In the previous paper, consumptive use of water, total readily available moisture (TRAM), irrigation interval and water quantity per irrigation were discussed and estimated from the initial conditions in which all the consumptive areas were equally wetted due to a great deal of rain. In this paper, TRAM and water quantity per irrigation system were estimated by a numerical model from the initial conditions in which the consumptive areas were separated into the wetted and the unwetted zones after drip irrigation.
As a result, it was found that a considerable amount of water was saved for the reasons that the consumptive use of water was less in the wet and the unwet fields after irrigation in comparison with those obtained in the equally wet fields after the rain. Furthermore, since the water quantity and interval in irrigation decreased in the wet and the unwet fields, the advantages of drip irrigation methods were explained from the results based on the principles of less-water quantity and shorterirrigation interval.

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The measurement of pF-moisture characteristics of soils requires saturation of the soils before setting of those in an apparatus. However, it is not clear how much time it takes to saturate the soils in 5.1 cm tall samplers. Insufficient saturation of the specimens causes errors on the test results of pF-soil moisture characteristics of the soils.
This paper discusses the saturation time of undisturbed soils in 5.1 cm tall samplers. The term “saturation” does not refer to “complete saturation”, but to “the state where a soil specimen does not absorb water any more”.
Tests for saturation and permeability with undisturbed soils were carried out. The saturation processes were analyzed with the finite element method for saturated-unsaturated flow. Discussion on the experimental and numerical results has led to the following conclusions:
1. Exudation of water over the upper surface of soil in a sampler does not mean the completion of the water absorption of the soil.
2. The standard saturation time of undisturbed soils in the samplers, 5.1 cm tall, is as follows:
1) Single-grained soils
Sandy soils … about 0.5 day
Other soils … about 5 days
2) Aggregated soils … about 10 days.

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A mathematical model including the conditions of irrigation flow rate, irrigation water quality and fertilizing as operating variables was built for estimating the nitrogen outflow from paddy fields. This model consists of balance and rate equations such as nitrification, denitrification, bioturbation and other relevant rate processes.
Six experiments using lysimeters under various paddy field conditions were carried, out to estimate the structure and verify the validity of this model.The model simulated the nitrogen concentration in surface water under various conditions with enough accuracy, reflecting annual changes and the effect of fertilizing. High stability of the model was checked by sensitivity analysis. Phenomena inside of experimental paddy fields were described well. This model will be applied to actual paddy fields after used in large-scale fields for more verification.

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The location of bifurcation points for reducing the construction costs of a pipeline system is discussed.
The topology of a pipeline system is more desired to be given artificially than to be given automatically under the complicated society or nature. Precise positions of each bifurcation point seem to be given by the maximum duty of water and water head at the end of each pipeline under one topology. Furthermore, the model for giving the positions of each bifurcation point easily and directly by the maximum duty of water was proposed by using an optimum diameter exponent. This model is called the tension-analogy model in this paper.
The bifurcation point connected with three fixed-positioned nodes has already been discussed using an optimum diameter exponent. On the other hand, it is reported that the positions of many bifurcation points can be given by using tension, on the basis of the minimum work principle under one topology. As the tension-analogy model is based on the minimum work principle too, it is desired that each bifurcation point converge to the optimum position.
The convergence of each position, of bifurcation point was confirmed through numerical examples after the order estimation of the parameters. In this example, the positions of bifurcation point near the source was moving as the numerical order of the optimum diameter exponent.
As this tension-analogy model is based on an analogy of the tension balance, the estimation of the moving distance at each time step is easily given. Some aplication examples can be easily prepared, if the optimum diameter exponent is used as the index.

