A drainage structure model in a paddy field used as an upland field is given. The model has a drainage structure based on a tank model according to the macro-pore concept and runoff-component separation.
The respective models were defined by rain-discharge data from fields in which several drainage facilities were constructed. As a result, the observed and calculated values corresponded extremely well, giving validity to the models.
In the observed data, the discharge from the under drain or surface drainage discharge differed according to such factors as the disposition of the under drain. These differences appear in the parameters of the model.
Accordingly, by examining the variable parameters of the soil type and the drainage method in the field units, we could predict the variable rainfall-discharge processes in the field lots.

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The one-dimensional vertical model to estimate the vertical heat and mass flux due to surface cooling in lakes and dam reservoirs is presented. Derived from the heat conservation principle of water column considering both the convective and diffusive heat flux, this model is compared with the previous circulation models in which only the diffusive heat flux is taken into account. The following assumptions are made in the present model:
i) The decrease in water temperature is remarkable within the thin layer below the surface;
ii) The cooled water mass intermittently falls to the bottom layer or the depth where the temperature of ambient water is equal to it without turbulent mixing;
iii) Finally, water temperature has a maximum value below the surface and decreases gradually as depth increases.
Hydraulic experiments are carried out in a cylindrical acrylic tank and the above assumptions have been confirmed. Moreover, reasonable agreement of sinking velocity of cooled water mass calculated by the present model with the observed one was obtained. The ability of the model to estimate the thermo-convection has been established and it is concluded that the model can successfully be applied to the vertical circulation problems of dissolved matter, such as dissolved oxygen, in water basins using the time varying temperature profiles which can be easily and accurately obtained by field measurements.

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Cement stabilization through mixing is one of the possible methods for improving weak calcareous sediments in coral reef areas. In this paper, isotropic consolidation tests and drained triaxial compression tests were performed on uncemented and artificially cemented calcareous sand to investigate their stress-strain and strength behaviors. Major conclusions obtained in this study are as follows.(1) The friction angle of uncemented sand decreases as the confining stress increases because it is easily crushed.(2) In isopropic consolidation tests the preconsolidation pressure increases as cement content is increased.(3) The effect of cement content on strength and deformation behavior is (a) Young's modulus increase, but Poisson's ratio is only slightly affected, (b) cohesion at peak strength increases significantly, while the friction angle decreases only slightly, (c) friction angle at residual strength remains relatively constant.(4) The effect of cement mixing on strength and deformation behavior is significant in sand with fine passing 75μm sieves than those with no fine.(5) Void cement ratio law for design of concrete mix proportion can be applied to the evaluation of strength of artificially cemented calcareous sand deposits.

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This study was carried out to improve the windproof capability of vinyl film clad greenhouses. Generally, vinyl film clad greenhouses are often collapsed due to the strong winds, because they have very light weight structures. In such a case, as it is considered that the pile foundations are subjected to uplift and vibration at the same time, and an investigation on the uplift capacity of pile foundations by only the static load or the ground vibration is considered to possess several problems.
Therefore, this paper discribes the results of an experiment on the decrease of the uplift capacity of short piles under various conditions mainly being the frequency and acceleration of the horizontal vibration and pile length of embedment. The pile used in the pull-out test is a cylindrical concrete pile generally used in greenhouses, and it is subjected to some on uplift load before being vibrated by a vibrator, that is to say ; an uplift load less than the static ultimate uplift capacity (Q_S). Pile diameter is 43 mm and pile length of the embedment is from 20-40 cm. Pull-out tests were conducted for dry sand of soil placed at either a density of loose and dense.
From these results, the following conclusions were obtained: The dynamic ultimate uplift capacity of pile under horizontal vibration (Q_D) decreases far larger than in the case of a pile by the static load. The smaller the frequency is, the larger Q_D decreases. For the same frequency, the larger the acceleration is, the larger Q_D decreases. The rate of decrease in Q_D becomes smaller due to the increase in the pile length of the embedment and the unit weight of sand.

