A side-view finite element model to simulate thermal stratification in man-made reservoirs is proposed. Using flat-shaped rectangular, trapezoidal and triangular elements which consist of vertical and horizontal 1-D elements, the model can avert numerical inaccuracy caused by large aspect ratio and can consider the depth dependent field variables as vertically continuous. Treatment of the velocities near the inclined slip bed is modified to satisfy the continuity condition and treatment of confluences is newly introduced to meet the complex geometry conditions. Vertical eddy diffusivities are estimated by newly proposed parameterization using Brunt-Vaisfili frequency. Capability of the model is investigated through few demonstrative computations for hypothetical and real reservoirs, comparing the computed results and the theoretical or observed data available. As a result the present model is proved to be a practical tool for hydro-thermal analysis in man-made reservoirs and expected to contribute toward the development of water quality models.

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A side-view finite element model is developed to simulate dissolved oxygen (DO) inreservoir. Taking the relationships among flow, water temperature, nutrients, planktons and DOinto consideration, the model consists of three sub-models, i. e., 1) Flow and Temperature (FT) sub-model, 2) Phytoplankton (PP) sub-model and 3) D0 sub-model. The results from FT and PP sub-models are directlycast into the final DO sub-model through advection, diffusion and source terms. Based on the fact thatthervertical distributions of water temperature and DO are highly correlative, the model uses the verticaldiffusivity expressed in terms of Brunt-Vaiala frequency by which strong effects of thermal stratification onthe distributions of the field variables can be reproduced. Verification of the model is carried out incomparison with the measured data in A-man-made reservoir and the long term model behavior is tested through thecomputation in Bman-made one. The results show that the model is capable of satisfactorilyreproducing the DO distribution in a vertical plane and thus can be an alternative tool for forecasting DO in areservoir.

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Mechanisms in sealing during a rainfall is so complex. Initial moisture content is not always the dominant factor in clod break down as many researcher have suggested. Two experiments were conducted with a Japanese acid soil (Kunigami mahji soil, LiC) to clarify the mechanisms of clod breakdown due to raindrops. In the first experiment the relation between clod breakdown and sizes of raindrops and clods were studied with a single drop former for different initial moisture conditions. The effect of clod and raindrop sizes on the structure of surface seal under a multiple drop rainfall simulator was observed in the second experiment. Two clod sizes, 1 to 3 and 3 to 5 mm, and three initial moisture conditions, from airdry to near-saturation, were employed in this study. Kinetic energy of drops was varied from 0.34 to 18.1 J m^-2 mm^-1 by changing dropsize and falling height. Clods with different moisture conditions showed similar breakdown features when raindrops were smaller than clods. In contrast, when raindrops were larger than clods, the initial moisture condition affected clod breakdown.Slaking predominated when raindrops were larger than clods and initial moisture content of clods was low. The structure of the seal was also affected by raindrop and clod sizes.

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The influence of soil properties on erodibility is important in predicting the magnitude of soil erosion, especially from the fields where the soil is undergoing ripening processes. In order to understand the processes of soil ripening in a newly reclaimed upland field, selected properties of soils from fields with long histories of cultivation, newly reclaimed, and a sedimentation pond were determined. This was done to obtain data that could provide information for countermeasures to be developed to minimize the effect of erosion, maintain good soil conditions and promote high agricultural productivity. The primary objective of the study was how to protect the Nagara River from the pollution of eroded material from the newly reclaimed field. The results indicated that physical, chemical, and biological soil ripening processes wereproceeding steadily. Poor structure and no aggregates characterized the soil of the newly reclaimed fields. However, soils of the fields with long histories of cultivation had some aggregates. Some of the soils, particularly those with the history of manure application, were dispersive. Their well dispersive properties and the absence of aggregates rendered them susceptible to water and wind erosion. Countermeasures are required to enhance soil ripening of newly reclaimed fields to improve soil physical and chemical properties and mitigate the effects of erosion. Results of the sedimentation volume test showed that provision of infield sedimentation ponds and the use of filters to trap dispersed soil particles is essential in order to prevent pollution of nearby waters. The condition of soils, for example, formation of aggregates and development of structure, can also be improved through crop rotation and fallow methods. It was expected that optimum method and application rate of gypsum could effectively minimize dispersion of soils by enhancing flocculation and aggregate stability.

