Generally, earth canals in paddy fields in developing countries collapse due to erosion and flooding under strong rainfall. Consequently, farming is often hindered. For sustainable maintenance and management, it is important that the irrigation facilities are made of technologies that can be implemented by the farmer themselves and with available materials. The wooden canal protection is a construction method, which satisfies this requirement. This paper aims to evaluate the durability of the wooden canal protection for local implementation at Ghana. By the visual inspection of the experimental plot, the main deterioration factor of the wooden canal protection has been termites, and the service life has been estimated to be about 12 months at the hill side in main canal susceptible to termites and about 28 months at the swamp side in main canal and in the branch canal which are hardly affected by the termites.
Variability components of daily inflow rate of wastewater were examined through application of the state space model, and variability characteristics were considered for actual rural sewerage facilities. The daily inflow rate of wastewater was separated into (a) the trend component, (b) the seasonal change component, (c) the weekly change component, and (d) the precipitation-corresponding component. These components were well correlated with influent quantity. The value predicted by the state space model well explained actual inflow discharge data. The daily inflow rate of wastewater was associated with (i) influent quantity that corresponding with the population in a basin, (ii) the dynamics of population in a basin, (iii) the amount of precipitation, and (iv) events such as summer or new year holidays. The analysis using the state space model has a few remained issues on prediction precision of the precipitation-corresponding component and interpretations of the seasonal change mechanism. However, this analysis is effective for characteristic extraction of variability components of daily inflow rate of wastewater on actual rural sewerage facilities.
We evaluated the influence of a change in product specification (namely, an increase in standard strength) on the cross-sectional stiffness (CSS) of centrifugally reinforced concrete (RC) pipes. Because different manufacturers make RC pipes in different ways, we evaluated the CSS of RC pipes made by various companies and the stiffness deterioration characteristics of the pipes at the time of crack occurrence. The CSS of RC pipes complying with the previous Japanese Industrial Standards (JIS) was 28% less than that of pipes complying with the current JIS. The main factor in this difference is thought to be different values of elastic modulus of the concrete used. In addition, RC pipes made by different manufacturers showed differences in CSS before and after the initial cracking. We confirm that deteriorations such as cracking and reduced thickness lower the CSS of RC pipes. Overall, the results of this research revealed that the stiffness of RC pipes in service must be evaluated considering their manufacturer and the industrial standard with which they comply.
Maintenance measures are being implemented in irrigation facilities nationwide. Mortar materials are frequently used for repairing degraded cross-sections of irrigation canals. These materials are used to repair abrasions caused by sand and running water. In addition, these mortar materials are sometimes used to repair canal drops damaged by the impact of falling stones. In this study, we simulated a falling stone by dropping a steel ball in order to evaluate the durability of mortar materials used for repairing the damaged area of a drop. As a result, we confirmed that the durability of the repair material was highest for fiber-reinforced cement mortar, followed by polymer cement mortar, and normal concrete. In addition, we confirmed that by setting the thickness of the fiber-reinforced cement mortar or polymer cement mortar to 30 mm, it can be expected to protect the existing concrete.
Farmland fragmentation is considered to have negative impacts on agricultural productivity in many parts of the world, yet innovative solutions to the problem are few and far between. A prerequisite to quantify the magnitude of these negative effects and draw socially and economically optimal policy strategies is to acquire accurate geographic information such as the location of farming farm lands, the connection of roads and footpaths, and the time required for farmers to reach their multiple farm lands. In this study, we developed a new methodology to spatially detect individual farm lands, village footpaths and farmers' commuting routes to farm lands, and then applied the proposed algorithm to an original set of GPS track data from Yunnan, China, where very little geographical information was available despite a high degree of land fragmentation faced by local farmers. Our analysis of farmers' route selections revealed that, under the condition that farmland fragmentation increases the commuting time, some villagers make long detours to avoid steep slopes on their way to farm lands.
Huge landslides in the upper reaches of the Tedori River have caused a long period of high turbidity in the river, predominant since May 2015. This turbidity has caused concerns about recharge of groundwater in the downstream alluvial fan. In this study, the measurements of paddy percolation and underflow water, before and after the occurrence of high turbidity, were used to examine its influence on groundwater recharge functions. The measurements included water requirement rates in an area covering the Tedori River alluvial fan and river discharge observations in the section of the river that flows through the alluvial fan. The results revealed that the amount of paddy percolation decreased significantly in response to the elevated turbidity, and the volume and width of the riverbed underflow water were reduced. The amount of groundwater recharge was estimated based on these measurements, which revealed that groundwater recharge from paddy percolation was reduced by 270 mm/year (36%), and the recharge from riverbed underflow water was reduced by 591 mm/year (61%). The total groundwater recharge was reduced by 861 mm/year (36%), a value that corresponded favorably to the empirical groundwater level measurements.
