Not only the environment inside a fishway, but also that of the route to the fishway is considered as one of the important factors for river creatures to succeed in upstream migration. This study aims to evaluate the upstream migration of Ayu and the flow characteristics at the downstream of an ogee crest weir including fishway under the different river flow conditions. We clarified the flow velocity and direction at the downstream of the weir near the fishway entrance for Ayu. We also focused on the number of Ayu migrating through the fishway and the number of the fish trying to migrate over the weir directly, and the fluctuation of flow on the weir during the migration season of Ayu. Considering the flow velocity and direction, the flow preferred by Ayu appeared at around 20 m to 40 m away from the left bank fishway when the water depth on top of the weir crest was 9.7cm. Results of hydrological measurement and analysis showed that the flow depth fluctuation, which was observed when a lot of Ayu tried to migrate over the weir, occurred intermittently after the month of June in the past three years. Generally, it has been reported that the main migration season is in May in the research area, but this study showed the possibility of predicting the suitable days for observing the migration after the main migration season.
There is a possibility of influencing the roughness coefficient of abrasion concrete canal that is the index of the hydraulic performance. Therefore, it is necessary to figure out surface roughness of the canal to recognize the hydraulic performance. In this report, using the three dimensional image of canal surface by image analysis software, from the picture taken with the digital still camera, with the aim of figure out the surface roughness that obtained a simple, united value of concrete canal. From the image analysis result, the model version was able to reproduce the canal surface asperity excellently, compared with the actual value measured by the laser displacement sensor. The camera pixel affected to surface asperity reproducibility, however, the calculated roughness coefficient from three dimensional image was not affected by difference of camera pixel count. Moreover, from the result of the three dimensional image, taken a picture at real concrete canal, it is able to obtain asperity of concrete canal surface with good accuracy.
Effective renovation of irrigation and drainage facilities through stock management measures is highly needed because of drastic decreases in budgets of agricultural public investment. The present study aims to develop an estimation model for main irrigation and drainage capital stocks with considering stock-management measures. This model can evaluate two effects which mean to use old facilities to the end of lifetime with low dead-costs and to reuse old parts of facilities in renewed facilities. Applying this model to the Japanese macroeconomic statistics demonstrated that the chronological trend of capital stocks of irrigation and drainage facilities were different from our expectation based on the point estimations published by Ministry of Agriculture, Forestry and Fishery. Furthermore, predicting capital stocks of irrigation and drainage facilities by this model can help policy decision making on agricultural public investment and evaluation of stock management measures.
To determine habitat use of vegetation area and different depth by fishes and freshwater prawn in a pond, we conducted trap sampling in a small pond of southern Isawa ward, Oshu city, Iwate prefecture. We collected six fishes and one prawn species (Palaemon paucidens), respectively. Acheilognathus tabira erythropterus appeared only in the bottom during spring and it resulted from their spawning behavior. Rhinogobius sp. and the prawn appeared in both the surface and the bottom. Misgurnus anguillicaudatus mainly appeared in the bottom. These results seemed to relate the ecological traits of each species. Since the present study showed that both open water and vegetated area were utilized by each species, various environments should be maintained for conserving habitats of pond-dwelling aquatic organisms.
It is necessary to select the appropriate repairing material and method for the purpose of accomplishing the efficient maintenance and management of agricultural canal. The surface covering method is one of the general repairing methods to the concrete structures. The variation amounts of crack width of reinforced and plane concrete canal were focused in this study. Restriction effect against the movement of crack of surface covering method using alkali resistant glass fiber net was verified experimentally. As a result, variation amounts of crack width were large difference between reinforced and plane concrete canal. Especially, the crack variation amounts of plane concrete canal was more than two times larger that of reinforced concrete in daily examination. In small scale canal which have no soil behind both sides and canal axis was extended from east to west, the crack variation amounts were almost same in spite of their “position” north side and south side, at the same concrete canal. Surface covering material showed restriction effect when using alkali resistant glass fiber net. For that reason, appeared crack width to the surface covering material was repressed within harmless amounts to the function of reinforced concrete canal.
In order to obtain a reliable appraisal data for irrigation projects, we estimated annual changes in soil moisture content within a 40-cm surface layer for the past 33 years (1978 to 2010) from April to September as well as drought frequency using the soil tank model. The investigation was conducted on pasture lands of Okunakayama Highland in Iwate Prefecture. Our results showed that decreasing of volumetric water content ratio which had lower amounts of the soil moisture than depletion of moisture content for normal growth mostly occurred between 1978 and 1999. It suggests that the serious drought had apparently caused damage on a comparatively large scale in this area when the decrease in volumetric water content ratio which had lower amounts of the soil moisture than depletion of moisture content for normal growth continued for more than 8 days, and had occurred about 6 years within the 33-year period. However, the drought was unevenly distributed over the period, and all these serious damages were occurred during the 22-year period from 1978 to 1999 and that no drought had occurred for 11 years since the year 2000.
With serious problems caused by aging of farmers and diversification of residents, irrigation districts which manage most agricultural water facilities must serve not only farming but also non-farming needs, such as drainage from housing areas. It is therefore important to develop a new method for the participation of non-farmers who account for 90% of rural residents. This study focuses on the method of collecting costs from non-farmers for the irrigation district system which is specifically for farmers only. It examines the case of Kahokugata District which was the first district to adopt this method in 2009, and shows how difficulties were solved. Moreover, the possibility of management by diverse participants is clarified by proposing a 5-step model for diverse participation.
The authors of this paper enhanced the previously reported model for planning the transportation and application of digested slurry to farmlands as a fertilizer. The following 2 functions were added to the model to modify for larger quantity of digested slurry. (1)Operation with plural vacuum trucks of digested slurry. (2)Installation of intermediate tanks into the transportation and application system. These functions were examined by simulation with hypothetical conditions. According to the simulation results, the number of vacuum trucks with the shortest waiting time minimized labor and fuel. The installation of an intermediate tank also reduced the labor and fuel in longer distance of transportation. The simulation results indicate that the added functions are useful for planning more effective transportation and application of digested slurry to farmlands.
Over the past decade the Land Improvement Act has mandated eco-friendly land development practices. Studies of fishes, published mostly in the recent decade, were reviewed based on their method of evaluating current or potential future habitat conditions. Evaluation is an indispensable element for adaptive management. There are some issues in studies of Suitable Index models for HEP, etc. These issues are the tendency for many studies to construct excessively complicated models and to not disclose the details of their models. It is necessary to disclose model details to achieve progress in aggregation of information about models. Understanding the detailed construction of numerous models will enable future model builders to construct better, more complete models. Disjuncture of water areas is also an urgent issue that has motivated research. For that reason real progress has been made in understanding fish migration. As a result studies which evaluate the status rice paddy irrigation networks or lead to such evaluations have recently appeared. At the same time, the spatial scale treated in such studies has broadened. Several issues surrounding evaluation of management benefits considering spatial placement of habitats are described in this review.