The authors proved, in the previous study, that both expansion and contraction of sticky soils containing much clay and organic colloid in swampy rice field are remarkably large. Therefore, fi ssures are easily formed on the surface in arid and draining seasons and with lowering of ground water table.
The authors made an experimental study on the influence of the fissure growth on water loss, especially clue to evaporation and percolation. As a result of the study it was found that evaporation increases with the enlargement of the surfacearea and the gradient of the vapour tension, and so the period of time required in drying is greatly shortened. On the other hand, percolation increases
suddenly with the enlargement of fissures and with the increase of their number. However, much water and a long time are required for the disappearance of such fissures.

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In this experiment the authors indicate, using Wagner's pots, that physical and chemicat properties of paddy soil are closely related to plant growth and vertical percolation.
Vertical percolation has an effect of decreasing the concentration of reducing substances and increasing the value of oxidation-recuction potential. The root of rice plant accelerates leaching of iron and calcium compounds and increases the size of water-stable aggregates of soil. The yield in nonpercolation plot is inferior to that in percolation plot. The difference between the two plots is due to changes in soil properties.

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This study aimed at the principles underlying the infiltration of water into dry sand and the permeability in the ensuing percolation stage after the wetting front has reached the bottom of sand column. The relations between the rate of water entry and time were examined by the equation of infiltration:
q=K_I (1+H/y) where, q: the rate of water entry in cm/sec; H=h₀+h_K; h₀: the depth of top water in cm; h_K: pressure deficiency of the water film at the wetting front in cm; y: the depth of wetting front below surface in cm.
Air-dry sand and glass particles were packed to uniform apparent density in transparent tubes, 5 cni in diameter.
in the infiltration stage, a constant depth of water was maintained at the top of soil column by means of a Mariotte tube and the rate of water entry (q) was measured. The depth of wetting front below surfa'ce (y) was also recorded. In the ensuing percolation stage, the rate of flow and the distribution. of hydraulic pressure were measured.
From these data the rate of water entry (q) was plotted as a function of the length of infiltration zone (y). Then the permeability coefficient of infiltration stage (K_I) and the pressure deficiency of the water films at the front of infiltration (h_K) were found. Results:
1. Water saturation ratio during infiltration reached nearly 100% and did not vary with depth.
2. The equation of infiltration q=K_I (1+H/y) agreed with the experimental data.
3. Kp, coefficient of water per eability in the second stage (percolation), was equal to K1, that in the first stage (infiltration).
4. The value of air pressure in front of the wetting front was nearly equal to the atmospheric pressure.

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From the second law of motion, the author has derived equations of the viscous flow of incompressible fluids through porous media from macroscopic point of view, under the assumption that the fundamental hydrodynamic relations between stress and rate-of-strain for viscous incompressible fluids are also satisfied by the fluids in pores and that the porous media are saturated, isotropic, and geometrically stable at a constant temperature.
An important point for consideration of macroscopic motion is its relationship tomicroscopic one. Such macroscopic quantities as velocity, pressure, etc. are, therefore, directly defined from the' corresponding microscopic ones from the standpoint that such physical quantities should be invariant in transformation; and the quantities thus defined are supposed to be analytical throughout the space through proper conception in order to render the subject amenable to exact mathematical treatment, though the microscopic ones defined only within the effective pores but not within the solid particles.
The equations of macroscopic motion derived on the basis of the above considerations involve inertia terms which have never been derived from the Navier-Stokes equation, and drag force terms by which the concept of drag in percolation flow is to be physically clarified ; but, on the other hand, they do not contain the so-called macroscopic viscous term, which cannot exist essentially, as shown in this paper. Moreover, it should be noted that the quite natural con equence that the drag force consists of viscous drag and pressure drag as shown here has never been verified theoretically and has been recognized even incorrectly, and a deeper exploration will result in more theoretical derivations of Darcy's or Forchheimer's law and, necessarily, also of “permeability”, clearing up the role of these in the fundamental equations.

