In the readjustment of paddy field base with bulldozers, depth of soil cut by bulldozer's blades can not be so deep for the reason that bearing capacity is low, and the surface soil which is good for plant growth should not be mixed with subsoil. Distance of carrying soil determining the efficiency of earth work is not constant, therefore the efficiency is low in cases of both short (0-5m) and long distance (80-100m).
Volume of cut soil entering a blade (Q) increases with operation distance until the blade is filled with soil.
Q=Q₀{1-exp(-D/ph)}(4)
Speed of a bulldozer in soil cutting can be shown as eq.(5)
dD/dt=A log(1+D/100)(5)
Volume of the soil transported by the bulldozer, when cutting depth is constant, is derived as the following equation.
_??_(7)
where Q₀: blade capacity (m³), D: distance (m), h: cutting depth (m), p: constant determined by Q₀ and h, f: bulk factor of soil, a: ratio of speed of bulldozer going forward and backward.
The maximum rate of soil transportation by distance is given when the differential of eq.(7) equals zero. The combination of bulldozers will improve the efficiency of earth work when the properties of showing ability to remove soil is suitable to cutting, banking or transporting soil. For instance in the combination of two bulldozers of heavy weight type (BD19) and medium type (D6C), the heavy type is good for the transportation of soil and leveling, while the middle type is good for cutting. This can be inferred from the properties of two bulldozers carrying soil as shown in Fig. 4 (3). Assuming standard amount of work as 100% when the medium type operates in the distance of 0-45m, and the heavy type in 45-100m, the rate of efficiency by reversal combination changes to 96%, and when two bulldozers work independently in the same farm block, the ratio turns out to be 98%.
The efficiency of the earth work in paddy fields will be improved by the selective combination of bulldozers.

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In order to realize the distorted hydraulic reservoir model on which the various tests with respect to wind-wave interactions may be made, the similarity criteria of the wind-driven circulation in shallow freshening reservoir is theoretically discussed in this paper. The model scale of wind velocity, λ_w, defined as the ratio of the model wind velocity at a certain height ζ_m to the prototype wind velocity at a unique height above the undisturbed surface, is ultimately determined. Before we arrive at λ_w, the model scale of wind stress coefficient, λ_s, related to λ_w, is expressed in terms of λ_w and λζ_c equal to ζ_m/10.0 through introducing the Wu's concept that the range of wind velocity may be divi-ded into breeze, light wind and strong wind regimes. Finally, we find throughout the present paper that the distortion of a scale model should be small from a viewpoint of the similarity of wind velocity, and that the numerical values of λ_w for three regimes are very like each other if a hydraulic model with certain geometric scales is designed.

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Recently, the simulation by numerical model is growingly employed in the analysis of runoff mechanisms. This paper deals with the important aspects to be considered in applying this method to runoff practice of low-lying basins.
Firstly, a runoff system from fields to downstream facilities was set up hydraulically; then the numerical model for this area was established, and the solution procedure was illustrated. Secondly, after applying the above method to the Hachiro-gata Polder, the calculations were compared with the measured vatues of this area. Through this study, the primary points to be considered in applying this method to the practical problems have been listed as follows:
1. Tributary canals show high roughness, which requires careful consideration in employing difference equations;
1. Tributary canals show high roughness, which requires careful consideration in employing difference equations;
3. For basins involving many branch drain channels of short lengths, calculation points should be distributed at small intervals sufficient for accurate water level determination.
4. Therefore, in order to obtain the knowledge of waterlevel over a low-lying basin correctly, one must consider the whole status concerned on the basis of available measurement records.