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Concentrations of pollutants were investigated in a streamlet flowing through a forested catchment (23.8ha) covered for the most part with Japanese cypress (Chamaecyparis obtusa S. et Z.). The study area (34°52'N, 136°16'E) was located in the basin of Lake Biwa, in Shiga Prefecture, Japan. The water samples were collected at the end of the catchment once a week from January 1988 to September 1991.
The average concentrations (C_W3) weighted with the discharge of TN, TP, and TCOD_Mn were calculated from the data obtained for 3 hydrological years as 0.528·m^-3 (NO₂-N 0.6%, NO₃-N 75%, NH₄-N 3.8%, DON 11%, PN 11%), 0.0121·m^-3 (PO₄-P 29%, DOP 15%, PP 56%), and 1.8·m^-3 (DCOD_Mn 67%, PCOD_Mn 33%), respectively. The ratio of TCOD_Mn: TN: TP was 150: 44: 1 calculated from C_W3, and the atomic ratio of N: P was 97: 1. The ratios of arithmetic mean concentration (C_A3) to those of baseflow (C_B3) were calculated as 1.44, 1.53, and 1.70 with regard to TCOD_Mn, TN and TP, and those of C_W3/C_B3were 2.00, 2.07, and 2.63, respectively.
The maximum/minimum ratios of the yearly arithmetic mean concentrations (C_Al) obtained from the data for 3 hydrological years were 1.36, 1.18, and 1.22 with respect to TCOD_Mn, TN and TP, those of the baseflow (C_B1) were 1.83, 1.48, and 1.62, and those weighted with discharge (C_W1) were 1.78, 1.32, and 1.96, respectively.

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The authors have developed what they have called an “anaerobic submerged iron contactor process” as a simple and inexpensive phosphorus removal method suitable for small-scale domestic wastewater treatment plants. In this process, iron contactors are submerged in ordinary anaerobic tanks, and phosphorus anions in the sewage are chemically combined with iron cations produced through corrosion of the contactors. Then, the compounds produced are precipitated and removed together with biological excess sludge. The corrosion is induced by the activity of sulfate reducing bacteria in biofilm on the iron contactors.
In this study, lavoratory experiment were carried out to examine the basic characteristics in this process, and the following findings were obtained.
(1) A high rate of phosphorus removal could be achieved with no significant unfavorable effect regarding the treatment of BOD, COD, SS and denitrifecation in comparison with the ordinary anaerobic filter process.
(2) The stagnation of wastewater in anaerobic tank caused a decrease in T-P removal.
(3) To obtain a continuous high rate of removal of phosphorus, it is possible to need the periodic backwashing to prevent the biofilm from thickening to an excessive extent.
(4) Close interrelations were found between the T-P removal rate and mole ratio of the iron cations dissolved from the iron contactors to T-P loading, and between the molar ratio and T-P concentration of the wastewater treated.
(5) Corrosion rate of the iron contactors was influenced by the changes in the BOD removal by the iron contactors.
(6) More sludge was produced by this process than by the ordinary anaerobic filter process. However, the sludge produced contained a lower percentage of water and was superior in dewaterability.

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Field observations were carried out to investigate the movement of acidic pollutants through snowpack during melting process. The amount of ion contained in snowpack under field conditions was measured. With partial melting of snowpack, anions and cations rapidly flew down through the snowpack. The rapid movement of ions was supported by a field experiment using methyleneblue as a tracer. More than 70% of ions retained in the snowpack was released at an initial stage of the partial melting, when compacted snow disappeared. Ion concentration of meltwater in this period was estimated to be concentrated by more than 7 times as high as the average concentration in the snowpack. Ions flowing down through snowpack transiently accumulated on an ice layer. Ions accumulated on the ice layer were released as the real melting season began.

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In water harvesting systems for small scale field irrigation, the relationship between the reservoir capacity (V) required to irrigate a hectare and the catchment area (A) was obtained by the water balance simulation method. The result has revealed that the relationship is approximated by the following equation:
A=α/(V-β) ⁿ
where the value of β equals the amount of water required for irrigation for a period during which time there is no influx into the reservoir, and the minimum reservoir capacity of the area.
The relationship is influenced by the rainfall characteristics, stormwater runoff characteristics and methods for irrigation. This means that as the amount of rainfall, the runoff coefficient of stormwater, or the amount of water-saving irrigation increases in a catchment area, the capacity of reservoirs has become less in magnititude. The phenomenon has become more marked as the area decreases.

