The object of this experimental study is to clarify the characteristics of water flow during infiltration in artificially layered slopes having a banked soil layer, a buried plant layer and a natural subsoil. Masa sandy loam, natural plants and gravel (separated from the Masa sandy loam) were used as experimental materials. In the infiltration experiment, the advancing wet front apparently stopped at the interface between the top Masa sandy loam and the second plant/gravel layer and lateral water flow occured along the interface.
The refraction law of saturated water flow was extended to an unsaturated condition and applied to the above lateral water flow at the interface taking note of its relationship to the incidence angle, the refraction angle and the hydraulic conductivities. Eventually, it became clear that, when fine materials overlay coarse materials and the interface is inclined, such an extreme refraction possible as either the angle of incidence or the refraction angle becomes 90 degrees is. The apparent stop of the wet front could be attributed to the extreme refraction of the water flow.
The relationship between the partial type water flow and the refractive type water flow was suggested conceptually, pointing out the importance of these water flow in the field.

View full abstract

This paper deals with the characteristics of model parameters, P, K and T_l of the storage function model defined by the following equations,
_??_
in which, S_l is the hypothetical storage depth of rain wa ter over a watershed considering the time lag T_l between rainfall excess r_e and flood runoff discharge Q.
First, the meanings of these parameters are examined by considering the similarity between this model and the kinematic runoff model. Moreover, the expressions for K and T_l are modified utilizing the Hack's law for engineering convenience.
Next, the statistical characteristics of these parameters obtained by applying a mathematical optimization technique of the 89 flood data in 22 watersheds are discussed through examination of the probability distribution of a parameter, and through comparisons between observed and simulated hydrographs and/or peak discharges. The usefulness of the modified expressions for K and T_l mentioned above, are also examined.

View full abstract

An investigation was made to estimate soil surface evaporation separately from evapotranspiration. Monteith's equation was used in this study.
A two-reservoir soil moisture model was adopted. Transpiration was set equal to the potential rate until soil water potential reached-0.063 MPa (pF 2.8): beyond which the ratio of actual tanspiration to potential transpiration decreases with decreasing soil moisture potential. The model for soil evaporation was also divided into a potential rate stage limited by the available energy, and a non potential rate stage regulated by soil resistance.
The results were in good agreement with the evapotranspiration estimated by the Bowen ratio method.

View full abstract

The dry surface layer in sandy soil appears to be due to the amount of solar radiation during the summer season.
In addition, the soil moisture distribution is uniformed in the wet zone of lower layer located just bellow the dry surface layer. The two-layer system of soil moisture content is, therefore, formed in sandy soil.
The diurnal temperature variations in the soil are remarkably affected by the formation of the dry surface layer, because the thermophysical characteristics are changed with the moisture content of the soil.
In this paper, the two-layer sand model was applied for analyzing the diurnal temperature variations and the results were ascertained by field tests.
The results obtained are summarized as follows.
1) The theoretical treatment was proposed for evaluating the thermophysical characteristics of the dry surface layer due to the two-layer model.
2) It was clarified by numerical analysis and field tests that the two-layer model was useful for analyzing the diurnal temperature variations in sandy soil with a dried surface.
3) The quantitative interpretations were tried for characteristics on the effect of heat insulation and the damping factor of temperature amplitude caused by the dried zone in sandy soil surface.

View full abstract

In order to estimate the existing modes of interparticle linkage in clay suspension, a calculation technique based on both the double layer theory and the hetero-coagulation theory was developed. The probability of the existence of FF (face to face) linkage, EF (edge to face) linkage and EE (edge to edge) linkage was estimated for different salt concentrations and for different pH levels.
FF linkage was expected to be present in high salt concentrations (>1.0 mol/dm³ for monovalent ion, >0.3 mol/dm³ for divalent ion), no linkage was expected at intermediate salt concentrations (0.05 to 0.5 mol/dm³ for monovalent ion, 0.02 to 0.2 mol/dm3 for divalent ion) and EE +EF linkages were expected to be present in low salt concentrations (<0.05 mol/dm³ for monovalent ion, <0.02 mol/dm³ for divalent ion), respectively.
At high pH (>pH 9.2), no linkage was expected to exist, so the suspension should be dispersed. As pH decreased below pH 9. 2, EE and EF linkages increased in number, therefore, the system was considered to be flocculated.
As mentioned above, this technique enabled us to estimate the dispersion-flocculation behavior of the clay suspension at any given condition of equilibrium solution.

