In any irrigation project, the command area must be well-balanced with the available water resources.At the planning stage of the project, the data accumulated may not always be reliable enough for the examination of this balance.Therefore re-examining this balance some years after the starting of project implementation when enough data have been compiled would be meaningful.If the result of this re-examination in a rice double cropping project indicates that the available water resource is not adequate, the return period of the year in which water can not be supplied in the dry season will have to be estimated and appropriate countermeasures for meeting the water shortage problem formulated.
In the irrigation planning of reservoir-fed irrigation system of single cropping, the reservoir should be usually full on the first day of the season.A drought year that returns roughly once in every ‘N’ years may be defined as the ‘reference year for design’.Water must be supplied with certainty in this year.On the other hand, in a double cropping project, the reservoir may not be full on the first day of the season.The water volume in the reservoir usually recedes every dry season, and recovers in the rainy season and fallow period.The water storage in the reservoir repeats this up and down movement every year.The concept of the ‘reference year for design’ can not be applied to a double cropping project.Some new concept and planning methodology will have to be devised and proposed.
In this report, as a case study of Muda Irrigation Scheme in Malaysia, the author illustrates an example of the re-examination of the demand-supply balance in the reservoir, and proposes a simple method to estimate the return period of irrigation-less dry season.He also cites an example of a method to prepare countermeasures to meet this water-shortage problem.The author considers that these methods will be suggestive to projects in tropical monsoon areas under similar conditions.

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Three field investigations were carried out to identify the microbial concrete corrosion occurred in the rural sewerage facilities.It was found that the outline of their corrosion mechanism was almost the same as that of concrete sewer pipe. There are, however, the following characteristics.
1) They tend to become anaerobic condition because of the large fluctuation of inflow.
2) They have high concentration of not only hydrogen sulfide but also carbon dioxide.
Consequently, the hierarchical relation is showed to summarize the microbial corrosion of concrete in wastewater treatment plants.

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Thirty-one field investigations were carried out to prevent the microbial concrete corrosion occurred in the rural sewerage facilities. It was found that the corrosion mechanism was well defined by the hierarchical relation already reported. The following proposals, therefore, are made with the preventive methods to the microbial corrosion.
1) Fundamental measures such as controlling the generation of hydrogen sulfide are difficult to apply because of the uncertain effect and the cost problem.
2) The protective coating of concrete is the best way at the present time. The designation of protective coating should be classified with using three indexes of the condition, which are the concrete surface pH, the concentrations of hydrogen sulfide and carbon dioxide.

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Dynamic Programming (DP) is one of the most powerful methods to decide optimal policy in reservoir management.A variety of algorithms for its computer implementation have been presented by which numerical difficulties encountered in the direct application of DP can beeliminated.Discrete Differential Dynamic Programming (DDDP) is an iterative algorithm in which the recurrent equation of DP is used to search for an improved trajectory in the neighborhood of trial trajectory called ‘corridor’.DDDP has an inherent drawback that sometimes it may produce non-optimal solution when corridor size remains invariable during the iteration. In this paper, a methodology in that the corridor size is reduced at next step after no improvement is achieved proposed to augment possibility of attaining to optimal solution.Using the deterministic DDDP so modified, an optimization model applicable to multiple-reservoir system with the reservoirs connected in series by linkage canals is formulated by which reservoir storages are so optimally regulated that the gap between targeted and actual storages, integrated over both all the reservoirs involved and the whole period of reservoir operation, may be minimized.A demonstrative operation of the model is carried out with its application to the system containing five reservoirs. The results indicate that with successful computational sequence it is amply possible to obtain a guide to regulating the imbalances of storage by use of the model developed.

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Soil physical properties vary with time and location in fields.Although the well-known scaling method based upon the similar media concept (proposed by Millar and Millar1956) has been widely used for describing heterogeneous soil physical properties in fields, the similar media concept can be applied only when the geometrical similarities among soils are guaranteed.A non-similar media concept was introduced to the scaling theory.This new scaling concept could predict air entry suction and saturated hydraulic conductivity as a result of changes in the bulk density using characteristic lengths for solid and pore phases, and a shape factor for solid phase.The comparisons between experimental data and predictions for several types of soils revealed that the scaling of saturated hydraulic conductivities using the non-similar media concept had an advantage over the traditional Kozeny-Carmann equation. The relation between soil structures and shape factors was discussed in detail.It was shown that the applicability of the non-similar media concept depends on the reliability of the shape factor for solid phase.

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Discharge water chemistry at a reclamation farmland catchment at the Gojo Yoshino area in Nara Prefecture is explained as a mixture of representative soil water, groundwater and rain water.Rain water, soil water and groundwater were determined as the source waters (end-members) using Principal Components Analysis (PCA), which deal with nine conservative solutes (alkalinity, nitrate, sodium, potasium, calcium magnesium, chloride, dissolved silica and sulfate).
Based on PCA, discharge water chemistry was characterized by two independent components: the former has a strong positive correlation with sodium, calcium, magnesium, chloride and dissolved silica, and the latter with nitrate and potassium.Discharge water separation at storm runoffs into three end?members results in large contributions of rain water and soil water to discharge water, and12%to 19%of the discharge water was groundwater.Agreement of measured and calculated concentrations using this separation method was not so good except for alkalinity and nitrate.The reason for this appears to be instantaneous large changes in soil water chemistry during storm runoffs.

