When the reclamation of a new paddy field in a volcanic ash field with excessive percolation is carried out, it is an important to control excessive percolation. The authors conducted an experiment with the object of getting fixed percolation after the control of the soil water content by only using compaction or rolling of a Bulldozer.
From the above experimental results, it was clear that it was important to control the soil water content on the base of the optimum water content of 70% and to compact it by rolling the whole field with a Bulldozer. Summarizing some more results, they, are as follows:
1) Percolation was reduced from the excessive figure of 2, 000 mm/day to the adequate one of 20mm/day, by Nerishirokaki (Kneading of surface soil) with soil water content of about 75% hich is between PL and LL.
2) From the results of the unconfined compression tests, the percolation coefficient was at a minimum where the treatment of water content was about 70% which is a little higher than PL.
3) In the Course Test, the percolation was reduced from the excessive level of 2, 000mm/day to the adequate one of about 10-30mm/day by Bulldozer rolling after controlling soil water content about 70%.
4) We observed from the results of vertical variation of γ_d that the depth influenced by Bulldozer rolling was 25-30 cm under the soil surface.

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We have found a simplest and economical method for making a new paddy field. That is, even in a volcanic ash loam table land of excessive percolation, we could control the excessive percolation to adequate one only by compaction with a bulldozer after control of the soil water content of the field at about 70%. In this paper, we discussed and considered about the adequate number of rolling of bulldozer, controlled percolation and expenses for making a new paddy field on thejbasis of the investigation of the water requirement in depth during 2 years after compaction with a bulldozer. The chief results are shown as follows:
1) As the soil water content in the field was about 50% when making the new paddy field, we controlled it at about 70%. This control made the soil structure loose and proved a good effect in rolling the bulldozer.
2) We made tests 4, 6 and 8 times by rolling bulldozers of D-8 and D-80 types. From the viewpoint of percolation control, we could get adequate percolation after 4 times rolling of the bulldozer of D-80 type.
3) The cracks on the soil surface were 3-4 cm in width and 16-18 cm in length. However, according to the investigation of depth of water, these cracks do not promote the percolation.
4) By simplifying the process in making the new paddy field, we can cut down the expenses to 31, 852 yen per 10 a.
Thus we obtained a clear prospect to make a new paddy field at exceedingly small expenses.

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This paper deals with the water consumption of a single paddy field and its seasonal and inter-annual variations during 1959-1968 in northern Japan. The values of water consumption items were measured by the “N” type gauge, the “Sato” type gauge, and the variable-head permeameter. The investigated years were grouped into three types on the basis of the standard deviations of the climatic condition, rice plant growth, and water requirement in depth: the high temperature year type, the normal temperature year type, and the low temperature year type.
The ten-year average value of evapotranspiration of Sendai, Miyagi Prefecture, was smaller than that of Kuroishi, Aomori Prefecture, which is located far north of Miyagi Prefecture. It may be roughly said that evapotranspiration and transpiration of the high temperature type years were about 20 percent larger than those of the normal temperature type years, and that those of the low temperature type years were about 10 percent smaller. As regards transpiration, its peak appeared differently according to the temperature year type.
Percolation through ridges was very large compared with vertical percolation under the root zone, and it showed seasonal and inter-annual variations.

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In clayey paddy field, the estimation of drainage discharge is very important for rational planning for underdrainage. In this paper, the relationship between the area of ponded parts of the clayey paddy field and drainage discharge has been reported.
When clayey paddy field is partially ponded with water, the fundamental equation for calculation of drainage discharge was derived from the two dimensional view point (equation 13). This is based on the asumption that the soil surface of paddy field has random undulation, this equation (13) was applied for partially ponded paddy field to obtain the total discharge (equation 19).
In order to judge the linearity between the ponded area and drainage discharge the equation (20) has also been formulated. This linearity factor was calculated under several conditions and it was found that this linearity factor was applicable to actual paddy fields. This linear relationship has also been experimentally confirmed with clayey paddy field in Shonaka reclaimed land. Water balance calculations were carried out using this linear relationship and the result were compared with the experimental data obtained at Shonaka test field. Very good agreement on linearity factor was observed. If this linear relationship is established with extensive experiment, it would be very convenient for estimating soil moisture change after rainfall. Therefore, these results were very useful for rational planning of underdrainage.

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Previously, underdrainage discharge was customarily expressed as standard value of 1l/sec/ha when planning underdrainage system. However, this standard measurement is insufficient in case of underdrainage system where the soil permeability is very high. Therefore, the capacity of the underdrainage system must be determined after taking into consideration soil permeability and permissible drainage velocity.
Therefore, an equation was derived for showing the relation among underdrainage discharge, water level at the laterals and main drain, and the quantity of storage water at the soil surface by using the relation of the underdrainage discharge and waterlogged area which was stated in the previous paper in case the underdrainage system having laterals and main drain.
This equation was expressed in finite difference and the calculations were carried out by the relaxiation method. This equation was confirmed by comparison with experimental data obtained for clayey paddy field. As an example of application of this theory, it is possible to carry out rational planning of the underdrainage system which could not be done before with the help of this theory since the equation takes into the consideration solution of problems which arise from the difference in quantity of ponded water at different paddy fields and also the time required for drainage.