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Bentonite is used for various purposes in agricultural engineering works to control excessive percolation through soils, and this effect is due chiefly to its swelling property.
We made bentonite absorb various electrolytic solutions of different concentrations, and we made clear the difference of the quantity of swelling by each solution by experiment. In addition, we considered the results of the experiment from electrolytic dissociation, ion-radius and ionization tendency, and we carried out a comparative experiment as to kaolinite which has mineralogical properties quite different from bentonite. According to the experiment, in case a few cations are solved in solution, the degree of the swelling of bentonite is controlled by the concentration of the solution and is dominantly affected by the number of cations.
On the contrary, in case a great number of cations exist in the solution, the swelling quantity of bentonite is remarkably controlled by ion-radius and ionization tendency rather than by elctolyte dissociation: swelling in more suppressed in case of smaller ion-radius and weaker ionization tendency.
In this case, therefore, hydration of cations seems to have the function of dehydration inversely. On the other hand, the swelling of kaolinite, which has a fixed lattice structure, however, is generally little, and it was made clear that its swelling quantity is hardly influenced by the concentration of solution. Consequently, it is considered by this experiment that the difference between kaolinite (external swelling only) and bentonite (both external and internal swelling corresponding to its expanding-lattice structure) in swelling is due to inter-layer swelling.

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We have been studying swelling properties of bentonite in electrolytic solutions of various concentrations in order to make clear the properties that cause its swelling. According to the former report, it was known that the swelling quantity of bentonite differs with the kind of solutions, their concentration, and with the method of treatment in case of the same concentration. In addition, in order to make clear the relation among the above properties from the viewpoint of crystal structure of bentonite (montmorillonite), we investigated those data in detail by X-ray diffraction, X-ray photograph and chemical analysis.
Consequently, we knew that inter-micellar swelling (swelling between particles) is far greater than intra-micellar swelling (swelling between crystal latices) and we computed quantitatively the difference between intra-micellar swelling and inter-micellar swelling. From these results, we made clear that intermicellar swelling changed sensitively with the concentration of solution and intra-micellar swelling is hardly influenced by concentration excepting the case of very thick solutions, and even when the swelling was suppressed by adsorption of thick solutions, intra-micellar swelling was restored and swelling quantity was more or less recovered when it was dried and treated with distilled water.

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Groundwater is a very important source of irrigation and city, water supply. Scientific researches of available discharge of groundwater are indispensable in their exploitation. The velocity and direction of groundwater stream are very difficult to fathom. The methods hitherto used for this purpose are as follows:
(i) measurement of the gradient of groundwater level using pipes or wells;
(ii) tracing of groundwater labeled with salt, fluorescent substances, or radioisotope solution;
(iii) electrical or seismic exploration.
The method (ii) is very common but several hours are required even in the measurement at only one point.
The author studied a new method of the measurement of the velocity and direction of groundwater stream by means of porous pipes driven in the ground, and found that this method could save much time.
(a) The relation between U₂ (velocity of stream in the inside of the pipe) and U₂ (that in the outside of the pipe) was analyzed as follows:
U₂=U₁2_k2/k₁+k₂=2U (k₂≥k₁)
k₂=equivalent of the coefficient of permeability corresponding to the seepage through the holes of the pipe,
k₁=coefficient of permeability of the ground.
(b) The direction of groundwater stream in the inside of the pipe is perfectly coincident with that in the outside of the pipe.
(c) The velocity of groundwater stream is obtained by the measurement as is indicated in Fig. 4.
R₁, R₂: fixed electric resistances;
R₃, R₄, R₅: variable electric resistances;
E₁, E₂: sources of electricity;
S₁, S₂: switches;
A: source of heat;
B: pickup (thermister);
Am: ammeter;
G: galvanometer.
The velocity is calculated by the formula
U1=KL/2T
U₁: velocity of groundwater stream;
L: distance from source of heat to thermister;
T: time of the movement of heated water from source of heat to thermister;
K: coefficient.

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Flap gate is most widely used for the purpose of water control in reclamation land. In this study, its discharge characteristics were analyzed in two-dimensional efflux. First, the efflux from a gate was divided into submerged and free-jet effluxes, and the discharge coefficient was determined experimentally for flap gates with different values of unit weight. Next, the relation between the inclination of flap gate and head water and tail water depths was obtained.

