The summer in 1994, the heavy drought was occurred by high temperature and low rainfall, and maize was received serious damage. But in 1995, the drought injury was not so serious although the meteorological conditions were almost the same during the growing season of maize as the year before. This difference of the damage between above two years was explained by the difference of the amount of rainfall during Baiu, the rainy season.
Almost fodder maize fields have not been irrigated even if drought damage were expected. It may come from the fact that the irrigation of maize field is very troublesome task and the effect to the harvest and quality have not been clarified so far. The authors presented a laboursaving irrigation method for maize and the deep-rooted crops by the results of water balance analysis and the yield of maize in 1994, 1995 and 1996. The proposed irrigation methods are shown as follows.
(1) Irrigation in the end of rainy season, once a growing season, is quite enough for high production.
(2) The amount of the irrigation water is decided in order to supply the water deficit to the field capacity in the soil from the surface to 1.0m depth.
The merits of the irrigation method are as follows.
(1) The laborious tasks for irrigation are greatly decreased.
(2) This method moderates the peak demand of irrigation water by the time led of about 1 weekbecause the end of rainy season falls about one week before the peak water demand.
(3) The result of verifying experiment showed that maize yield under the irrigation increases about 12% more in dry matter production than that of non irrigated field.
(4) The methods are expected to eliminate many difficulties of rotating the standardized sprinkler system under the conditions of tall grass height because the plant height of fodder maize at the end of the rainy season is still low.

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It has been proved that pH values caused by algae in ponds and lakes increase rapidly in the daytime, but it is very rare for such values to reach or surpass pH 10 near the terminal section of a main irrigation channel build with concrete.
To clarify the mechanism of the quality change in water flowing through an irrigation channel, field measurements of changes in the flow process and of diurnal changes at the channel terminal point were carried out in the main irrigation channel in Goshogawara, Aomori Prefecture. The results indicated that under the proper weather conditions pH values increased especially rapidly from a point approximately 3km away from the end section of the main channel. pH variation has a tendency to increase in the daytime and to decrease at night. Because green algae (cladophorales) propagate in this section in summer, the pH variation appears influenced by the photosynthesis of green algae.
The hourly pH variation caused by green algae collected from the terminal section of the Goshogawara main channel has been investigated in a small glass tank in our laboratory. The pH variations obtained during the laboratory experiment reflected the results of the field experiments. The laboratory experiment was repeated under various conditions, and the results indicated that the alkalization of irrigation water by green algae is dependent on light and water temperature. Moreover, the growth of green algae is influenced considerably by the water quality. It is interesting to note that green algae do not exist in the terminal section of the main channel after the discharge of waste water from drainage canals.

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There exists a well known elementary Bernoulli-Euler solution for beam deflection, which was derived from bending moment only. A correction equation of this solution for shearing force also exists, which shows that deflection depends on Poisson's ratio and the depth-span ratio of the beam. However, these equations are theoretically applicable for plane stress only. One of the objectives of this paper was to come up with elastic beam deflection equations for both plane strain and plane stress. These equations were derived using a stress function different from the Airy one. As a result of many numerical computations for an analytical solution, the properties of beam deflection and accuracy of the finite element method were investigated. In addition, an elementary solution and correction equation for shearing force for plane strain beam deflection were also obtained in this paper. Using these results, the reasons for the difference in the deflections between plane strain and plane stress were discussed.

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Since existing equipment and materials are used for the installation of a pressure-reducing pipeline system which automatic control valves, there is the outstanding problem that the series arrangement of the automatic control valves causes self-excited pressure vibration. At present, a new type of automatic control valve with improved operating mechanism has been developed. In this paper, the theoretical model of this new type of automatic control valve is prepared, and the validity of the model is confirmed by verifying the results of a hydraulic test through simulation.
In addition, the variation of flow rate in the case of series arrangement of the new type of automatic control valves is reproduced by preparing a model on the assumption of a pipe line at the actual site. As a result, it is confirmed that if the new type of automatic control valve sufficiently operates in response to the variation of flow rate, the pressure at the downstream side of the reducing valve is controlled by the fixed pressure, and such a disadvantageous phenomenon as resonance does not occur. Even in the fast changing conditions of flow rate where water hammering pressure occurs, the new type of automatic control valve is capable of controlling the water hammering pressure to certain extent. Therefore, it is expected that it has also some effect on a sudden change of conditions.

