The authors conducted an investigation of soil moisture content in a paddy field which consists of volcanic ash soil named Kanto Loam.
Soil samples were taken either continuously or at regular intervals along straight lines in the field and their moisture content was measured. Then, the autocorrelation function and power spectrum of the moisture content series were obtained and analyzed:
1) Soil moisture content varied from place to place. The variation contains a random wave and some dominant waves which are divided into three kinds (cntimeter wave, meter wave, decameter wave). We call this fact the distribution characteristics of regular fluctuation of soil moisture content.
2) It is also said from the above viewpoint that the conclusion of preceding reports (see references (1) and (2)) is regarded as appropriate, i. e. the optimum size of sample for measuring ω(moisture content) is estimated at about 25cc, and stratified sampling by the square mesh method will be desirable.
3) The roughness of the surface of paddy field will be one of the causes of regular fluctuation of soil moisture content.

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The estimation of evapotranspiration from the hay field in Hachiro-gata was made by means of the combination method as well as the water balance method. Almost the same results were obtained independently, by the two methods. The latent heat due to evapotranspiration was about 90% of the net radiation, and the evaporation from the 20cm pan which was mounted above the canopy was about 1.4 times as large as the evapotranspiration from the hay field.

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In the optimal design of drainage systems in the basin, it is a matter of importance how to deal with hydrographs of water level in a lake as much as how to evaluate hydrographs of flood runnoff in a drainage basin faced to the lake. In the lake the flood water is concentrated from many watersheds through rivers, drainage channels and pumps, and discharged to sea by channels. Therefore, the hydrograph of water level at a point of the lake changes its shape greatly corresponding to the conditions of rainfall in the watersheds, wind in the lake and water level in the estuary.
First, a simple triangular model is proposed to simlate the hydrograph of water level at a point in the lake in this paper. The height of peak from the initial water level, the location and duration of the increased water level in the model at the point are estimated from the rainfall depth at an adjacent observatory by applying the linear regressional models of two and three variates ; and the initial water level and beginning point of the model are evaluated by random numbers from specific frequency distributions.
Next, an expedient method is considered to estimate the dimensions of the model of hydrograph, W_H, at a point from the rainfall depth, B_H, at an adjacent observatory under the conditions: that, no-corres-pondinding recording periods exist between W_H and B_H, but there exist corresponding Periods between W_H and W_M, W_M and B_M and B_M and B_H, in which W_M and BM mean water level and rainfall depth at the point M, respectively.

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This paper deals with models for supplementing and generating rainfall data used for the optimal design of drainage systems. The content is outlined as follows:
1) The role of random components to be taken into account in a linear regressional model is discussed for supplementing non-recorded rainfall data at a point on the basis of the long-term data observed at an adjacent observatory.
2) The character of random numbers to be used in the model is examined for estimating rainfall depths for various durations such as one-day, two-days and three-days. There exists some statstical rela. tionship between random numbers 833 used for estimating three-day rainfall and ε31 for one-day maximum rainfall included in the three-day rainfall, for example. Then, the practicability of the simple method putting ε31= ε33 in place of the strict method considering the statistical relation between them is examined by help of the technique of the Chi-square test.
3) There are two methods to obtain simulated rainfall data at a point for a long-term. One is to generate simulated data based on the supplementary data at the point, and the other is to supplement data based on the generated data at an adjacent point. Then the merits and demerits of these two are discussed from the stochastic viewpoint and the engineering practice.

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The object of this study is to prevent the erosion caused by the freezing and thawing of the relation between the characteristic of soil water in fields and the pattern of freezing and thawing.
The fields for research lie in Memuro town and Shihoro town in the Tokachi district of the eastern part of Hokkaido. The research was executed during the period from December, 1971 until April, 1972.
The following are the results obtained.
1) The outflow of fine particles under the scale of silt was evident.
2) The effluent ton-mineral consisted of metahalloysite, montmorillonite-like clay, and quartz.
3) Ice lenses produced in the effluent hydrophobic soil were thick, and their length was also large. In comparison with them, very thin ice lenses and small pulvarent ices were produced in the part accumulated with hydrophilic soil (Fig. 9, 10, and 11).
4) Destroy of the aggregate with hydrophobic soil in the effluent part and its regeneration were slow. but they were rapid in the part accumulated with hydrophilic soil (Fig. 15).

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The furtherance of drying in the marshy heavy soil ground of the Hachirogatalagoon was evaluated from the following two viewpoints.
(1) How much the hardness of the ground should by considered as an aim of the drying?
(2) What a working method is effective for the furtherance of drying?
In regard to (1), evaluation was made by the results of trafficability test using 6 types of machines in eight test fields of different hardness.
It was clarified by this test that the hardness of ground of 1.3kg/ cm² is a minimum condition as the mean cone bearing index of depth 0-30cm, but 1.8-2.0kg/ cm² is desirable for farming as an urgently necessary aim.
In regard to (2), the following working methods were investigated in the test field.
(a) Overall plowing
(b) Half plowing
(c) Farm drainage ditch.
These working methods were compared with the case of natural state, and pursued what sort of difference was found in the physical indexes. qc. groundwater table, and bulk density etc., clarifying the character of these working methods to some extent.

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The oxidized layer, pH value, and Cl quantity were investigated, laying stress how the soil texture differed chemically by the difference of works-overall plowing, farm drainage ditch, and the case of natural state etc.
By this investigation it was clarified that the change in soil is advanced quickly within the plowing depth by the overall plowing. Next, the following 3 cases were compared-super-deep-tillage (depth 50-60cm), deeptillage (depth about 35cm), and non-tillage, clarifying that the base of turned tillage cuts off the contin uation of moisture movement, and obstructs the drying of soil below this base.

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In order to obtain a guiding principle for the design of a green house, theoretical and experimental investigations were tried out concerning the wind pressure around a one-gabled house in the two-dimensional flow.
In this house the inclination angle of roof is taken at 10°, 15°, 20°, 25°, 30° and 35° and the ratio of the height to the width of eaves at 0.23, 0.32, 0.41 and 0.50.
From the results of investigation the following conclusions were obtained:
(1) Good agreement between the theoretical and experimental results is obtained in the case of the inclination angle being larger than 20° irrespective of the value of the ratio mentioned above.
(2) The change of the inclination angle affects considerably the wind pressure distribution on the roof surface on the up-stream side, and when it is near 20°, a comparatively stable distribution is obtained.
(3) The change of the eaves height also influences the wind pressure distribution on the roof surface of the up-stream side and considerably when the angle is less than 20°.
(4) On the surfaces except the roof surface of the up-stream side the wind pressure distribution is not influenced so much by the change of the inclination angle and the height of the eaves.

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