The authors have proposed the Internal Loading Method as a new strength evaluation method for buried pipes. Previous studies have demonstrated the applicability of the Internal Loading Method to flexible PVC pipes. This paper reports on the result of applying this method for non-flexible RC pipes. Experiments were performed with RC pipes with a kerf on them. As a result, the Internal Loading Method can detect a kerf on the inner surface and on the outer surface as well. It was also possible to evaluate the depth. The possibility of damage by the application of this method is examined considering the load-deformation relationship and the amount of deformation residuals. The results showed that little damage is liable to occur as far as the load and deformation are controlled properly. Finally, this method was concluded to be applicable to both of PVC and RC pipes, because it can measure ring stiffness of pipes in wide range.
In large-sized paddy fields with groundwater level control systems in the town of Moseushi, Hokkaido, ponding depth levels and groundwater levels were observed. In the same paddy field, irrigation requirements were compared among the three types of paddy rice cultivation: direct-seeding cultivation without puddling in flooded paddy fields, transplant cultivation, and direct-seeding cultivation in well-drained paddy fields. The observation results are as follows. 1) In transplant cultivation and direct-seeding cultivation, changes in the groundwater level depend on soil puddling. However, differences of percolation in those cultivation styles are small. 2) The difference of the total volume of water as a sum of irrigation water and effective rainfall is 10%-30% in all cultivation methods because the groundwater level around the paddy fields is high and the amount of percolation is small. 3) The quantity of water intake during the period of shallow water management in direct-seeding cultivation is comparable to the puddling water requirement in transplant cultivation. 4) On the assumption that direct-seeding cultivation will increase in the future, the timing of water intake after mid-summer drainage of paddy fields is likely to vary depending on the cultivation method when the drainage starts at the same time in transplant cultivation and direct-seeding cultivation.
This study was conducted to investigate the effects of low salinity stress on growth, yield, water use efficiency (WUE), and fruit quality of cherry tomatoes cultivated under a soilless condition. The experiment was conducted using Hydroponic Power's Pot under six salinity levels (electrical conductivity (EC): 0.78, 0.91, 1.10, 1.26, 1.41, and 1.58 dS m-1), with three pots (six plants) in a completely randomized design in each treatment. The results showed that plant fresh weight, soil-plant analysis development (SPAD) value (leaf chlorophyll), and dry weight were significantly affected by salinity stress at EC = 1.58 dS m-1. Tomato yield was significantly affected by salinity stress when EC reached 1.41 dS m-1, and was more sensitive than growth variables. Fruit quality was improved with increasing salinity. Evapotranspiration was also significantly affected by salinity stress at EC = 1.58 dS m-1. However, WUE for yield (fresh fruit) and biomass were not significantly different among salinity levels. The SPAD value (leaf chlorophyll) was the most sensitive indicator for salinity stress. The salinity threshold of the tomatoes was 1.41 dS m-1 to achieve higher fruit quality and yield by using Vegetable Life A nutrient solution.
Kankyou-yousui-suiriken, the water right for biodiversity conservation, is permitted as a special water right that envisages the diversion of water in a river into other water environments. Conversely, other water rights are generally permitted for off-stream use. Because such water environments are not subject to the River Act, the significance of this system offers the river administrator a new and supplementary option concerning low-flow management. Having the major shift of conception of water in a river, this water right is novel in valuing the sustainability of biodiversity. It also shows some peculiarities in that this water right is permitted only when other water-right holders enjoy full appropriation, and it is provisional in terms of a short renewal period. One of the practical cases of this water right is utilizing irrigation and drainage infrastructures for the purpose of improving water quality by dilution. In this respect, it should be noted that land improvement districts (LIDs) could make many contributions to this water-right system through experience and knowledge in operation, maintenance, and management of related facilities. In fact, these contributions would minimize the initial investment and management costs. Involvement of LIDs could result in a win-win situation for both a right holder and districts.