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Flow in regular cross-sectional channel with locally varied resistance zone near the one-sided wall is chosen as the subject of this study. The resistance zone is composed of pile series arranged like vegetation belt or rough stone zone. The lateral distribution of depth-averaged velocity within a cross section is firstly estimated from equation of motion in which we consider the eddy diffusion due to interaction between distributed piles. Secondly longitudinal water level is calculated on the basis of one-dimensional specific energy equation taking account of the lateral velocity distribution due to the pile zone.
The comparison of the experimental results with the calculated values supports the availability of the analyses.

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Many model experiments with glass side walls were carried out observing shear bands. If the ratio of width (W)/height (H) was small in retaining wall model experiments, total passive earth pressure coefficient measured by earth pressure cells at the central section would be overestimated for the influence of side wall friction. Threedimensional (3-D) elasto-plastic finite element analysis employing the dynamic relaxation method was applied to the model experiments (passive mode rotation at the toe) using air-dried Toyoura sand to estimate the effect of side wall friction. Measured total passive earth pressure coefficient for glass side wall (side wall frictionangle of 6°) was higher than that for lubricated glass side wall (side wall friction angle of 0°) when W/H was 1.05. We can say that the application of 3-D analysis was useful to estimate the effect of side wall friction and the behavior of model experiments were well simulated.

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A comparison was made between the leaching efficiency of continuous ponding and intermittent ponding in terms of desalinization and desodification of a highly saline soil. Intermittent ponding was more efficient than continuous ponding in leaching total soluble salts. However, a reduction in the water soluble ions in the soil was quite different with ion species; Cl^- and SO₄^2- as anions, and Na⁺ and me as cations were removed more efficiently in intermittent ponding than in continuous ponding, but the opposite was the case with Ca²⁺. During leaching, desodification and desalinization were found to occur simultaneously, though desodification was achieved to a lesser extent than desalinization in both cases. Intermittent ponding proved to be more efficient than continuous ponding with respect to desodification. The soil exchangeable sodium percentage was calculated based on ion activities and cation selectivity coefficients, instead of using the traditional calculation from the sodium adsorption ratio of soil water.

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A method using the consolidation deformation analysis by the elasto-plastic finite element method based on the infinitesimal deformation theory was proposed in order to evaluate the bearing capacity of saturated clay grounds. Sekiguchi and Ohta's model as the constitutive model of soils and Akai and Tamura's method as the tequnique of consolidation analysis were used in this method.
The proposed method was applied to undrained bearing capacity analyses of normally consolidated and saturated grounds whose mechanical properties were isotropic and homogeneous, and the applicability of the proposed method and the effect of the element type on the results of the analyses were investigated. As a result, it was cleared that the ultimate bearing capacity of the ground obtained by these analyses, in which isoparametric quadrilateral elements using the reduced integration were used, was approximately coincident with Prandtl's solution.

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In thebay which rivers flow into the head of a bay, the river water entrain the sea water in the bay and promote the sea water exchange. In this paper, theoretical formulation of potential effects of the sluice gate in the finite depth estuary were carried out. And the enlargement effect of the entrainment rate by the potential effects of the sluice gate were investigated. The results indicated that potential of the entrainment rate (Q) is related to four parameters such as the densimetric Froude number at the outlet of river water (F_do), the relative depth of the river mouth and the bay (R), the relative opening rate of the gate (G) and the supply of sea water at the bay mouth. Moreover, the decreasing of the relative opening rate of the gate influence to the increasing of the outlet densimetric Froude number of river water, the relative depth of the river mouth and the bay and the potential of the entrainment rate. After all, the sluice gate promotes the sea water exctange of the bay.

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In order to establish the stabilization method of soil foundation, the method of estimating the strength of fluid stabilizing soil was devised by introducing the model of composite column.
On the assumption that the substance made by hydration constructs a rigid part of the fluid stabilizingsoil and the continuum of soil-water constitutes a soft part, the composite column was supposed to consist of therigid part and the soft part.
By this model, relation between volumetric ratio of rigid part and consolidation yield stress as an index of the strength of fluid stabilizing soil was drawn out analytically.
Many consolidation tests were carried out by using specimens of fluid stabilizing soils, in different volumetric ratios of the rigid part. But, the specimens were kept to the void ratio of the soft part must have a constant value, even the volumetric ratios of the rigid part are different.
As the result, it was recognized that there was a correlation between volumetric ratio of rigid part of the specimen and consolidation yield stress, and the mechanical constants were obtained to be incorporated in the model of the composite column.
In consequence, the parameters of the model of composite column were decided quantitatively.

