The distribution of the shear stress was same both laminar flow and turbulent flow in the case of one-dimensional uniform flow that the velocity varies only in a vertical direction. In this study, the shear stresses of laminar flow in the case of two-dimensional uniform flow, that the velocity varies in both vertical and transverse directions, were obtained theoretically in a rectangular open channel. In order to examine to what extent the solutions were conformed to two-dimensional turbulent flow, the comparisons between the theoretical solutions of boundary shear stress and the past experimental results of them in smooth open channel turbulent flow were done. As a result, it was shown that the mean shear stress on the side wall and channel bed accord with the experimental results well.

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This study deals with practical and reliable method to calculate interior boundary conditions. Interior boundary conditions are compatibility conditions connecting two subcritical flows between which a supercritical flow or a hydraulic structure exists. The Preissmann scheme, an implicit finite difference scheme, is widely used for an open channel unsteady flow calculation because of no restrictions on Δx and Δt. Interior boundary conditions, which are essential for the Preissmann scheme to calculate a partially supercritical flow, are sometimes very complex. In such a case, it is difficult for the ordinary Newton-Raphson method to obtain a convergent solution.
In this study, four interior boundary conditions corresponding to typical hydraulic structures were used. The mechanism of non-convergency was analyzed and means were then sought to improve numerical convergency. For this purpose, a smooth curve was used to replace a complex discharge equation in interior boundary conditions, and several relaxation rates in the Newton-Raphson iteration procedure were applied. These means in combination were more effective for improving stability and convergency without reducing accuracy.

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Characteristics of hydraulic jump and wave at the bed protection structures of abrupt drop provided with the artificial roughness (strip and block type) were analyzed experimentally.
The occurrence conditions of hydraulic jump were obtained by considering the flow resistance factors by roughness and the pressure head at the drop. The results were verified by tests. The roughness arrangement effective for reducing the tailwater depth was found to be at the relative spacing, SL/SK, of 7-10 for strip roughness, and the relative roughness concentration, SA/ F, of 15-20 for block roughness.
The relative length of roller (L_r/h₁) increases linearly with the inflow Froude number (F₁), and strip roughness and block roughness were found to reduce the length of the roller in jump by 40% and 30% respectively in comparison with smooth bed jumps.
The velocity distribution in jump over roughness is not similar. In the boundary layer, velocity distribution in correlated by the power law, but the exponent varied from 1/8 to 1/2.In the free-mixing region, the velocity distribution agrees well with the corresponding portion of the curve of the plane turbulent wall jet on smooth walls.
The decay of the maximum velocity in jump is more rapid, and the growth of the boundary layer thickness is faster when compared with the corresponding smooth bed jump.
It was found that the occurrence condition and quantities of interest, such as the coordinates of the wave crest, the plunging point, or the length of bottom separation of the waves agree approximately with the wave at abrupt drops.

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The series tank model is developed for daily NO₃-N loads, which is one of nutrient, from a forest. Daily NO₃-N loads are calculated by the model which is applied to two kinds of method. One is LQ method. This time, four types of LQ equation are used. These are two kinds of straight type (L=aQ^b) and two kinds of curved type (L=aQ^b. The other is C.C. method and model uses the series tank model as follows. The series tank has runoff coefficients and coefficients which can determine NO₃-N concentration for each tank's runoff holes. In order to determine unknown model parameters, the value of x₂ error estimated standard is used.
Two types of method which are used to evaluate model's errors. One is the balance error ratio (%) to estimate error of difference for a term and the relative error ratio (%) to estimate error of individual variety.
From the investigation the author derived the results as follows.
1) LQ methods can estimate daily NO₃-N loads within less than-5 % of the balance error ratio and about 20 % of relative error ratio.
2) If seasonal changes of NO₃-N concentration is introduced in C.C. method, it can estimate within-5% of the balance error ratio and 20% of the relative error ratio.
3) Analyzed loads are influenced greatly by estimated discharge. Hence it is necessary how precision the runoff discharge can be estimated.
4) In a forest, if the balance error ratio of within ±10% can be permitted, LQ equations determined with the eleven data which can observed once a month can estimate daily NO₃-N loads enough.

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The analysis method is presented herein to study profile of sand dunes on the basis of our non-equilibrium bed load formula which has been derived in the previous report and is called'K·T model' in this paper. The non-equilibrium parameter of the model is derived by comparing the bed load transport rate obtained by the K·T model with that on wavy bed indicated by single sinewaves. The equation presented by Fredsoe for calculation of dune profile is modified using the K·T model and the above parameter. The dune profiles obtained by this analysis showed close agreement with those observed in movable bed experiments. The phase lag of the bed load transport rate on the dunes is estimated by the comparison of those dune profiles.