The aim of this study is to predict the risk of water stress at crop fields in polder and to suggest the water management methods for the water stress reduction. A numerical model was introduced using SWAP model to predict the soil water movement under various cultivation in a reclaimed field. To verify the model accuracy, field measurement was performed in a crop field located in Isahaya Central Polder, Japan. Simulated volumetric water content had good agreement with measurement. Water stresses due to wetness and drought were quantified using difference between potential and actual transpiration rates under water stresses due to wetness and drought. The result indicated that the water stress due to wetness after heavy rainfall was reduced relatively quickly. On the other hand, the risk of drought increases under continuous drought weather. The water stress was predicted under the scenario for drought year and water management methods for reduction of the water stress could be devised.
Phosphate adsorption on kaolinite is affected by pH and the electrolyte concentration, but the reasons underlying these effects are not fully understood. The reason why the amount of phosphate adsorption has a maximum at a certain pH is also unclear. Here we used Iriki kaolinite (from Japan's Kagoshima Prefecture) as a material, and we measured the phosphate adsorption at different pH values and electrolyte concentrations by the batch method. Sodium chloride was used as the supporting electrolyte. The amount of phosphate adsorption at ≤1 mM equilibrium phosphate showed a maximum value at pH 6.0. The adsorption increased with the increase in the electrolyte concentration at pH 4.0-6.0, and it decreased with the increase in the electrolyte concentration at pH 3.0. We propose a simplified surface complexation model represented by a competitive Langmuir adsorption equation. The values calculated using the model agreed well with the measured values. Based on the model and the measured zeta potential, we speculate that the characteristic phosphate adsorption reaction was caused by a protonation/deprotonation reaction of aluminol groups and phosphate ions, changes in the potential of the adsorption surface due to the pH, and changes in the potential by the phosphate adsorption itself.
The terminal pipelines of the Miyagawa Irrigation Network in Mie prefecture are increasingly being clogged due to the accumulation of Asian clams. To counteract this clogging, the Miyagawa Land Improvement District conducts sludge discharge operations at 35 points along the pipeline. In this study, we examined the transport of Asian clams using sludge discharge data from Myojo Sludge Discharge Point No.1, located on Main Channel No. 1. Asian clams were dislodged during times of high water velocity, such as during the rice planting season and the period after the mid-summer drainage. In addition, our survey of pipelines with an inner diameter of 2,000 mm suggests that Asian clams inhabit sediments that accumulate in the notch that occurs where a pipe joins a pipe fitting. According to our study of Asian clams collected in such notches during in-pipe surveys in December 2016, more than 90% of the Asian clams occurred in high-density aggregations of approximately 6,000 individuals m-2. In addition, our numerical calculations of bed load transport indicate that there is a high probability that Asian clams with a shell length of 20 mm or greater may inhabit a pipe fitting for multiple years.
Under promoting the stock management of water facilities, roughness coefficient becomes the important index in the hydraulic performance diagnostics of the concrete open channel. However, in the in-use open channel, roughness coefficients calculated from flow velocity and depth measurement are inaccurate. Therefore studies to identify the roughness coefficient from the arithmetic average roughness of the open channel wall have proceeded. However, there are joints at equal distance in the open channel. Joints may affect the frictional resistance of the open channel. In this study, we examined the influence that joint widths of the open channel gave frictional resistance by model channel flume experiments which consisted of three kinds of different roughness walls. As a result, the water depth decreased in and around the joint, and it recovered near the middle between joints. On the other hand, the frictional resistance of the open channel did not depend on the joint width which are 0 to 2.2% of one span in the three kinds of model channel flume experiments.
Biostimulation of a petroleum-contaminated soil is a remediation technique that stimulates indigenous microorganisms capable of degrading pollutants aided with the addition of phosphorus, nitrogen compounds, and oxygen. This study was conducted to evaluate the purification effect of bioremediation for petroleum-contaminated Kunigami-maji soil in the northern part of Okinawa Island. The soil remediation tests in our laboratory showed that the concentration of petroleum hydrocarbons decreased in the primary reaction and removal rate constants varied depending on the conditions of soil water contents and supply of nutrients and oxygen. It was concluded that the addition of nutrients and aeration of the soil were effective in enhancing purification when the gravimetric water content is adjusted to less than 23%. Furthermore, water content was the most important factor among influential factors as evident from multivariate analysis of soil remediation test data.