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The colloidal stability and charge characteristics of allophane and imogolite were examined with attention to the fundamental features of the suspensions. The point of zero net charge (PZNC) of non-deferrated allophane was pH 5.9, and that of the deferrated, pH 5.1. Allophane coagulated near PZNC. PZNC of non-deferrated imogolite was pH 7.2, and that of the deferrated, pH 6.0. Imogolite coagulated under all alkaline conditions although net negative charge increased with pH above PZNC. The relative viscosity of imogolite was consistent with stability, the high viscosity corresponding to the coagulated thick fibers. The stability of allophane under alkaline conditions clearly decreased with the addition of imogolite by 10%. Imogolite is widely found in Andosols, and thus is considered to be one of the principal materials that disrupt the stability of soil suspension in particle size analysis.

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The Pinhole Test for identifying dispersive soils was carried out to study the response of a volcanic ash derived soil to acid rain. The variable charged, undisturbed and packed Kanto loam (Tama loam) soils from Hachioji, Tokyo, Japan was used in this study. The 2: 1 mixture of sulfate and nitric acid solutions having a pH of 2 to 5 was applied to the soil column of 5cm in diameter and 5cm in length, and having a hole of 1 mm in diameter at the center of the column. H⁺ in the acid solution exchanged and removed adsorbed metal ions in the soil, hence charge characteristic of the soil and species of adsorbed cation has changed. There was no decrease in the permeability of the undisturbed soil upon percolation of acid solutions while the permeability of some of the packed soil columns showed large change with a pH 2 and 3 acid solution. The undisturbed Tama loam soil showed no soil loss during a percolation while the discharge of the packed Tama loam soil showed turbidness with a pH 2 and 3 acid solution. It was suggested that natural soil structure made the soil more tolerable to acid rainfall.

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Incorporation of the fuzzy rule-based relaxation scheme into steady state unconfined groundwater flow models (FEM and BEM models) is proposed, aiming at improving computational convergence in determination of a free surface (DFS) and/or in solution of a global matrix equation (SGE) by the successive over-relaxation (SOR) method. The scheme proposed excellently performs its expected role as a convergence accelerator as well as a convergence stabilizer despite its essential simplicity. Performance of the scheme for DFS problem hardly depends on whether the modeling strategy is FEM or BEM. Use of the scheme in SGE also results in less iteration requirement, but is less effective in saving computational efforts than that in DFS. When the non-interrelated two schemes, for DFS and SGE problems, are operated in parallel, they produce a favorable multiplier effect on computational execution so that the total processing time can more effectively be reduced than by any single operation of them.

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This study analyzes the redistribution of cooperative land, which was done through land tenure reform since 1981, in rural areas of the Red River Delta, Northern Vietnam. Field surveys on plots allocated to farmers were conducted in villages and hamlets of three communes.
Equity was the guiding principle of land redistribution. Equal land redistribution, however, could not be done in a commune as a whole but within each traditional village and hamlet independently. Depending on local conditions, the villages and hamlets' land was divided into area units, which are homogenous in soil, irrigation and drainage conditions, wherein an equal acreage of land was given to each person. The total acreage of all family members in an area unit made up a plot, the location of which was allocated randomly.
This equal land allocation has been done to realize an equal share of the risk of exposure to drought and flood damage, equal duties and equal harvest stability for each household. It enables the communities to overcome poor irrigation and drainage by optimum water management decisions. However, it brought about fragmented and scattered land holdings, thus requiring intensive labour input in cultivation. Irrigation and drainage improvement is a prerequisite for land consolidation in the future so as to increase the productivity of labour and land.

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In Akai and Tamura's consolidation analysis method, two methods (A and B) are used as the technique to evaluate the hydraulic gradient. The hydraulic gradients in the x (horizontal) and y (vertical)-directions in the method A, and the hydraulic gradient between the two neighboring elment's centers of gravity in the method B are evaluated from the difference of the total head or the pore water pressure between them based on the finite difference approximation method. In this paper, firstly the method B was extended in order to be applicable to the ground whose permeability was anisotropic. Secondarily, the finite element analyses using the methods A and B for the one and two-dimensional consolidation analysis models composed of triangular elements were carried out. And then, the differences among the results obtained by these analyses were investigated by comparing these results with the theoretical solution and the results obtained by finite element analyses using Sandhu's type method-for the same models.

