A method was applied to measure soil moisture indirectly by obtaining the attenuation of energy of ultrasonic waves which propagate through a solid porous media buried in soil. The results are summarized as follows:
1. A glass block, that is, a material “G-5” as shown in Table 1 and 2 was developed. G-5 has a smooth p F-moisture ratio curve presented in Fig. 1 and the moisture in the block buried in soil is considered to respond well to the soil moisture. It is also able to bond tranceducers on the both parallel planes of the block.
2. Five materials were used as solid porous media (Table 2) and PZT tranceducers (Table 3) which have resonant frequencies 1, 1.8, 4.5 and 9.5 MHz were employed. The blocks were formed as shown in Table 4. The relations between the degree of saturation of block and the ultrasonic attenuation were obtained (Figs. 4 and 5).
As a result, it was proved that the measurement of soil moisture is possible by using 1 MHz ultrasonic waves and the block G-5 (Fig. 6). Moreover, the influence of ultrasonic attenuation characteristics by underground temperature and electrolyte ions in a vegetation land was negligible as presented in Fig. 7-10, so it is considered that there is no need of correcting the measured values for them.

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The effects of weather conditions on the water consumption of the paddy field were studied with the measured values during 1959-1968. Evapotranspiration and percolation through ridges showed a great change according to daily weather conditions. The ratios of evapotranspiration on clear days (of 10-hour and upward sunshine duration per day) and cloudy days (of less than 4 hour sunshine duration per day) to partly-cloudy days (of 4.0-9.9 hour sunshine duration per day) were ±28 percent. The ratios of percolation through ridges on clear days and cloudy days were +54 percent and -24 percent respectively. Percolation through ridges was also dependent upon ridge soil moisture.
Evapotranspiration of the paddy field in Sendai, Miyagi Prefecture, showed peculiar values 22-27 percent less than those in Iwamizawa, Hokkaido, and Kuroishi, Aomori Prefecture, both of which are located far north of Sendai. This peculiarity is accounted for by the fact that Iwamizawa and Kuroishi have longer sunshine duration than Sendai.
A practical method of estimating evapotranspiration of the paddy field is presented here on the basis of an equation containing a new climatic index to be called CLIMATIC INDEX OF EVAPOTRANSPIRATION OF THE PADDY FIELD. The equation follows:
ET=0.256C^0.562· ET
The estimated three-year averages of ten-day periods of evapotranspiration of the paddy fields throughout Japan showed an erroneous range of ±0.5 to ±0.8 mm per day.

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By the consolidation of sloping paddy field the height of ridge is increased. So the chance of ridge disruption is also increased. In this report, the phenomenon of ridge disruption and its cause are analyzed based on the field investigation. The following results are obtained:
1. Ridge disruption occurs very frequently within the first three months after construction. Therefore, various measures for the prevention of disruption should be applied in this period.
2. By comparing the disruption ratios in A and B methods, where A is an ordinary method and B is a good compaction method during the ridge construction, it was found that the ratio of B-method is lessthan that of A-method.
3. The ridge disruption ratio is increased with increase of ridge height. According to an investigation at Wadayama Area, Hyogo Prefecture, the ridge disruption ratio is proportional to the 2nd-3rd power of height.
4. There are three most important causes of disruption. They are the seepage water, bad compaction and overflow of the ridge. Most of the disruption occur during or just after a heavy rainfall.
5. As a result of the comparison of ridge construction cost of A and B methods at Wadayama Area, it was found that if the height of ridge is more than 2.0 m, the B-method is suitable.

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For the purpose of studying the effective utilization of rainfall, experiments were conducted by setting the depth of irrigation start at 10, 20 and 30 cm by using Kyodai field soil.
The results obtained were as follows:
1) In case of a shallow irrigation system in which the depth was 20 or 30 cm, the soil moisture of adeeper layer was more utilized, because the capillary moisture moves upward. Therefore, as the deeper layer has less moisture, rainfall is effectively stored there and more availably utilized. But, as the moisture is constantly lower in each layer in case of depth of 30 cm, the state is considered to be on the dangerous side a little.
2) From the relation between the soil moisture and root distribution, it was found that the absorption of moisture by upland-rice was performed near the surface layer within a depth of 10 cm. And the root of about 7 or 9 % penetrated into the deeper layer.
3) The role of deeper layer than 20 cm was considered to provide a passage, of moisture to move in the upper layer or to store the rainfall and moisture in the layer. Therefore, a shallow irrigation system is considered to be able to store the rainfall more than in a deeper system.
4) A depth of 20 cm had less available rainfall than that of 30 cm, but the former was nearly equal to the latter in the irrigation water, and superior to the latter in growth and harvest, as well as in safety for the moisture management. Therefore, the irrigation start at a depth of 20 cm is considered as the best irrigation system.

