Evapotranspiration is one of the most important factors in irrigation and water resources plannings.Many approaches have been made to estimate the evaporation from water surface, soil, and vegitation.However, few studies on the evapotranspiration from a large area including various types of surfaces, such as a river basin, have been made due to the complexity of meteorological condition on each surface.In this paper, water balance method is used to estimate the seasonal change of actual evapotranspiration from a small catchment in the northern part of Kyoto.Comparison of estimated evapotranspiration (E_t) with pan evaporation (E_p) represents that the seasonal change in E_t is different from that in Ep.(Fig.3-5) The ratio, E_t/E_p, in winter, during which potential evaporation is less than 2.0mm/day, is approximately 1.0, while the ratio in summer, during which potential evaporation is greater than 3.0mm/day, is approximately 0.8.(Table 1) Judging from this fact, we may assume that soil-plant system in the catchment changes the ratio, E_t/E_p, in response to atmospheric condition.Comparison of temperatures in soil and air may provide reasonable evidence for this assumption.

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For the purpose of studying the utilization of available rainfall and the effect utilization of water quantity, experiments were practised with setting the various water depth per irrigation and the various depth of irrigation start, namely 10cm-10cm, 10cm-20cm, 10cm-30cm, 20cm-20cm, 20 cm-30cm, 30cm-30cm and non-irrigation section, by using Osakafudai Field Soil.
The results obtained were as follows;
Firstly, the purposive difference was recognized with regard to water quantity, available rainfall, and harvest.
Secondly, the more available rainfall increased, the more water quantity decreased.And the singlevalued relation existed in between available rainfall and water quantity, and its correlation was cleared to be very high.
Thirdly, in case of the shallower depth of irrigation start such as 10cm-10cm or 10cm-20cm section that the period is short from irrigation to next and the deeper water depth per irrigation such as 20 cm-20cm or 30cm-30cm section that the period is long, the utilization rate of available rainfall or the effetive utilization rate of water is apt to be depended on rainfall pattern or timing.Because the former is much numbers of irrigation and apt to dry right away at the shallower soil layer, the latter is much water quantity per irrigation and high moisture content at the deeper soil layer.
Fourthly, 20cm-30cm section was judged as the best irrigation method of all thse experimental results from utilizing rainfall availably, having the effect of saving irrigation water, being expected to utilize effectively soil moisture at the deeper soil layer and not being depended on the climate conditions so much.

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Under the trickle irrigation method, it is important to discuss the basic problems of the shape and volume of conic wetting zones and the soil moisture content distribution within the conic wetting zones, which affect the nozzle spacing, water application efficiency and salt accumulation.In this paper, these basic problems were discussed with the numerical method and experiments under the conditions of two-dimensional infiltration into dune sand.
1) To solve the nonlinear diffusion-type water flow equation in unsaturated soil, K-θ curve, pF-θ curve, D-θ curve, etc., which were measured by the laboratory and field experiments using dune sand, were required for the numerical calculation.
2) The soil moisture content distributions measured by using the gamma-ray attenuation soil moisture detection apparatus, under such a two-dimensional model as in the case of the calculations, comparatively agreed with those obtained by the numerical method.
3) The iso-soil moisture content curves obtained by the numerical method under the initial conditions of the trickle discharge q=0.5cm³/cm min and 0.8cm³/cm min, and θn=0.005-0.008cm³/cm³ (air dried dune sand), were discussed until the process, which the wetting fronts of the conic wetting zone on z axis distributed to the main root zone (25/30cm of depth from sand surface).
4) Within the conic wetting zone, the soil moisture contents θ close to the line source were 0.15-0.17cm³/cm³, and wetting area of θ=0.10-0.15cm³/cm³ took the largest of the total conic wetting zone. Furthermore, the iso-soil moisture content curves distributed larger for z coordinate (vertical) than for x one (horizontal), especially, the higher iso-soil moisture content curves approached gradually to the steady state close to the sand surface.
5) In the case of conditions that K showed approximately 10 percent smaller of those of dune sand, the soil moisture contents close to the line source were 0.26-0.28cm³/cm³ and the iso-soil moisture content curves distributed smaller than those of dune sand, however, θ=0.15cm³/cm³ of iso-soil moisture content curve distributed larger close to soil surface than those of dune sand, which approached to the steady state.
6) The iso-soil moisture content curves distributed larger with the increase of the initial soil moisture contents, especially those became larger for the depth direction with the increase of the nozzle flow rate in dune sand.

