Change of water pressure within a fingering flow field is one of the important factors for the mechanism of finger persistence. To clarify the change of water pressure, a model was presented for the formation of finger tip and ensuing growth of distinct fingers during ponded infiltration into a fine-over-coarse layered soils. The basic assumption of the model was that the sublayer had a water entry threshold which controlled water penetration under the condition of increasing water pressure. The relationship between finger length and water pressure at the interlayer plane was derived from the model. This relationship indicated that water pressure at the interlayer plane necessarily decreased with the increase of finger length. The model included two parameters, hydraulic conductivity within a finger and wetted fraction, which were not known prior to the experiment. Experiments of infiltration into fine-over-coarse layered glass beads for initially air dry conditions were conducted to verify the relationship. The derived relation could be fitted well to the experimental data. The hydraulic conductivity within a finger was the only fitting parameter, whereas the wetted fraction was obtained from the measurements. The mechanism of finger persistence could be explained by the fact that when the sublayer had a water entry threshold which controlled water penetration under changing water pressure, water pressure at the interlayer plane and within a finger decreased with increasing finger length and became lower than the water entry pressure of the sublayer.

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Methane Concentration in Aerial Shoots, Rhizomes and Roots of Phragmites australis (Cav.) Trin. ex Steud was investigated in Phragmites stands of the Hachirogata Central Polder, and in the Hedoro ground artificially made at Yamagata University farm (lysimeter), where P. australis are planted.
The results obtained are as follows.
1. P. australis showed a marked development of the lysigenous aerenchyma throughout the whole plant (Roots ⇒ Horizontal Rhizomes ⇒ Vertical Rhizomes ⇒ Aerial Shoots ⇒ Leaves).
2. Methane concentration in P. australis decreased in this order ; roots, horizontal rhizomes, vertical rhizomes and aerial shoots.
3. Methane concentration in P. australis increased with rising of the air temperature, the water temperature and the soil temperature, from May to July, and those respectively decreased with lowering of those temperatures, from July to October.
4. Methane concentration in the basal about five internodes of P. australis at the flooded wetlands was very high, and its gradient was very large.
5. Methane concentration in the basal internode of P. australis at the nonflooded wetlands was lower than that at flooded wetlands and was decreased as depth.
6. Methane concentration in the horizontal rhizomes of 0-year-old which grew in autumn, gradually decreased in the direction of the tip in the horizontal rhizomes.
7. Horizontal rhizomes of P. australis at the nonflooded wetlands were found most abundantly in the layers between 40 cm and 60 cm depth. Methane concentration in those horizontal rhizomes was very high in comparison with that of another layers.

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In 1993, heavy rain fell on southern Kyushu. It occurred everywhere in the area, and this district suffered considerable damage from flooding. The disaster at this time was characterized by the seepage failure of Shirasu talus deposits. To clarify the mechanism of this failure, the relationship between the hydraulic gradient and slope angle is discussed for an outward flow normal to the slope. Experimental results are presented and correlated with the existing theories.
In case that the slope angle is less than the internal angle, the relation of hydraulic gradient and slope angle obtained experimentaly agrees approximately with the traditional continuum theory under the outward-directed flow perpendicular to the slope ; namely, the deposits fail due to a smaller seepage force as the slope increases. The difference of two failure patterns, boiling and surface sliding, will occur at the angle between 13°and 20°; that is, the boiling occurs at lower angle than those angles and the surface layer slides at higher angle than that.

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In the field, it has been recognized that cylindrical macropores, predominant in vertical direction, exist in some stratum and these macropores play an important role in soil water flow under saturated condition. In this paper, in order to clarify the heterogeneity of saturated hydraulic conductivity (K_s) in the stratum mensioned above, a pore structure model is proposed. In the model, the macropores are represented by a bundle of straight parallel capillaries of different diameters, and an inverse relation between the pore diameter and its number per unit area is assumed. Based on the model, means, variances and frequency distributions of K_s in samples with different volume (same in height, but different in area) were examined theoretically by using probability theory. Under the assumptions that K_s is approximately determined by the numbers of macropores included in the sample and no spatial structure exists for K_s, the results are summarized as follows.
1. The expected value of the mean of K_s is independent on the area of the individual sample.
2. The expected value of the variance of K_s is inversely proportional to the area of the individual sample.
3. There is no analytic solution about the frequency distribution of K_s. For the help of the numerical simulation, it is considered that the frequency distribution of K_s is fitted to lognormal distribution for the smaller area of the individual sample, and it is fitted to both normal and lognormal distribution for the larger area of the individual sample.
4. From the results described above, the sampling scheme to estimate the mean of K_s in the field was discussed. The conclusions are, (i) a factor related to the accuracy of estimating the mean of K_s is the total area of the samples, (ii) the area of the individual sample and the number of samples should be determined for the convenience of measurement to match the total area of samples to the accuracy of estimation required.

