The individual travel cost model for valuing non-market benefits is applied to estimating environmental benefits derived from improvements in water quality of the Lake Tega. A trip generating function to travel costs and water quality is first estimated. The trip generating function is then used to estimate consumers surplus both before and after the improvements in water quality. The contingent valuation method is also applied to estimating trips per individual after the improvements in water quality. The environmental benefits from improvements in water quality of the Lake Tega related to recreational activities were estimated at ca. 151 million yen annually.

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We derive precisely the fundamental equation of the nonlinear flow in porous media based on Forchheimer's resistance equation and explain in detail how to solve this equation by the direct iterative procedure using the finite element method. We apply this procedure to seepage through embankment dams and compare the characteristics of the nonlinear flow with that of the linear flow. The results are summarized as follows:
1) The locations of the free surface of the nonlinear flow are higher than those of the linear flow and the equi-potential lines of the nonlinear flow move toward the downstream.
2) The maximum hydraulic gradient occurs near the downstream toe of dam and its value is about 0.5 and not so much different from that of the linear flow.
3) The positions of the exit point of the nonlinear flow become higher and there are more difference between the positions of the exit point of the nonlinear flow and those of the linear flow, as the constant ‘a’ of the Forchheimer's resistance equation becomes smaller and/or the constant ‘b’ becomes larger.
4) The locations of the exit point of the nonlinear flow are about 5% to 25% higher than those of the linear flow.
5) There are more difference between the discharge of the nonlinear flow and that of the linear flow, as the constant ‘a’ of the Forchheimer's resistance equation becomes smaller and/or the constant ‘b’ becomes larger.

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The authors suggest a model which estimates evapotranspiration using soil water suction, Leaf Area Index, potential evapotranspiration. The model is as follows ; ET= {f1 (ψm) ×f2 (LAI) +g1 (ψm) ×2 (LAI)}×E_p, ET: Evapotranspiration, f1 (ψm), f1 (LAI), g1 (ψm), g2 (LAI): Coefficients which represent relationship between soil water suction, LAI and evapotranspiration respectively, Ep: potential evapotranspiration. We can calculate crop coefficient using this model.
In this report, we discuss the model at first. After that, we discuss on crop coefficients of soybean.
In this report, we discuss the model at first. After that, we discuss on crop coefficients of soybean.
Calculated crop coefficient using measured 0.1 m depth soil water suction is about 10% smaller than that of abound in soil moisture.
No dimensional soil surface evaporation and transpiration decrease with soil water content per volume. They are fitted by linear and exponential lines respectively.

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A numerical procedure for solving the time-dependent, incompressible Navier-Stokes Equations and the heat and salinity transport equations, coupled through the density-state equation, is presented. The method is based on a set of finite element equations formulation and timemarching procedure. The finite element formulations consist of two steps, i.e. a first step for the vertical distributions of the primitive variables of interest through the depth using Chebyshev polynomials and a second step for the horizontal distributions of the coefficients of the polynomials using a two-dimensional triangular basis set. And the time-marching procedure is executed with the Kawachi and FT explicit schemes combined with the velocity correction technique. The fully three-dimensional reproduction of the convective currents and salinity and heat transports is accomplished with the aid of Petrov Galerkin integrations with the well-defined triangular basis set in the horizontal domain. As a demonstrative model operation, vertical circulations with caballing effect and inverse gravitational circulations with topographic heat accumulation effect are analyzed in hypothetical water bodies. The computed results have shown quite good agreement with the expected ones. Consequently the model is proved to be a useful tool in analyses of density driven flows.