Model tests are conducted to investigate the behavior of low stiffness pipes such as thin Polyvinyl chloride (PVC) pipes (VU) subjected to internal pressure and external load. The test results show that the deformation of VU subjected to external load is induced by not only moment but also axial load. In the case of VU pipe buried in medium dense sand (relative density 61%), the ratio of axial strain to bending strain is 40% when the surface load is 150 kPa. The axial strains of the pipes buried in the sands of different densities (relative density 61% and 39%) by external load are almost same, which means that axial strain is insensitive to soil stiffness. The axial strain of VU buried in medium dense sand subjected to internal pressure and 150 kPa of surface load is above 10% smaller than that to internal pressure and 0 kPa of surface load. This indicates that the axial strain is reduced as the surface load is large. Moreover, results of tests used with duct pipe that is thinner than VU show that these tendencies become more prominent for lower stiffness pipe.
Continuous irrigation with running water (CIRW) experiments during nighttime were conducted in conventional paddy fields, to study the effect of nighttime CIRW on average water and soil temperature during 20 days after rice heading date and rice quality. By irrigations with total irrigation amount of 986 and 782 mm (123 and 78 mm per one time irrigation), 20 days average water temperatures after rice heading date were 2.3 and 2.2 °C lower at inlet of paddy field, respectively, and were 2.2 and 0.8 °C lower at center of paddy field respectively, than 20 days average air temperature. However, average water temperatures under the CIRW with 782 mm total irrigation water amount were lower near the inlet of paddy field, but higher near the outlet of paddy field, than those under conventional irrigation water management. Average water temperature and average soil temperature during 20 days after rice heading date showed almost the same temperature, and measurement depth did not affected average soil temperature. Ratio of chalky kernel under CIRW was lower than that under conventional irrigation water management during high air temperature condition, however that did not decreased by CIRW during low air temperature condition.
The Internal Loading Method (ILM) has been proposed as a way to evaluate the strength of buried pipes. The evaluation criteria must be determined through constructing a numerical analysis model that can simulate behavior of buried pipes. In this study, the ILM was applied to centrifugal reinforced concrete (RC) pipe sitting on ground, and the proper boundary support settings for 3D elasto-plastic finite element analysis were examined. In addition, we tried to calculate the elastic modulus from the relation between the experimentally and numerically obtained values for load and deformation. The results showed that the stress state under loading could be analyzed accurately by assuming nonlinear springs under the pipe. In addition, the accuracy of analysis for the behavior of the RC pipe can be improved by using the calculated elastic modulus for the analysis. Finally, we confirmed that there is a possibility accruing flexural cracks on two directions of the RC pipe in case of excessive loading.
The ultimate goal of this study is to clarify the relationship between the soil moisture transfer characteristics and the occurrence of tuber damages in Chinese yam in the large scale agricultural land in Byobusan-area, Aomori Prefecture developed by the government. The authors conducted volumetric water content monitoring by installing soil moisture sensors at the depth of 10, 30, 50, 100 and 150 cm of Chinese yam upland field with the deep underdrainage at Toyotomi and Shariki construction fields. Numerical simulations on soil moisture transfer in one and two-dimensional directions were also conducted in order to verify the drainage effect the deep underdrainage laid down the upland field. From the results of soil moisture monitoring in the period of thickening growth of Chinese yam, the soil water was reliably drained by internal drainage after rain and thus the soil was not in an excessive moisture condition at the depth of 50 cm, at which the growth point is expected to exist. In addition, the soil at the every depth installed the soil moisture sensors did not reach the water saturated condition throughout the growing period. Focusing on validation of the volumetric water content caused by 63 mm amount of precipitation on July 24 to 25 by using the two-dimensional numerical model, we found that the surplus soil water was reliably drained toward the deep underdrainage especially in Toyotomi construction fields which had low permeability.
The authors conducted experiments to investigate the burst swimming speed of the Japanese fish minami medaka (Oryzias latipes) for designing canals and fishways in paddy fields in consideration of the ecosystem. The following results were obtained in the range of body lengths from 2.0 to 2.9 cm; 1) the burst swimming speed of the minami medaka was found to be 33 cm・s-1 (velocity of pipe flow, 17 cm・s-1) to 58 cm・s-1 (velocity of pipe flow, 32 cm・s-1); their burst swimming speed was 14-24 times their mean body length per second. 2) The minami medaka repeated this instantaneous swimming speed, advancing by approximately 5 cm at a time; the mean of the instantaneous swimming speed was about the same at 1.03 times of the burst swimming speed upon entering the burst swimming section. 3) Under the pipe velocity from 20 to 30 cm・s-1, more than 65% of the individuals swam distances of 30 cm.