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Sand particles as the subject of sedimentation treatment in a sand basin are flown in the form of bed load when the flow in the sedimentation ditches is a normal flow, and shifted sediments are deposited from the inlet of the sedimentation ditches forming sediment terrace, and fine sand particles that could not be deposited at this terrace are deposited by flowing down tractionally along the bottom of the sedimentation ditch from the end of front slope of the terrace forming thin deposition layers. In this case, even when the finest particles at the limit of deposition are flown in the form of suspended load, they will, after precipitating onto the bottom of the sedimentation ditch, be made to flow down tractionally on the surface of deposited sand, until the critical tractive force of particles and the tractive force in the sedimentation ditch are brought into equlibrium.
Denoting the water depth above the deposition surface by h, the width by B, the hydraulic mean depth by R, the mean velocity by U, the bottom slope of ditch by i, and the density of water by ρ, the tractive force at an arbitrary cross section of sedimentation of sedimentation ditch having a uniform rectangular cross section can be expressed by _??_Eq.(3)
Taking the discharge of ditch per sec at Q and the critical tractive force of smallest particles of limit deposition at τ_c, we put k=τ_c/(ρi) in a cross section where τ becomes equal to τ_c, and the velocity fluctuation coefficient in the ditch is considered to be α, then Eq.(3) is rewritten as
_??_Eq.(5)
Therefore, putting the thickness of sedimentation layer whose cross section becomes τ=τ_c when the allowable amount of deposited sediments is reached at D, the depth H of the sedimentation ditch in this cross section is expressed by H=h+D, so that the cross sectional dimension of an optimum ditch for topography of construction site of the sand basin can be determined from Eq.(4) or Eq.(5).
Although it is not easy to determine the length of ditch precisely, if the position at which the sedimentation of smallest particles at the deposition limit has been finished when reaching the allowable amount of deposited sediments, is made to be about 10 times the height of the front from the sediment terrace, then by investgating some other few methods, it is possible to determine an appropriate length of the sedimentation ditch.

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Pipeline water conveyance systems have two fundamental characteristics: firstly, the head loss distribution to each pipeline section can be controlled as desired; and secondly the flow capacities affect considerably its construction costs. Therefore, it is a very important design problem to allocate suitable head loss to each section and to determine the optimum capacity (pipe diameter).
The problem to determine the optimum pipe diameter can be stated as follows: under a given total head loss finding the head loss allocation or pipe diameter of the each section so as to minimize the sum of the construction cost of each section.
Generally, either Dynamic Programing Method or Differential-Calculus Method is applied as searchtechniquc of optimum solution to a nonlinear optimizing problem of this type. Here, latter method alone is considered. Let Cost Potential corresponding to the Lagrange multiplier be defined for each section as,
φ_i=h_i/y_i
where y_i and h_i are the cost and head loss at ith-section respectively.
Then the optimum conditions require the following equations to hold at each node.
Σφ_i=0
Thus by using φ_i, the optimum conditions are expressed by the very simple form. Furthermore, we can easily derive optimum conditions in terms of Cost Potentials to other problems of similar structure.

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Compacted soils suffer a change in shearing properties caused by moisture contents anti creep stresses.
The effect of creep on shearing strength is relatively small and that on the strength factors c' and φ' is negligible. But the creep stress have great influence onstress vs. strain curves, and the initial tangent modulus of deformation becomes greater as the creep stress becomes greater.
The moisture content has an influence on shearing strength and stress vs. strain curves. Shearing strength of cohesive soil is greater in dry side than in wet side o foptimum moisture content. The shearing strength of sandy soil is hardly influenced by moisture content, but is infl-uenced by its dry density.

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We have recognized hystere3is phenomenon in the seasonal change of trafficability and ground water table in the field of Hachirogata Lagoon.
This phenomenon is closely related to soil caracteristics which alter by the wet and dry condition.
We have found out that there is sometimes on increase of trafficability even in the wet season when the trafficability usually decreases.
In order to clarify this phenomenon, we have measured the pF-moisture ratio, dispersion ratio, sediment volume and shrinhage ratio, etc.
It was concluded that this phenomenon occurs when there apper cracks in the soil layer and moderate supply of water accelerates hardening of marshy heavy clay soil.

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