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Innovative approximate solutions regarding an unsaturated water flow equation for internal drainage under a high groundwater table condition have been derived. This was obtained based on approximate separation of variables, i.e., depth z and time t. For soil whose unsaturated hydraulic conductivity was described as an exponential function of the matric potential, soil water flux f was approximated by the product of two functions, i.e., the drainage rate to groundwater (a function of t) and the distribution function (depending on z only). When groundwater level is fairly high, the distribution function is nearly equal to that derived from the linear differential equation, whereas the linear function of z is applicable for low groundwater level. Drainage rate r (t) could be determined by the “water balance equation” of the soil layer. With some limitations, numerical results obtained by the approximate solutions agreed well with the finite-difference solutions, includinig those for soil whose water characteristics are of the Brooks and Corey type. These solutions provided better understanding of various relations, for exaniple, between the drainage rate and water flux at an arbitrary depth.

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Optimum water management of irrigated crops requires timely detection of water stress. This study was conducted to investigate the practicability of using the imitation leaf method, a newly developed approach by Qiu et al., to detect crop water stress. Measurements of transpiration, soil water status, canopy and imitation leaf temperatures, stomatal resistance, root distribution, and micro-meteorological parameters were made in one hectare sorghum (Sorghum bicolor (L) Moench.) field to verify the imitation leaf method. New formulae were developed to calculate crop water stress index (CWSI). In the proposed equations, the upper limiting canopy temperature was equivalent to the imitation leaf temperature and the lower limiting canopy temperature could be calculated by suggested equations, where aerodynamic resistance was avoided by introducing the imitation leaf temperature. The parameters included in these formulae were imitation leaf temperature, canopy temperature, air temperature, air vapor pressure, and solar radiation. It is not so difficult to measure these input parameters under field situations. Experimental results showed that CWSI calculated by the imitation leaf method was consistent with the Jackson's CWSI. Furthermore, soil water status is reflected by the suggested method. Therefore, it was concluded that the detection of CWSI by imitation leaf temperature was a suitable and simple method.

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A governing equation is formulated for the stream function of the steady Darcy flow through isotropic and nonhomogeneous porous media, newly considering its definition domain. The present approach differs from the method in which it is based on the governing equation for anisotropic porous media. A Galerkin-type finite element method is used to solve the equation of stream function for such typical flows as a flow under a sheet pile, a flow due to subsoil pipe drains in a paddy field with layered soils and a flow through earth banks with a free surface. For the last one, in particular, clearing the boundary condition which requires for a stream function at a discharge surface, the saturated-unsaturated flow net over the entire porous domain including the unsaturated region are numerically obtained from both solutions of stream functions and potentials which are obtained by finite element method.

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The existing empirical, approximate, analytical, quasi-analytical and numerical solutions for predicting time to ponding (t_p) were reviewed and compared in this paper. The quasi-analytical solution can provide a rough range of t_p. As it is not confined to any special soil physical property, thus its solution could be used as a benchmark to test other solutions, especially to validate the feasibility of numerical solution.
There are some doubtful points in the universal application of the Parlange and Smith (P-S) approximation and the general solution of the Broadbridge and White (B-W). These two solutions are not always warranted to use. A Taylor expansion of the P-S approximation shows that the P-S solution is identical to the quasi-analytical one only if rainfall intensity (R) is much larger than the soil saturated hydraulic conductivity (K_s). If R is at near K_s near and the soil physical property is strongly soil water content dependent, the P-S solution may cause large discrepancy. This conclusion is not consistent to the theoretical analysis by B-W. The Mein and Larson (M-L) model has a fatal weakness that is caused in the empirical decision of the suction at the wetting front. The numerical model developed in this study can present a good solution to the tested sand and clay soils.
Time to ponding decays exponentially with the increase of R at any initial soil water content (θ_n), but the exponent is not always equal to 2. No matter what R is high or low, tp varies linearly with _n. R plays the most vital role on the decision of t_p. An empirical model was put forward by us, which can express clearly the relationship between t_p and R and θ_n, however, it needs to be validated in further study. We discussed the shape of the soil water profile and the depth of the wetting front at t_p. Finally, an analysis of the sensibility of the numerical solution was also presented in this paper.