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In case of wide area farmland block, it is necessary to maintain the condition to control the drainage freely, Especially in case of heavy clay soil, in as much as the effect of underdrain was often unsatisfactory, it has become an important practical problem at many places. Following causes can be presumed for it.
1. Low value of permeability coefficient.
2. Flooding water on partial surface does not vanish for long time.
3. There is no drying period sufficient for extension of the crack, and others.
In order to resolve these problems, we proposed “sand underdrain” as a countermeasure and performed a series of experiment by lysimeter.
The sand underdrain is that whose digged-up part of the traditional ordinary underdrain is replaced by sand and it has a rapid drainage function by the open ditch drainage. The lysimeter used for experiment is shown in Fig. 1. Measurement of the drainage discharge was performed by the self-registering discharge meter. Soil used was the actual paddy field soil and its composition was as follows:
under 0.01mm 60%
0.01-0.05mm 37%
0.05-0.3mm 2%
over 0.3mm 1%
The experiments were executed after the following items:
1. we set one plot for non-underdrain, two plots respectively, for ordinary underdrain and sand underdrain.
2. Surface soil 10 cm in depth of the sand underdrain was replaced by the original soil and it was put in the condition stirred by surface soil puddling.
3. one plot was set for ordinary underdrain and other two plots for stirred-up sand underdrain of 20 cm width and 30 cm width each.
Results of the experiment were shown in the figures. It was clarified that the rapid drainage by sand underdrain has a more distinguished effect than the ordinary underdrain or the non-underdrain shows. Although the effect decreased to some degree when the surfase was put in the stirred condition, a considerable effect was still observed, and furthermore, it was clarified that there is no change by the difference in width of sand underdrain.

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The stochastic techniques for generating or supplementing hydrological simulated data such as heavy rainfall at a place and water level hydrograph in a lake were generally discussed by the authors in previous papers. Besides such data processing, however, there remain some problems to be taken into consideration in the practice of optimal design of drainage systems in a drainage basin. Then, the methodology for finding an optimal drainage pump capacity in a drainage basin composed mainly of paddy fields is developed in this paper by applying the techniques of stochastic simulation as a goal of our studies. The discussion is carried out in detail by taking an example in the Anba River Basin facing to Lake Shinji near Matsue, Japan. The content is outlined as follows:
(1) The data of rainfall over 30 mm for one-day storm and 50 mm for two and three-day storms in summer at Hirata Station near the basin are generated for a period of 60 years. These data are distributed for each sub-period corresponding to the growth stage of crops every year. For the generated and distribution of the data, the techniques of the Monte Carlo method are utilized.
(2) Runoff hydrographs at the outlet of the basin are estimated by using unit-hydrographs constructed corresponding to the magnitude of rainfall depth in the basin.
(3) Hydrographs of water level of Lake Shinji at Kimachi Station near the mouth of the Anba River are obtained through rainfall depths at Hirata by the help of regressional analysis.
(4) Hydrographs of runoff discharge at the outlet of the basin are changed to those of inundation water level by considering the water volume exhausted through the river channel and hypothetical drainage pump.
(5) Inundation damage is estimated for each hypothetical pump capacity for a period of 20 years that means the pump life. Through the evaluation of damage, the gross benefit produced by installation of the hypothetical pump is calculated. Costs of installation, operation and maintenance of the hypothetical pump are also estimated. Through such a procedure, the benefit is easily found to reveal the lower limit of the optimal capacity of drainage pump.

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Rolling resistances are calculated assuming four types of contact pressure distribution in this paper, which are uniform, trapezoidal, triangular with the maximum contact pressure at the end of the track and triangular with the maximum at the back end (Fig.2).
The rolling resistance, when contact pressure distribution is triangular shows the largest value in four types.It is smallest in the uniform contact pressure distribution.

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In this paper, the vibration modes of an earth dam are studied. The statical mechanical behavior of it has already been investigated. To investigate the dynamic behavior of earth dam under seismic force, it is most important and useful to learn the vibration modes and eigen frequencies of the dam.
Large scale multi-degree-of-freedom-system formed by a finite element vibrating system, which idealizes the earth dam is handled numerically by a computer to give the vibration modes and eigen frequencies. In this paper, the influence on the modal component caused by the nonhomogenity of the dam material and the foundation-dam interaction is studied, and vibration characteristics of the dam are investigated.
As a result, a two-dimensional vibration system shows different patterns of vibration from those of the conventional shear wedge model. The mechanical effects of the foundation-dam interaction under the dynamic condition becomes significant as the ratio of the Young's modulous of the foundation to the dam becomes to unity.
These results obtained here will be used in the next issue-Part.2.

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Experimental investigations were done concerning the wind pressure distribution about one round shaped roof house in the two or three dimensional flow.
The round shaped roof house, herein, took two types of roofs as one was semi-circular and the other was semi-elliptical.
The wind direction was considered as the same as the previous report (II).
From the investigated results, the following conclusions were obtained.
(1) As the wind direction angle increases from 0°C to 90°C, the wind pressure distribution about one round shaped house becomes comparatively stable, i. e. absolute values of the wind pressure coefficients on the roof become smaller and smaller.
(2) The difference of the wind pressure distribution between two round shaped houses is not so large, but at the upstream side in the round shaped roof surface, the absolute values of the wind pressure coefficients on the semi-circular roof are a little larger than those on the semi-elliptical roof.
(3) As the compressive pressure appears on the round shaped roof surface near to eaves as well as on the upstream side wall, this fact should be considered at the design of the Green Houses.
(4) Comparing results in this case to the previous report (II), in the case of one gabled house, the difference between the distribution of the wind pressure on the roof surfaces are founded to be considerable.

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