It is known, concerning with infiltration into fine-over coarse layered soils, that water pressure at the interlayer plane increases rapidly when wetting front arrives at the plane and decreases after the occurrence of water penetration into the sublayer. This fact suggests that water entry threshold plays an important role in the occurrence and persistence of fingering flow. However, clear characterization of water entry threshold has not been given with relation to fingering phenomena, yet. Process of water penetration into packed glass beads with average diameter of 0.4mm was investigated. First, we measured the values of water entry threshold for initially dry and wet conditions by changing supply water pressure. Next, we measured infiltration flux under constant supply water pressure which was lower than the value obtained by the first measurement. In the first measurement, the value obtained for initially wet glass beads was lower than that for initially dry condition. For initially dry glass beads, we obtained the result that there was a discontinuous point of infiltration flux with the increase of supply water pressure. Therefore, the value of water pressure obtained by increasing supply water pressure could be regarded as a water entry threshold. On the other hand, obtained value for initially wet condition was not regarded as a water entry threshold because of continuous increase of infiltration flux. The values of the water entry threshold were discussed on the basis of the water characteristic curve for wetting process of the packed glass beads.

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An on-farm questionnaire survey was carried out in a typical upland irrigation district of western Japan to investigate factors which influenced water use during the 1994 early crop growing season. The survey included irrigation frequency, type and area of crops grown, farm labour, irrigation equipment and others ; the variables were investigated by a form of quantification theory ( ‘suryouka-riron 1 and 2’). The partial correlations for the full-time farm households indicated that water use was most influenced by crop type while farm labour was the most influencial factor in the part-time farm households ; cropped area was least sensitive to water use in both cases. The combined farm households indicated an optimum irrigation frequency of 5 to 6 irrigations per month. About two-thirds of the irrigators preferred applying water during the morning and evening periods possibly to avoid the extremely hot, afternoon, weather usually associated with summer. Quantification method type 2 indicated that irrigation frequencies of 4 to 7 times per week were mostly on farms of about 0.1 to 0.4 ha which also grew various crops as the main crop. 3 to 4 irrigations per week were mostly on leafy vegetables usually grown on farms of about 0.5 to 0.9 ha and with water mostly applied through drip hoses. Irrigations of 1 to 2 times per week were usually on wet fruits mostly grown on farms of about 0.1 to 0.9 ha with water mostly applied through drip hoses and normal hoses. Irrigations of 1 to 2 times per month were mostly on grass (lawn) usually grown on farms of more than 1 ha with water mostly applied through sprinklers. The various on-farm factors identified in this study were hence associated with crop production, farm management and socio-economics ; their influence on water use may have resulted in less water usage compared to the designed water duty of crops grown in the district.

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To reduce water application in drip irrigation, a control based on the fuzzy theory has been designed, and examined its validity in field experiments using melon plants. For the measurement of soil water content that is need for the control, the TDR technique was used. The probe of the TDR was set at the distance of 5 cm from a melon stock. This position of the probe was suitable judging from the profiles of measured water content. Water was applied to six drip-lines with different water quantities according to the control conditions and irrigation condition of everyday irrigation or every two-days irrigation. The applied water quantity was estimated from the measured water content and its change from last measurement. As the results; soil water content was controlled reasonably within a narrow range of about 0.06 to 0.12 cm³ cm^-3 in any drip-line. Cumulative irrigated water quantity was saved by about 20 to 30 percent of the control (basic application) for everyday irrigation. For every two-days irrigation, the saving of water application more than 50 percent of the control was realized, however accompanied with a little yield reduction. We concluded that the fuzzy control with soil water measurement by using TDR should be very useful for controlling water application, and thus for water saving in drip irrigation.

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The purpose of this experiment was to develop a method of economical phosphorus removal from rural sewage. In the experiment, ferric chloride solution was added into an activated sludge reactor.
The experiment was done at a rural sewage facility which has a capacity to treat the wastewater of 940 people. The facility consists of two parallel treatment processes, which use the same sequencing batch reactor (SBR) activated sludge process.
The results are as follows:
1. T-P concentration of the treated water of the SBR which had ferric chloride solution added into it was 0.5 mg/l or less. T-P concentration of the treated water of the SBR without addition of ferric chloride solution was 1.7mg/l on average.
2. The phosphorus removed by ferric chloride solution was assumed by the next equation (1). “rc·Pin” in the equation (1) means the assumption of phosphorus removed by activated sludge.
ΔP_Fe=ΔP-γ_c·P_in(1)
3. The relationship between Fe of added ferric chloride solution and phosphorus removed by ferric chloride solution is approximated by the following equation (2).
F_e/ΔP_Fe=a·F_e/P_in+b(2)
4. Based on the equation (2), the ferric chloride solution for phosphorus removal can be estimated by the equation (3).
V_c=b·P_in·ΔP_Fe/C_Fe·(P_in-a·ΔP_Fe)(3)
V_c= the volume of ferric chloride solution necessary for phosphorus removal (l)
ΔP_Fe= the phosphorus removed by ferric chloride solution (g)
ΔP= the phosphorus removed at the SBR with ferric chloride solution (g)
r_c= the phosphorus removal rate of the SBR without ferric chloride solution (-)
P_in= the phosphorus loading of the SBR with ferric chloride solution (g)
Fe= iron in added ferric chloride solution (g)
a, b= the constants calculated by the least squares method, 4.19 and 1.81, respectively
C_Fe=Fe concentration of ferric chloride solution (g Fe/l)

