We observed concentrations of gas phase component (oxygen, carbon dioxide) in the layer (the subsoil layer, umber loam) of the open system dropping percolation at paddy fields of volcanic ash for three years. Soil air extracted at 60 cm depth were selected from the interface of levee between the paddy fields to the central part of paddy fields (5.5 m, 12.7 m, 22.5 m from the levee).
Following results were obtained in this study.
1) Oxygen concentrations in the layer of the open system percolation decreased in irrigation period (the minimum value was 10 % mark at the point of 5.5 m, 9% mark at the point of 12.7 m and 8-9 % at the point of 22.5 m), whereas increased in non-irrigation period and soon became the fixed value (the maximum value was 16 % mark at the point of 5.5 m, 15 % mark at the point of 12.7 m and 12 % mark at the point of 22.5 m) It was thought that these annual changes depended upon soil temperature, gas diffusion and mass flow of gas accompanied with moisture content change caused by.drying and drainage.
2) Carbon dioxide concentrations increased slowly after ponding and became the maximum value early in September (about 9% at each three point in paddy fields), then decreased to the stable value (about 5% at the each point) last December.
3) It was recognized that the oxygen concentrations lowered with the horizontal distance from the levee to the center, whereas the carbon dioxide concentrations had the fixed value with the distance. Formation of carbon dioxide was approximately equal to oxygen consumption.

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The interactions of ions in salinity soil solution are factors determining ion uptake by roots. To clarify the relationship between these parameters, differences in uptake due to root washing in solutions of Na⁺, K⁺, Ca²⁺ and Mg²⁺, were studied by the method reported previously.
The transpiration stream concentration factor was found to be nuity in all case. Exudation differed according to the cations, and decreased in CaCl₂. The opposite was noted in all other cases. These findings were shown in relation to K+ concentration in roots. The each cation would thus appear to be a determinant of uptake.

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It is generally difficult to read the ultimate bearing capacity of flexible batter piles under horizontal loads from load-deflection curves.
In this paper, the fitting method is introduced to determine the ultimate bearing capacity of flexible batter piles in homogeneous sand under horizontal loads and its applicability is discussed experimentally.
Model tests were carried out using instrumented flexible piles of wide-ranging flexibilities.The piles were buried in loose, medium and dense sand at batter angles β = 0°C, ±15°C and ±30°C and were subjected to incrementally increasing horizontal loads.
Reasonable agreement was found between the present theory of ultimate bearing capacity and the theory of Meyerhof and Ranjan (1973).

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The physical (dry bulk density, pF, cone index etc.) and chemical (C1^-, Sa₄^2-, Na, EC etc.) properties of soil in each soil profiles were investigated in a Phragmites australis plot and a bare soil plot of lysimeter, where pipes of soil sampling are opened for about three years from April 25, 1985 continuously without closing at a depth of 70 cm, to elucidate the influence of P. australis on the physical and chemical improvement of Hedoro ground. After comparing the P. australis plot with bare soil plot, it became clear that the improvement of Hedoro ground by P. australis is very effective in the physical and chemical properties of soil.
The results obtained are as follows.
1. In the layers between surface and 10 cm deep of bare soil plot, the dry bulk density increases, compared to that in the P. australis plot. In the layers 20 cm and 100 cm deep of P. australis plot, the dry bulk density increases remarkably, compared to that in the bare soil plot.
2. The water retentivity in the P. australis plot becomes remarkably lower in layers more than 10 cm below the ground surface, compared to that in the bare soil plot.
3. The depth of the invasion of gaseous in the P. australis plot is greater than that in the bare soil plot.
4. The cone penetration index in the P. australis plot is greater than that in the bare soil plot in the layers between surface and 100 cm deep.
5. Exchangeable Na and exchangeable Ca contents of soils in the P. australis plot become lower in layers more than 70 cm below the ground surface, compared to those in the bare soil plot.
6. Exchangeable K content of soil in the P. australis plot becomes lower in the layers 10 cm and 70 cm deep, compared to that in the bare soil plot.
7. Cl^- concentration of the soil in the P. australis plot becomes remarkably lower in the layers 10 cm and 100 cm deep, compared to that in the bare soil plot.
8. EC (mS/cm) of soils in the P. australis plot and bare soil plot is 0.4 and 1.7 in layers 10 cm and 50 cm deep respectively.
9. pH of soils in the P. australis plot and bare soil plot is 4.9 and 6.4 in layers more than 100 cm below the ground surface respectively.
10. SO₄^2- concentration of the soil in the P. australis plot is greater in the layers 50 cm and 100 cm deep and is very small in layers more than 30 cm below the ground surface, compared to that in the bare soil plot.
11. The base saturation percentage of soil in the P. australis plot becomes lower in layers more than 70 cm below the ground surface, compared to that in the bare soil plot.