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The extensive groundwater management of a wide basin requires utilization of a combinational optimization method in conjugation with groundwater dynamics to make the most appropriate management, so as to solve problems of competition and cooperation for the limited conditions such as water light. The proposal for evaluation method of hydraulic characteristics including “safe yield capacity” of shallow wells (diameter: 3-5m, depth: 8-15m) has already been described in the previous work as the fundamental study of this research. In this study, more than 40 shallow wells were divided into several groups. Each group consists of several adjoining wells with its own “group safe yield capacity” and is regarded as subsystem. We treated the discharge management as a scheduling problem among autonomous decentralized subsystems and proposed the water volume allotment method based on the quantitative elements, such as working time and idling time, figured by human expert. Moreover, the method was embodied in the form of three steps appropriate algorithms of the scheduling system among subsystems. An applicability of this method was shown by an example.

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A method was developed for designing microirrigation laterals on nonuniform slopes based on the required average emitter discharge and the required uniformity of water application. The lateral discharge equation is used to express the relationship between the pressure head and discharge at the inlet of a lateral in order to find the required operating pressure head of the lateral. The hydraulic analysis was performed using the back step and forward step methods. When the required average emitter discharge, the required uniformity of water application, and one parameter-either the length or diameter of a single lateral, are given, then the unknown parameter, the operating pressure head can be accurately designed using personal computers. The diameter, the best submain position and the operating pressure head of paired laterals can also be accurately designed. The design procedure was included.

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There are some problems peculiar to the rotational upland field, whose soil condition and water use are different from the ordinary upland fields. One is that the depth of the effective soil layer, soil moisture extraction pattern, and the soil moisture condition when irrigation is started in the rotational upland field, are different from ordinary upland field. The other is that the furrow irrigation methods of rotational upland field are devided into two types, permanent or temporary ponding in furrow, whose water use is different. This paper clarified the above two problems by investigating many test fields. The results were summarized as follows.
1. In the rotational upland field that remains plowsole layer, soil moisture is consumed only in the upper soil layer above the plowsole and not consumed in the lower layer than plowsole. The depth of effective soil layer is about 25cm. On the other hand, in the rotational upland field whose plowsole layer is destroyed, soil moisture is consumed in the deeper layer, and its pattern is that the moisture consumption becomes gradually small downward. And its depth of effective soil layer is about 50cm.
2. In the rotational upland field whose plowsole is destroyed, irrigation is started when the soil moisture suction decrease to about pF2.6. But in the rotational upland field that remains plowsole, irrigation is started at the higher soil moisture content, bellow pF2.5-2.6.
3. Furrow temporary ponding irrigation is applied to the crops that require the good drainage and high airpermeability. This irrigation is the way that when the field is dried, the furrow is ponded, infiltrated and saturated, and then the ponding water on the ground surface is released. Amount of each irrigation is about 150mm and irrigition interval is changing according to meteorological conditions.
4. Furrow permanent ponding irrigation is applied to the crops that require the high water content in the effective soil layer. The irrigation is the way that the furrow keeps to be ponded by making the use of low permeability of lowsole layer. At the begining of irrigation period, 80-100mm of water is irrigated for initial ponding in the furrow. Afterward, the amount of each irrigation is 5-20mm and irrigation interval is 2-3days.

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Surface runoff loads were measured in two test fields at the Agricultural Field Laboratory. After plowing, one test field was paddled, while the other was not. For the paddling field, nitrogen fertilizer (containing 80% of coated urea and 20% of no-coated ammonium), P₂O₅ and K₂O were spread over the field and then plowed. For the no-paddling field, coated fertilizer (containing 90% of urea and 10% of K₂O) was treated in the nursery box and P₂O₅ was applied uniformly to top soil.
After paddling, the concentrations of the on-paddy field water of the paddling field was increased and its transparency was decreased more than the no-paddling field. Surface runoff loads from the paddling field were increased 19 times (SS), 5 times (BOD), 12 times (D-COD), 9 times (T-N) and 14 times (T-P) as much as the no-paddling field. It appeared that the method of cultivation without paddling is useful for reducing the surface runoff loads from the paddy fields.

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In this study, properties of the peak discharge and retention in a terraced paddy field catchment are compared to those of a forest catchment in Japan. The results show that the runoff coefficient of peak discharge in the terraced paddy field catchment is slightly larger and the concentration time is shorter than those in the forest catchment. The comparison of calculated specific peak discharge for given rainfall intensity reveals that the discharge of the terraced paddy field catchment is about 1.55 times greater than that of the forest catchment. Through the analysis on retention of rainfall, it is concluded that the retention capacity of the terraced paddy field catchment is smaller and the percolation rate is lower than those of the forest catchment.

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