A spiral water wheel had been invented in Toyama Prefecture in the twentieth century. Unlike conventional water wheels, the wheel can be operated, for example, in low water head and levels. In this study, we tried to generate electricity by employing the wheel at an agricultural irrigation channel. Through the results of performance experiment as an example, we found that the spiral water wheel was operated most efficiently when it was placed parallel to the channel bed which gradient was approximately 25 degrees. It was also found that the micro hydropower system developed here was suitable for electric generation at the point of sudden drop of an irrigation channel. The build-in blades of the micro hydropower system had a spiral shape form; therefore, the blades could catch kinematic and potential energy both without loss. The blades could convert water energy into electrical or mechanical energy efficiently even in a small channel.
The processes of the gate flushing accumulated sand under the movable gates of the diversion dam were investigated through several hydraulic experiments. The experiments took into account the effect of quantity of flow, the water difference in the upstream and downstream, and the distribution of sand as dominant factors. The experimental results show: 1) flushing is performed regardless of any other factors when the quantity of flow is large. 2) Sand accumulates downstream in a shape similar to a mountain when the downstream water level is high, and that this influences the processes of flushing. 3) In the case of a one-sided distribution of sand, flushing becomes difficult because most of the flow quantity passes by the section without sand. 4) The accumulated sand is flushed within a narrow area around the gate.
This paper presents the calculation of the carbon dioxide emission by using the carbon dioxide intensities related to the Asato landslide control works site, which is located in the area of Shimajiri mudstone in Okinawa, Japan. Among the three categories of contributory causes responsible for carbon dioxide emission related to such landslide control works, namely the operation of construction machinery, the production of construction machinery and the production of building material. The category of production of building material has recorded the highest carbon dioxide output of over 65 percent, of which about 90 percent has originated from the production of cement and rolled steel in blast furnaces. The carbon dioxide emission from the operation of the backhoes, dump trucks and air compressors have accounted for about 65 percent of the emission within the category of construction machinery operations. Among the carbon dioxide emission values recorded due to the landslide control works, slope works have generated the highest percentage of emission of over 50 percent followed by the pile works and the earth works. Thus, there is a possibility of achieving a reduction of the amount of carbon dioxide emitted from landslide control works through the reduction of the production of building material.
This study was conducted in order to understand the conditions and amounts of irrigation water used in large, sub-irrigated rice paddy fields. On-site monitoring of subsurface water levels was conducted, as well as the delineation of: irrigation water supply routes; the quantity of irrigation water at each crop growth stage; and the time/rate of each water intake. It was found that when sub-irrigation is carried out during initial irrigation, the irrigation water quickly raises the level of subsurface water in the underdraining filter material, rising to the plow layer level before spreading horizontally. Results indicate that even in large rice paddy fields, a mostly temporally uniform water supply to the entire field is possible. In direct-seeding cultivation, the amount of water per intake was large at the beginning of irrigation and in subsequent intake for shallow-water management. Between mid- and late May, a significant spike in regional water demand may be seen because water is required both for land preparation in fields used for transplant cultivation and for the beginning of irrigation and shallow-water management in fields used for direct-seeding cultivation.
There is an urgent need to design disaster mitigation measures for agricultural irrigation facilities in the event of a large-scale earthquake. At the time of a large-scale earthquake, facilities could be unexpectedly damaged, so disaster response to prevent further damage after the facilities are hit is important. However, disaster response doesn't always work smoothly when a large-scale earthquake occurs. To establish risk management aimed at improving disaster response capabilities for the management of irrigation canals, this study targets typical main irrigation canal, which consist of headworks and open channels, toward identifying risk sources that hinder disaster response at the time of large-scale earthquakes. Results from an interview survey of facility managers found that their main concern in terms of disaster response immediately after the occurrence of an earthquake is the determination of whether water flow in the main irrigation canals should be halted or not. Therefore, Fault Tree Analysis (FTA) was applied to identify risk sources that cause errors in judgement by facility managers in such circumstances. Results clarified not only the risk sources that can currently be dealt with within the framework of existing facility management, but also additional risk sources for which measures have yet to be discussed as a part of a regional disaster prevention plan involving local residents.
A method using two-dimensional resistivity surveys was proposed to efficiently detect the range of cracks. In the method, a conductive liquid was injected into the cracks, resistivity surveys were performed before and after the injection and the distributions of changes in resistivity were calculated. To examine the applicability of this method in the fields, numerical and field examinations were conducted. In the numerical experiment, the horizontal range estimated by the survey line parallel to the crack was found to be almost equal to the actual crack length. The vertical range estimated by the survey line perpendicular to the crack had low correlation with the depth when the depth was larger than the length. However, high correlation was observed when the depth was smaller than half of the length. In the field experiments, the horizontal range estimated by the survey line parallel to the crack detected the crack length. The range of cracks, estimated by the survey line perpendicular to the cracks, detected the crack depth when the depth was smaller than the length. The results indicate the possibility of detecting the range of cracks by estimating the crack length based on parallel survey lines and the crack depth based on perpendicular survey lines.
Pore water pressure and liquefaction in a saturated sand bed induced by tsunami are theoretically and experimentally discussed. A governing equation on the basis of the Darcy's law is presented, and a centrifugal model test is carried out to verify the applicability of the governing equation. In addition, numerical simulations are performed in one-dimension, giving observed sea levels by GPS buoys on 11 March, 2011 (MLIT Japan) as the input data, in order to evaluate pore pressure and liquefaction by the actual tsunami. Moreover, parametric studies are performed assuming a permeable layer as silt, and the influence of permeability on liquefaction is discussed. Experimental results show that the effective stress decreases due to tsunami. It is evident that the calculated values are in good agreement with the observed values, and the governing equation is applicable to evaluate the liquefaction potential. In addition, it is revealed that liquefaction can occur due to the actual tsunami even if the permeable layer is comparatively good drainage like sandy soil. It is also clear that the excess pore water pressure ratio increases with the decrease of permeability at the shallow depth, and the influence ranges up to the depth of 4 m below the ground.
The population of far eastern catfish Silurus asotus has been dwindling due to reduction of the places for spawning in temporary waters. In this study, in order to clarify catfish life history from spawning to growth of juvenile, field investigation was conducted in consolidated paddy fields in Utsunomiya city, Tochigi prefecture. Preliminary field observation found several catfish gathering for spawning in one farm drain, and hence detail investigation was carried out for that farm drain from May to June 2012. Although the farm drain is made of concrete flumes and has several hydraulic drops, large portion of the bottom of the ditch was covered with muddy sediment and occasional heavy rain could realize the continuity of water body over the drops. This condition enabled the farm drain to become reproductive area for catfish despite some disadvantages. Besides, the young catfish grew by 2.6 times in total length for a month. They moved to downstream in the farm drain and finally migrated to the river connected with the ditch. Thus, this habitat served as a nursery area for juveniles. The abundance of feed organism for the juveniles and presence of mud substratum in the farm drain were considered to provide good conditions for it.