The liquefaction in the bed underwater wave pressure is closely related to many disasters like soil mass movement, scoure, etc. To increase effective overburden stress by loading on the bed surface is one of the effective methods for preventing such disasters. This paper is for studying numerically the liquefied zone from the bed surface and loading on the bed surface for preventing them using Biot's consolidation equation.
The liquefied zone increases as the wave amplitude, the amount of air and water in the bed increase and as the wave period, the permeability and compressibility in the bed decreases. In this case, the loading on the bed needs to increase so as to prevent liquefaction.

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This paper refers to the simulation of the variations in the groundwater in the very wide area surrounding Lake Biwa. The simulation is undertaken in the implicit finite difference method.
In its calculation, on the spacewise domain under consideration of 1 km mesh interval in both x and y direction, the mesh points, corresponding to Lake Biwa and forming the irregular internal boundaries, are given the measured water level of the lake.
The domain divided into paddy field, paddy-residence mixed area, city zone and mountainous area is given the different hydraulic constants and ratios of infiltration (rainfall and irrigated water) and evapotranspiration, respectively.
As a result of comparing the calculated value of the variations in the groundwater with the measured one, the assumption of values mentioned above is considered good for practical use.

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To clarified the mechanism of the effluence of nutrient salts from paddy fields, the runoff behavior and material balances of nutrient salts (N, P) have been investigated in detail during four irrigation seasons in two types of paddy fields, located in the low plain areas of Niigata which have alluvial soil and improved underground pipe drainage systems. One block is the Sadoyama district which is irrigated by open channels, and the other block is the Dohgata district which is irrigated by pipelines. The following results were obtained:
(1) Total N load balance depends more heavily on the water balance in each district than total P loading. Sadoyama district has a large water balance level in Japan, in contrast Dohgata district has small quantities of irrigation and drainage water. So Sadoyama district has more quantities of input and output loads of total N than Dohgata district.
(2) Concerning total P load balance, the balance effluent loads of P are large values in both blocks. This is an uncommon case in paddy field investigation in Japan. These results are characteristic of the P effluent of paddy fields which has alluvial soil and underground pipe drainage systems.
(3) From July to August, the paddy field of Sadoyama had N and P effluent loads lower than input loads. That is to say, Sadoyama district had acted on the basin as a water purifier. Especially total P that was brought with reused irrigation water has been greatly removed from the water by the paddy fields.
(4) Daily effluence of load has been very changeable. Large effluent loads occurred at periods Of paddling, rice-planting and heavy rainfall.
(5) During thr non-irrigated seasons only in 1987-1988, the balance effluent loads of N and P were investigated in Dohgata. The result showed considerable balance effluent loads of N and P.

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An innovated method for jointly managing a group of dams taking water from a single and multiple sources of river to integratedly control as a system the required quantity of water to be reserved or discharged dependent on situation is proposed here. The method, which has newly been established after carefully studying various conventional dam management measures, is designed to ideally suite for minimizing flow waste by the efficient combination of following four basic concepts in controlling flows:
1. Concept of ‘move-water-first’:
Before relying the supply on still water in the reservoir, moving water from the inlet channel is taken first.
2. Concept of ‘take-then-refill’:
In order to save total discharge amount from the whole system, excess water in a dam or dams tending to easily becoming full is discharged first.
3. Concept of ‘simulated operation’:
An operational simulation rule to forecast droughty water level in dry seasons is established so that intake control is made accordingly.
4. Concept of ‘proportional banking’:
Calculus to define respective proportion of water supplies for multiple users is established by dividing daily intake quantity with usage amounts to enable impartial distribution regardless the storage fluctuations.
Rules with the above four concepts have proved their excellent efficiency when compared with conventional Space Rule and the like.

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In a thin water layer of a depth of about 2-3 mm, the mass of detached soil particles by the action of hydraulic positive pressure impulse which is generated immediately after the impact of a waterdrop (Process I) is more than that by the action of hydraulic negative pressure generated by the process of expansion and contraction of a cavity in the water (Process II, III). By process I of soil detachment, the soil particles are pushed into the water and a crater appears on the surface of the soil.
In this paper, the experiment was conducted to investigate the relationship among the volume of detached soil, the water depth, the impact energy of a waterdrop and the size of soil particles. The volume of detached soil was obtained by two measuring methods. One was the method for measuring the volume of excavation on the surface of the soil and the other was the method for measuring the mass of soil particles which was splashed out. Experimental results showed that the volume of detached soil depends only on the impact energy under the water depth of 0.3×H_max-0.4×H_max (H_max is the maximum height of the cavity), and in a deeper water depth than the above mentioned depth, the volume of detached soil proportionally decreases inversely to the square of the water depth. These tendencies coincide well with the calculated results based on the model of soil detachment which was proposed in our report (III).