View full abstract

The dispersion-flocculation behavior and the rheological properties of bentonite-water systems were measured at different valences and concentrations of added salts. In addition, the cation composition of the equilibrium solution was measured.
The measured data of the equilibrium solution were used to estimate the probability of the presence of each interparticle linkage mode, and the experimental results were examined in relation to the estimated presence of the interparticle linkage modes. The results were as follows:
1. In the sedimentation measurements, the aggregated state was observed in the pressence of FF (face to face) linkage, the flocculated state was observed in the presence of EE (edge to edge) linkage+EF (edge to face) linkage and the dispersed state was observed in the presence of no linkage, respectively.
2. The >20 pm particle size fraction, the 10-20μm particle fraction and the <10μm particle fraction were found to dominate in the presence of FF linkage, EE+EF linkage and no linkage, respectively.
3. The plastic viscosity and the parameters of rigidity (extrapolated shear stress and residual strength) showed their minimum values in the presence of FF linkage. The plastic viscosity showed its maximum value in the no linkage condition. On the other hand, the parameters of rigidity were found to increase in the presence of EE-I-EF linkage.
As mentioned above, the experimental observations were satisfactorily explained by the concept of the existing mode of interparticle linkage for both the NaC1 and CaCl₂ added samples. The technique described in the former paper is believed to be useful in the semi-quantitative understanding of the dispersion-flocculation behavior and the rheological properties of the bentonite-water systems.

View full abstract

The dispersion-flocculation behavior and the rheological properties of bentonite-water systems were measured on samples adjusted at different pH levels. The cation composition of equilibrium solution was also analyzed. The technique described in the previous paper was applied to estimste the probability of the existence of each interparticle linkage mode. The experimental results were interpreted in relation to the estimated existence of the particle linkage moles. The results were as follows:
1. In the sedimentation measurements, no linkage, EE (edge to edge) +EF (edge to face) linkage, EF linkage only were expected to exist at the ranges of >pH 9. 2, from pH 6. 7 to pH 9. 2 and <pH 6. 7, respectively. The impossibility of FF (face to face) linkage was expected.
2. With no linkage, the systems showed the dispersed state. In the presence of EE-FEF linkage, the systems showed flocculation.
3. The particle size fractions of <2μm, the 2-10μm and the 10-20μm dominated in the presence of no linkage (>pH 9. 2), EE-FEF linkage (between pHs 6. 7 to 8. 9) and EE linkage (<pH 6), respectively.
4. The plastic viscosity showed its maximum value under the conditions of no linkages of any kind (>pH 9. 2), and decreased adruptly between pHs of 9 and 7 with the appearance of EF linkage. The parameters of rigidity showed their maximum value in the presence of EF linkage (<pH 7), and decreased significantly with the decrease of the number of EF linkages.
In conclusion, experimental results were explained successfully by the concept of the expected existing modes of interparticle linkages. Therefore, the double layer theory and the hetero-coagulation theory applied in this manner were revealed to be useful in the semi-quantitative understanding of the dispersion-flocculation behavior and the rheological properties of bentonite water systems.