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An unsteady flow modelling system is often used to obtain steady conditions in open channels. To be more precise, if the boundary conditions are fixed, initial flow perturbations are allowed to dissipate or propagate out of the system. In this paper, the optimum difference scheme for that technique, dynamic relaxation, and the conditions to maximize the convergence rate are discussed.
The theoretical analysis shows the convergence rate of dynamic relaxation depends on absolute value, (λ), of the eigenvalue of the amplification matrix of a difference scheme and smaller (λ) accelerates the convergence rate. In this meaning, Preissmann sheme (weighting coefficient θ=1) with unconditional stability has a very good convergence rate because (λ) can be close to zero by taking sufficient large time step Δt in comparison to space interval Δx. Moreover, it shows good accuracy because it can compute the boundary points with second order accuracy in regard to Δx.
The time required for computations per Δt is almost the same as that with explicit schemes, for reasons of adopting the double-sweep method as the technique for solving the linearized difference equations derived from the Preissmann scheme. As a result of numerical experiments, the necessary number of time steps to get a steady-state solution using the Preissmann scheme isless than onetenth of that with explicit schemes.

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In a thin water layer on the surface of soil, a hemispherical cavity is formed beneath its surface due to the impact of a waterdrop. This cavity, after expanding in water for a few ten milliseconds to reach maximum radius, about three times the waterdrop diameter, begins to contract and finally vanishes leaving cylindrical water waves which propagate around the point of waterdrop impact. During expansion, contraction of the cavity in the water, lift up and movement of soil particles on the soil surface can be observed. In this paper, the differential equation which expresses movement of the cavity in the water was derived on the assumption that the flow of water generated by the impact of the waterdrop is a potential flow.
From this equation, it became clearly that the hydraulic pressure on the bottom of water layer shows maximum peak value at the instant of the impact of the waterdrop and decreases rapidly to a value lower than the average static hydraulic pressure (negative pressure).
The experiment was conducted to investigate the interrelationships among peak hydraulic pressure impact energy, water depth and waterdrop diameter.
The experimental results indicated the maximum peak pressure depend only on the impact energy at a water depth of 0.3×H_max-0.4×H_max (H_max is the maximum height of cavity), and at a depth greater than this, the maximum peak pressure in inversely proportionally to the water depth squared.

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The incomplete Cholesky conjugate gradient method (ICCG method) was used in 3-dimensional finite element programs designed to maximize the computing efficiency on a microcomputer. Numerical experiments on stress analysis proved that the ICCG method needed lesscalculation time and data storage than the ordinary Gaussian elimination method. A satisfactory convergence was achieved in about 30 iterations on every example problem tested in this study. The computing efficiency of the ICCG method is particularly explicit on calculations involvin a matrix with large bandwidths.
Three-dimensional analysis of a fill dam gallery subjected to both static and thermal loads was attempted using this ICCG-incorporated finite element program. The static and thermal stress states of the gallery constructed on the dam foundations with different physical properties were analyzed.

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Four air-dry soil samples from 4 locations in Ehime Prefecture were subjected repeatedly to a series of treatments: water soaking-feeezing at-20°C-thawing-drying at 110°C, and the treated soils were examined for particle-size distribution, ignition loss, plastic and liquid limits, pF-water retention curve, and X-ray diffraction behaviors of clay minerals contained. Three out of the 4 soil samples were from the C horizons (30-40 cm) of upland soils derived from granite, crystalline schist and mixed sandstone and shale, and the rest was from the A horizon (5-20 cm) from a paddy field. The textural class ranged from silty sand (SM) to clay (CL), according to UJSSMFE system.
No change occurred in the particle-size distribution of soils even after a treatment repetition of 70 times, indicating that the treatments caused no disintegration of coarser particles nor aggregation of finer particles. The repeated treatments, however, caused the ignition loss, plastic and liquid limits and water retention at pF's below 3.2 to decrease significantly. The decrease was interpreted in terms of a decline in the reversibility of water adsorption by soil particles, and in terms of a change in the aggregate structure.
It was shown by X-ray diffraction (XRD) analysis of the clay fractions (<2μm) that the hydrazine intercalation ratio (HIR) of halloysite was significantly decreased by the repeated treatments. The HIR herein refers to the ratio of diffraction intensity (peak height) at 10Å to that at 7Åof the hydrazine-treated samples. Its decrease means, therefore, that the layer-to-layer bonding of halloysite has been tightened by the repeated treatments. It was noticed also that the 2: 1 type layer silicates, such as vermiculite and its intergrades to chlorite, collapsed or became liable to be collapsed due to the repeated treatments. Such changes in the XRD behaviors of clay minerals may imply that the repeated treatments have removed the interlayer water and have rendered its re-penetration difficult, and so, were thought to be responsible at least partly for the decline in water adsorption reversibility stated above.