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The settling patterns of kaolinite, montmorillonite and illite suspensions with different initial water content were investigated experimentally under various salt concentrations. Especially, the settling pattern of illite was similar to some marine clays which were already reported. With regard to the settling pattern at high water content, the values of zeta potential qualitatively supported the changes in settling patterns of the clay suspensions. In this case, the settling pattern of kaolinite was state of flocculation independent of salt concentration. On the other hand, the settling patterns of montmorillonite and illite shifted from the state of flocculation to dispersion when the salt concentration was decreased.
The effcts of initial water content and salt concentration on settling rate of the clay suspensions were also investigated. The settling rate of montmorillonite was fastest independent of initial water content and the formed floc size was largest among the clay samples in sea water. The settling rate of kaolinite was not affected by the salt consentration. On the contrary, the settling rates of montmorillonite and illite were reduced when the salt concentration was decreased. In this case, the floc shape of kaolinite was not changed, while thats of montmorillonite and illite shifted from the state of flocculation to dispersion.

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A decision support model is developed to optimize the reservoir reliability, which is defined as the probability such that the storage remains in a prescribed admissible storage domain until a prescribed final time provided that the current storage is observed in the admissible storage domain. From the water balance continuity equation, which proves that the storage is a continuous Markov process, it is deduced that the reliability is governed by the Fokker-Planck partial differential equation. An optimal control problem is formulated so that the reliability at the current state is maximized. The maximum principle that gives the necessary condition to maximize the functional which is equal to that reliability is described using the adjoint variable, which is a probability density function. The coefficients in the governing equations of the reliability and the adjoint variable are estimated from time series data of the storage. Incorporating the estimated coefficients into a finite element model of parabolic equations, a numerical model that determines the contribution weight of the strategy to the functional is presented. The model is applied to a decision making problem of an existent dam. Considerations are given to the relation between the release restrictions in droughts and the time when the reliability is to be maximized.

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In this paper, a new method for estimating the probable depth of 1 hour rainfall based on the time concentration of a rainfall was presented, utilizing a method similar to, but more accurate than that previously developed. The method previously developed was based on the transformation of the square of time concentration C² using the Slade type III equation having an upper limit less than or equal to 1. While, in this study, the time concentration C were transformed using the same equation but allowing a limit greater than 1. In addition, the characteristics of the parameters in the equation was discussed. It appears that the probable values of the time concentration and maximum depth of 1 hour rainfall, which were estimated based on the method presented herein were better estimates than those previously obtained from the first method especially for 24 hours rainfall of less than 300 mm.

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A steady flow numerical model of sudden transitions in open channel networks is developed. This model is designed to handle sudden horizontal transitions, sudden vertical transitions, or both. The governing differential dynamic and continuity equations for gradually varied flow in open channels which can as well be applied for sudden transitions, the nodal equations at junctions and the boundary equation are transformed into finite element equations by the weighted residual method. The resulting continuity integral equation is further reduced to a weak form. At sudden vertical transition sections the resulting dynamic equation is appropriately modified taking submergence and down-windiness into consideration so as to ensure functional regularity that the Newton-Raphson method requires. The resulting equations are assembled over the whole domain of interest to obtain a global equations system which is iteratively solved by the Newton-Raphson method. Numerical results from hypothetical channel networks with multi-hydraulic structures demonstrate that the model developed, even under flow reversal conditions, is capable of generating highly satisfactory results.