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History and cause of change in form and size of field lot on several rice paddy area in Ishikari mire region, Hokkaido, Japan, were examined with reference to settlement period, rice paddy development period, and soil classification. Form of field lot was affected by the differences in starting period of settlement and development of rice paddy, and it is especially regulated by the frame of settlement block. However, the farm land consolidation projects which were carried during 1970's, have changed the form of field lot itself dramatically. As a result of these projects, the form of field lot is almost completed as the same form with nowadays. With these projects as a Wilting point, field lot size has been standardized, and local difference has been disappeared. Further enlargement of field lot size is now under progress in some farm blocks of several areas, but its progress is moderate than the change happened in 1970's. Moreover, some area with peat shows decrease in the rate of large (more than 1 ha) farm area.

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Floatation behavior of flocculated blue green algae has been analyzed as a function of the concentration of blue green algae. The applicability of Richardson-Zaki's equation was confirmed when the floatation velocity is expressed as a function of the ultimate volume of the cake of blue green algae. It was observed that the hindered floatation characteristics of blue green algae can differ eminently even though the relation between floataion velocity and diameter of single floc is same. The relation between the ultimate volume of the floatated cake (φ_sd) and the dried weight concentration (c) was approximated as:φ_sd c^0.85.

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Examination was made of the effects of hydroxy-aluminum as an stabilizing agent on the mechanical properties of clayey soils. Aluminum contributes remarkably to a soil structure, but has less direct effect on soil strength. Increase in hydraulic conductivity by formation of the soil structure accelerates the rate of soil dehydration, and thus soil strength was expected to be improved rapidly. This is important and effective in practical use since difficulty lies in the early stage of dehydration in the case of clayey soil. A suitable amount of hydroxy-aluminum was found to be 25% of CEC, or 4-6 g kg^-1 of Al to oven-dried soil, and almost no effect was found with excess application. Unconfined compression test was done using inundated soil samples to eliminate the effects of matric potential on soil strength, which was found to increase somewhat by the addition of hydroxy-aluminum.

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In this paper the standard Soil Conservation Service runoff curve number method (CN method) is studied at first by using the observed data of the experimental watershed of scrub forest at the Pothwar plateau in Pakistan. The distribution of the calculated curve number (CN) of each runoff event has some expanse for this watershed. However, rainfall excess estimated by the mean CN value shows its applicability to the watershed. Secondly, the simple unit hydrographs (UH), i.e. triangular and exponential types are applied for the estimation of storm hydrographs. CN value is set as 91 for the rainfalls during a monsoon period in predicting the time variation of effective rainfall. The results are acceptable despite the simplicity of the model, though the predicted peak discharge for the big storm is slightly underestimated. This simple method of flood estimationeeds two parameters for triangular UH, one parameter for exponential UH and one parameter for CN method. It is easy to set from the small amount of observedata.

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The locations of diversion dams should be chosen by judging from the stabilization of low-water courses in front of their intakes. It is directed that a change of low-water course has close relation to the migration or the suppression of alternate bar, but their relations have not yet revealed clearly. We experimentally studied their relations in many meander channels in some of which bars can migrate and in some of which bar migration is suppressed. Basically, the stabilization of a low-water course is obtained in the meander channel whose bend angle is larger than the critical one, and alternate bars cannot migrate downstream in that channel. The critical bend angle becomes smaller as the meander-length becomes longer. We also discovered the phenomena that critical bend angle changes with different hydraulic conditions and that low-water course is almost stabilized in spite of the migration of alternate bar in some channels.