In general, underground structures significantly lose a stability when the supporting soil liquefies due to a seismic motion. In particular, a decrease in the bearing capacity of the backfill due to liquefaction leads to the serious damages of pressure pipelines subjected to thrust force. Nevertheless, the specific liquefaction-countermeasures for the backfill material of pipelines has not been described sufficiently in the present design criteria for irrigation pipelines. It is crucial to clarify the interaction between the lateral resistance force of the liquefied soil and the displacement of the pipeline. In the present study, we conducted lateral loading experiments to examine the influence of the loading rate of the pipe on the lateral resistance force of the sandy soil under different hydraulic gradient. The experimental results showed different types of velocity dependence of the lateral resistance force depending on the excess pore water pressure. In the saturated sand, the lateral resistance force decreased with the increase of the loading rate because the excess pore water pressure on the passive side of the pipe increased rapidly. On the other hand, in the perfectly liquefied sand, the lateral resistance force increased linearly with the loading rate of the pipe.
The aim of the present study was to clarify the effect of a mid-summer paddy field drainage regime on the conservation of Sympetrum frequens. We investigated the theoretical lower threshold temperature and total effective temperature required for S. frequens egg and larval development under laboratory conditions. The lower theoretical threshold temperature and total effective temperature for egg hatching under early, typical and late inundation conditions were 5.7°C and 55.2 degree-days, 5.6°C and 36.8 degree-days, and 6.8°C and 21.7 degree-days, respectively. The theoretical lower threshold temperature and total effective temperature for larval development to the 10th-instar stage were estimated at 5.6°C and 909.1 degree-days. We then estimated the water temperature in paddy rice fields in Miyagi Prefecture based on meteorological data represented on a 1-km grid. Mean days to hatching and days required for larval development to the 10th-instar stage were estimated based on the paddy field water temperature, theoretical lower threshold temperature, and total effective temperature. These results were then represented in a GIS to show the mean time to hatching in days and the time required for development of 10th-instar larvae. Finally, we compared the estimated time required for the development of 10th-instar larvae and the timing of mid-summer paddy field drainage. We considered that the drainage of paddy fields in mid-summer would be conducted before the development of 10th-instar larvae. Based on these findings, we consider that the adoption of a mid-summer drainage regime by rice farmers after S. frequens larvae development to 10th-instar stage would promote the conservation of this species. The risks associated with mid-summer drainage are also discussed.
Terraced field slopes is an element that gives the uniqueness of the area to the landscape of terraced fields. In the terraced field slopes, there are earth slopes and stone masonry. If the origins of the kind of terraced field slope is clear, when the farmland consolidation and the landscape conservation were planned in the terraced field areas, it may be also used to select the construction method of terraced field slope. This study quantitatively indicated the relationship between the type of the terraced field slopes and the surface geology. Rock classifications and geological epochs on 464 terrace field districts in Japan were analyzed. As the results, in the igneous rock, districts of stone wall have majority. However, in volcanic rocks, all districts that have surface geology before the late Pleistocene of the Cenozoic were earth slopes. In plutonic rocks, districts of stone wall have majority, too. However, districts of 27% that have weathered granitic rocks were earth slopes. In sedimentary rocks, 90% districts that have surface geology after the Paleogene of the Cenozoic were earth slopes. And 97% districts that have surface geology before the Paleogene of the Cenozoic were stone masonry. In the accretionary complex and metamorphic rocks terraced field slopes were almost stone masonry.
The aim of this study was to elucidate the current status of salt accumulation at three irrigated farmland sites. The site is situated within a sedentary village of nomadic people located in the northern part of the Xinjiang Uygur Autonomous Region, China. We investigated the characteristics of the salt-affected soils and salt accumulation mechanisms by conducting field surveys and analyzing the irrigation water and groundwater, as well as the physicochemical properties of salt accumulated soils collected from varying altitudes. The surveyed area is situated in an arid clime, where the annual pan evaporation exceeds approximately 10 times the annual precipitation. Our surveys suggested that the salts contained in the groundwater at a depth <1 m migrate and elute near the surface from lower soil layers through evaporation. We identified that the salt-affected soils fell into categories of either saline or saline-sodic soils, compared to the saline-sodic soil, saline soil was situated at a higher altitude and had a lower clay content, and majority of the salts precipitating at the ground surface consisted of highly soluble sodium sulfate.