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In an oxidation ditch, an aerator applying falling water is effective. Higher than 90% of the BOD removal ratio and 80% of the nitrogen removal ratio are achieved constantly using intermittent aeration. 60-70% of the phosphorous removal ratio is also obtained.
In this paper, dephosphorization using intermittent aeration and adding a coagulant in an oxidation ditch employing falling water as the aerator was studied. Intermittent aeration when the mixed liquid temperature was low for the purpose of removing nitrogen was also investigated.
As a result, it was found that higher than 90% of the phosphorous removal ratio was obtained using intermittent aeration and adding an iron chloride (FeCl₃) solution as the coagulant. The optimum quantity of the addition was that the ratio of Fe (mol) in the coagulant to P (mol) in untreated water was equal with one. When the mixed liquid temperature was low, the optimum operation for removing nitrogen was carried out under intermittent aeration by 1 hr of aeration and 2 hr of as non-aeration one cycle. This operation was also effective in dephosphorization.

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This paper describes the proposal of a stabilized box foundation method (SBF method) for reinforcing soft ground and reinforcement mechanism for bearing capacity on clay.
The SBF method is a method to make box-shaped vertical walls by overlapping cement columns in the ground on which structures are to be constructed. In addition to the functions of the cement column method, this method has the following functions for reinforcement: 1) to decrease the settlement by preventing the lateral flow of soil mass below the foundation by the box, 2) to decrease the settlement by decreasing the clay layer thickness due to the drawing down of the place where a load is to be transmitted, 3) to increase the bearing capacity due to the effect that the box and soil mass confined inside of it function as a deep foundation.
The loading test results of the model foundations on homogeneous clay were found to agree well with the theoretical values of bearing capacity of the foundations.

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Residual strength, designated to be the minimum drained strength, was measured for slip-surface soils using a ring shear apparatus. The reduction to the residual stength needed a long shear-displacement for reorientation of the clay particles, and the residual state was attained after the displacement of 40-60 cm for the mudstone-derived soils and 200-300 cm for the conglomeratederived soils, suggesting the usefulness of the ring shear test which allows the long-distance displacement in one direction for the measurement of residual strength in the laboratory. The ring shear test, however, took a long time because of testing under a drained condition, and the minimum shear-displacement to the residual state varied with the nature of the slip-surface soils and with the magnitude of normal stress in the soil.
The parameter of the residual strength, expressed as φ_r, depending on physical and mineralogical properties, the clay content (<2μm), plasticity index, and smectite content were correlated with φ_r. The relation of φ_r to the plasticity index was manifested by the equation φ_r=48.8·I_p-^0.440 for mudstone-derived soils and the relation to the smectite content was shown by equation φ_r=10.2-0.045·S_m for soils containing smectite. The estimation of φ_r based on these regression equations is indirect but quick, and it may have some prospect after elaboration of the equations by testing for soils which are widely different.

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This study is for the purpose of clarifying the properties of dissolved oxygen content (DO) in seepage water of open and the closed system percolation and the availability of pressure causing entry pores (p_k) that distinguish these DO properties. I used undisturbed soil having opensystem percolation that we had reported about.
In the experiment, DO in seepage water and pressure head were measured at short intervals in the vertical plane, and then, the drain level was controlled by the soil column models. The composition of the soil column models corresponded to the stratified soil (3 layers) of a paddy field that we had observed to be the open system percolation. As a result of this observation, the following information was obtained.
1) In case of the low drain level, both surface soil (positive pressure, Kuroboku soil) and plowsole (negative pressure, Kuroboku soil) became the closed system percolation and DO in this seepage water was about 2 ppm. Subsoil (negative pressure, loam) became the open system percolation and DO of this seepage water rapidly increased to a class of 6 ppm and retained their oxidation state in soil column models. However, in case of the high drain level, all layers became the closed system percolation (positive and negative pressure) and it was observed that every layer's DO in this seepage was about 2 ppm.
2) It was recognized that the increase and decrease of DO in down seepage water was caused by whether the pressure head of subsoil was larger than p_k or not.
It follows from the above results that the DO properties of the increase and decrease appeared in seepage water of the open and closed systems and that p_k's availability for distinguishing this phenomenon was high.

