A linear programming model is developed to optimize the allocation of pollutant from non-point sources in a watershed. The use of Arc View GIS software is incorporated to calculate the flow length from each land management unit as a non-point source to the outlet of the watershed. The formulated model is applied to a subcatchment of Yasu river basin in Shiga prefecture, Japan. Optimization is carried out at different weight values depending on decision-maker's preference order of land management unit type with respect to mean load discharged from unit area. It is observed that optimum discharged load of total nitrogen changes with the change in preference order. This model can be useful for determining optimum discharged pollutant loads from different land management units of a watershed for different preference orders based on need of decision-makers.

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In many design practices for rehabilitation or construction of earthen embankments, a deterministic approach is employed for seepage flow analysis, assuming hydrogeological homogeneity of embankment soils. Since in fact soil permeability is heterogeneous, such a conventional approach may often mislead engineers into making an inadequate design with less structural safety and less economical efficiency. This paper intensively investigates reliability of seepage analysis based on a statistical approach that can consider spatial variations of soil permeability. First, random fields with mean, standard deviation and spatial correlation structure are generated, and then finite element seepage analysis in these random fields is performed. The statistical analyses are then implemented through the procedure of Monte Carlo simulation. The statistical solutions to a confined seepage flow problem are compared with the theoretical solution based on deterministic approach. As a result, the mean flow rate Q_m becomes far from the theoretical value Q_t as the global standard deviation σ_k and/or the correlation distance a increase. The spatial correlation structure, not to mention the mean and the standard deviation of permeability, is shown to have a significant effect on seepage flow rate.

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This paper deals with the characteristics of water quality in rivers and reservoirs in Nakajima Island, which is located in the western part of Seto Inland Sea, in order to develop self-reliant water resources. Nakajima Island is mountainous with steep sloping granitic soil and the greater part of land is used for the orchard. Nutrient salts (T-N, NO_3-N,NO_2-N, NH_4-N, T-P, PO_4-P), pH, Cl^-, EC, Fe, and Mn were measured once a month from December 1998 to November 1999. At the same time, the amount of fertilization on the orchard was investigated to reveal the affect on water qualities. The major results are as follows ; 1) The concentrations of nitrogen both in rivers and reservoirs are high in May and October, due to the spring and autumn fertilizations. Especially, the intensive fertilization in early and middle autumn makes the concentration to be the highest level in October. 2) The averaged concentrations of nitrogen and phosphorus in each study area are related to the ratio of the orchard area to the study area. 3) The concentrations of nitrogen and phosphorus in reservoirs are less than those in rivers. Moreover, the concentrations in reservoirs with water plants are lower than those in the other reserviors.

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This paper deals with the purification system of stored rainwater in a small pond by renewable energy sources such as solar or wind. However, the energy harnessed from the sun or wind depends upon the temporal weather conditions. Therefore, it is necessary to create hybrid solar-wind energy, to recharge it into car battery bank, and to obtain reliable energy to purify the stored rainwater by pumping or aeration by diaphragm blow operation at a later time. This system increases the dissolved oxygen by photosynthesis of aquatic plants such as Egeria Densa Planch, which has high tolerance to water pollution. Filtration by zeolite and active carbon shows that energy bank system works effectively and water purification of phosphorus and the nitrogen have also decreased effectively.

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The landslide area, Okimi landslide, is situated in Kamiya District, Maki Village, Higashikubiki County, Niigata Prefecture, Japan, and is a typical devastated forest land caused by landslides. In this paper, in order to provide basic knowledge for water balance in a landslide area as one type of forested area, the outflow characteristics of two watersheds are investigated. The runoff addition and reduction curves are derived through recording the waterstage of the measuring notch during three water years as the hydrograph from two watersheds. In addition, the change of electronic conductivities for both A and B watersheds is obtained by the data from the field observation. The results lead us to the conclusion that (1) in the devastated area, there is the possibility of recording a large value of runoff compared with the input data as the precipitation, (2) by using the electronic conductivity value, the inflow through the ground water route to this watershed from the other watersheds is included.

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Semi-closed pipeline systems are usually constructed as demand-oriented systems by installing a decompression facility with a float valve in the intermediate pressure regulating facilities and/or in the inflow works of farm ponds. A disk valve is often used as the float valve for the pressure regulating facility. However, even when the capacity of the decompression tank with the disk valve is sufficient, rotation or chattering of disk valve can occur when water is diverted at a low flow rate or when water diversion starts or stops. This can in some cases cause a strong water hammer. In this paper, a dynamic balance model is developed that describes the rotational vibration of a disk valve system balancing a float and a disk, and incorporated into the commonly used pipeline flow model in order to simulate the transients in a pipeline system with disk valve systems. A sample application of the system simulation model is made to a real pipeline system to examine critical situations that can generate chattering. The results show that a decreasing flow in stopping water diversion and even a constant flow of 20% or less of the design flow rate are prone to chattering that may cause successive water hammers or saw-toothed pressure waves. It is also demonstrated that, regardless of capacity of decompression tank, the chattering generates a water hammer.

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In the Amami and Okinawa area, Japan, there are a great number of settling basins established in order that suspended sediments, which float from cultivated fields to rivers or sea areas, can be sedimented and removed. Currently, there has been an increase in the number of requests for water storage in these settling basins in cultivated fields with no irrigation reservoirs in order to utilize the water for irrigation. Since settling basins are utilized as a water source, water should always be stored in settling basins. Therefore, it is necessary to investigate how this water affects the function of settling turbid water in settling basins. This paper aims at experimentally investigating the feasibility of using a settling basin as a storage basin for irrigation water use. For this, two extremities of initial water storage in a model basin, i. e., empty and full storages, are considered. The turbidity (the concentration of suspended sediments) and the quantity of water leaving the basin from its outlet are measured to evaluate the amount of suspended sediments not trapped in the basin (i. e., escaping from the basin). Different tests with different initial water storages are comparatively conducted to estimate the effect of keeping the storage full for water use on the primary function of the basin. The results show that in both cases of initial water storage the equilibrium levels to which the outflow turbidities reach as time passes are the same. The amount of the escaping suspended sediments for the initially empty storage is slightly less than that for the initially full storage. It is thus concluded that the settling basin could be used as a storage basin for irrigation water use as well.

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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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