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The relation between stress and strain of compacted sand and gravel and tuff are made an experiment with drained triaxial compression test. From the results, the modulus of deformation E₅₀ of densely compacted specimen was made small by looseness with setting errors. For the correction of the errors, it is reasonable that modulus of deformation is obtained from the maximum gradient of stress-strain curve.
The intercept (apparent cohesion) τ_0s and internal friction angle φ_sat constant axial strain ε are functions of ε.τ_0s attains its maximum value at small strain and decreased rapidly with the increment of ε. On the other hand, φ_s increases gradually and keeps the value greater than φ in wide range of ε. From these results, the usual method in which only φ is used for sand and gravel is on the safe side for wide range of ε.

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Since the easily decomposable organic matter is necessary for denitrification by denitrifying bacteria, in the previous study dextrose was mixed in the incoming water to make a C/N ratio of 12. But the secondary treated water from the sewage treatment plant includes little organic matter, hence a new experiment was carried on with the same conditions of the previous study but without carbon source.
The analytical results of purification rate, adsorption rate and denitrification rate by using the data of two experiments (incoming water with and without dextrose) are summarized as follows:
1. The effective factors for purification rate were carbon source, the kind of soil, N concentration of the incoming water and soil water condition. The mean purification rate without dextrose was 27%, which was 15% less than that with dextrose.
2. The kind of soil, N concentration and soil water condition have an effect on adsorption rate.
3. For denitrification rate, carbon source was the effective factor, and the kind of soil and N concentration seems to be significant. The mean denitrification rate without dextrose was 21%, less than 16% compared with the mean value of mixing dextrose.

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In the previous study, it was shown that purification rate and denitrification rate were influenced by different kinds of soil, carbon source and nitrogen concentration in waste water.
But the amount of purification had reduced after 30-40 days from the beginning of the experiments. So the experiment was further repeated in which waste water was supplied intermittently (30 days irrigated-30 days non-irrigated-30 days irrigated) in order to discover the influence of intermittent irrigation for adsorption of soil and the number of denitrifying bacteria.
In this experiment, five factors were changed, i.e., irrigation method (continuous and intermittent), kind of soil (clay loam and Kuroboku soil), carbon source (mixed and unmixed), N-concentration (20 and 100mg/l) and soil water condition (saturated and unsaturated).
The result of this experiment showed that the purification capacity had recovered by decreasing of adsorption amount of soil and increasing of denitrifying bacteria after the resumption of irrigation.
The analytical results of purification rate, adsorption rate and denitrification rate by analysis of variance are summarized as follows:
1. The effective factors for purification rate were the kind of soil, carbon source, N-concentration of incoming water and irrigation method. The mean purification rate of intermittent irrigation was 49%, which had increased 8% more than continuous irrigation.
2. For adsorption rate, the interaction between the kind of soil and N-concentration was shown.
3. All five factors were effective for denitrification rate. The mean denitrification rate of intermittent irrigation was 39%, 8% higher than continuous irrigation.

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The consolidation characteristics of slurry clay with initial water content of 300 to 1000% were investigated using centrifugal model tests and numerical analysis. The value of t₉₀/t₅₀ for slurry clay consolidation increased with increasing compressive strain, while the value in theory decreases with increasing compressive strain under the constant coefficient of consolidation, whenself weight effects are neglected and the change of clay layer thickness is considered.
The permeability-volume ratio and volume ratio-effective stress relationships were found to be linear in logarithmic scale for slurry clay, while these relationships for natural clay deposits are linear in semi-logarithmic scale. A good agreement was observed for the slurry clay between the settlement behaviour measured in the centrifugal model tests and predicted from numerical analysis based on the permeability-volume ratio and volume ratio-effective stress relationships in the logarithmic scale. The volume ratio-effective stress relationship of slurry clay is usually determined by using the relationship between the water content and the effective stress after the centrifugal consolidation test. It was also indicated that the volume ratio-effective stress relationship can be obtained from the amount of settlement in the centrifugal consolidation tests under different acceleration levels or in the self-weight consolidation tests under different thickness of clay layer as well.

