In this paper, to clarify the actual situation and time variation in internal reuse of return flow from the district, the water balance of the reservoir water in a main drainage canal was analyzed at the paddy irrigation district in Goka town, Ibaraki Prefecture, where is being conducted the pipeline project. The followings were clarified: 1) Return flow to the drainage canal from beneficiary paddy area was estimated to be 14.3 mm/d from the variation of the storage water amount in the canal at night, which the pumps were stopped. 2) The averages of daily usage amount of storage water in the drainage canal and daily amount pumped by all pumps in the district were 3.6 mm/d and 19.2 mm/d, respectively. The returned water from the paddy fields was accounted for 19% of total amount pumped up by the pumps. 3) The storage water in the drainage canal, which is stored in the evening, is used in the next morning. The peak discharge pumped up from the river at the Kawatsuma pump station was reduced 1.0 m³/s or more by the effects. 4) The outflow ratio of available water at the district where has a small reservoir capacity to the return flow from paddy area, has big hourly variation. 5) By the consideration of the water use situation after the project completion, we suggested that it is desirable to continue the connection of the downstream pump reservoirs and the drainage canal from the view point of the pump operation cost and the water amount.

View full abstract

There is a growing interest in the small-scale hydropower generation project that utilize irrigation canal operated by land improvement districts (LIDs) due to the introduction of feed-in tariff as well as amendment of land improvement law. However, only a few studies have identified obstacles faced with LIDs when they introduce the small-scale hydropower generation into their irrigation facilities. Taking Toyama prefecture as a case study area, this study conducted interview surveys to the Shōgawa Rengo LID, Toyama federation of land improvement association and Toyama prefectural government, to identify obstacles that Shōgawa Rengo LID faced with when it introduces the small-scale hydropower generation into its irrigation facilities and the way how it coped with those obstacles. In addition, questionnaire survey was carried out directed at twenty LIDs with potential to introduce the small-scale hydropower generation system, which identified that LIDs do not always have enough knowledge and experience necessary to handle administrative procedures as well as consultation with stakeholders, due to lack of human and financial resources, when they introduce a small-scale hydropower generation system. Finally, this study suggested that the federation of land improvement association could fill those gaps as it has enough technical expertise and experience to support LIDs.

View full abstract

This study was an attempt to investigate the effect of slag content on the compressive strength of river sand (RS) and oyster shell aggregate (OS) mortar in different aspects; fineness of slag, different percentage of slag content, cement types and use of chemical admixture (super plasticizer). Compressive strength of moist cured specimen was measured at 3, 7, 28, 91 days. Slag could be used up to 85% in partial replacement of cement and 75% slag content will give the highest strength for OS mortar. The compressive strength of RS-slag mortar could be lowered at initial stage but finally will increase about 17% than that of no slag mortar. OS mortar strength increased by adding chemical admixture with or without slag condition. Oyster shell aggregate could be used as fine aggregate and slag could be added with it to increase the compressive strength.

View full abstract

Continuous irrigation with running water (CIRW) experiments were conducted in an experimental paddy field during the rice ripening period, and the effects of water temperature decrease by CIRW on rice temperature, air temperature inside rice canopy, and soil temperature were studied. Decreases in water temperature induced decreases in leaf and air temperatures in the rice canopy for the lower part of rice, but barely affected those for the higher part of rice. Rice temperature decrease due to 1°C water temperature decrease was 0.54°C, 0.34°C, 0.28°C, and 0.11°C, respectively, at 30, 50, 70, and 90 cm height in rice canopy. In addition, increases in wind speed decreased the cooling effect on air temperature inside rice canopy. These results indicate that the effects of CIRW on rice temperature were most pronounced for the lower part of rice and decreased with increasing height within the rice plant. On the other hand, decrease in water temperature effectively decreased soil temperature compared to rice and air temperature inside rice canopy. The decrease in daily average soil temperature became pronounced with decreasing depth from the soil surface. Decrease in daily mean temperature of soil at 1, 4, 9cm depth for each degree drop in water temperature were estimated to be 0.86°C, 0.80°C, and 0.73°C, respectively.

View full abstract

Irrigation earth dams designed and constructed not following the modern codes often exhibited excessive deformations with cracks when subjected to strong seismic motions. The major cause is a large reduction in the undrained shear strength of saturated soil by undrained cyclic loading. To understand this phenomenon, a series of undrained cyclic loading triaxial tests followed by undrained monotonic triaxial compression tests were performed by using saturated soil specimens compacted to different dry densities. With an increase in the compacted dry density, the initial undrained shear strength increased significantly and the increasing rate increased with dry density. The strength reduction rate by a given undrained cyclic loading decreased with dry density. These results indicate that good compaction is very effective in increasing the seismic stability of irrigation earth dams via its large effects on undrained shear strength subjected to undrained cyclic loading. The effects of compaction on drained shear strength are much less significant, therefore, when designed based on drained shear strength, the effects of compaction on the stability of irrigation earth dam are largely under-estimated.

View full abstract

Pump stations for irrigation and drainage are important structures that handle water for an area as well as farmlands. Many pump facilities must be periodically rebuilt. However, information to evaluate the deterioration progress is presently lacking for pump facilities. In this study, we carried out a questionnaire survey on the maintenance of pump facilities to determine the actual situations and problems.
As a result, we confirmed that the main causes of trouble of the bearing characterizing the deterioration depended on wear that occurred with increase of the operation time. In addition, we showed the appropriate timing for evaluation and repair can be determined by quantitatively diagnosing the deterioration of parts. Therefore, we propose the application of condition based maintenance about pump facilities is important to prevent the progression of deterioration.

