Water requirement of paddy field is an essential part of irrigation planning. Canals are developed like a network in paddy fields and occupy a considerable percentage of the total paddy field area in Saga and Fukuoka prefectures.
Experiments and observations were conducted and are still in progress to clarify the mechanism of reducing percolation phenomena of water from paddy field to canal.
The apparatus used in the experiments is shown in Figures 12 and 13. Rice plants were transplanted from seeding bed into the apparatus. This work was carried on during the crop season from 1960 at the experimental paddy field of Kyushu University. The results of the experiments are shown in Figures 16, 17 and 18.

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The authors are systematically analyzing the mechanism of sorting of sediments in the process of erosion, transportation and sedimentation in catchment areas, reservoirs, rivers and the sea. The present report concerns the analysis of the sediments in the mouth of Yoshino River; 179 samples obtained by boring were used. Mechanical analysis was made on the basis of JIS A 1204, and the degree of sorting was examined by the phi scale of Krumbein, Inman, etc.
Size parameters such as M_dφ, M_φ, σ_φ, Q_dφ, P_dφ, α_dφ and β_dφ were obtained from the results. The grades of σ_φ showing the degree of sorting were analyzed by Rominger's classification. Main interesting results are as follows:
1) The degree of sorting unconformably changes at the depths of 10m, 30m and 50m; these planes of unconformity correspond to the changing planes of sediments.
2) The planes of unconformity are best indicated by such size parameters as M_dφ and σ_dφ.
3) As to the relations between phi mean diameter (M_φ) and phi deviation measure (σ_φ), the value of the latter increases and sorting linearly bdcomes poor for the value of the former both increasing and decreasing starting from a limit diameter (M_φ=2 to 3). The relations are shown by reflexive linear formulas (Eqs. 9 and 10).
4) As to the relations between phi. mean diameter (M_φ) and phi kurtosis measure (β_φ), the.value of the latter also linearly increases for the value of the former both increasing and decreasing starting from M_φ=2 to 3. These are also shown by reflexive linear formulas (Eqs. 11 and 12).
5) As to the degree of sorting, the sediments are very well sorted or well sorted in the top. layer (alluvium), and are well sorted or normally sorted in the second layer (diluvial clay bed). In the third layer (diluvial gravel bed and the clay and gravel bed weathered on the ground), however, grading is poor, falling in the ranges from normally sorted to very pooly sorted. These suggest the general tendency that transported soils are well sorted and residual soils are pooly sorted.

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The boundary layer theory for the smooth open channel was apllied to the gradually contracted open channel flow. Then the decrease of layer thickness and the variation of velocity profile along the flow were investigated.
According to the theory, the relation between δ, the layer thickness from side wall, and ζ, the layer thickness from bed is shown as η=βξ(η=δ/b, ξ=ζ/h, β=(h/b) ^r, h;depth, b; a half of width), in the process of layer development, but in the last state of uniform flow h≅b the relation becomesη≅βξ.When a steady state flow in which the layer has developed fully contracts its cross-section, the layer begins to decrease its thickness. If η>, βξ, η alone varies with ξ=1 and since η=βξ, η varies together with ξ.
In the gradually contracted open channel, the more the cross-section varies, the more rapidly the layer thickness decreases, despite of η=βξ or η>βξ. When the variation of cross section is same, the layer thickness in the channel with side contraction (db/dx<O, dh/dx<O) decreases more rapidly than in the channel with weir (db/dx=0, dh/dx<0).
Then, the equation for the layer thickness and the approximate graphical solution in the channel with weir is shown.
From this solution, it is shown that the layer decreases sooner for larger discharge under the same weir height or for higher weirs under the same discharge.

