Minqin Oasis is one bridgehead of the windblown-sand line in North China, and also one of the most seriously desertified areas in China. The special geographic situation has decided its history as one of sand-control and water-preservation. Noticeable improvement had once been made in the area. However, as the changes of natural conditions, especially the shortage of water resources, the eco-environment was getting fragile gradually, and desertification threatening the oasis's survival. Based on the analysis of the variation mechanism of the water resources in the oasis, relationships between the exploitation of water resources and the changes of hydrological cycle have been brought to light. Then, eco-environmental problems are revealed as the following four facets : water quality worsening, deterioration of ecosystem, land degradation, and sandstorm weather evolving rapidly and widely. The trend of the oasis's wane would not be easily reversed if no practical and effective measures had been taken. Therefore, it is very important to understand the interaction between human and the environment, to realize and follow the natural laws, and to develop and utilize the natural resources moderately in order to make the survival development in Minqin Oasis.

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It is of great significance to employ a statistical approach to the seepage problem with spatially high variability of soil properties. In our earlier work, it has been demonstrated that with the increasing standard deviation of permeability coefficient the mean seepage flow rate decreases and its covariance increases, and this is a result of spatial spanning of lower or higher permeability. Using the percolation theory, this paper attempts to reproduce such spatial spanning that forms "impervious wall" or "flow path". Spatially correlated random permeability fields are generated, and the finite element seepage analysis is carried out for each of these fields to examine percolation properties. As a result, it is shown that the indexes of percolation (i. e., threshold and threshold probability), defined in the percolation theory, could characterize the total flow rate in random permeability field with the same means, standard deviation and correlation distance.

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This paper describes a water conservation study conducted in two catchments, one in forest and the other in grassland, in Sado, Japan. The investigation characterizes various runoffs of the two catchments. The results show that total outflow of the forest watershed is less than that of the grassland in the no-snow spell. The runoff model is shown to reproduce observed outflow patterns in Sado and this model is a satisfactory method introduced from the verification plots. In particular, the amount of storm runoff from the forest catchment is small. The data suggest that the runoff is uniformed at the catchment area in forest. It is desirable for water resource management that the runoff water is supplied without significant variation. It is expected that afforestation enables the continuously unchangeable water supply.

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In a semi-closed pipeline system, if the water diversion stops or if it is diverted at 20% or less of the design flow rate at a decompression system with a disk value vibration, called chattering of disk, can occur at the small opening, and often cause a strong water hammer. The placement of an oil damper between the float and the balancing arm is considered to effectively prevent the chattering. Even if a sudden pressure change occurs in the pipe conduit, the oil damper temporarily absorbs it or reduces the vibration of the disk valve by dissipating its kinetic energy and thereby making the motion of the float less sensitive. This paper presents a rotational vibration model of the disk valve system with a built-in oil damper, and numerically investigates the effects of such a system on transient flow in the whole pipeline system. As a demonstrative example, the methodology presented is applied to a real pipeline system with 8 disk valves. Computational results indicate that the chattering can successfully be suppressed by use of damper, but the water hammer caused in stopping water diversion cannot significantly be reduced. It is therefore concluded that even in the system equipped with the damper an additional capacity (say, corresponding to 3 min × design flow rate) should be provided in a decompression tank to eliminate the water hammer.

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The river water in high water flow, which has not been utilized for any purpose, could be new water resources for the areas which have not enough rainfall. As water resources, both the amount and the quality of water should be taken into consideration for water use. The characteristics of water quality changes during high water flow in rivers, especially in small rivers, depend on water quality components, nature of the soil in river basins and rainfall intensity. Therefore, the accumulation of case studies has been expected. This paper deals with the water quality (turbidity, pH, T-N, NO_3-N, NO_2-N, NH_4-N, T-P, PO_4-P, BOD) changes during high water flow in Ono River, Matsuyama City, Japan. Based on the investigations conducted for four rainfall events, two of which are heavy rain and the others are moderate, the following facts are obtained ; 1) The peaks of turbidity appear before the peaks of water discharge appear. The data plot of turbidity against water discharge shows a hysteresis loop. 2) For NO_3-N, interrelation between water discharge and concentration, and interrelation between water discharge and load are strong. 3) PO_4-P concentration decreases with increasing water discharge during heavy rain due to the dilution effect. 4) The load of BOD and water discharge are adequatelly correlated, though the fluctuations of BOD concentration during rain events are complicated.

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Settling basin is an essential need, when river water is withdrawn from middle-high water flow in which water is highly turbid. A novel fan-shaped settling basin is tested and the hydraulic structure in the basin is investigated by hydraulic model experiments. A radius of the fan-shaped basin model is 320 cm and a central angle is 30 °. Both a submerged weir and a submerged rectangular orifice are installed in the upper stream of the basin to rectify the inflow. Measured discharge coefficients of the weir and the orifice are very similar to the conventional values. Wake region in the basin, where a counter flow is seen in the upper layer and a jet in the lower layer, expands to the distance of 100-140 cm from the orifice, which is roughly equal to 10 times as large as the depth of the orifice upper edge. Coefficient of variation is introduced to evaluate the non-uniformity of the flow in vertical transversal planes of the basin. Using the coefficient of variation, the difference in the variation of flow between the wake region and the other region is quantitatively evaluated.

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Rice plant response to salinity in irrigation water was experimentally measured to investigate its salt tolerance. Different three irrigation waters, (1) natural groundwater, (2) diluted sea water with electric conductivity (EC) of 1,400μ S/cm, and (3) the same with 1.8OOμ S/cm, were supplied to the rice plants of the same variety that were growing in different three growth chambers in a greenhouse. The experiments had been conducted for consecutive three years under a scheduled watering and dewatering management. The results show that the waters (1) and (2) produce indistinguishable difference in growth of the rice, while the water (3) delays increasing the number of young shoots and hence, after the panicle formation, reduces the transpiration by about 3mm/d compared with the water (1). The water (3) also causes etiolation of the plants. This salt injury becomes most serious at the end of the panicle formation stage, 7 to 9% of the stems being injured. Use of the water (3), however, causes insignificant yield reduction. This invites us to the conclusion that the maximum allowable salinity level of irrigation water without yield reduction (i. e., rice plant salt tolerance) may be around 1,800μ S/cm in terms of EC.

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Instructions are given to prepare the manuscript of an English paper submitted to the Journal of Rainwater Catchment Systems. Being a model in itself, the document demonstratively prescribes the layout of the manuscript. Manuscripts should be typed on one side of white A4 size paper when they are submitted. Accepted manuscripts will be off-set printed. Titles of papers, names and affiliations of authors, abstract, keywords, main texts, headings, references, equations, mathematical symbols, captions of figures and tables and so on should be in specified fonts. All references cited should be collected together at the end of the paper. Figures and Tables with their captions should be placed appropriately.

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Instructions are given to prepare the manuscript of a Japanese paper submitted to the Journal of Rainwater Catchment Systems. Being a model in itself, the document demonstratively prescribes the layout of the manuscript. Manuscripts should be typed on one side of white A4 size paper when they are submitted. Accepted manuscripts will be off-set printed. Titles of papers, names and affiliations of authors, abstract, keywords, main texts, headings, references, equations, mathematical symbols, captions of figures and tables and so on should be in specified fonts. All references cited should be collected together at the end of the paper. Figures and Tables with their captions should be placed appropriately.

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