View full abstract

It has taken about 30 years to measure soil water and density using gamma-ray attenuation. During this time, more accurate and precise, measurements were needed and error analyses were also promoted. The representations were by Fritton and Gardner et al.
Erros are divided into those of random and systematic. Major systematic errors in this measuring system, when using a narrow beam-attenuation equation, are caused by both count errors in counting instruments and the non-narrow effect by gamma beams, Lbut cannot separate in attenuation experiments. The last cause which can hardly be seen in many related paper is difficult to estimate. However, through the accordance of resolving times between attenuation experiments proP4sed here and an inverse square low experiment, it can be neglected if geometry of the detection instruments is configured as 120 mm for the source-detector distance (SDD), 11 mm for source-side distance (SSD), over 40 mm for the detector-side distance (DSD) in hole-slits with 4 mm diameter. The other is estimated by the count error estimation of twin-resolving time system, a different kind of efficiency equation of count loss from the usual. Especially, time built-up factor B_T was introduced to estimate all errors by observed counts rates in one.
And twin-resolving time is decided by attenuation experiments for lucite plates using known linear absorption coefficients and material thickness under assured geometrical condition to get 7.48μ sec for bipolar semi-Gaussian pulses.
Bulk densities of soil and water are estimated using this analytical resolving time and compared with gravimetric values. The results are satisfactory, so, this proposed method is believed to over come the faults of the method by Fritton.

View full abstract

This work deals with the effect of the head difference between inundation and drainage levels (DH) and initial void ratio of puddled soils (e₀) on the settlement and permeability of puddled soils. Based on the observation results of lotus fields, experimental conditions were determined for laboratory experiments. Main results are as follows:
1) An increase in both the DH and e₀ brought about an enlargement of the settlement of puddled soils. However, their respective mechanisms must be taken account. An increase in the DH causes an enlargement of the seepage force, but on changing e₀, it is necessary to consider the difference of settling forms (free settling, coagulation settling and self-weight consolidation).
2) In our experimental conditions, it was affirmed by particle-size analysis that the effect of free settling can be disregarded. The inferior limit void ratio of coagulation settling for this lotus soil is suggested to be about 5, by the results of settlement near the surface of the soil where the load is too small to be taken into account.
3) Corresponding to settlement process of puddled soils, the relationship takes the form of the “S” type, between the settlement velocity and time, and the form of the “L” type, between the drainage rate and time in semilogarithmic coordinate. Inspite of the enlargement of the settlement, the duration of the settlement was found to be shortened for the increase in e₀, and seldom changed for various of DH. Moreover, the average hydraulic conductivity in the direction of height at the end of the experiments increases with e₀, but the relationship between e₀ and log k is nonlinear.

View full abstract

As simulated daily rainfall sequences become popular in the study of water utilization, the establishment of a method to simulate rainfall conveniently and practically is highly desirable.
Essentially, the phenomenon of rainfall could be considered in itself to be the process of a physical mechanism unfolding in the atmosphere which contributes to water balance in macroscopic terms. Because this is important, this paper proposes a kind of tank model for rainfall simulation, which can maintain an even water level despite evaporation, the transfer of water vapour from the adjacent atmosphere, and rainfall.
A number of devices were used in the tank model. One distinctive device was that the height of the hole in the tank, which mainly controls the influx of rainfall, could be raised and lowered in accordance with a random number and with seasonal fluctuations. Because of this, the tank model can provide an intermittent rainfall sequence which can be regarded as realistic. The results simulated by the tank model for a few particular areas are effective even in representing regional rainfall characteristics.
The question of how to estimate the parameters of the tank model, which could be decided mechanically depending upon various atmospheric conditions, still remain.
The method proposed in this paper could be regarded as having good adaptability for purposes of simulating daily rainfall sequences.