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Use of a river water is controlled by the lowest discharge which gives a stable water supply through a year at least, because a river discharge unstably fluctuates depending on the water balance of the basin.To expand a use of a river water, therefore, it is necessary to regulate a fluctuation of a river discharge and to increase the lowest discharge by a storage capacity such as a dam.In this paper, the evaluation theory of the relation between the lowest discharge (Q) and a storage capacity in a river basin (V), which is named as “the critical water balance method”, is newly proposed.
The relation between Q and V is investigated, and then it is confirmed to be represented by a parabolic curve.And also by using coefficients of the parabolic curve, it is clear to be able to evaluate a watersupplying capacity from a river basin and a potential water demand for a basin. The Q-V relation from this method will play an important role to discuss a comparative analysis between river basins, and an evaluation of natural and artificial storage capacity in a same dimension, an appropriate use and development of water resources in a river basin.

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From the viewpoint of irrigation water project, an observational study has been performed on management water requirement which is one of the structual elements of irrigation water requirement in the actual observation area having open channel system in “Fukuokazeki”from 1981 to 1989.And its analytical results were summarized as follow.
(1) In this area.both lot?management water reauirement and canal-system-management water requirement being observed at the same time, it was clarified that these waters could be compensate for each other in the farm level.
(2) Mechanism of occurrence of maintenance water for necessary water depth was theoretically made clear, and the water consisted of a large part of canal-system-management water.
(3) The canal-system-management water requirement occured in branch canal has closely relation to the labour of water management and also that water clearly has the function in compensation for labour of water management.
(4) Direction for analysis of design of paddy field irrigation could be shown from the standpoint of quantitative evaluation of management water requirement.

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This study aims at developing an evapotranspiration submodel (ET submodel) as a component of a rainfall-runoff process model.As a basis for developing a new ET submodel, evapotranspiration under various soil and vegetative types was analyzed numerically using SPAC (Soil-Plant-Atmosphere Continuum) model.The simulation result showed that the ratio of evapotranspiration to potential evapotranspiration is determined by average water content of a certain depth of soil layer which is corresponding roughly to the root depth of plants there.Accordingly, for each of given conditions of soil and vegetation types, a curve to express the relation between evapotranspiration ratios and degree of saturation could be obtained.The logistic curves that take different shapes for different soil and vegetation types were employed to develop a new ET submodel. The ET submodel having a simple storage type structure can calculate actual daily evapotranspiration from its storage level and the potential evapotranspiration data at the corresponding time.The soil and vegetation types are taken into account as the parameters representing the curves.In simulation of daily evapotranspiration using the new ET submodel, the model was found to be able to reproduce the result of the SPAC model satisfactorily.Then finally the ET submodel was incorporated in a simple runoff model and examined in a runoff analysis of a watershed.In application of the runoff model equipped with the ET submodel to simulate discharges of a watershed near Khon Kean, the computed hydrograph for 10 day showed good coincidence with the observed one.Thus it was confirmed that the developed simple ET submodel can work properly as a component model in long-term runoff analysis.

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The well mixed density flow in tidal river estuary through ebb and flood process during a tidal period includes both many kinds of hydraulic characteristics and unstability problems, because of the rapid transient stratification or disappearance of internal-surface.
This paper reports the results of an analytical consideration depended on field data and their measurement confirmation in the Hiji River.
A classification scheme to define the pattern of two layer flows given by the combination of two directions of currents and magnitudes of mean velocity is presented with field observations.
The verification of this algorithm proposal for eight kinds of flow patterns is derived from new measurements which are composed of the internal, the external and the stability Froude number and applied mass deficit law.
Two measurements of the latter facilitate a comprehensive understanding of the hydraulics for transient flows of both at the second part of flood flow and the seventh part of ebb flow.
After the above discussions, it is demonstrated that three kinds of two layer flows assumed to be quasi-steady state are approached by means of the internal surface resistance analysis for the exchange flow (wedge with counter current), the salt bottom wedge and the arrested surface wedge.
Two results of the former are sufficient to show the usefullness of the proposed scheme.

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In this study, the control of alkali-aggregate reaction on concrete was attempted by adding rice husk ash to mortar containing one of reactive aggregates. Three experiments were carried out and the following results were achieved.
1) Adding rice husk ash to mortar by over 7% of cement weight made the control of alkali-aggregate reaction possible.
2) Extracted liquid, obtained by either boiling or immersing rice husk ash in distilled water was added to mortar. This method was unsuccessful in controlling the expansion of mortar bar.
3) Extracted solid, obtained by boiling rice husk ash in distilled water was added to mortar.In this case an expansion controlling effect was also observed by over 7% of cement weight.

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An analysis is dealt with here about the applicability of an unsteady flow computational method to a tidal low flatland's water balance.The model is based on the Preissmann implicit scheme.The subjected basin was disassembled to such components as channels, hydraulic structures and fields.They were modeled to computational units and were treated as ‘key’ elements, of which the whole area's model was composed. ‘Ooe’river's basin in the ‘Takasu’ polder, which is situated between the ‘Nagara’ and ‘Ibi’ rivers, was the subjected region.
The results obtained by simulating the winter period in 1992 were:
1.The unsteady flow calculation, considered not appropriate in the case of long?-period simulation, became possible nowadays through the development of hardware, software and calculation methods.
2.Present method showed a high potential for analysing runoff process in which mechanical forces play main roles.
3.Because of a physical model, a large number of data were required and the expected results were dependent directly on the quality of data.

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This paper provides an overview of computational fluid dynamics with emphasis on its recent advance in finite difference method.The typical structure of the linear convection equation, the invisid Burgers'equation and the convection diffusion equation is hightlighted and the way in which these equations are converted into computer-executable appropriate algorithms is illustrated. Especially, spatially third-order accurate schemes and more higher-order schemes (including the CIP scheme) will also be considered.
Some illustrated solutions of above equations will be obtained and finally typical solutions of two-dimensional incompressible Navier-Stokes equations will be shown.
The above solutions have been incorporated into some computer programs, and these listings are given in this paper.

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[in Japanese]

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