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A runoff model that is based on runoff function of linear concentration and storage is built and proved to be useful in modelling the rainfall-runoff relations for small agricultural watersheds.
The features of the model and the results of its application to several small agricultural watersheds are as follows.
(1) Assuming the linearity of runoff process, instantaneous unit hydrographs are derived for typical 7 concentration patterns, that is, even, and increasing and decreasing rate with time to the lst-3rd power. Then t-hour unit hydrographs are formulated where t-hour is the duration of unit rainfall.
(2) Total runoff is assumed to consist of 3 components, that is, surface runoff, interflow and baseflow, to each of which a runoff function with proper parameters is assigned.
(3) Effective rainfall to surface runoff is separated using φ index and that to interflow is evaluated based on the formula in which lost rainfall is related to rainfall input and a measure of saturation on the watershed. It has 2 parameters which are mode of rainfall loss and upper limit of loss, respectively.
(4) Tests for the model to reproduce runoff hydrographs were carried out using rainfall-runoff data where parameters were approximately fitted on computer monitor and then depletion constants of surface runoff and interflow were optimized by 2 variate optimization procedure, whereas the optimal effective rainfall to surface runoff was selected for minimum error among the effective rainfalls with optimal depletion constants.
(5) The tests show that goodness of fit is 0.2-0.4 mm/h in standard error and 10-20% in relative error, which proves fairly good performance of the model.
(6) Problems of model performance should be discussed in the future as to concentration patterns and mode of rainfall loss, and an elaboration will also be needed to involve nonlinearity of runoff process for a better reproduction of hydrographs.

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Modelling is based on the equations of water motion and heat transport which are densimetrically coupled via the equation of state. The heat transport equation expressed in terms of water temperature includes the internal absorption of short wave solar radiation. Since these equations lack expression of the vertical free convection by which a surface layer of limited depth is to be isothermal, a reasonable technique is employed to make the model reproduce the effect of such a convection without destroying the mechanism of the forced convection that can be expressed by the equations. Spatial integration for building the 3-D numerical model is implemented by consistently using the Galerkin approximation in all space coordinates with the basis functions: the 2-D linear and Chebyshev polynomial functions in the horizontal and vertical, respectively. Time is stepwise marched with a combined use of the Kawachi and forward time schemes of explicit type. The capability of the model is tested by simulating different two thermally stratified flows in a hypothetical reservoir and a real irrigation tank, and comparing the latter simulation to the data available. The results show that in computational practice the model is capable of satisfactorily reproducing the 3-D structures of thermal stratification.

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Underdrainage is indispensable in promoting the development of large farming lands and multipurpose paddy fields. Recently, underdrains have been constructed extensively.
Exploratory digging and physical tests were undertaken to analyze the drainage mechanism and the efficiency of earthen (clay) pipes, known to have a relatively long durability and good drainage effects as underdrains. They were set in the fields for about 25-30 years. When exploratory digging of underground drainage conduits was carried out at farming plots, itwas found that the coal cinder and the rice straw used as covering materials, which were setin paddy fields and are closely associated with the draining capability of underdrains had lost their effectiveness. As a result, some soil particles migrated and were deposited in the pipes. However, judging from the condition of the accumulated soil, the combination of crack shapes on the soillayer and the smooth passage of water through conduits, buried earthen pipes could remain free from significant changes with time (approximately 30 years). Based on the porosity and water permeability coefficient, the pipes had achieved effective drainage of water.
In estimating the durability of the clay pipe in the fields, the absorptive and drainage functions were considered to have deteriorated and the draining function of the underdrain was considered ineffective, when the deposited soil at the outlet occupied 50% of the cross-sectional area of the pipe. The period during which the deposited soil amounted to less than 50% of the crosssectional area of the pipe was then defined as the durability period of the underdrainage pipes. All the layers of the deposited soil in the drain pipes were measured one by one and the correlation graph, relating time lapse to soil accumulation, was prepared to calculate the efficiency of the clay pipes. According to these analyses, the durability of the underdrain pipein the fields was estimated to be abaut 50 years.

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In order to elucidate the relationship between the amount of suspended soil and the discharge of runoff within a certain period of time, an observation of the amount transported from reclaimed farmland was made. The peak of the density of suspended soil and that of discharge occur at almost the same time when the source of suspended soil is distributed throughout the basin. Their relationship is expressed in a parabolic curve. Newly reclaimed farmland is likely to be unstable because the differential settlement and the slope failure are common, and at the same time, there is a strong probability of large-scale erosion. The result has revealed that the erosion of land surfaces in pineapple fields is constantly underway. And the source of suspended soil is the place where unlined canals or branch roads are laid.

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In this paper, a new method for constructing the master recession curve is proposed. Moreover the proposed method is applied to nine study areas in eastern Japan that there are not any regulation or diversion structures in the reaches above the measurement station. Then, the recession constants were related to droughty discharge and rainfall from the practical point of view.
The results indicate that the new method is both objective and useful and that the reciprocal of recession constant for a given study area gives an total index of low flow.

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[in Japanese]

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