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Study on agricultural land conversion as a function of family size by means of a simple time series model is important for the construction of the multi-purpose models.
It is clear that the dynamics of family size on surburban area can be divided using the influence degrees of a “mother city” into its surroundings. It is important to know the interaction among regions.
In this paper, the dynamics of social phenomena including agricultural land conversion can be explained by a brief differential equation. This time series model is considered the base of agricultural land conversion model.

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Recently, lots of the environmental disruptions have arisen all around the world: atmospheric pollution, water pollution of rivers, lakes and seas, reckless deforestation and so on. Especially, the eutrophic lakes and marshes caused by water pollution have become a serious problem in Japanese agricultural areas. It is well known that paddy fields have water purification functions, however it has been reported that water quality pollution has arisen from inadequate water management in the period of fertilization. Therefore, it is important that we grasp the state of water quality and make a plan for a better purification function.
The purpose of this paper is to investigate trend of changes in water quality thoroughly and survey the nitrogen input and output in a rice field (Chiba Prefecture) (Fig. 1). To investigate the water purification function of a rice field, the valves of the underdrain were opened, then polluted irrigation water flowed through the soil layer to the underdrains during the irrigation period except for the fertilization period.
The result was that the mean value of T-N of irrigation water was 1.71 mg/l, that of drained water was 1.07 mg/l (Table 6). Similarly, the T-P of irrigation water is 0.10 mg/l, that of drained water was 0.11 mg/l (Table 6). The quantity of reduction from the inflow to outflow about nitrogen and phosphorus showed 14 kg·N/ha and 0.05 kg·P/ha (Table 8), respectively. Also, this field did away with 42% of the nitrogen of inflow (Table 8, Fig. 6). To compare with trend of changes in water quality between irrigation water and drained water by underdrains, both were the same value or the concentrations of irrigation water was higher than that of drained water, except for COD (Fig.3). Therefore, nitrogen and phosphorus can be reduced through the use of underdrains. However, the concentration and outflow load of COD increased. The mean value of COD of irrigation water was 10 mg/l, that of drained water is 16 mg/l (Table 6). This trend was due to the outflow of metallic elements (Fe, Mn), reducing matters and combined sulfur, in subsoil.

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In the first paper, we reported on the water quality purification function in a paddy field. In this paper, pot tests under several different conditions of water quality load were carried out (Fig. 1, Table 2).
The results of several research studies by pots and lysimeters have already been reported ; however, no generalized relation to the percolation rate and difference in soil texture has been done.
The purpose of this paper is to survey the relation between the purification functions of flooded soil and the concentration of irrigation water, the percolation rate and existence of paddy rice. Also, the influence of the concentration of irrigation water and percolation rate on the growth of rice is investigated using growth analysis.
The result was that the percolation load of the outflow in T-N and NH₄-N was very small compared to the inflow load while the irrigation water concentration was 1-10 mg/l and percolation was 2-40mm/d (Table 2, Fig. 4). In addition, the rate of reduction from the inflow to outflow was 70-99% showing that the water quality of nitrogen was purified (Table 2). Also, the result of the growth analysis showed that the concentration of irrigation water would influence rice (Table 3). Therefore, whether the concentration of irrigation water is high or low, nitrogen can be reduced through percolation. However, it is necessary to keep a low concentration of irrigation water in order to increase the production of rice.

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Planning experts' mind processes were analyzed for irrigation canal reform projects' draft planning by iteration of a simulation test run and model revision of an expert system model.
First, the actual situation of the canal to be reformed is diagnosed regarding seven points:(a) adequacy of water resources, (b) function of diversion dams, (c) main canals, (d) laterals, (e) O and M, (f) drainage and (g) water pollution. With these seven points, the diagnosed troubles' degree is expressed by numbers 0, 1, 2, 3, which are denoted larger when the degree of trouble is worse. They are arranged in a “present state list (or vector) ” and input to the model. Second, the model makes a “future state list” by adding to the present state list the values of estimated degeneration which will occur when no project is performed in future.
This model then selects the actual project measures by scrutinizing from higher rough planning levels to lower more detailed levels in a decision tree. “Result lists” are obtained by subtracting “effect lists” assinged to each branch point of the tree; thus the trouble degrees are reduced as a result of each project measure. After superimposing several sets of the most desirable result lists, rough sketches of project types are finally recommended.
This model was applied to several irrigation. canals in the Tone-river basin and were in good agreement with the experts' possible decisions.

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