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The authors developed evapotranspiration (ET) submodel in the last report. In the ET submodel, evapotranspiration ratio which is used in estimation of evapotranspiration value is decided corresponding to soil water content distribution. Hydraulic conductivity used in ET submodel is calculated using soil scaling method and is smaller than that of the actual watershed. In the calculation by the ET submodel using hydraulic conductivity obtained by the soil scaling method, percolation is smaller and evapotranspiration is bigger compared to the value calculated by water balance. In the soil, there are saturated-unsaturated flow part which is called matrix part and macro pore part in which saturated-throughflow is dominant and water flows rapidly. That is why hydraulic conductivity in the actual watershed is bigger. To incorporate the ET submodel in the runoff model, the runoff model has to be able to express that kind of inhomogeneity of soil. Therefore the multistory slope tank model is developed, in which the ET submodel corresponds to the matrix part of soil and the runoff tank corresponds to the macro pore part of soil.
In the application of the multistory slope tank model, the parameters values except for those obtained in the literature were calibrated and good results were gained. In the process of calibration of the parameters, some knowledges that distribution of hydraulic conductivity of runoff tank or step number of the tanks influence resultsof runoff analysis were obtained.

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This paper elucidates the mechanism of hydraulic fracturing in fill dams from the view point of fracture mechanics by taking into accounthe effect of the pre-existing (initial) crack. A laboratory experimental procedure is presented, by which an applied fluid pressure, required to induce hydraulic fracture at the tip of a predetermined crack in a soil specimen, is measured reliably and then, by interacting the size of the crack size with the applied fluid pressure, using an equation of linear elastic fracture mechanics (LEFM), a soil parameter called fracture toughness _IC is obtained which is an indicator of the soil's resistance to fracturing. The mechanism of hydraulic fracturing in fill dams is then discussed based on the obtained results and a countermeasure against the risk of hydraulic fracturing in fill dams is also recommended.

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Some numerical aspects of the upwind TVD scheme, the 2 step Lax-Wendroff scheme and the Preissmann scheme are discussed for discontinuous flow analysis in open channels. The TV-stability analysis indicates that the 2 step Lax-Wendroff scheme has no TV-stability, and the Preissmann scheme has a bounded stable range with an upper and a lower limit derived from the TV-stability theory. Numerical experiments show that the upwind TVD scheme needs larger computational effort than conventional difference schemes, however, it is quite accurate and does not generate spurious oscillations close to discontinuous points. Furthermore, the 2 step Lax-Wendroff scheme cannot suppress numerical oscillations for discontinuous flow analysis; it is hard to apply the Preissmann scheme to the numerical analysis of flows including subcritical and supercritical flows.

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Optical methods, i.e., the classical light absorbance and dynamic light scattering (DLS) were tested in order to clarify the applicability to study the kinetics of flocculation of montmorillonite suspension (pH=10.0 ± 0.5). The validity of these methods was confirmed by flocculation experiments of the standard latex dispersion. For a suspension of montmorillonite, it was found that (i) the electrolyte (NaC1) concentration which corresponds to the crossover between dispersion and flocculation was between 1.0 ×10^-2N and 3.0 ×10^-2N, (ii) in the range of low electrolyte concentration, qualitatively the same result was obtained by these two methods for the rate of flocculation compared with the electrolyte concentration, (iii) in the range of high electrolyte concentration, it was clarified that DLS was more effective during the process of the rate of flocculation measurement used in this study, however it was impossible to obtain an exact rate of flocculation in this range. On the basis of these results, the possibility of future improvement was discussed to obtain the reliable data of the rate of flocculation of montmorillonite suspension in the region of high electrolyte concentration.

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In order to estimate the impact of acid precipitation to aquatic ecosystems in snowy areas, the quality and quantity of both precipitation and stream water at a small experimental catchment (34.7ha) were studied. Using the observed data obtained during three years, balances of three kinds of acidic anions, those are Cl^-, NO₃^- and SO₄^2-, in the catchment were investigated. Accumulation and melting of snow had a strong influence on the movement of anions in the catchment. It was suggested that the effluent of meltwater with high anion concentration in the early stage of snowmelt might temporarily raise the anion concentration of stream water. Each anion exhibited different characteristics of outflow to the stream. The consumption of NO₃^- by biological activities and the production of SO₄^2-by weathering seemed to be the major factor for balances of anions in this catchment.