Areas in which the scale expansion and the aggregation of farmlands are not expected in the future require an appropriate method of preservation based on the characteristics unique to each area. Under these situations, we conducted a pilot experiment to construct a collaborative system of endogenous farmlands preservation with support from Godo District, Fujimi Town, Nagano Prefecture. This paper reveals following two points; the first is farming characteristics of farm land users, and the second is changes in farmland use from viewpoints of farmland leases and wildlife damage management. We utilized these outcomes at a roundtable conference. The conference consisted of three steps through which to share information and discuss a future plan toward endogenous farmlands preservation. We explained the changes and current situations of whole farmlands and indicated six practical challenges by utilizing GIS. We found many changes in participants’ consciousness and actions throughout the conference. Promotion of recognizing the importance of collaboration between local farmers and new comers, and the establishment of intermediary organizations are important elements to help solve the practical challenges and promote this project.
We propose a simple measurement method employing a profile gauge as a quantitative abrasion measurement technique for use during cementitious surface repair work. This method begins with the installation of anchors at two locations on the coated surface to serve as reference points. Next, the area enclosed with the abrasion surface and the reference line connecting the reference points, within certain range in reference line, is calculated from photographed image. And the average distance to the coated surface is obtained by dividing this area by the measurement range length. In order to clarify the degree that various factors impact the measurements, we conducted field measurements on channels with coated surfaces and compared the results of measurements of abrasion quantity using a high-precision laser displacement meter with the results of measurements by the profile gauge. The results showed that when used to measure quantity of abrasion of channels with smooth surface coating, this new method obtained measurement values little different from the values obtained by the laser displacement meter. The accuracy of a single measurement estimated based on the field measurement was the laser measurement value ±0.4mm. It has a potential to be an effective simple measurement method of abrasion of cementitious surface.
With emphasis on the hydrological conditions, this study analyzed changes in agricultural land use from the 1950s through the 2000s in the northeastern region of Thailand where rain-fed rice cultivation predominates. Spatial distribution of hydrological conditions was obtained from time-series images of a synthetic aperture radar. Overall, the paddy fields expanded from the wetter areas toward drier areas. However, there were variations in the rate of increase of paddy fields in drier areas within the study area. This was due to differences in the degree of mixture of spatial distribution of the hydrological conditions, an uneven distribution of population, and the level of progress in flood prevention.
This study aims at establishing a groundwater model for the 100-meter aquifer of a coastal area of the Mekong Delta, and applying it to simulation of the groundwater heads under possible changes in rainfall and groundwater management in the future. The model, iMOD, was calibrated using historical data of groundwater level and model input requirements. It was confirmed that the calibrated model could work properly to reproduce the distribution of the groundwater table and its response. For scenario setting, several cases of future rainfall conditions for the period from 2015 to 2035 were set up based on the downscaled output from the global climate model with bias correction. For each of the combinations of climatic conditions and pumpage, model simulation was carried out to estimate groundwater tables. The results showed: (1) If the groundwater pumping stays at the same level as present, groundwater heads can maintain the present level under increased recharge from the future rainfall, whereas slight decline in groundwater heads would continue under the current rainfall; (2) If the groundwater pumping increases along with increasing water demand, significant consecutive drawdown of groundwater tables will happen. Particularly when considering some reduction in recharge due to rainfall loss and uncertainty of rainfall, groundwater depletion might be more serious; (3) Reduction in pumping rate was found to contribute much for recovery of groundwater.
