??Using a siphon to transfer water along a dike out of a reservoir is an extremely economical water intake method. However, because the pressure at the top of the siphon is less than atmospheric pressure, air released from the water collects at the top. The accumulation of air reduces the pipeline’s capacity to transport water. In the worst case scenario, the water flow in the siphon stops completely. Therefore, a new automatic air evacuation system to remove air from the siphon pipe that does not use the safety flow pump was developed.
??In pipeline systems connected with 5 irrigation reservoirs in the M irrigation project of Okinawa Prefecture, siphon pipe systems equipped with automatic air evacuation were used. Through the use of this system, the pressure in the long distance siphon pipes decreased, and as a result, the system was unable to maintain a consistent flow. Measurement instruments including a pressure gauge and a flow meter installed in the system verified hydraulic performance in long distance pipes that were using automatic air evacuation. The results revealed that when the equipment was operating normally, the siphon flow formed temporarily, but over time the siphon flow degraded and finally ceased. It is hypothesized that the cause of this is related to the longitudinal profile design of the long distance pipes. Important points to consider in the design of future siphon pipe systems that are equipped with automatic air evacuation are discussed.
??Water resources at Dalad, Inner Mongolia had been investigated by groundwater sampling and metering during 2002-2006. Since Dalad is located in the middle reach area of the Yellow River basin and classified as arid or semi-arid area with less than 360mm precipitation and more than 2,200mm potential evaporation, the river water is not sufficiently supplied to the area and therefore, farming inevitably depends on mainly groundwater resources. During the investigation period, three procedures ; 1) 18 sampling tube wells were installed or prepared in the southern part of the study area to find the fluctuation of the groundwater level and water qualities such as pH and EC, 2) location, approximate withdrawals and water qualities at almost all the existing wells in the southern part of the study area were identified and measured simultaneously, and 3) 14 sampling tube wells were used to find the water levels and water qualities, were carried out. The obtained data show that the groundwater resource of the study area is recharged by mainly the groundwater flow from the Desert Kubuchi and partly by the seepage water from the Yellow River. The amount of the groundwater tended to decrease slightly in the study period, but it might be due to the condition of the precipitation and might not connect to depletion. Some ionic matters indicated by EC seems to be conveyed by the flow directing to the North in the southern part of the study area and then EC at some wells showed relatively high values as more than 3.00mS/cm. Only, EC and pH did not show significant defect and degradation as a whole study area. As a result the followings are indicated. Inadequate groundwater withdrawal might induce more serious draught of the Yellow River and also inadequate fertilizer application might worsen the groundwater quality especially in the middle part of the study area. Therefore, continuing observation is essential to maintain the water resources at Dalad.
??Upstream migration and distribution of freshwater fishes are investigated in the lower reach of an agricultural canal flowing into the sea. The survey on upstream migration was conducted using two fixed nets installed at the drop structure nearest to the sea and the distribution survey was carried out using a cast net and two scrape nets in the basins and downstream areas of 19 drop structures including structures of groundsill, a vertical drop, multistep drops, and an inverted drop. During the surveys, a total of 1,136 freshwater fish belonging to 4 orders, 8 families and 17 species were captured by two fix nets, a cast net and two scrape nets. The distribution survey revealed that ayu, Plecoglossus altivelis altivelis, loach, Misgurnus anguillicaudatus and Japanese dace, Triborodon hakonensis were broadly distributed within the study area. Conversely, the habitats of Ayukake, Cottus kazika and Kajika, Cottus sp. were limited to the area near the sea and the growth of these fishes were inhibited in such a simplified habitat within the concrete flume.
??In order to develop a small-scale fishway for Amur stickleback, 25 experiments were conducted using hydraulic models of (1) pool-and-weir fishway with orifices, (2) pool-and-weir fishway without orifices, (3) Chidori-X type fishway with orifices, and (4) Ice-Harbor type fishway with orifices. The results of the experiments showed that (i) Amur sticklebacks had a tendency of passing through orifices in the experiments with orifices and the ascending speeds of Amur sticklebacks were faster in the experiments with orifices than without orifices, (ii) the ascending ratios of Amur sticklebacks were higher and the low-speed region of the pool was wider in the pool-and-weir fishway with orifices than other fishways, (iii) the ascending ratios of Amur sticklebacks were affected by the water temperature, (iv) Amur sticklebacks had a tendency of migrating in the daytime, not in the nighttime, and (v) the small-scale fishway for Amur sticklebacks was successfully developed to deal with higher difference in water level, by increasing the number of pools and setting 0.025m for the difference in design water level between adjacent pools.
??A-weighted sound levels between 78 to 89 dB were observed immediately above the dropping point of nappe on the water surface in the stilling basin of drop structures of the Togashi main canal of the Shichika Irrigation District, Ishikawa, Japan. According to the noise distribution survey conducted at the noisiest drop structure of 89 dB, A-weighted sound pressure levels between 62 to 67 dB which exceeded the Japan's environmental quality standard were observed in the cross-section adjacent to ordinary houses located 25 m downstream of the drop. Therefore, the noise reduction experiments of gabion mattress, using the 1/8 scale-downed hydraulic model of the drop structure of water-cushion type, were conducted. The experiments showed significant reduction of sound levels in the cases of trapezoid-shaped and inverted trapezoid-shaped gabion mattress with single or double-slit. Then, the flow velocity measurement showed that the sound levels above the dropping point of nappe were positively correlated with the mean flow velocities in the stilling basin.
??In this study, we aimed to examine the effects of mulch culture on the quality and production of plum. As a result of two years’ experiment that ground surface was covered or not by vinyl black film from July 1st to December 31th, the following effects of mulching were clarified. 1) The mulching can prevent the soil moisture from extremely decreasing and suppress its fluctuation during the continuous dry weather in summer, and increase soil temperature. 2) The mulching tended to hasten leaves fall in autumn, which suggested that the differentiation and formation of flower buds and commutation of nitrogen from leaves had been promoted. 3) The mulching tended to make the total production of plum increase and the variation of individual fruit weight reduced, which expected to improve those economic value. In addition, it was clarified that both of the average individual fruit weight and the total yield of plum were increased if the soil moisture content was maintained around the field capacity during summer season when evapotranspiration was very high.