View full abstract

In developing countries, promoting emission reductions of greenhouse gases (GHGs) in rural areas in parallel with achieving improvement of local livelihood is prioritized because large part of GHGs is emitted there. Clean development mechanism (CDM) was institutionalized in the Kyoto Protocol to convert emission reductions achieved in developing countries to carbon credits (CERs) revenue. For emission reduction and cost saving through substituting cooking fuel with biogas, a CDM project introducing household biogas digesters (BDs) to 961 farm households was established in rural area of the Mekong Delta, Viet Nam. The planned emission reductions from the CDM project were 1,403tCO₂•year^-1, nevertheless the CER value of 30US$•tCO₂^-1 in 2008 was found not enough to cover the project cost. The household biogas CDM project was financially unfeasible: however, the methods to introduce BDs or to evaluate emission reductions from BDs clarified in process of the project will be useful when a national emission reduction plan in Viet Nam is formulated in future.

View full abstract

Sulfur hexafluoride (SF₆), chlorofluorocarbons (CFCs), stable isotopic composition of oxygen and deuterium (δ¹⁸O, δD), radioisotope tritium and dissolved major ions in groundwater were measured for groundwater age dating to provide indication of the groundwater flow mechanism in the Shimekake landslide area, Yamagata, Japan. It can be found from this study that SF₆ is effective in dating the shallower groundwater, and tritium is effective in dating the deeper groundwater in the landslide. The comparison of the results of groundwater age dating and the observed groundwater chemistry suggests that older groundwater indicates the lower (Ca²⁺+Mg²⁺)/HCO₃^- ratio, especially, and this ratio can be thus applicable to the validation of age dating. Investigating δ¹⁸O in groundwater with depth, in addition to topographical and geological data, can reveal the multi-layered groundwater flow in the landslide block, and can be effective in implying that groundwater flows into the landslide block from different recharge areas with different residence times. It is thus deduced that when used together, these environmental tracers applied in this study can help to classify groundwater drained from countermeasure works in a landslide area based on groundwater age.

View full abstract

The numerical analysis in order to understand the percolation discharge behavior of inorganic nitrogen in apple orchard in the three years of period from 2011 to 2013 was done. The spatiotemporal dynamics of inorganic nitrogen concentration in the soil water under fertilization and non-fertilization condition were revealed. In the numerical analysis, not only physical and chemical properties of apple orchard soil but analyzed taking account also nitrogen mineralization and nitrogen fixation by legumes. As results, in the non-fertilization condition, although annual average NO₃-N concentration in soil water was below the 10mg/L, whereas approximately 20mg/L in the fertilization condition. In addition, as a result of calculation of reduced fertilizer amount that the annual average NO₃-N concentration of soil water from 0 to 100cm in depth becomes less than 10mg/L, it was also found that the reduced fertilizer amount is required as ranged from 12 to 59kg/(ha･year).

View full abstract

The amount of irrigation water, soil temperature and population density of a pathogenic bacterium Ralstonia solanacearum before and after soil solarization were investigated in 6 greenhouses (located at Kaizu city, Gifu, Japan) in order to obtain the basic information of water requirement for the control of R. solanacearum via soil solarization in managing tomato cultivation. Our results showed that the soil temperature was influenced by airtight state of a glasshouse, temperature differences between inside and outside of a greenhouse, and duration and climatic conditions of the solarization period. The density of R. solanacearum decreased markedly after soil solarization with daily average soil temperature greater than 40°C for consecutive 10 days or 3 days under anaerobic condition, which was consistent with previous studies. The amount of irrigation water ranged from 155.6 to 495.2 mm (average: 291.3 mm) for 2 greenhouses where soil solarization was effective, which corresponded to 104 - 346% (average: 218%) of the amount of water requirement from some state to become saturation state.

View full abstract

Fish densities and environmental factors in seasonal water-flow sections were compared to those in permanent water-flow sections in agricultural canals. Densities of Gnathopogon elongatus elongatus and Misgurnus anguillicaudatus were lower in seasonal water-flow sections than in permanent water-flow sections. A significantly low density of M. anguillicaudatus was observed in seasonal water-flow sections although the mud substratum, which supported the habitation of M. anguillicaudatus, was larger than in the permanent water-flow sections. On the other hand, even in seasonal water-flow sections, a high density of fish that is frequently sourced from permanent water area, such as Carassius spp. And Opsariichthys platypus, was observed. Therefore, populations of fish with limited migratory ability, such as M. anguillicaudatus, may become endangered or extinct in agricultural canals with only seasonal water-flows.

View full abstract

The strength characteristics of hardened geopolymer paste using two types of fly ash, which have different chemical components, were experimentally examined. The compressive strength of geopolymer using PFBC fly ash had remarkably increased within 7 days. On the contrary, the compressive strength of geopolymer using JIS fly ash had increased mostly after 28 days. In addition, the tensile strength to compressive strength ratio and the bending strength to compressive strength ratio of geopolymer using a PFBC fly ash were larger than those of cement-based materials. There was a large difference in particle size and shape between PFBC fly ash and JIS fly ash by SEM observation, i.e. the PFBC fly ash was aggregated from particles of an irregular size and shape, whereas the JIS fly ash was aggregated from relatively uniform and spherical particles. The difference in the strength characteristics of the geopolymers could be attributed to the different properties of the fly ashes.

View full abstract

There were the following typos in the figure, “Irrigation, Drainage and Rural Engineering Journal Vol. 80 (2012) No. 3 p. 261-266”

View full abstract