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Gypsum is one of the most commonly used soil amendments. The effects of gypsum application on infiltration and erosion were studied on acid Kunigami mahji soil (Typic Hupludult, light clay). Soil was sampled at Okinawa Japan, and sieved through 3 mm mesh screen. Air dried (0.5 to 6 weight %) and moist (25 weight %) soils were packed into an acrylic plastic box of 30×50×10cm in depth, and placed on a 6 degree slope. Initial bulk density and saturated hydraulic conductivity of the soil were 1.15g cm^-3 and 320 mm h^-1, respectively. The 2.5 or 5 t ha^-1 rate of gypsum were applied to the soil surface prior to the simulated rainfall. Rainfall intensity and kinetic rainfall energy were 32±2.2 mm h^-1 and 14.1 J m^-2 mm^-1, respectively. During a rainfall events, runoff, sediment concentration, and splashed loss were measured.
Runoff started earlier in gypsum treatment for both initial moisture conditions. Gypsum treatment caused a rapid increase in sediment concentration in runoff after the runoff initiation, however, the final sediment concentration in gypsum treatment was similar to that in control. Saturated hydraulic conductivity of the 1 cm thick surface crust layer was 1.1 to 4.6×10^-5 cm s^-1, and not affected by gypsum treatment.
It was concluded that gypsum treatment promoted soil dispersion and might cause more risk of water erosion of the Kunigami mahji soil.

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A method of capacity design of farm reservoirs in large branchingpipeline systems is presented.
The state equation for the systems is linearized into a pair of differential equations of the second order for the forced oscillation. Inertia terms due to water columns in the pipes can be ignored in the super low frequency range specified with a basic period of 24 hours.
Super low frequency responses of the systems are analyzed in the complex number domain to obtain an approximate but useful relation between the water surface areas of reservoirs and the amplitudes of water levels.
On the other hand, time changes in daily water consumption are well expressed with short Fourier series of the basic period of 24 hours. Thus the Fourier series can be used as the system inputs for the design.
For given effective depths of reservoirs, adequate reservoir surface areas are first calculated from the relation between the surface areas and the amplitudes. Each reservoir capacity is then determined with the effective depth and the surface area.

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This paper presents a revised diffusion wave tank model for the analysis of drainage systems in lowland areas. A forward-in-time finite difference scheme with the time weighting factor θ ranging from 0.6 to unity is employed instead of the currently used time-centering scheme. The scheme is proved to have better performances regarding the solution convergence. Infinitive discontinuous partial derivatives are appropriately approximated to avoid overflow error during the running time. An effective double sweep algorithm for the simultaneous solution of dendritic channel networks is proposed. Using the algorithm, the size of the coefficient matrix is reduced from N×N to just N×5, where N is the total number of the channel tanks in the system. Execution time is also significantly shortened.

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Reservoir capacity requirement to meet water demand can be one of the effective indexes for water resources evaluation of river discharge at relatively high water demand levels.
Paddy field irrigation is the biggest user of water in Japan. A method is established in this study to evaluate river flow as a water source for paddy irrigation using stochastic reservoir capacity requirement (CR). Historical inflow records at 10 reservoirs with a recorded duration of 21 to 35 years in natural conditions throughout Japan are used for the study.
Actual paddy irrigation requirement patterns are analyzed to establish a standard requirement pattern. In this analysis an irrigation season of 125 days is divided into three subseasons: the transplanting season, the ordinary season and the terminal season. A seasonal water demand coefficient is given to each season. Of the three, water requirements during transplanting season are the largest because of high water demand for puddling. CR is calculated on the basis of the following conditions; i. e., that the beginning of transplanting season varies from April to June and that water demand levels grow 0.5 to 5.0mm/d of specific discharge from the catchment areas.
The main results obtained are as follows:
1) CR varies greatly with the change in the beginning day of transplanting season. This means farmers can choose their transplanting season so that CR is at a minimum, if other conditions allow it.
2) The transplanting season that sets minimum CR is influenced by water demand level, too. CR totally reflects the stochastic structure of river flow time-series.
3) Analyzing the patterns of CR, 10 reservoirs are classified into 4 regional groups. In the Tohoku and Hokuriku regions, the earlier the transplanting is, the smaller the CR becomes, while earlier transplanting in the Kyushu region results in bigger CR.
4) The major season of water deficit in the Kyushu region is the transplanting season. This is one of the reasons why farmers cannot concentrate all of their transplanting in the early spring.