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It has been well known fact that decrease of water table in a polder affects on neighboring ground water table, although it is capable of attempting to alleviate in decrease of water table by setting up polder ditch. In this time, effect of a ditch affecting under-ground water table was undertaken. Here, the effect of polder ditch in a field where is overlain by semi-pervios layers will be discussed with some analysis on under-ground water variation of Uchinada which was influenced by the Kahokugata impoldering project, and the writer has mentioned that value of the leakage factor λ=√kDd/k' should be considered as an important factor.
Strata which consist of aquifers covered by semi-pervious layers can be regarded as a under-ground water flow with gravity pressure, and following equation was driven: dψ₁/dψ₂=1/cosh (α/λ)
Here, ψ₁: piezometric head at a endpoint of polder ditch
ψ₂: piezometric head at another endpoint of polder ditch having distance of a from ψ₁.
k: permeability coefficient of aquifer
k': permeability coefficient of semi-pervious layer
D: depth or thickness of aquifer
d: depth or thickness of semipervious layer
Under-ground water table variation at a end-point dψ₁ is influenced by variation at another endpoint dψ₂, and it is recognized through α/λ as a parameter.
On the other hand, when if strata had complex boundary conditions, it is enable to replace for equivalent single stratum concerning to permeability, then it is recognized that under-ground water table variation can be roughly determine by α/λ in the same way from the result of calculation as twodimentional flow. Although, in the limit of example of calculation, there is no acute identification of α/λ value between two methods. Namely, in case of two-dimensional flow shows small value, this means effect of alleviation in decrease of water table is present. This difference perhaps caused by an assumption for the carrying the analysis out Anyway, it can be said that λ is the important factor relating to any cases, and it is suggested that semi-pervious layer plays an important roll in polder ditch.

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In this paper, the authors investigated the hydraulic coefficients based on the field test for a recently developed rigid PE pipe of large diameter, to provide a technological basis for rationalizing the pipe distribution system for sprinkler irrigation.
The results obtained are summarized as follows:
(1) Measured values of the coefficients in hydraulic flow formulas were: f=0.011-0.012, C=170-177, for the 600 mm straight pipe, and f=0.018-0.019, C=130-132, K_s=0.33-0.34, n=0.011 for the inverted siphon, respectively. The cause of increased resistance against flow for the inverted siphon is regarded due mainly to the effect of air in the pipe.
(2) Judging from the coefficients and Reynolds numbers forthe straight pipe and inverted siphon, the Darcy-Weisbach formula can be applied for the former pipe and the Scobey formula for the latter.
(3) Diagrams (Fig.3, 4) were prepared for the purpose of estimating the coefficients for a pipe of the same kind of any given diameter from the coefficients measured within the region of diameter where Hazen-Williams formula or Scobey formula is applicable respectively.
(4) In using a certain constant in place of correct coefficient in a restricted range of dismeters it is preferable to adopt two respective constants for two sub-divided range of diameter, e. g. by dividing a total range of 65-1, 500 mm at 300 mm, rather than to use single constant for the whole range.
(5) Both the values of C determined with the Matsuda's slide-rule for hydraulic use and of K_s from the nrenared nnmnaranh (Fig.5) acrreed accurately with correspondina logarithmic calculations.

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In this paper, the fundamental hydraulic characteristic of a gate are taken up from the view point of the operation of a diversion.
Discharge expression of a gate could be arranged by using two functions of specific energy and opening height of the gate in either case of free efflux or submerged outflow.
Discharge expression of a fixed weir could be arranged by using only a function of specific energy in either case of perfect or imperfect, or submerged overflow. Using these characteristics, the authors investigated the gate and weir system in order to realize various ratios and capacities of discharge didided by the diversion.
As a result, it was made clear that a gate can be substituted by a weir in case of division by n gates. Besides, if the expressions of various coefficients (of contraction of the gate and discharge of the weir) are known, it was indicated that the discharge into a diversion work and the capacity of discharge divided by the diversion can be computed from the measured values of the opening height of gate and the depth of overflow. Moreover, the sequence of computation in operating the gate and an example of Fukuyama Diversion Work of the Nikko River are shown.

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It is necessary to measure the specific surface (S. S.) of different soils by some suitable method for investigating the physical and engineering properties of fine-grained soils.
This is because the specific surface has a significant effect on the water film or surface activity of soil particles, and such a constant that covers a wide range of numerical value is very useful for the classification of fine-grained soils.
In this research, the magnitudes of specific surface of various soils are measured by the B. E. T. method, and some relations between S. S. and W_L(liquid limit which is one of the very important engineering properties of soils) are obtained. The W_L test is carried out on the samples of three groups as follows:
Group (1) Mixed samples of Bentonite and Kaolinite
Group (2) 32 samples which are mixed 6 non-swelling soils
Group (3) 24 samples which are mixed Bentnite and 5 non-swelling soils.
These experiments have proved the following matters:
(1) The S. S. of soils is very useful for the classification of fine-grained soils.
(2) The following linear formulas hold between S. S. and W_L:
For samples of group (1) and (3)
[W_L] =6.4 [S. S.]-26 (S.S.>12.0m²/gr)
[W_L]=3.7[Mixed Bentonite (%)]+12.4,
for samples of group (2)
[W_L] = 1.2 [S. S.] + 13.9.
(3) An approximate relation between the thickness of water film on the soil particles and S. S. is given.
(4) The quantities of swelling clay contained in the sample soils can be estimated by the measurements of S. S. and W_L.

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