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This report concerns the experiments to verify the characteristics of the gradually contracted open channel theoretically obtained in last report.
In these experiments, it was verified that there are two types of contraction, i. e.η=βξ and η>βξ and varies together with η in the former type and η alone varies atξ=1 in the latter. Then n, the exponent of the power law of a velocity distribution profile, varies with contractions of cross section. The variation of n with weir contraction differs from that in with side wall contraction. The variation of n with weir contraction is shown by the experimental equation n=1/7Ar^1.775
It has been confirmed by the experiments that the uniformity of the velocity profile at the throat or crest appears more rapidly in side wall contraction than in weir contraction under the same variation of cross section. And then, the uniformity of velocity profile at the crest in weir contraction depends on the decrease of η and n, but the profile is effected more largely by n rather than by η
The velocity profiles obtained by experiments agree with calculated results. This may be applied to the design of the rapid acceleration divider

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This report is a proposal of the design for the rapid acceleration divider which is based on the characteristics of gradually contracted open channel.
Hitherto, we designed to satisfy the two conditions, i. e.
1) the flow over the weirmust be perfect overflow and
2) the back water level due to contraction mustlie below the permissible water level in the upper stream of the divider.
Therfore, according to this method, the division accuracy cannot be presumed without modeltests.
In this report, the auther added the third condition, that is 3) the division accuracy must be held below the permissible accuracy, to the above conditions and proposed to satisfy the three conditions in the design.
If the third condition cannot be satisfied in field circumstances, design may be made first, to satisfy the conditions 1) and 2), the velocity profile of diversion position calculated and then the distances of splitter walls decided on the basis of the profile.

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1) In this paper, an outline of the model test and the material test of Tori Arch Dam, and the mode of preparation of the model are given.
We studied, by the model test, stress and deflection distribution on the upstream and downstream surfaces of the dam body at normal water load, stress in the thrust blocks and in the area along conduits, which cannot be sufficiently obtained from mere calculations, and finally investigated the safety of dam, the condition of destruction and particularly the safety of narrow area at the right bank foundation.
The similarity relations between model and prototype are shown by the equations (1-1), (1-2) and (1-3). The scale of the model is 1/100 to the prototype as shown in Fig. 9 and 10. In the test within the elastic limit water pressure only was considered and it was given with mercury. In the destruction test oil jacks were used to represent water pressure, deposit pressure and dead load.
2) We tested the mechanical properties and the composition of materials for the model, confi rming the next results. The elastic modulus of plaster-celite mixture definitely changed with varying composition and was constant regardless of the age of the material after completely dried. The Poisson's ratio of plaster-celite was 0.22 and was nearly equal to that of concrete.
3) The elastic modulus was 4×10⁴kg/cm² in dam body and 10⁴, 1.4×10⁴, and 2×10⁴kg/cm² from the upper to lower part of foundation in model test. We preliminarily constructed the foundation, then excavated it and made the dam body slightly larger than the planning size. The body was then trimmed to the designed section by a special trimmer.

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When negative pressure occures at some part of water flow, water is separated. and cavities are formed there, because water cannot resist tensile stress. Wherever the absolute pressure falls to (or close to) the vapor pressure of water, cavities are also formed. They will be carried along with water flow and collapse at the place of high pressure. This phenomenon is called cavitation.
The magnitude of the pressure created by the cavity collapse is enough to erode and destroy the surface of a hydraulic structure. The accumulative erosion and destruction may endanger the hydraulic structure. Although the damaging or “pitting” of structural materials by cavitation has been variously attributed to chemical action, electrochemical action (corrosion), high tension in water, etc., present evidence indicates conclusively that the destructive action is essentially a mechanical one, being caused by the impact of water mass on the surface of the material.
This paper describes what material is applicable to cavitation experiment, and how is the process from occurrence to erosion and destruction. This experiment has been done with various conditions and shapes of the solid surface.
It is found from the result of the experiment that, in order to prepare the most adequate test-piece (made of “plaster of Paris”) for surface erosion experiment of cavition, the water content must be five to six times as much as that of the standard mix ratio and the stirring time must be two times as long as that of standard mixture. By using this material, it becomes comparatively easy to obtain the erosion of cavitation on the test-piece surface within a short test period.

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