??There is a case where a self-excited pressure variation is generated in low-pressure pipeline systems using an automatic pressure-reducing valve. For example, the pressure acting on the tube and valve is higher than the expected pressure and results in damage to the equipment. This study aims to explain the upstream and downstream pressure variations of the valve by carrying out pressure measurements in an actual pipe, in order to identify the mechanism of the self-excited variations and take effective countermeasures. For a reducing valve set up in the middle of the pipeline, the results indicated that the pressure variations that occur soon after opening the valve propagate upstream and downstream without attenuation, maintaining a constant amplitude, and generate continuing pressure variations that resemble self-excited oscillations. In addition, numerical simulations based on the wave model are conducted to evaluate the relationship between the response of an automatic pressure-reducing valve and the hydraulic transient phenomena in a pipeline system. If the pressure-reducing valve is adjusted for high-sensitivity, pressure variation due to external disturbances in the terminal region (downstream of the valve) may increase because of the period of pressure oscillation in the conduit of the upstream and downstream parts of a control valve.
??This paper develops a simple mathematical model for determining an optimal installation timing of the overhead lines (Tegusu) to reduce predation from piscivorous birds, such as Phalacrocorax carbo (Kawau), to Plecoglossus altivelis (Ayu) taking into account of its decaying protection effect. Temporal dynamics of the total number and the individual body weight of P. altivelis are described with the system of ordinary differential equations for non-renewable population. Then, this paper formulates and numerically solves the governing equation of the optimal installation timing to simultaneously minimize the total predated P. altivelis and the cost to install and maintain the overhead lines. Extensive comparative statics of the optimal installation timing against model parameters is carried out to investigate its dependence on river environment and attitudes of decision makers.
??A mathematical model was presented and parameter studies of the model were performed to investigate changes in the effect of stream drying on aquatic community dynamics in response to species specific characteristics. The community in the model was composed of producers, grazers and predators, and the river was assumed to have pool-riffle structure. Grazers and predators could move between the riffle and the pool according to their habitat preference. The temporal scale was enough short that grazers and predators did not reproduce. When the flow reduction began, grazers and predators tended to move from the riffle to the pool by the time the riffle dried up. Both of them could survive in the pool during the stream drying. After the stream drying ended and the water depth recovered, they tended to move from the pool to the riffle. The parameter studies on the sensitivity of grazers and predators to the flow velocity and the predation pressure for grazers revealed following: (i) grazers and predators which had the higher sensitivity to the flow velocity had advantage to reduce the decrease in their density due to the stream drying, (ii) predators had advantage to reduce the decrease in their density due to the stream drying if grazers had the higher sensitivity to the flow velocity, (iii) grazer density in the case of the stream drying became larger than that in the case of no flow reduction if predation pressure for grazers was high relative to the natural mortality rate of grazers, and (iv) the lower sensitivity of predators to the flow velocity had positive effects on grazer density after the stream drying if the predation pressure for grazers was high relative to the natural mortality rate of grazers.
??Aquatic fauna found in 21 man-made biotopes that were established in agricultural and rural development projects in rural areas in Ishikawa Prefecture, Japan, were surveyed. A total of 117 species were captured or observed, including nine species of amphibians, 14 species of fish, 75 species of aquatic insects, ten species of crustaceans, and nine species of mussels and snails. Mostly aquatic insects made up the 38 species of odonates found. In addition, 24 coleopteran species and ten hemipteran species were discovered in the biotopes. The Red Data Book of Japan lists Rana nigromaculata, Cipangopaludina chinensis laeta, and Oryzias latipes latipes as endangered species, and these species were captured in 18, eight, and six out of 21 biotopes, respectively. In addition, two nonindigenous invasive species, Procambarus clarkii and Rana catesbeiana, were captured in 11 and six biotopes, respectively. The numbers of species varied greatly among biotopes, ranging from four to 59, suggesting that the effect of biotope on biodiversity was not uniform.
??This study examined the geological structure and groundwater flow at the basin boundaries in Shirakawata basin and Higashi-soedo basin, the basin of main drinking water source of Miyako Island. From the results of the boring survey and the vertical electrical sounding, in northwestern part of Shirakawata basin, it was found a new continuous of groundwater with adjacent Higashi-soedo basin. In the northern part and northwest part of Higashi-soedo basin where the connection was pointed out with the adjacent basin, the situation was confirmed, and more detailed aquifer shape was revealed. Also, it became clear that the groundwater flowed out to the adjacent basin at these basin boundaries from the slope of groundwater surface in the vicinity. We estimated the outflow amount at these basin boundaries, from the cross sectional area of the outflow part, the hydraulic gradient of the groundwater, and the coefficient of permeability.
??On the small islands of Okinawa, reliance on groundwater is high. The main land use in areas of groundwater recharge is sugarcane fields. To model groundwater recharge in these fields, it is important to analyze infiltration, so the appropriate choice of soil hydraulic parameters is important. Sugarcane crops can take up to 2 years to mature, so the effects of time on soil physical parameters and groundwater recharge need to be considered. To model groundwater recharge, we collected 49 soil core samples 4 times in 2? years in 7 fields and measured soil physical parameters. Using cluster analysis, we classified the data and groundwater recharge, which was simulated in Hydrus-1D software. Values of bulk density, saturated hydraulic conductivity, and soil hydraulic parameter n were related to time after planting. Cluster analysis identified 4 clusters according to groundwater recharge rate and soil physical condition, and the results were affected by the time of sampling. These results indicate that it is necessary to take sampling date into account while simulating groundwater recharge in sugarcane fields.
??Low-yield of rainy season rice in the lower part of a paddy field zone, attributable to delayed field ponding and transplanting, and non-usage of any of the paddy fields for dry season cropping were concerning issues in N Village in the central part of Laos. Early field ponding and transplanting in the lowland, and dry season cropping in upper areas of the paddy field zone were expected to be possible using existing reservoirs located in the upper areas. Therefore, storage capacities, design of water facilities, and ownership, utilization, and management of reservoirs on two rivers were investigated. The reservoir capacities are 4,400 m3 on each river. Intake management was difficult with existing irrigation facilities, and most stored water could not be utilized. It was necessary to install new intake equipment adaptable to the village needs. Each reservoir was individually owned as fishponds. The benefits of irrigation were considered to be limited to a part of water users. In order to build a consensus among all water users, it is imperative for all water users, including reservoir owners, to aim at achieving an overall benefit at the village level through efficient use of water resources.
??The Takakuma Experimental Forest at Kagoshima University experienced record rainfall in September 2016. Following this event, we investigated sediment yields related to various types of erosion and collapse along forest roads and slopes within this forest. In particular, we focused on a 6.8-km2 study area. To evaluate the effect of rainfall intensity on erosion and collapse, we compared results from September 2016 (when maximum hourly rainfall was 154 mm.) with those from September 2005 (when maximum hourly rainfall was 55 mm). The numbers of forest roads and natural slopes damaged by erosion and collapse in September 2016 were greater than in September 2005. Moreover, when erosion and collapse were of the same type, sediment yields recorded in September 2016 were between 1.4 and 11.5 times greater than in September 2005. Thus, total sediment yield in September 2016 was about 3.1 times greater than in September 2005. Our results suggest that both frequency and magnitude of erosion and collapse are correlated with rainfall intensity in this area.