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The change of carbon content, pH, dissolution of amorphous matter, and its effect on the consistency limits of soil by H₂O₂ treatment were measured using andosols and hedoros, or lake bottom muds. When 30 cm³ of 6% H₂O₂ was used on 10 g of soil, the pH of the topsoil of andosol lowered from 5.8 to 4, and Hachirogata hedoro from 6.4 to 3.3. These pHs recovered when treated with an increased amount of H₂O₂. Oxalic acid formed by H₂O₂ treatment lowered the pH, and as it was combined with aluminum or iron in the soil, the pH gradually recovered, In relation to the pH drop amorphous matter dissolved. More than 80 % of aluminum as free oxides or hydroxides were dissolved from hedoros during the H₂O₂ treatment. Hachirogata hedoro greatly changed in the plasticity chart by air-drying, but showed only a little effect of that after the H₂O₂ treatment. On the contrary, the effect of air-drying on the topsoil of andosol did not show any substantial change before and after H₂0₂ treatment. Free oxides and hydroxides were found to have a great effect of air-drying on Hachirogata hedoro.

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The critical coagulation concentration (CCC) of montmorillonite was measured at various salts and pH levels, and compared with that predicted by the DLVO theory. The CCC of monovalent cations was in accordance with the hydrated cation radius, and ratios of divalent to monovalent cations agreed with the Schulze-Hardy rule. The CCC in Na₂SO₄ solution was found to be high compared to that of NaCl or NaNO₃ below pH 6.5. Since SO₄^2- cancels more the positive charge at the edge than Cl^- or NO₃^-, pH 6.5 at which the effects of anion valence disappeared was considered the point of zero charge (PZC) of the edge. Effective PZC as a net charge of the edge including the face negative charge in the vicinity of the edge is introduced. Predicted CCC agreed with that measured under alkaline conditions assuming the effective PZC of the edge at pH 4. However it did not agree under acidic conditions where multiple interactions disturb edge to edge (EE) or edge to face (EF) interactions with small contact areas. Coagulation with EE and EF linkages may not occur easily at low pH unless face to face repulsion is depressed by salts.

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Alluvial soil in Fukaya, locating at a basin of Tone River in Saitama prefecture, has been perceived to be a ‘good’ soil. Recently, however, some fields in this area were damaged and the drainage efficiency is being degraded. The objective of this study is to investigate and evaluate the physical fertility of the field in the viewpoint of the drainage efficiency and the physical and chemical properties of the soil including the aggregate stability.
The pattern of hardness profile and the dispersion of the hydraulic conductivity in each field, and the stability of aggregates influence the drainage efficiency. The combination of these factors and other physical and chemical properties of soils also affected the drainage efficiency. Physically fertile fields were classified into two types; the first, all the properties of the soil have advantage for good drainage and, secondly, the favorable properties of soils compensated the unfavorable properties of them. On the other hand, soils in physically unfertile fields were either possessing worse properties or exceeding the unfavorable properties to their favorable properties. The balance of each physical property of soils, as well as their spatial heterogeneity, was crucial to keep them physically fertile.

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Aquifer management depends on estimation of aquifer parameters. For a confined aquifer it is common to arrange a pumping test and analyze the data by Theis graphic matching procedure to estimate aquifer transmissivity (T) and storage coefficient (S). This method is time-consuming and may lead to errors if matching of field curve to the Theis theoretical type curve is not proper. Therefore, genetic algorithms (GAs) have been used to estimate T and S. They have been applied to the Comilla region aquifer, Bangladesh. Results show that there is a good agreement between the Theis graphic match point method (TGM) and GA. Moreover, this GA is more efficient than that of TGM, because it has minimum sum of square of errors. Results of the parameters sensitivity analysis show that in every observation location there is a unique set of T and S value which would result in minimum sum of square of errors. Therefore, GA could be an efficient tool for aquifer parameters estimation in the near future.

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In a previous paper of our study to develop a design procedure for the throughflow embankments, a onedimensional head loss equation was developed to understand the basic of the hydraulic properties of the rockfill disposition. In this paper, as the second phase of the study, water flume model tests are conducted to investigate the hydraulic transmissibility of the two-dimensional rockfill structure. A gabion weir with vertical upstream and downstream faces is selected because it has been widely employed to control the floodwaters. It is found that the discharge through the gabion weir is related uniquely to the upstream water level and the length of the weir. Based on this result and the assumption that the coefficients in the one-dimensional head loss equation are valid in the twodimensional flow, an equivalent hydraulic gradient is introduced to estimate the discharge flow through the gabion weir. A small design example is given to show how to use the equivalent hydraulic gradient. Some limitation of the Dupuit's assumption in the two-dimensional flow through coarse rockfill structures is also mentioned.

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Diurnal soil temperature fluctuation in a bare field was analyzed with a model which included heat exchange at soil surface, heat conduction in soil, and evaporation through dry layer. The measured solar radiation, soil thermal conductivity, water content profile and daily evaporation rate were used as input data. The soil temperature calculated by the model agreed well with those measured in various meteorological and soil conditions
Then, the effect of thickness of surface dry layer on the soil temperature was examined with this mode. As the result, developing of the dry layer increases temperature amplitude in the dry layer but decreases the amplitude in wet layer beneath the dry layer because the dry layer has high thermal resistance while it reduces evaporation rate.