View full abstract

The use of a buffer pond in the cylinder intake rate test has been supposed to minimize horizontal seepage below the bottom of the cylinder. This paper discusses the influence of horizontal seepage on the test results and examines the effect of the buffer pond.
Finite element simulations for the tests with the cylinders driven 20cm deep were carried out with 6 different soils, following which the results were compared with those of one-dimensional infiltration.
The discussion leads to the following conclusions:
1. No buffer pond is necessary for soils whose coefficient of permeability is smaller than 5×10^-4 cm/s.
2. For soils whose coefficient of permeability is greater than 5×10^-4 cm/s,
a) As a 10 cm wide buffer pond is not effective in minimizing horizontal seepage, a wider buffer pond is recommended.
b) A buffer pond made of a frame driven into the soil layer is not effective in minimizing horizontal seepage.
c) The log (time)-log (cumulatve infiltration) data in which the cumulative infiltration is smaller than 1.5 D_max should be employed for obtaining the intake constants. D_max can be obtained from the next equation:
D_max=200 [(Saturated volumetric water content?Initial volumetric water content)](mm)

View full abstract

In this paper, we propose a method of calculation to predict quantitatively the onshoreoffshore sand movement and the wave deformation on a wave-current coexistent system by making certain assumptions about a river mouth. Results calculated by this method were compared with experimental data obtained for the coexistent system in a two-dimensional wave tank.
The distribution of wave height on the breaker zone, which was required for calculation of the sand transport rate, was analyzed by the use of a BORE MODEL. The model was established on the assumption that the value of energy loss in a breaking wave was equivalent to one of bore. The wave height distribution on the offshore side of the breaking point was presumed for the third order approximate solution of Stokian waves on the coexistent system. The breaking point was obtained by use of Miche's criteria equation.
The local sand transport rate could be calculated by use of a POWER MODEL. The predominant direction of sand transport was recognized using a judgment equation derived from the experimental results.
Using the calculated distributions of the wave height and the sand transport rate, the transformation of sea and river bottom was estimated on the basis of the equation of continuity of the sand transport rate.
The results obtained by these analytical methods agreed well with the experimental results.

View full abstract

The time marching approach, using waterhammer analysis and giving steady flows in pipelines as the asymptote of unsteady flows, can be improved to reduce the number of iterations usually required for convergence to about a one-hundredth. The proposed method using a simple calculation algorithm is useful for steady flow analysis in large scale pipelines.
The main points obtained are as follows:
1. Rapid convergence to a steady flow can be attained by solving an optimization problem as follows: The objective function is the spectral redius of a coefficient matrix, which is included in a state equation composed of both perturbed characteristic finite-difference equations and linearized boundary conditions. The spectral radius can be minimized through varying system parameters to imaginary ones provided that the energy and mass conservation equations are kept constant in the real and imaginary pipelines. Though many optimization parameters are required in the original problem, the author proposes a simple method with only one optimization parameter, which can approximate the optimal solution with high accuracy.
2. Handy method of dynamically controlling the time step-size, i. e., the optimization parameter without calculating the Jacobian matrix can be introduced.
3. Simple calculation algorithm, estimating the Darcy-Weishach's friction factors with the Colebrook-White formulas, can be shown.

View full abstract

An experimental study on the conditions for occurrence and the scouring characteristics of hydraulic jumps during abrupt drops, namely the A jump, Wave and B jumps, was done.
First, the cause of the wave generation was investigated, and it was found that the magnitude of the pressure head on the downstream side of the drop had a large affect on the jump form. The occurrence conditians for a variety of jump forms were obtained by examining the characteristics of the pressure head at the drop. The results were verified by tests. The ratio h₂/h₁ (h₁, h₂: the up and downstream depth of the jump, respectively) at the boundary was affected largely by D_r (D_r=D/h₁, D: the height of drop) and the Fr number of the jet flow and the occurrence range of the wave narrowed with the decrease of D_r and F_r. The wave free drop shape was evidenced.
The following scouring characteristics were obtained: the A jump hardly scoured its downstream bed: the wave significantly scoured the bed more than the B jump except when there was no apron; the scour became large when the wave was exchangedt a sloping jump with the same stream conditions.
This test deduced the following ; provided that the bed is paved as far as the point where the wave has the largest bed velocity, the wave is not necessarily a disadvantage.
An approximate method for estimating the apron length to prevent scouring was demonstrated.

View full abstract