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The physical and chemical properties of mud and benthos distribution in Imazu tidalflat, located in the west of Fukuoka City, were investigated. The clay content of mud varied in the range of 2 to 36%, being higher at the mouth of the rivers, the water route, and the constantly submerged places. A positive correlation was found between the organic matter and clay contents in the mud. The total number of benthos was rather greater at the mouth of the rivers than the constantly submerged places. With increasing the organic matter content, the total weight of annelida increased in the mud occasionally exposed to the air, while it remained small in the constantly submerged mud. The annelida inhabits the mud with the redox potential of-350 to 0 mV, but the total weight of annelida was smaller in the mud with lower or higher redox potentials. The distribution of annelida in the mud indicated that the mouth of the rivers was highly polluted.

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The detail of dynamic response of an intake tower in a reservoir is not enough clarified. Its base lies deeply below the reservoir water surface, so that it is difficult to identify the base exciting wave and to measure the ground motion. The earthquake acceleration records have been kept at the top of the intake tower since April 1995. The dynamic response of a tower model was analyzed on the basis of the seismic waves observed by the seismographs which were set in the foundation of an embankment dam apart from the tower.
Following two models were presented in this study; One is R-model which is a cantilever on rigid base subjected to bending and shearing forces, and the base causes rocking vibration. The other is F-model which is a cantilever directly stood on foundation base.
The dynamic response of these modes were computed based on the resulting vibration modes obtained for eigen value analysis.
Due to the difference in the geographical locations of both the dam and the tower, the accuracy of the proposed models were evaluated based on the rms values of their respective power spectrum density functions. A useful information for designing an earthquake resistant intake tower was presented by calculating the maximum top displacement and section forces.

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This paper deals with mechanical properties of asphalt mixtures for hydraulic structures. Various combinations of test specimens by six kinds of asphalt mixtures varing five different binders with aggregates and small amounts of additives such as asbestos and PAN fiber were made to perform this study. The bending beam test applied for this experiment is carried out at constant strain rate and three different strain rates were applied to the specimens at the temperature over the range between-20 and + 20°C. The flexural strength, the strain at failure and the stiffness at failure versus temperature were mainly examined throughout the experiments on asphalt mixtures. From the results of our experiments, it becomes clear to induce the following conclusion. The correlation between the flexural strength and the temperature is finally estimated and demonstrated. The flexural strength of asphalt mixtures added by small amounts of additives showed higher values compared with those without additives, the strain at failure with additives showed less values at high temperature, and the stiffness at failure with additives showed higher values at high temperature.

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Soil physical properties of uncultivated paddy fields in semi-wet sloping land were investigated in order to study the response of the fields to heavy rain. It was revealed that the upper soil layers of uncultivated fields have very high hydraulic conductivity because of well developed cracks which reach 70 cm deep layer and macropores created by plant roots. The x-ray stereoradiographs showed also macropores made by small creatures in the plow layer. One-plot intake rate tests were carried out in two uncultivated field lots. One was after a long drought and the other was after a long spell of rain. The levee heights of fields were measured and found to be very low compared to ordinary cultivated fields. Based on these data obtained from the field investigation, hydrological properties of uncultivated field, ordinary cultivated field and modern large-sized cultivated field were studied using computer simulation models which include water balance and soil physical condition of field. The models were characterized by intake rate, levee/bund height and the structure of field outlet. Two initial conditions were given to uncultivated and cultivated paddy fields, respectively, one was after a drought and the other was after rain. A heavy rain of 123 mm per day was inputted to the models. According to the results of the simulation, a rapid surface outflow over a low portion of the levee occurred in uncultivated field whereas water gradually flew out to drainage canal through the field outlet in cultivated fields. The reason for the above difference is essentially the difference in the levee height. It was concluded that the management of field outlet is very important when preventing water disaster in uncultivated paddy fields.

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When new catch basin is constructed in a polder, environmental impact assessment is essentially required for water quality preservation. To perform the environmental impact assessment, we must assess future water quality which is estimated by an ecosystem model in the catch basin. In the ecosystem model, pollutant loads of runoff from the catchment area are calculated by using the data collected from the catchment area. An L-Q equation is widely used for such purpose. The L-Q equation is very simple, but there is a problem that accuracy is not fair in thecertain case. This problem is particularly remarkable where irrigation water is taken from outside of the catchment area. Research concerned with this issue is lacking. Therefore, we select a catchment area where paddy field irrigation is performed, and conducted a survey for hydrology and water quality. The accuracy of L-Q equation is investigated and methods for its improvement is suggested. Authors verified that the accuracy of L-Q equation was improved by dividing the calculation term into two period ; irrigation and non-irrigation periods.