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Regarding the water harvesting systems for small-scale field irrigation, the reservoir characteristics were elucidated using the water balance simulation method. Replenishing of the reservoir with other sources of water leads to a reduction in the size of the reservoir capacity. That is also reduces the construction and land costs. The size reduction effect from such a supply is greatly influenced both by the catchment area, when it continues; and by the time during which it lasts when it is conditional. When a reservoir (designed for an irrigated area of 1 ha and a catchment area of 6 ha) has a capacity of 5, 000m³, the average pondage factor of the inflow is about 50%, and the ratio of water use is 40% or so. The water pondage system scheduled for several years is more advantageous than that for a year because of the reduction in the reservoir capacity. As reservoirs decrease in size, sensitiveness to the unit of water balance becomes striking. It is desirable to operate small-scale reservoirs on a daily basis, not every 5 or 10 days or on a monthly basis.

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The interaction among seepage, stress and stability of earth dams during impounding and drawdown of reservoir is investigated by a finite element procedure. The procedure is based on superposing between saturated-unsaturated seepage analysis and stress analysis. The finite element mesh employed in saturated-unsaturated seepage analysis remains invariant during iterative calculations. By using the same mesh in the stress analysis it is possible to evaluate directly the effect of body forces such as seepage force, buoyancy and surcharge due to saturation on the behavior of effective stresses within the dam. The dam is assumed to behave elastically after completion of construction. Using stress levels mobilized in the finite elements, values of safety factor along the circular slip surface are calculated to assess the stability of the dam. The strength of soil is described by Mohr-Coulomb's failure criterion.
Numerical results show that the stability of earth dams during impounding and drawdown of reservoir is strongly influenced by the change of principal stresses within the dam, and that the manner of this change is governed by the distribution of body force which occurs during seepage. The safety factors of the dam are given as a function of step during impounding of reservoir and time after drawdown. The stability of the dam with a horizontal drain is also examined.

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Characteristics of snowcover-snowmelt, freezing-thawing, runoff and soil-loss were investigated by a slope lysimeter for defining soil erosion at the snowmelt and thawing period were investigated using observations. The results are summarized as follows:
1) Runoff percentage of snowmelt at the freezing plot was higher than that at the unfrozen plot, because of the ground depression intake due to freezing. Also, the percentage at freezing grassland was higher than that at freezing bare soil. It is supposed that the intake rate of grassland is higher than bare soil due to the influence of grass roots.
2) Soil loss of the frozen bare lysimeter with snowmelt is more than 13 times the unfrozen lysimeter. It is thought that the permeability and erodibility of soil were changed with ground freezing.
3) Soil erosion was controlled efficiently by grass, that is, the soil loss from the grassland was 1/6 times than that of bare soil under the freezing condition. In addition, a similar effect was recognized even for the unfrozen condition.
4) Runoff of the unfrozen lysimeter was much more than the prefrozen lysimeter after snowmelt and thawing. It is because the permeability of ground increases due to freezing and thawing.
5) Soil loss changes with rainfall were normal. Namely the soil loss was between the prefrozen and unfrozen for rainfall of small EI₃₀. For large EI₃₀, the soil loss after thawing was much more than the unfrozen plot. This is due to the increasing of the surface soil erodibility through freezing and thawing.

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For predicting the flood runoff from a reclaimed upland field, storage function model was applied and the efficiency was verified by kinematic wave model and by tank model. Runoff data was collected for 8 years from the field with furrow, non-furrow and mixed condition. The optimum model parameters and the parameters of rainfall excess equation were obtained by an optimization technique. The values of the optimum parameters of storage function model are presented in graphical and tabular form along with kinematic wave and tank models.
Then, interrelations were examined between the parameters of the storage function model and those of the kinematic wave model.

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The prevention of reddish soil loss in the Kunigami Maaji area is very important in the light of environmental conservation of the coral reef region in Okinawa, Japan.
To understand the reducing effect of covering and aggregation due to the membrane made from chemical stabilizer on the quantity of soil loss in a cutting surface of ground and a plowed layer, soil erosion tests were carried out on six field experimental plots, where each plot was 20 m in length, 2m in width and 4.3° for the slope. The main results are as follows.
(i) The cutting surface of ground was easy to erode because of deterioration due to weathering such as a change in the drying and wetting conditions.
(ii) Plowing was effective in reducing the amount of soil loss in the cutting surface of ground.
(iii) The aggregation formed by mixing of chemical stabilizer was effective in reducing the amount of soil loss in the plowed layer.
(iv) The amount of soil loss could be reduced by covering the cutting surface of ground with a membrane formed by the spraying of a chemical stabilizer.
The surface covering with a membrane made from a chemical stabilizer was a useful method to control the soil loss in a cutting surface of ground during reclamation.

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