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A questionnaire investigation of the water management was done in two pipeline irrigation districts of paddy fields in the Niigata plains. From the investigations, it was made clear that careless water management was done at the fields of the farmers who felt that the supply volume of the water from the pipeline valves was enough. At such hydraulically advantaged paddy fields, visits to check the water supply from the valves were less frequent. By the time the hydraulically disadvantaged fields had enough water, a lot of excess water was generated at the fields with less frequent visits. This excess water became the management water requirement, increasing the demand for irrigation water supply.
Using the expanded node energy method, the volume of water from the valves in the pipeline network was calculated to show that careless water management caused the increase in the management water requirement. The management water requirement was simulated by changing the time interval between field visits for checking the water supply, and by adjusting the valve at every field. As a result, it was proved that lengthening the time interval between field visits has a tendency to increase the management water requirement, while partially closing the valves at the hydraulically advantaged nodes was able to reduce it.
In the future, such pipeline network simulations done using the expanded node energy method will become useful means for investigating various water management methods.

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In Inaho area of cold, light snowfall Tokachi district, investigations were carried out for influences of soil freezing on soil erosion which is a marked characteristic in this district.
As a result of this, it revealed about the soil erosion in the snowmelt period that eroded damage occurred much more in slopes incidental to the upland field of reclaimed fields than in the upland field itself. Following findings were obtained for this characteristic.
(1) A rill erosion occurs due to a drain overflowing its diversion ditch incapable of keeping its sufficient sectional area to flow down the drain in the snowmelt period, because the snowfall in the winter time covers the sectional area of the diversion ditch.
(2) In a period when, with a soil in the slope frozen in the winter, the frozen soil layer still stays in the snowmelt time, seepage water causes a surface plane slip and a seepage slip in the middle of slope, because it flows down in this frozen layer making it a quasi-river bed.
(3) Due to such an imperfection of soil erosion protection works as a shortage of drainage, diversion ditch, etc., along the tractor passage in the reclaimed field, a rill erosion is caused by a surface run-off water which originally is to pass through its drainage canal to the outside of this district, but runs off in the slope.
Also concerning the dangerousness of soil erosion due to its slop aspect, it revealed that a period in which a frozen layer remains in the soil layer of a slope facing the north is longer than that in a slope facing the south in the snowmelt time, and its snow coverage remains much there due to the sun shade, therefore, the dangerousness is highly expected.

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Flow curves (data on shear stress vs. shear rate) were obtained for Na-montmorillonite suspensions at solid ratios up to 2.6% from steady-state shear experiments with cone-plate viscometer. These results exhibited typical pseudo-plastic flow pattern with some yield stress, and were expressed by a Herschel-Bulkley model.
Yield stresses τ₀ were estimated from the flow curves, and they revealed high dependency on solid ratio φ₀, such that τ₀ changed according to the 7th power of φ₀. Then extrapolation of this relationship to higher solid ratio leaded accurate correspondence to the liquid limit test data for Na-montmorillonite paste. This result indicated that the relationship between τ₀ and φ₀ could explain plastic flow properties of samples over the wide range of water content from suspension paste to liquid limit.
It was also examined from theoretical viewpoint by the Michaels and Bolger model. Assuming a uniform and parallel arrangement of clay particles and adopting the van-der-Waals attractive force as an inter-particle force factor in that model, we calculated theoretical values for yield stresses of Na-montmorillonite. They showed good agreement qualitatively with the measured tendency although calculated values were less than 10^-5 of measured ones.