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For management of groundwater in wide basins, we should couple the analysis of groundwater dynamics with combinational optimization to deal with constrict conditions such as water right. In this paper, a new evaluation method of hydrodynamic characteristics (safe yield capacity etc.) of shallow wells was proposed by applying the cluster analysis to the yield and water level in the wells (diameter: 3-5m, depth: 8-15m) located on the mid-and lowerpart of alluvial fan. The method was verified to estimate the critical yield of each well by using results of step drawdown test conducted over ten times a well and data of discharge and water level obtained in 1985 (usual year), 1993 (rainy year) and 1994 (thought year). This quantitative evaluation is useful, when deciding the distribution of discharge in the well groups in the water supply control scheduling.

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Diversity and complexity of soil moisture movement give difficulties of determining the effective soil layer (ESL) in applying soil moisture depletion method for non-rice crops in paddy based land. This paper aims at analyzing the reasons of these diversity and complexity based on the data of total 16 crops in the Philippines. Firstly, features of soil moisture movement were shown with changes of total potential gradients, and classified into three types. Furthermore, the conditions having appearance of three types were identified. Secondly, a mathematical model was made to quantify root water absorption ratios and analyze the reasons. Finally, typical example (s) of each type was analyzed by the model, and the appearance conditions of diversity and complexity were studied. The results indicated that (1) the diversity and complexity are caused by appearance of the maximum root water absorption ratio at the subsurface soil layer under high evaporative demand and by smallness of supplemental flux for the absorbed water due to low permeable soils, and (2) the difference in diversity and complexity is controlled by appearance and magnitude of the maximum absorption.

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The soil moisture depletion method will be the best suited for developing countries to obtain the real data of crop consumptive use (CU) due to the relative simpleness and low application costs. CU is the depletion amount in an effective soil layer (ESL). Resent studies suggest for the bottom depth of ESL to apply zero flux plane (ZFP) although the conventional method suggests to apply a depth at which moisture content hardly changes during an irrigation interval. The ZFP is a boundary between upward water movement by evapotranspiration and downward one by gravity, and identified with total potential gradients (TPGs). Applying ZFP for ESL can exclude gravitational water from the depletion amount. In order to prove the applicability and usefulness of ZFP for paddy based land, the authors evaluated CU amounts for 16 crops with ZFP. For verifying the usefulness of applying ZFP, the CU amounts evaluated with ZFP were compared with those with the conventional method, and the accuracy of CU amounts was evaluated with the existing evapotranspiration data and FAO data. The results indicated (1) increase of data utilization for determining CU, and (2) less error than the conventional method for estimating evapotranspiration due to less inclusion of gravitational water.

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Geosynthetic has been used for the purpose of making permeability smooth at many construction fields. However, drainage capability has deteriorated due to the same kind of soils being attached to small articles to small holes at the filter processing repetition of drain over a long period of time. New geosynthetic with pretty large holes was obtained by point the aimed at drain condition of the ground piping with pretty large gap at their joints that were buried in paddy fields showed drain maintained for a long period of time and very little soil flowed out from the pipe. The experiment for many days was carried out for purpose of checking of penneability and soil drawing-out for the new filter together with a couple of other geosynthetics. It was suggested that the new filter is a useful device for a relatively long durability and good percolation effect without flowing out a lot of soil and is possible to be applied to construction fields as a new filter material.

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In region of Chiba prefecture coast, the operation which preserves an underground water level using irrigation water highly can be doing. This operation an underground water stop said. It is said that this operation has the effect which makes an underground water level of neighborhood whole rise, as a result it has a water for irrigation supplement effect to field, too.
But, the benefit of a field isn't objectively proved. In fields of Kujukuri coast area, we investigated a relationship of rainfall with an underground water level with rainfall and drainage water level etc. As a result, we defined following.
We define effect of an underground water stop exerts on underground water level rise effect in Kujukuri area where soil texture is mainly soil. And, we define effect of an underground water stop has an effect on water for irrigation supplement of a field place.

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A large fluctuations of water surface is observed in the Isawa Main Canal, Iwate Prefecture. High surface wave due to the intensive vortex in the stilling basin below the drop structure moves downstream. This phenomenon results in a large scale of surface fluctuation. Countermeasure to reduce fluctuation without over all reconstructing the flume are studied by hydraulic model experiments. Surface fluctuation is reduced by floating a buoyant body whose shape is a inverted trapezoid or a flat sheet. The effects of reducing fluctuation by some types of buoyant bodies are clarified by the image analyzing system.
What is the most effective shape of buoyant body or possible problem is examined in a half-size flume compared with the original one. It reduces under half of one at some test case. However, because the test body cannot float by itself, the proper height of fixing a body is studied again by flume experiments.

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[in Japanese]

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