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In irrigation systems with onen channels. it is often observed that a certain amount of the irrigation water taken from the headworks is spilled out to the drainage canals directly, without being utilized in the paddy plots. Some spilled water is necessary for the delivery of irrigation water in the whole command area and it can be defined as the “Delivery Water Requirement”. The objectives of this study are to observe actual occurrences of spilled water and to identify the components of the Delivery Water Requirement. For these purposes, a field survey was done at I and T irrigation districts, in T Prefecture.
The results obtained from the field investigation and data analysis are as follows;
1. The spilled water ratio, defined as the portion of the amount of spilled water divided by the total intake water, ranges from 37% to 96% in I district and from 37% to 94% in T district.
2. Spilled water was divided quantitatively into two components: 1) Delivery Water Requirement, and 2) Surplus Intake Water.
3. Delivery Water Requirement was found to be made up of two elements: 1) water needed for adequate distribution of irrigation water at distribution points in the irrigation system, and 2) water needed for maintaining flow depth in the canals to ensure water acquisition for the paddy plots.

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One of the main environmental hazards caused by reservoir construction is the increase of turbidity of water in the down stream of the reservoir. In natural rivers, the turbid water during a flood is flown away with the same flood surge. If there is a reservoir, the turbid water would be retained in the reservoir and discharged water would be turbid through long period after the flood. This type of problem becomes even more serious when the reservoir water stratified by temperature in summer is stirred up in the beginning of winter. The stirred turbid water would be released from the reservoir. This study used the field measured data of a flood in 1993 in and around Anou Reservoir in Mie Prefecture. The close investigation proved the existence the above mentioned phenomena. The results are studied with one-dimensional simulation model and good agreement of the calculated result with the actual measured data was shown.

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To achieve a high rate of nitrification in contact aeration tanks, it is important to provide appropriate countermeasures for the mass propagation of large invertebrates such as Asellus and Physa. Because they consume a large quantity of biofilm.
Herein, experiments were carried out to examine the countermeasures for abnormal growth of large invertebrates, and the following findings were obtained.
The invertebrates tended to increase in number in autumn to winter and spring, and the trend was more evident in Asellus. Nitrification was decreased in such seasons. Therefore, countermeasures must be more important in those seasons.
The lower the wastewater loading for aeration tanks was, the more nitrification was achieved under the abnormal growth. Therefore, in actual plants, the decrease of loading for aeration tanks might be a good countermeasure in the proper management for anaerobic filter tanks. The employment of contactors having a larger specific surface area in aeration tanks might be also worthwhile.
In model aeration tanks, 5mg/l of Cartap, an insecticide, for Asellus and 20mg/l or more of AlCl3 for Physa were effective in decreasing their number. The Cartap effect was also confirmed in the actual plant. The treatment must be done in the order of aeration tanks in which Asellus generated. Otherwise, the inflow of new seed Asellus from the front aeration tanks might shorten the effective period of Cartap.

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Sound characteristics, such as the scoustic power level (PWL), the A-weighted sound level (L (A)) and the power spectrum of flow in a water-cushion-type drops were studied in fields.
The results of this study are summarized as follows:
1) It was found that both the scoustic power level and the A-weighted sound level increase linearly with the drop of energe (E_D) per unit width canal and the energe loss (ΔE) increase for a range of E_D=170-5490 (N·m/s·m), ΔE=0.46-2.25 (m), respectively.
2) The ratio of diminishment of A-weighted sound level in the traverse direction of the water-cushion-type drops tends to be higher than that in either upstream or downstream direction. And, value of the ratio of diminishment of A-weighted sound level in the traverse direction was high about 15% in comparison with the downstream direction.
3) From the relationship between the power spectrum and the frequency, the spectrum of flow in the water-cushion-type drops tends to be approximate to white type noise.

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