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In order to optimize irrigation water and to prevent saline problems in arid and semiarid regions, it is essential to accurately predict solute transport in soils and an evaporation rate. The convection dispersion equation (CDE) is widely used to predict solute transport. In this paper we examined the validity of the CDE for solute transport near an evaporating surface. An evaporation column experiment was conducted using Tottori dune sand with a shallow water table of NaCl solutions. Water and solute movements were observed. The diffusion and the mechanical dispersion coefficients as well as hydraulic properties for the Tottori sand were independently determined. The Richards' equation and the CDE were simultaneously solved with the finite difference method. Water vapor movement and crystallization of excess salts were also included for the prediction. The calculated concentrations near the soil surface were smaller than the measured data. This underestimation resulted in a significant delay of the salt crystallization at the soil surface compared to the observation, which would greatly reduce the evaporation rate. Since the CDE uses an analogy of the Fickian law to describe the mechanical dispersion, the dispersion term overestimated downward movement of solute regardless of the upward convective transport. The apparent dispersion coefficient, which agreed with the measured data in the evaporation experiment, was 1/3 of the dispersion coefficient in an infiltration experiment. Further theoretical and experimental investigations on the mechanical dispersion in an evaporation process are needed to prevent the unrealistic backward solute mixing.

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Usually, detail of procedures regarding decisions about public projects is not clearly observed. This paper's objective is to analyze the procedures regarding decisions regarding the planning of land improvement and environmental conservation projects in the Inba-numa basin. The decision procedures were simulated by a model which used a knowledge-based system, because it is difficult to use the ordinaly System Analysis or Operations Research for this kind of decision analysis. The knowledge-based system model includes a heuristics which was obtained from some experts by questionnaires in three public offices in the Inba-numa basin. The heuristics means the inference origin of the experts' experience. Input data were evaluated by the inhabitants and planners, and their estimation of the influence on the project. This heuristics consisted. of an elimination-by-aspects (EBA) rule and an additional-utilities (AU) rule. EBA uses the parameter S which is larger/less than the aspects' value. AU means total evaluation of the aspects' value. The output were compared with the actual system's evaluation consequence.
It was found that the model's output and consequence of the real system was almost the same as the results. Decision of the real system could be, therefore, represented by the heuristics.

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In this study, we evaluated the relationship between pF value and shear strength in compacted and unsaturated decomposed granite soils depended on the different weathering. Three kinds of decomposed granite soils were used for the tests. The shear strength was measured by the direct shear testing apparatus. pF value was measured by the automatic recording tensiometer.
Firstly, we evaluated the relationship between water content and the shear strength. The shear strength related to the water content was depended on the, weathering of materials.
Next, we used pF value instead of the water content, and we evaluated the relationship between pF value and shear strength. The shear strength related to pF value could be evaluated by independently from the weathering of the materials. All pF values corresponded to the changing point of shear strength were approximately 2.5.

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This study dealt with the relation between land use in watersheds and outflow of eutrophic components in semi-mountainous regions. The area investigated was Hara Village of Nagano Prefecture, which is located in the south-east part of the Lake Suwa catchment. The eutrophication problems of Lake Suwa are serious, so it becomes important to investigate land use effects on outflow of eutrophic components.
In Hara Village, seven rivers were selected for the investigation of land use effects on outflow of eutrophic components. According to the results of 9 September 1994, there was a tendency that specific loads of T-N, T-P and SS increased with the increase in percentage of upland fields. On the other hand, the specific loads decreased with the increase in percentage of paddy fields.
Agricultural land consolidation projects have been conducted in the middle basin of the rivers in this area. In the projects, agricultural roads added a function of drainage. It became clear that surface water on upland fields was drained to paved agricultural roads, and directly discharged into rivers. However, some eutrophic components, such as T-N, NH₄-N and T-P, are in surface water as not only dissolved but also suspended, so the surface water on uplandfields should be discharged into rivers after settling the suspended solids.

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This paper describes suggestions for seepage settling basins placed as an underdrain for the lower portions of basins in order to control muddy water runoff from cultivated land during rainfall. In basic laboratory hydraulic experiments, this method experimentally shows the function of promoting the gravity precipitating effect on suspended sediment. The primary causes are the decrease of horizontal velocity on approach to the outlet and the occurrence of flow in the direction of gravitational force due to underdrainage in the basin. In addition, the function depends on the filter material of the underdrain. In terms of sediment concentration reduction, there is no effect when the filtering pebble size is more than 2.0 mm, sediment concentration reduction is effective with filtering sand of 0.25-2.0 mm. With this filter material sand, it was possible to reduce the kaolin sediment concenration from 260-840 mg/l to a sediment concentration of 10-50 mg/l or less.
A technical problem to be solved in the future is to decrease underdrainage discharge due to filling of the gaps of the filter material by the suspended sediment.

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Onjaku soil, the weathering product of basalt, is distributed in Uwaba area, north western part of Saga Prefecture. Onjaku soil which consist mainly of halloysite and chlorite as clay mineral is classified as clay soil according to Japanese Standard Soil Classification. The general features of this soil are great specific gravity of soil particles, high water content for small clay fraction percentage, and small dried density of around 1g/cm³.
The present paper investigates the compressibility of compacted Onjaku soil and its settlement behavior due to water immersion. The characteristics of soil compressibility, due to water immersion, changed for soil samples compacted below optimum water content, and expansion or settlement occurred, while the soil compressibility remained unchanged and no settlement occured for soil samples compacted above optimum water content, with saturation degree greater than around 85%.

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[in Japanese]

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[in Japanese]

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