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This report is the result of a runoff analysis by the infiltration method in a loam upland covered with volcanic ashes. In this basin the infiltration capacity is large, but the subsoil is not so permeable as the surface soil. Therefore, at the time of heavy rainfall, the infiltration capacity is much influenced by the maximum infiltration rate of subsoil. Moreover, when the ground water level is raised up to the ground surface by heavy rainfall, the area without any infiltration capacity increases to occupy a large percentage of the basin.
On these conditions, the authors calculated the runoff at the time of the typhoon No.22 in 1958 when the rainfall amounted to 280mm. The values calulated by the following methods coincided with the measured hydrograph.
(1) In regard to the movement of surface soil water, the authors assumed such formulas as follows:
dM/dt=-cM, M=M₀e^-ct, f=fc+qi, qi=K(M-M)
where, M: excess moisture content of surface soil over the field capacity;dM/dt: the rate of M moving into subsoil; M_o: maximum value of M; t: time from M_o to M; f: infiltration capacity; f_c: maximum infiltration rate of subsoil; q_i: seepage rate from surface soil that provides the source of interflow; M: the minimum value of M when q_i first appears; c and K: constants.
source of interflow; M: the minimum value of M when q_i first appears; c and K: constants. The infiltration capacity before reaching M_o is very large. In the intermisson between rainfalls themoisture in the surface soil moves down into subsoil, and the infiltration capacity is recovered. The condition corresponding to M_o usually takes place before the surface soil becomes saturated. This is be-cause the ground surface is undulatory, and the excess water in surface soil is easily discharged by seepage.
(2) In case of heavy rainfall the channel runoff in the basin floods. Therefore, the infiltration method is to be modified as follows:
i=f+re re=ΔS+
qs=ΔSf+ΔSe+qe ΣΔSc=Sc qe=K. Scm
where, i: rainfall intensity; re: rainfall excess;ΔS: the rate of surface detention; S: surface detention; q_s: surface runoff; ΔS_f: the rate of flooding storage; ΔSc: the rate of channel storage; S_c: channel storage; q_c: channel runoff; K and M: constants.
(3) The runoff from each part of the basin has a time lag in concentrating at the end of the basin. The time lag is influenced by many factors, and the authors assumed here as follows:
T=K.Q^-e
where, T: time lag; Q: discharge; K and c: constants.

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As an experiment on the mechanism of sedimentation in reservoir through tractional process, a dam, 20cm in height, was constructed across a rectangular channel having a uniform gradient (i_B=0.057), and mixed sand (d_m=1.07mm) was poured from the upstream side together with water at a constant rate of flow (q=56.66cm³/sec) by means of an automatic sand-feeder at the following ratios: q_B1=0.277cm³/sec, q_B2=0.518cm³/sec, and q_B3=1.012cm³/sec.
The accumulation of sand and the appearance of water surface were observed. A study of these data from the hydraulic standpoint and an analysis of the mechanism of sorting as well as general conclusions obtained from them will be reported subsequently.

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Based on the results obtained from a series of experiments on the mechanism of sedimentation in reservoir through tractional process, an investigation was carried out, chiefly from the hydraulic standpoint, on the rate of sediment transportation on sand dunes, on the relation between the rate and tractive force, and also on the gradient of sediment surface.
An analysis of mechanism of sorting and general conclusions will be reported subsequently.

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As an experiment on the mechanism of sedimentation in reservoir through tractional process, a dam, 20cm in height, was constructed across a rectangular channel having a uniform gradient (i_B=0.057), and mixed sand (d_m=1.07mm) was poured from the upstream side together with water at a constant rate of flow (q=56.66cm³Isec, cm) by means of an automatic sand-feeder in the following ratios: q_Bi=0.277cmVsec, cm; q_B2=0.518cm³/sec, cm; and q_B3=1. 012cm³/sec, cm. Conditions of sand accumulation and the changing appearance of water surface were observed each time. Based on the results of the, experiment, investigations were carried out, chiefly from the hydraulic standpoint, on the rate of sediment transportation on sand dunes, on the relation between the rate of sediment transportation and tractive force, on the gradient of sediment surface, and also on the analysis of the mechanism of sorting.

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