This paper presents an evaluation method for landslide behavior using elasto-viscoplastic finite element analysis and the particle filter (PF). As an elasto-viscoplastic constitutive model, the Mohr-Coulomb criteria with the over-stress model is employed, and the landslide displacements are simulated. The geotechnical parameters related to the creep behavior of a landslide are identified with PF in this research. The results of FE analysis using the identified parameters have good agreement with the observed data, and it is confirmed that the methodology presented in this study can be effective in evaluation of landslides. In addition, the counter measures for landslides are discussed based on the predicted displacement, and consequently, the possibility of the proposed method's practical use is verified for the mitigation of the landslide hazards.
There are growing concerns about functional deterioration due to wear damage by gravel in concrete agricultural channels. This paper presents the possibility of gravel mass estimation by the pulse-type hydrophone as one of the monitoring and diagnostic techniques contributing to their lifetime prolongation. The precedented formulation for gravel size estimation, as an inverse problem, has difficulty in physical and mathematical handling, and its routine application was impossible in a practical way. Therefore, by means of the analysis of the relation between gravel mass and sound pressure obtained from the results of experiments, we proposed the modeling procedure to be able to evade those ill-posedness. Based on the procedure, we developed the model which classifies the gravel mass into two classes from the observed pulse number of sound pressure divided in two classes. Consequently, it could give largely successful classified results for a group of gravel within a certain mass distribution.
We conducted triaxial compression tests using clay and sand materials to elucidate effects of the number of alternations of horizontal soft and hard layers on shear strength characteristics of a composite specimen. When the number of alternations in the horizontal soft clay layer and horizontal stiff clay layer was 1, the local deformation in the horizontal soft clay layer was strong. However, as the number of alternations became greater, the influence of heterogeneity was slight. Moreover, the shear strength characteristics of the composite specimen of horizontal soft clay layer and horizontal stiff clay layer tended to resemble that of homogeneous specimen with soft clay. Compared with the composite specimen with clay, the influence of heterogeneity in the composite specimen of the horizontal loose sand layer and horizontal dense sand layer was slight. The shear strength characteristics of the composite specimen of horizontal loose sand layer and a horizontal dense sand layer tended to resemble the average shear strength characteristic of each homogeneous specimen with loose sand or dense sand. Additionally, it was possible to express the process of concentrating maximum shear strain as combining an experimental photograph with the shear strain distribution calculated using few target points.
In recent years, renewable energy has attracted much attention as safe and clean energy to replace nuclear power generation; small hydropower generation is highlighted, which has a small output scale but is practical in terms of technology. In this study, the potential of small hydropower generation was examined for agricultural irrigation facilities from the headwork to the end of main irrigation canal managed by Meiji Yousui Land Improvement District. As a result, the maximum power output, the average annual power generation, and the maximum monthly power generation was the largest at the headwork and the industrial water division work and check stands followed it in this order. The power generation at the industrial water division work showed a seasonal gap between irrigation/non-irrigation periods but a more stable amount every year than other agricultural irrigation facilities. Year-round water flow in the mud drainage works, which are used a few times in a year in general, are expected to utilize their potential for the hydropower and to improve water environment in drainage canals and downstream river reaches.
We verify the gravel mass estimation method with a hydrophone in actual agricultural channels. In this estimation method, several models are created to classify the gravel mass into two classes, a large class and a small class. However, it is difficult to utilize the data acquired for identification on the site where various noise generation is conceivable. Therefore, we assumed that the number of pulses obtained by collision of gravel is represented by a unimodal probability distribution of the histogram with the sound pressure as the class and the pulse number as the frequency, and the data necessary for modeling was extracted. Moreover, in consideration of applicability to the site, the models were applied by removing the data assumed to contain background noise and multiple collision noise, regardless of the mass of the target gravel. As the result, good mass classification by the proposed models was confirmed, even in the site under the influence of noise all the time.
As an emergency measure in a sudden pipeline leak accident, an internal leaking preventive joint band is installed on a target section’s pipe joint. This band is often used alone; however, sometimes bands are arranged in series on a pipe for preventive maintenance. Although continuous installation of bands may cause a large head loss, a method of evaluating this head loss has yet to be established. This study investigated the optimum evaluation methods of head loss with arranging some bands in series and using it alone by hydraulic model experiments using the band of 3-mm thick. Our results found that head loss caused by arranging bands in a series can be calculated by adding the head loss of each band by the number of installation points, and the ordinary method―the formula for sudden contraction and expansion overestimates the band’s loss factor.