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The stability of montmorillonite was determined under NaCl solution combined with CaCl₂, MgCl₂, or AlCl₃. When the pH changed from 5.8 to 8.0, the stability increased considerably for all combinations except AlCl₃ due to the point of zero charge of the edge being at about pH 6.5. Montmorillonite dispersed at low electrical conductivity (EC) even when the sodium adsorption ratio (SAR) was low. At high pH, the system required high EC for coagulation under the same SAR. The water retention of montmorillonite treated with NaCl, NH₄Cl, KCl, CaCl₂, MgCl₂, and AlCl₃ was measured to estimate the effect on the structure. Clay saturated with Na⁺ exhibited almosthe same water retention in both drying and wetting processes, while with NH₄⁺, K⁺, Ca²⁺, Mg²⁺, and Al³⁺, it showed irreversibility once air dried. The basal spacing of air-dried montmorillonite measured by X-ray diffraction (XRD) followed the order of the hydrated ion radius within the same valence. The greater interlayer opening of air-dried clay with Ca²⁺, Mg²⁺, and Al³⁺ indicated the formation of a porous structure.

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In this research, concrete test pieces with different sizes and shapes, and standard cured specimens were made by the same mix proportion of concrete at the same time, and the influences of the development of strength, the effect of curing, and the effect of compaction were compared based on the method of ultrasonic pulse velocity.
As a result, the effect of curing decreased by becoming a massive concrete specimen. The strength development in the center part of a specimen is delayed because of this curing effect. Also, at the upper part of a mass concrete specimen, the disorder of compaction is not residual by becoming massive.
On the other hand, ultrasonic pulse velocity decreases as the length of the mass concrete specimen becomes longer, and the section size larger. As for the degree of length and section size of a specimen to the ultrasonic pulse velocity, section size was more influenceable than length.

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In a rectangular channel, a current water wheel set closely along channel cross section to get energy from the flow works as fluid resistance raising upstream water level. In this paper, authors direct their attention to the damming-up effects of a current water wheel. Hydraulic model tests are carried out to examine the relationship between raised water levels and the energy output of a water wheel by changing a load to the wheel, and then its results are applied to an existing irrigation channel. Based on the tests, the relations among specific energy and rotational speed and torque of wheel are formulated. Main results obtained are as follows; 1) Lower Froude number flow or lower initial water depth can get higher increase ratio of energy output. 2) The initial condition of Fr<0.5 at the design water levelmay not cause overflow, and the conditions that the ratio of blade height to initial water depth is less than 1/3 and Fr is less than 0.2 produce little output. 3) Simulation proves that damming-up effect on producing energy is remarkable when initial water depth is about a half of a wall height of channel.

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The objective of this study is to clarify the effect of the Shuhai, rural sewerage treatment system, to purify the canal water. We studied the water quality of the dual-purpose canal running through the Yokebori district, Kuki-shi, Saitama, where the JARUS-III, one of the major models for the Shuhai, was built in 1995. The canal ran through the settlement where household waste water was released. The period of study was from 1994 to 1997, covering before and after the start of operation of the Shuhai. Before the start of operation of the Shuhai, water quality worsened markedly during the non-irrigation period. But the water quality of non-irrigation periods have improved since the introduction of the Shuhai except for the canal below the Shuhai plant, where water quality improved only in organic pollutants. During the irrigation periods, the rise in the level of pollutant concentrations running through the settlement decreased clearly. Based on the study, we concluded that the Shuhai purified the canal water clearly and considered that it would necessary to implement the advanced waste water treatment system and the sludge recycling system.