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Three sorts of cohesive soils which were produced in Ehime Prefecture having different country rocks were subject to physical weathering treatment consisting of drying, water immersing and freezing to observe the properties of compaction, strength and water permeability experimentally.
The results were analyzed based on the changes in the physicochemical properties and behaviors of the aggregates. The following were able to be clarified.
(1) In Shirokawa sedimentary rocks and Ikazaki crystalline schist, the optimum moisture content (W_opt) was gradually reduced but the maximum dry denstiy (ρd _max) reversedly increased due to repeated treatment, changing into sandy soil. The change was more remarkable in the early stage of the repeated treatment. In Asakura granite, however, both W_opt and ρd _max fail to show any uniform tendency.(2) The maximum unconfined compressive strength (q_umax) varied qualitatively as corresponding to ρd _maxin each sample soil. However, when considering the q_umax producing mechanism, the behavior of the aggregates was equal to or more important than the compaction density. The moisture ratio at q_umax (W_{qu max}) abruptly was reduced in the 0 to 5 cycles in each sample, recovered in the 10 to 20 cycles, and then stayed almost constant in the 20 to 70 cycles: but in Asakura it was abruptly reduced again in the 10 to 20 cycles.(3) The value of (W_opt-W_{qu max}) was abruptly increased in the 0 to 5 cycles in each sample. Then, up to 70 cycles, it was simply reducing in Shirokawa and Ikazaki, while in Asakura it fail to show any uniform tendency.(4) The minimum coefficient of permeability (k_min) reversed to pa max, except for that in Asakura.(5) The change in the moisture ratio at k_min (W_{k min}) showeda similar tendency to that of W_opt, but in the 40 to 70 cycles, it tended to increase in each sample.

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Concrete sewer pipes are microbiologically corroded due to a two step reaction, i.e., productions of hydrogen sulfide (H₂S) and sulfuric acid (H₂SO₄) caused by sulfate reducing bacteria and sulfide oxidizing bacteria, respectively.
To estimate the in-situ corrosion rate, ordinary Portland cement mortar specimens (4×4×16cm) were placed in the manhole of a corroded pipe. The maximum and average corrosion rates were determined to be 3 and 1 mm/month, respectively. Temperature ranged from 25 to 30°C.
The ordinary Portland cement mortar specimens were placed in the vessel in the laboratory, too. The gaseous H₂S concentration was kept at about 500 ppm and temperature changed from 10 to 25°C. Specimens in the vessel were put into sewage, A-T medium or distilled water. The corrosion rate of the specimen dipped in the sewage was larger than that of the ones in the A-T medium. The specimens did not corrode at all in distilled water.
In addition, expansive cement mortar specimens and ordinary Portland cement mortar specimens were put into 5% Na₂SO₄ solutions, respectively. The former showed a greater deterioration rate than the latter.
It can be said from these results, that nutrients and temperature greatly affected the rate of corrosion. Corroded materials with a pH of from 0-2 mainly consisted of gypsum and ettringite was found at a much higher.pH. Since concrete sewer pipes are made with expansive cement, these are severely attacked by both sulfuric acid and sulfate.

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The high Froude number conveyance wave which is formed after cutting off the discharge is analyzed dynamically by using the theory of characteristics. This type of flow is a special case, but it is considered that in many points it has common features with other general conveyance waves with a high Froude number.
The definition of above-mentioned “high Froude number” corresponds to the condition of Froude number values larger than 1.5 (with the Manning formula) or 2.0 (with the Chezy formula).
The results are as follows:
Statical analysis based on the theory of uniformly progressive waves shows that the flow varies monotonously, however, that flow is never formed.
The flow itself maintains a mechanism in which monotony is broken and rolling waves are caused necessarily.
“Uniformly progressive negative surge” obtained from the statical analysis is the main component of the flow.
On the basis of the statical analysis “monoclinal falling wave” does not exist in the flow. However, that wave can be a component in a certain condition during the cutting off the discharge.

