Laboratory tracer experiments are conducted to investigate solute transport in 100-cm long, horizontally placed flow field under steady saturated water flow conditions. Uniformly packed homogeneous and two-layered flow fields having cross-sectional areas of 50×6cm^2 are of concern. NaCl breakthrough curves are measured with salt sensors inserted with regular intervals along the flow direction. Longitudinal and transverse dispersivities, retardation factor, leak duration at the source and source magnitude are estimated using genetic algorithm (GA) linked with an analytical solution of the advection-dispersion equation. The results show that the values of longitudinal dispersivity range from 0.0631 to 0.316cm while transverse dispersivity is estimated in the range from 0.0221 to 0.190cm in homogeneous or two-layered porous media. In addition, breakthrough curves corresponding to the identified set of values are recovered with good accuracy regardless of noise level, while retardation factor and source magnitude are less sensitive parameters to noisy data among others, indicating that application of GA to parameter estimation problem with noisy data is expected to recover the concentration profiles. Moreover, estimates in layered media depend on transport pathway of contaminant, suggesting the importance of observation location in parameter estimation.
Relationship between diversity indexes of fishes and environmental factors were evaluated. In this study, a field investigation was carried out in a paddy-field area in the eastern part of Shimane Prefecture. Parameters of this study were water qualities, fishes, and physical environmental factors (water depth, flow velocity, vegetation coverage, soil coverage of undersurface and habitat space) in drainage canals. Eleven species of fishes were observed in the investigation sites and diversity indexes were calculated by Shannon-Wiener method. Factor analysis was conducted with the diversity indexes of fishes and the environmental factors. As a result, higher values of diversity index were found with lower concentrations of chemical oxygen demand (COD), total organic carbon (TOC), nitrogen and turbidity. In addition, the higher indexes were also found with slower flow velocity and higher levels of vegetation coverage, soil coverage of undersurface, habitat space and water depth.
A former pipeline system for pumping water conveyance has been designed on condition that include a flywheel and other facilities for suppressing the negative pressure to 7 m or lower to prevent the water column separation. Authors examined the method for installing non-water hammer pressure check valve which is the improved swing check valve and used three in the series on the downstream in the place which is generating the negative pressure in order to suppress the water hammer pressure by sudden pump stop. The field measurement on water column separation in pump power failure and water hammer pressure caused by its recombination, and the effect of setting up the non-water hammer pressure check valve was carried out. The field measurement on water column separation in pump power failure and water hammer pressure caused by its recombination, and the effect of setting up in the series the non-water hammer pressure check valve was carried out. Then, it was possible to reproduce these phenomena accurately at the practical level by the simulation using the simplified model of non-water hammer pressure check valve and discrete cavity model of the water column separation.
This paper presents the water management and the actual condition of rainwater use on paddy fields in low-lying areas when using a cyclic irrigation system. The investigated area consists of low-lying land (574ha) and sand hills (1,731ha) in the Hirataki District, West-Tsugaru Region, Aomori Prefecture. The amount of irrigation water in the Tsugaru area is not enough to provide water necessary for rice planting during the irrigation period. Because almost no irrigation water of the Hirataki District is supplied from other areas, this area mainly depends on re-used drainage water and rain water stored in ponds and in drainage canals. Therefore, the dependence rate on rain water and the ratio of re-used drainage water is very high. The average values of the recycled irrigation water ratio to the total amount of irrigation water and drainage water over 19 years (1986 through 2004) are calculated as 82% and 74% respectively. The average values of the rainwater utilization ratio from the viewpoint of irrigation factors and drainage factors over 19 years are 105% and 72%. To maximize the use of rainwater, the pumped irrigation water in this area is stopped very quickly after the beginning of rainfall. Moreover, additional drainage discharge by rainfall is very low. The amount of stored rainwater that does not drain from this area to the river system may be re-used as irrigation water. It can be concluded that the rainwater utilization ratio is influenced by the rate of rainfall to evaporation during the irrigation period, and by the ratio of recycled irrigation water. This cyclic irrigation system in low-lying paddy areas need not have a bad effect on the surrounding environment and rivers. Moreover, the water management system in this area provides an effective case study of sustainable agriculture and presents one method to cope with dwindling water resources in the future.
In brackish lakes undergoing artificial salinity management, demonstrating countermeasure scenarios for optimum salinity management to protect water environments and increase the production of water resources is a very important issue. In fundamental research on this issue, the authors constructed a three-dimensional numerical model utilizing the operator splitting method to examine lake currents and salinity dispersion. We applied this model to Lake Togo in Tottori Prefecture, and studied the effects of wind speeds on the flow patterns of wind driven currents, sea water intrusion processes, and density stratification formation processes. The results of this study indicated that the form of salinity intrusion could be categorized into three types: stratified type at a wind speed of 1m/s, partially mixed type at a wind speed of 3m/s and well mixed type at a wind speed of 6m/s, and that the formation of density stratification could be seen under wind speed conditions of 1m/s and 3m/s. At a wind speed of 6m/s, the strong mixture effect of the wind resulted in almost no density gradient in the water depth direction, suggesting that vertical circulation was taking place on a large scale throughout all regions of the lake. Furthermore, under all wind conditions, the intruded saline had reached all regions of the lake 54 hours after the start of calculations, and the saline reached a level of 4 psu or more in all regions of the lake 150 hours after the start of calculations.