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This study investigated the settling behavior of Na-montmorillonite suspensions under the field of gravity. Na-montmorillonite suspensions, whose initial solid ratios φ₀ ranged from 2.0 to 3.0%, were placed on deionized water in the settling tube 20cm in total height. Then, solid ratio profiles of suspension columns were measured at various elapsed times until 30 days.
The settling characteristics of clay suspensions were examined by comparison to an ideal Newtonian viscous flow model. But, in this experiment, Na-montmorillonite suspensions behaved as a Bingham plastic flow, and remained in the upper part of settling tube. These results indicated that suspension layer was supported by some force, against the gravitational force.
Therefore, we estimated the yield stresses τ₀ and maximum shear stresses τ_max of Na-montmorillonite suspensions, and compared them numerically. The yield stresses τ₀ could be calculated, using experimental relationship between τ₀ and q50, obtained by means of steady shear flow test. They showed remarkably high value for dilute suspensions, ranging from 18.0 to 338.8 Pa.
Then, shear stresses in suspension column took maximum at the boundary between suspensions and the settling tube wall, and these values could be deduced by applying the Michaels and Bolger model to the hypothetical thin unit layer of suspensions. Neglecting the pressure difference of liquid and solids between top and bottom of the unit layer, we could obtain the maximum shear stresses τ_max at most 8 Pa, which applied lateral side of column upward. Hence, shear stresses were considerably less than yield stresses τ₀. Maximum shear stresses obviously resulted from the frictional force between suspensions and tube wall. Thus, uplifting of suspensions during 30 days could be ascribed to the frictional force, so settling behavior could be observed only just at the interface between suspensions and deionized water.

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Although soil is normally treated as a continuum in analyzing thermal conduction, it looks discontinuous from microscopic view because soil consists of solid and void space. Therefore, temperature inside the soil particle should not exactly equal to that of fluid in adjacent void space. To investigate the possibility of dealing soil as continuum for soils of large scale heterogeneity, the authors made a model soil column consists of air and gypsum balls (2cm in diameter), and measured temperature differences between particles and air at the same distance from heat source, during heating process.
The measured temperature differences were so small and scattered that we could not determine which were higher, and they were at most smaller than the differences exist in a distance of the particle radius along macroscopic temperature gradients. One-dimensional heat conduction equation for continuum were also applied to calculate temperatures in the experiment. The calculated temperatures well agreed with the observed ones, if the term of heat loss from sidewall of the column and the effect of contact resistance at the boundaries were included in the equation.
It can be concluded that soils with stagnant fluid in its voids can be treated as continuum for thermal conduction even if the domain of interest include only several particles, and there is no need to distinguish temperatures of particles and that of fluid among them.

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Theory of seepage failure of sand within a cofferdam is discussed. The Terzaghi's method is first discussed and a new method of calculating stability against boiling of soil-Prismatic failure concept-is presented. The Prismatic failure concept was applied to some typical examples, and the following results were then obtained:
(1) The theoretical critical difference H_c by the Prismatic failure (Friction) is nearly equal to one of the Terzaghi's method for the one-layered isotropic soil.
(2) The larger the degree of anisotropy k_x/k_z grows, the smaller the H_c value becomes for the one-layered anisotropic soil where k_x, k_z, are the coefficients of permeability in the horizontal and vertical directions.
(3) For the two-layered soil, the critical section is shifted from the lower edge of sheet piles to the boundary of the two layers when k_r is less than 0.635 where k_r is the ratio of coefficients of permeability of the upper and lower layers.
(4) The prismatic failure (Friction) is most appropriate from the viewpoint of shapes of critical prisms and H_c values.
(5) The prismatic failure (No friction) gives us an H_c value on the safety side.

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Features of finger flows in fine sand and quartz sand were investigated experimentally and the effect of types of finger flows on the leaching characteristics were analyzed. The average particle size of fine sand was 0.18mm and that of quartz sand was 0.64mm. Salt was mixed uniformly as far as possible in the amount of 1.65g per 100g air-dry sand. Three different initial water content (air-dry, 1%, 2%) and two different rainfall flux (30 mm/h, 180 mm/h) were applied as the experimental conditions. Transducerized tensiometers were installed in the sand through the panel by which the changes of suction within fingers were measured.
The results show that the shapes of wetting fronts were classified into four types, low-swell finger, high-swell finger, wavy front, and plane front. The values of suction gradients inside low-swell fingers were almost 0, suggesting that water movement inside them were mainly conducted by gravimetrical gradients. The changes of suction in low-swell fingers and in high-swell fingers were remarkably different. These differences were attributed to the differences of water content distributions within these two types of fingers.
Leaching characteristics of sands were significantly influenced by the types of wetting fronts. Especially in the air-dry conditions, where low-swell fingers were generated, their leaching efficiencies were very small (20%-67%) compared with those of other types.

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The suction and pressure methods have usually been used for the measurement of thunsaturated hydraulic conductivity of soil under the condition of steady state. However, there are some experimental difficulties in these methods caused by the clogging of the filter in the apparatus and its incomplete contact with the soil sample. It is also necessary in these methods to saturate the soil sample before the change of each suction or pressure stage.
In this paper, a simple method for the measurement of the unsaturated hydraulic conductivity is proposed, using the soil under the condition of the steady evaporation without troublesome problems as previously stated. The experiment using the apparatus made for this purpose is not only quite easy in practice, but also the water retentivity can be measured using the same apparatus constructively as used for this experiment. But the suction gradient can not be controlled in this method. So the nonlinear distribution of the suction through the soil sample must be considered for the precise calculation of the unsaturated hydraulic conductivity. For this purpose, two technics of calculation are proposed, called ‘the dual method’ and ‘the series method’ in this paper.
The calculated values of the unsaturated hydraulic conductivity by these two methods using the experimental data during the steady evaporation almost agree with the results of measurements by the suction method.