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An investigation was made of the applicability of the Fall Cone Test for determining both liquid and plastic limits of clays. The test was carried out on various kinds of clays for a 60°, 0.6 N cone and for a soil container 100 mm in diameter and 50 mm in depth. The penetration vs water content of the clay relationships were found to become, generally, straight lines on a double logarithmic scale in the wide range of the water content.
The mean values of penetration at the liquid and plastic limit for the Casagrande method were 12.0 and 1.3mm, respectively. The back calculated water content for these values of penetration on the penetration vs water content straight line were compared to agree well with the corresponding values of limits for the Casagrande method.
The undrained shear strengths of clay at the liquid and plastic limit calculated for 12.0 and 1.3mm penetration were 1. 25 and 106. 86 kPa, respectively, and were in good agreement with the vane shear test results.

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Effects of crust formation on water erosion were investigated using a rainfall simulator. The rainfall simulator was mounted 265 cm above the sample box and raindrops were produced from 1 mm dia. nipples using a pump. A 70 min simulated rainfall at an intensity of 33 mm h^-1 was applied to the surface of the soil repeatedly 4 times at 2 day, intervals (rainfall energy was 450 Jm^-2 h^-1).
The soil was clay loam taken from the surface of an orchard. The soil was sieved through a 3-mm screen and put into a 30×50×10 cm box at a bulk density of 1. 00 g cm^-3 with a saturated hydraulic conductivity of 1.77×10^-1 cm s^-1. The box was inclined to obtain 2.4, 6 and 11 degree slopes.
In each run, drainage at the bottom of the box and runoff were measured at 5 min intervals. After the simulation, splash and wash losses were weighed, and bulk density and saturated hydraulic conductivity of the surface soil were measured, and the cross section of the sample was taken using a SEM photograph.
By the simulation, a crust 3-mm thick was formed on the surface of the soil. According to crust formation, the runoff rate increased and infiltration rate decreased. Although particle size distribution of the surface soil remained constant, the bulk density of the surface soil was increased to 1.40g cm^-3, and saturated hydraulic conductivity of the whole soil decreased to 7. 0×10^-4cm s^-1. Saturated hydraulic conductivity of the crust calculated by applying the equation of continuity and Darcy Law for two layers was 8. 3×10^-4;-4. 3×10^-5 cm s^-1.
It was concluded that the formation of a crust has two effects on water erosion. The first was to strengthen the soil surface, and consequently, splash loss decreased. The second was to generate a runoff and to increase wash erosion. When an inclination of the slope was small (2.4°), the first effect was dominant, and when an inclination of the slope was large (11°), the second effect prevailed.

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Questionnaires were sent to the farmers in two districts where farmland consolidations have been carried out, and accordingly irrigation is done through open channels entirely separate from drainage channels. The results are chiefly as follows:
(1) Many of the farmers are not satisfied with conventional systems of irrigation through open channels.
(2) The main reason for their dissatisfaction is that their demands for irrigation often clash with those of others in terms of access timing.
(3) As a result, they would like a new innovated irrigation system.
Questionnaires were also sent to the farmers in three other districts where irrigation is done using a new system consisting of a regulating pond and pipelines. The questionnaires showed the following contrasting results:
(1) Irrigation is readily available when it is required.
(2) Time required for water management has been significantly reduced.
(3) Therefore, many of the farmers have evaluated this irrigation system very highly.
(4) As for the capacity of the regulating pond, while three times the volume of water normally required per hour is a little too samll, six times that volume is sufficient for uninterrupted and readily available irrigation.
(5) Through this system, water can be used not merely for irrigation, but also for other purposes, such as melting snow on roads.

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