This study aimed to analyze safety levels of the water supply for irrigated rice paddy fields in the major river basins of Korea in the early modern era, and discussed its process of development in comparison with that of Japan. The area of rice paddy fields that can be irrigated in a river basin was estimated based on drought low flow discharges at different occurrence probabilities, and the safety level of the water supply for rice paddy fields was evaluated based on those occurrence probabilities. The results were as follows: 1) summer low flow discharges of Korean rivers are much smaller than those of Japan; 2) safety levels of the water supply for irrigated rice paddy fields were rather low at 40-90 % a year of the water shortage probability, except for the Han River, which means that by the early modern era, Korea had developed rice paddy fields to use all summer low flow discharges; 3) the high safety level in the Han River basin is presumably attributed to the difficulty of paddy field development because of frequent flood damage; and 4) the fact that the total amount of stable summer discharge in the river basin is much less than the required amount of water to support the strong rice demand in the era is believed to be a background factor that contributed to the excessive expansion of irrigated paddy fields as well as rain-fed paddies.
Photovoltaic power (PV) facilities installed above cultivated farmland (hereafter, farming PV) have the potential to revitalise farming and rural areas. This study analysed local people's preferences and evaluations regarding potential positive as well as negative social and environmental effects caused by farming PV installation by utilising statistical methods, and implications were obtained regarding the technological development of and policies pertaining to farming PVs. Such implications were obtained not from the viewpoint of technological appropriateness but from that of social acceptability. Installation of farming PVs could be better accepted not in rural areas but on farming plots in residential and commercial areas. The needs for developing PV panels, which prevent glares caused by the reflection of sunlight, are not substantial compared to those pertaining to general PV development. The social demand for scenery-compatible farming PVs is not that large. However, it could be worthwhile to design farming PV systems that are more pleasing to the eye, including farming plots.
Subsurface irrigation system in paddy field is a system that can control the groundwater level by means of subsurface drains in paddy field, and their introduction into paddy fields is recommended by the Japanese government. Farm-oriented Enhancing Aquatic System (FOEAS) is one of the sub-surface irrigation systems, and case studies on FOEAS displayed the benefits of the system in terms of crop growth and changes in soil moisture. In a few studies, however, FOEAS was applied to rice cultivation such as the direct seeding cultures in paddy fields. In the present study, subsurface irrigation was conducted at the beginning of the rice cultivation period by v-furrow direct seeding. The changes of wetting area at the surface of the field were visually shown, and groundwater and the water budget were observed. The findings indicate that the wetting areas were distributed homogeneously by subsurface irrigation, and that the groundwater level rose inhomogeneously with the locations of observation points. However, invalid increase in irrigation without the valve closing and the automatic starting of irrigation needs further attention when the level of the level controller is set below the surface of the paddy field.
Improving the drainage performance of paddy fields with heavy clay soil in Hokuriku District, located in the center of Japan on the side of the Sea of Japan, is important for cultivation. Farm Oriented Enhancing Aquatic System (FOEAS) can control underdrain discharge. However, the drainage performance decreases with time because of degradation of the mole drain and decomposition of the filler material above the underdrain pipes. To evaluate the drainage performance of the mole drains, we conducted intake rate test and measured the groundwater level in a field converted from paddy to upland with FOEAS in Tsubame City, Niigata Prefecture. The basic intake rate measured above the mole drain was thought to decrease because of treading by farm machines. However, the drainage performance of mole drains under FOEAS implemented 9-11 years ago was found to be the same as that of the mole drains repaired prior to starting this study. When assessing changes in the groundwater table because of precipitation, we noted that the drainage performance of a mole drain was the same as that of an underdrain and repaired mole drains. Our observations show that the drainage performance of mole drain meets the designed underdrainage discharge required for multipurpose paddy fields.