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We experimented removal of pollutants from water of an irrigation pond by means ofrunning the water repeatedly through paddy fields that are adjoining the pond and were not expected to produce rice profitably in the summer and winter of 1993 and the summer of 1994. The pond, Kameike, locates in a rural area in Takamatsu city, and is approximately 7, 000m³ in volume.
The experiment revealed that provided the vegetation on a paddy field was developed enough, percentages of decline in polutant concentrations were high when the residence time was more than about 5 hours and that the shorter residence time was, the more removal quantities of pollutants per area per day were. For example, mean removal quantity of SS counted 32.9g ·day^-1·Em^-2 when residence time was 3 hours and 4.3g ·Eday^-1m-² when that was 3 hours in the experiment carried out in the summer of 1993.
Removal efficiency of SS was largely enhanced by the presence of filamentos green algae, e. g: Spirogyra sp., rice and weeds on the paddy fields.
Through the fact that removal efficiency of SS and Chl-a was constantly effective and COD, nitrogen and phosphorus were mainly removed in form of SS, the main mechanism of purification was thought to be removal of SS.
This purification method demonstrated efficient removal of pollutants. The equipment for the job is easy to handle. So we believe that this method is fairly practicable.

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The steady-state heat balance method and the heat pulse method were compared in order to estimate transpiration and to evaluate their accuracy. First, the flow rates in a glass pipe in which the sap flow of plants was simulated were measured for both methods. The results obtained in the experiment showed that the heat balance method tended to overestimate at flow rates higher than 100g/h. The heat pulse method requires a calibration coefficient to convert the measured heat velocity to transpiration rate. The experimentally decided coefficient was 0.76, while the physical properties of the materials used yielded a coefficient of 0.71. The flow rate evaluated by the heat pulse method agreed well with the discharge rate even with a flow rate higher than 100g/h. The computed sap flow was compared with transpiration from potted corn plants. The calibration coefficient for the heat pulse method was effected by the positions of the temperature sensors in the stem, while in previous experiments with plants of uniform size, the calibration coefficient was not effected. The hourly variations of transpiration were estimated by using both methods at the same time without using the predetermined coefficient for the heat pulse method.

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This study dealt with outflow phenomena of eutrophic components in the surface erosion processes on heavily fertilized upland fields. Soil was sampled in the upland field located in Hara Village, Nagano Prefecture. Soil erosion on upland fields is a serious problem in Hara Village. Using a slope model, an erosion test was conducted in the laboratory. In the erosion test, changes in surface water quality, such as T-N, NO₃-N, NO₂-N, T-P and SS, were observed. The concentration of T-N, NH₄-N, T-P and SS in the first stage was very high, and gradually decreased with the increase in accumulative surface runoff. Additionally, the concentration of T-N, NH₄-N, T-P and SS increased again, when rill erosion occurred after sheet erosion. The components of NO₃-N and NO₂-N were observed slightly in the erosion experiments.
This study made clear that eutrophic components not only dissolved but also suspended, such as T-N, NH₄-N and T-P, were included in surface water on heavily fertilized upland fields. Also the amounts of eutrophic components increased with the increase in SS components.

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We estimated seismic risk at the sites of water area reclamation projects in Japan after the World War II.
Firstly, we computed acceleration values of these sites using the attenuation equations for historic earthquakes with some damage and these adopted attenuation equations are in the specifications for highway bridges by the Japan Road Association. And using these results, we got both acceleration values expected once in every 100 years and maximum values for the three kinds of ground classification, and then, classfied these values into the seismic acceleration intensity scale followed the Japan Meteorological Agency seismic scale but more detailed. Moreover we investigated the soil characteristics of foundation grounds and the materials of reclamation dikes.
Secondly, we examined the liquefaction potential of the sites of these reclamation projects by means of comparing the values by using the above-mentioned seismic acceleration intensity scale of the expected values and maximum values with the acceleration values having occurred liquefaction. As a result, we could say that there might be a possibility of damage caused by liquefaction at a large number of project sites.
Thirdly, we made the name list of 25 earthquakes that liquefaction had occurred at or near the sites of water area reclamation projects by looking up these places on Maps for Historic Liquefaction Sites in Japan.
Lastly, we emphasized that the most fundamental thing is designing the dike of seacoast conservation project to be as large as possible.

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