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This study dealt with the state water quality conditions of irrigation ponds and the relationships between irrigation ponds characteristics and water quality. We conducted statistical analysis on 556 irrigation ponds. These ponds are located in the urbanized rural areas and flat rural areas throughout the country, and some water qualities such as pH, concentration of chemical oxygen demand (COD), total phosphorus (T-P) and total nitrogen (T-N), etc. were examined. Strong correlations were not obtained between the indices of irrigation ponds characteristics and water qualities. We conducted similar analysis on the categorized four groups of irrigation ponds characterized by hydraulic features and meteorological characteristics. In this analysis high relationships were found among the water qualities in each group of ponds. We also studied effluent nitrogen load on the basins, and found the fact that major constituent of effluent load is diffuse non-point source N. And relative intensity which affects water quality was investigated by the multiple regression analysis and parallel boxplots analysis.

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There are some studies of watering management of plant cultured in greenhouse horticulture field. It's available past technologies are limited. Accordingly, we investigated the conditions of watering management of the growth type of typical plant, chrysanthemum growing by lighting. The retarding culture of setting in spring, summer and autumn were carried out by hand watering by means of hose for the initial growth period, and their frequencies of watering were different in the growth type of them. After the initial growth period, the watering management in the period of setting culture differed in the different growth types. Because each growth type has different change of the stage of growth and control of growth. On the second harvest cultivation, it made clear that the watering management was different in each growth type in order to grow up sprouting of post-harvest stock of setting culture in summer.

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Muskmelons are in different demands for every stage of growth. Muskmelons are the typical crop plant cultured in greenhouse horticulture field in response to change of water. However, a few investigations about watering control technologies are found and the past available technologies are limited. So that, watering is carried out by sense and experience of farmer. To fulfill the function of irrigation system of greenhouse horticulture field, we have to make clear the conditions of muskmelons' irrigation. In this study, the conditions of amount of each irrigation, interval and actual management of soil-moisture during 90 days from setting to harvesting were investigated.

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The conditions of sun light and soil temperature in the plot, where white clover (Trifolium repens L.) is growing for prevention of weeds, were investigated and the suitable method for white clover growing was discussed.
The intensity of sun light and range of soil temperature under the canopy reduced from April to August when the plot was fully covered with white clover. As the results, weed growing was prevented in summer. However, some types of weed such as tall fleabane and annual sowthistle were found to germinate from October to November and hibernate the winter in the form of a rosette. According to this investigation, it was concluded that the seeding of white clover should be made from September to October with more than 100 plants/m² density in order to cover the ground surface with the plant in April for the prevention of weed growing in next summer.
These results are important for effective weed control to reduce the weeding labor.

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A change in soil bulk density followed by surge flow irrigation and its effects on irrigation efficiencies were examined for lessive which is one of the representative soil in the Three River Plain, China. The change in soil bulk densities was most remarkable at the soil surface and depended greatly on the bulk density before the surge flow irrigation. In the case of continuous flow, constants describing infiltration capacity, K and a, were decreased with the increase in the soil bulk density before the surge irrigation. Also, effects of surge flow on lowering infiltration significantly decreased with increasing in the soil bulk density. By using the simulation model, it was quantitatively revealed that ridge length and cycle ratio which are important factors on designing the surge flow system are closely connected to the soil bulk density before the surge flow irrigation.

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Although levee trees are well known as an element of traditional rural landscape, they are going to be disappeared in modem agriculture. In order to look for the way of its conservation, geographical conditions and farmers' intentions about levee trees are investigated in Kameoka City, Kyoto Pref and Nagahama City, Shiga Pref.
The result is that levee tites have been used not only for drying rice plant but also for protecting of levee or irrigation canal according to its environment such as geographical conditions. In order to conserve levee trees, therefore we need the follows:(1) to stipulate that levee trees are traditional rural landscape.(2) to avoid large-scale changes of geographical conditions by the standardized farm land consolidation, in order for levee trees to have functions such as protections of levee or irrigation canal etc. which levee trees have had until now.(3) to consider the reasonable arrangement and shape of levee trees so that levee trees may not hinder farming works.

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[in Japanese]

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