A facility, which lets flows in two steep non-pressure tunnels with different bed level confluent, and discharges the confluent flow into a conduit, is needed in Azusagawa-ugan district in Nagano Prefecture. However, it is impossible to apply existing confluent facilities to this district due to its unique field conditions. Therefore, a new confluent facility, which weakens a flow falling from a branch line tunnel by multistep, was proposed referring the multistep free fall type drop works constructed as a sewage facility, and was inspected by hydraulic model experiment. The assessment items for energy dissipation effect were the presence of the big fluctuation of water surface in a main line tunnel which occurred by a main line flow being obstructed by a branch line flow, and the presence of collision of a flow from the bottom step to a downstream wall in confluent facility.
Cementitious material coating work is frequently executed to repair agricultural use open concrete channels. However, spatial distribution of the neutralization depth of the cementitious material coating work caused by usage environment have not been clarified. It can be important basic information for planning the survey point and the sample size of a monitoring survey. This paper reports results of a multi-point investigation of the neutralization depth of cementitious coating works three years after execution. The results show that neutralization depths followed a normal distribution, and coefficient of variation was 20-40%. Neutralization depth at the side wall of the channel was larger above the water surface than that under water. Further, based on those results, it was estimated that 9 or more samples are required in order to obtain a 95% confidence level and 20% tolerance in evaluation of neutralization depth.
We examined the effects of remaining soil moisture and irrigation on dry season cropping in uncultivated lowland rice fields in a mountainous area of Vientiane Province in Lao PDR. In the un-irrigated soybean cropping experiment, the soil moisture decreased to pF3.0 (depletion of moisture content for optimum growth) within 3 weeks of sowing, and the remaining soil moisture was not enough for cropping. In the irrigated experiment based on the trial calculation of the water requirement and irrigation interval calculated from the results of soil moisture monitoring, the soybean yield was one-sixth of the national average. Although the calculated water requirement corresponded with the estimated total evapotranspiration during the planting period, it was less than the evapotranspiration at the middle stage of soybean growth. Following irrigation, while the soil moisture level did not return to the field capacity, the groundwater level increased in some cases. Cracks were present on the clay soil surface. The results suggest that high-intensity irrigation caused preferential flow through the cracks, which increased infiltration losses and decreased the effectiveness of the irrigation.
In this paper, the authors considered operation planning of a methane fermentation plant that applies digested slurry to farmlands as fertilizer in the start-up years of the plant. An evaluation tool was developed to conduct the planning. The tool estimated the input weight of raw materials to the plant and the volume of digested slurry applied to the farmlands based on annual and daily material balances. The tool also calculated annual CODCr volume load of methane fermentation reactors. According to estimates, the plant should start to operate a day before the digested slurry farmland application period each year because the plant can apply digested slurry to the farmlands in the first year of start-up. The trial calculation that predicted a longer start-up period of 8 years found that the accumulated load of CODCr of the methane fermentation reactor during the start-up period was less than half of the design value. This case suggested that it would be possible to divide the methane fermentation reactor tank into 2 tanks and respond to the spread of the use of digested slurry as fertilizer by separately improving each tank.
A de-icing agent, containing NaCl as the main component, is often sprayed on expressways in winter months to prevent freezing of road surfaces. The de-icing agent becomes scattered along expressways and over the edges by passing vehicles. Depending on the concentration of the agent, this scattering induces risk of inhibiting growth of plants and contaminating water. In this study, we summarized the index values for the influence of NaCl on agricultural crops, farmland soil and agricultural water. In addition, we investigated the amount of NaCl infiltration into the farmland soil located along such expressways and the amount of its inflow into agricultural water. We then evaluated the influence of NaCl based on results of the investigation. As a result, Cl concentration was found to be 90 mg · kg -1 at the 1.5-m ridge of road edge, which is 23% of the threshold value 400 mg · kg-1. Exchangeable Na+ saturation was 16.3%, which is 81.5% of the threshold value 20%. Electrical conductivity of the agricultural water was 0.15 dS · m -1 in the busy farming season, which is 50% of the threshold value 0.3 dS · m-1. All three values were below the threshold values, and thus, it became clear that the influence of the de-icing agent on farmland soil and agricultural water was extremely small.