks, is of crucial importance. This paper compares the numerical results using the RBSM (Rigid Body Spring Model) with the results of model tests for the tunnel lining and the ground under plastic earth pressure. To investigate the applicability of the RBSM, comparisons are made based on the deformation and damage patterns. The results show the numerical validity of the crack point sources and the crack generation loads.

In this study, we analyzed effect of pyrolysis temperature on fertilizer element concentration in biochar derived from three different livestock manure or compost: hen, broiler, and swine (broiler manure contain bedding litter, and swine compost contain bedding litter and plant wastes for drying). Macronutrients such as phosphate, potassium, and calcium showed an uptrend in nutrient content as the pyrolysis temperature got higher. Phosphate became less soluble at temperature above 600°C due to a decrease in the rate of easy-soluble form while the content of slow-release increased which also reflected in recovery rate of soluble form phosphate. Micronutrient content was different depending on livestock species; hen manure and broiler manure contained high levels of Zn, while swine manure contained high levels of Fe. Available Cu and Zn concentration showed downward trend at 700°C or higher temperature which indicates those elements changed into insoluble form. Wet acid digestion fraction of Zn was also showed downward trend above 700°C which indicates loss of Zn from biochar. Based on the results, manure biochar that has been pyrolyzed at 400-500°C would be good for supplying macronutrients, and that has been pyrolyzed at 400-600°C would be good for supplying micronutrients.

The field water management system provides “constant water level control,” which manages the water level within a certain range during the post-rice planting period in a paddy field. In the “constant water level control,” the water level in the paddy field rises to a set level due to irrigation, and then it fluctuates periodically, decreasing from the set level to the specified control range. The water requirement rate and irrigation water volume were calculated using the fluctuation range of water level data from the field water management system, and the calculation method and its accuracy were evaluated through comparison with actual measurements. Although the calculated and measured water requirement rates were influenced by the length of observation time, they showed a difference of approximately ±1.5 mm d^-1. The irrigation water volume during the post-rice planting period was calculated using the water requirement rate. A difference was found between the calculated and measured daily water volume, and the total water volume for a period of approximately 1 weeks was almost similar to the calculated value. Despite the difference between the calculated and measured daily irrigation water volume, the total irrigation water volume for ~1 weeks was similar. Inconsistent irrigation timing was responsible for the difference observed between the calculated and measured daily irrigation water volume.

In composite designing of rehabilitated pipes by spiral wound lining methods, evaluation of the ultimate state of adhesion between an existing pipe and its reinforcement member is important. If deformation on a rehabilitated pipe causes overall separation between the existing pipe and its reinforcement member, even small area of poor adhesion may cause serious degradation of its strength and rigidity. Specimens of full-scale rehabilitated pipes with SPR Method are prepared with different conditions of adhesion; overall bonded, overall unbonded, and partially unbonded. Overall unbonded specimens showed smaller strength and rigidity compared to overall bonded ones. However, both of strength and rigidity of partially unbonded specimens showed little difference to fully bonded ones. It is concluded that propagation of separation, which originates from an area of poor adhesion and leads to an overall separation, does not occur until the ultimate state of rehabilitated pipes, as far as good adhesive strength is secured in bonded area.

During flood overtopping on the rockfill embankment, there appear a flow seeping through the rockfill (throughflow) and a flow running over a top surface of the rockfill (overflow). Seepage analysis to calculate the throughflow requires the coefficient values which describes a nonlinear head loss equation of flow through the rockfill. In an integration method or a step method for the varied overflow calculation, a roughness coefficient which determines a magnitude of friction slope is required to be known. In order to design and construct a mechanically stable rockfill structure during flood overtopping, the hydraulic conditions of the throughflow and overflow should be properly calculated using reliably-determined hydraulic parameters such as the coefficients values of the head loss equation and the roughness coefficient mentioned above. Employing coarse gravels and cobbles 50 to 200 mm in diameter, two types of the laboratory water flume test are conducted to determine these hydraulic parameters. The coefficient values of the head loss equation are reported to show the highly significant relationship with the hydraulic mean radius of rockfill voids. The roughness coefficients of rockfill surface are found to increase with the rock particle diameter described by the predominant wave length of the rockfill surface configuration, and be 0.04∼0.06 for the rock particle size tested.

From 2005 to 2019, we conducted a survey of aquatic habitats in cooperation with a local elementary school in the Konsen area, eastern Hokkaido, Japan, in which a drainage channel and a related pond were constructed as part of the environmentally sound irrigation and drainage project. In the survey, we identified a total of 11 families and 18 species of aquatic animals: 7 families and 14 species of fishes, 3 families and 3 species of crustaceans, and 1 family and 1 species of amphibians, including several species that were listed either in the Ministry of the Environment or the Hokkaido Red List. Certain rare species such as Pungitius tymensis, Lefua costata nikkonis, and Phoxinus percnurus sachalinensis, whose habitats have decreased due to the development of the virgin wetlands, and whose populations are fragmented and extinct, were confirmed at high frequency. It was presumed that the newly constructed facility functioned as a habitat for the rare creatures that originally lived in the region.

This paper describes the historical evolution of artificial neural networks (ANN) technology from the initial ANN to the applied ANN, including deep learning. The paper also explains key studies associated with ANN technology in Japanese hydrologic and hydraulic engineering fields during recent 30 years. The key studies were selected from the peer-reviewed, water-related journals, such as the Japan Society of Civil Engineers, the Japan Society of Hydrology and Water Resources, and the Japanese Society of Irrigation, Drainage and Rural Engineering. We have pointed out the merits and demerits of ANN application to the water-related studies and have discussed the reason why deep learning has recently become popular in their fields. In addition, we have proposed potential future works of ANN based on valuable knowledge of past and latest studies.

There were the following typos in the article, “Irrigation, Drainage and Rural Engineering Journal Vol.91 (2023) No. 2 p. I_165-I_174”

There were the following typos in the article, “Irrigation, Drainage and Rural Engineering Journal Vol.91 (2023) No. 2 p. II_41-II_51”