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Undisturbed soil cores were collected from the soil horizons of seven paddy fields formed on five polders which were ripened after 13, 30, 73, 160 and 260 years from land reclamation. The total porosity, soil moisture retention, pore size distribution and cone index as measured in situ were studied to evaluate the soil structure development and to seek the relation between two soil structure indices.
The obtained results indicate that the moisture retention was more increasing with depth especially at low suction and was decreasing in course of time at the same soil depth.The highest cone index values of the plow sole was accompanied by the lowest water retention at low suction.The total porosity was increasing with soil depth and decreasing in course of time but the sub-surface drainage condition was counteracting its trend.The total porosity was divided into non-capillary pores drained until pF 1.5, capillary pores drained between pF 1.5-4.2 and very fine pores retaining the water at pF 4.2.The non-capillary pores were more pronounced in the plow zone especially after 73 years from poldering and had the same little amount in deeper horizons.The capillary pores were increasing with depth and decreasing in course of time, while the very fine pores followed a reversal order.
Since the development of soil structure in the plow zone was found to be governed by the cultural practices, the underlaying layers were only considered for drawing a proposed index for characterizing the soil structure development.By introducing the degree of saturation in the total volumetric percentages of very fine pores and solid phase, a highly significant correlation coefficient equals to 0.9315 was found with cone index.The correlation equation is
_??_
where;q_c=cone index in kg/cm², V_f and V_s=volumetric percentages of very fine pores and solid phase respectively, and S=degree of saturation during measuring cone index. The total volumetric percentages of very fine pores and solid phase “V_f+V_s” formed a response function of the soil structure development and were proposed as an index for its evaluation.

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It is very important to prevent the soil erosion which may occur on the uncovered slope after land reclamation.
In this paper, erosion phenomena are discussed with regard to topography, soil properties, snow melting and rainfall characteristics on the eroded slopes.
(1) Rill erosion on the surface occurs under the following three soil conditions:(a) Large hardness of the surface soil, (b) Small porosity, (c) Small saturated permeability.
The expansion of gullies is dependent on the following three soil conditions:(a) Small hardness of the surface soil, (b) Large porosity, (c) Large saturated permeability.
(2) The occurrence of gullies is dependent on the following three land slope conditions:(a) The steepness of slope over 15 in degrees, (b) The length of slope over 45 m, (c) The topography of natural down slope.
(3) The soil Properties and chamcteristics of slope at the occurrence limits of gullies intemct complexly, so that gully erosion, insitu, occurse xceeding or unreaching the limitting value thereof.Rather, the characteristics of slope rank soil conditions.
(4) Gullies which are caused by snow melting occurs certainly at the maximum snow melting velocity 9.2-9.6 mm/hr. However, the assumed lower limit will be the maximum snow melting velocity 6mm/hr.
(5) Gullies which are caused by rainfall will be surely formed by the precipitation of the total amounts over 26mm with the maximum rainfall intensities over 12mm/hr.

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This paper describes the fundamental characteristics of artificial rainfall for basic studies on the mechanisim of water erosion in sloping reclaimed farm land.
The slope plots for research of erosion were located in Sumomo, north-east Hiroshima.They are 40 m long and 30 m wide with a slope of about 7 degrees.Since the artificial rainfall is given by rain-gun, we need to find beforhand possible relation between natural rainfall and artificial rainfall by a preliminary fundamental experiment. We found a relative equation φ=A·exp [B·S^1·5] between the raindrop size and the destinated distance, and obtained thereby an accumulation curve of water-drop size. From these results, we can culculate the water-drop size and its number at optical point.
It became clear that kinetic energy in slope plots is given of an average value of 20.7×10⁴ erg/cm². 10 min., using the water-drop velocity simulated by electronic computer.This value of kinetic energy proves equivalent to the natural rainfall intensity 6.4 mm/10 min.as calculatd by Dr.Mihara's equation.
From these results, it became clear that we can compare artificial rainfall with natural rainfall in terms of the kinetic energy, and apply rain-gun to field test of water erosion.

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Many unsuccessful flood control operation rules and procedures at multipurpose reservoirs in Japan were analyzed, and some dominant factors which affect flood control at those reservoirs were clarified.Once the discharge in excess of planned maximum outflow is forced to be released owing to the insufficiency of emptied capacity, then the author defines this case as “the failure of flood control”.
20 unsuccessful flood control operation procedures were investigated by the author especially in view of the scale of flood and the actual operation procedures for release, then analyzed as follows.
1).In 11 cases the scale of flood was larger than planned one.In other 9 cases, only the defects of operation procedures caused the failures flood control.
2).These defects of operation procedures at reservoirs are: one is that sufficient emptied capacity was not able to be secured in advance, and the other is the decrease of emptied capacity by storing flood harmless to lower reaches at the beginning of flood.
3).These defects, being the same in essence, result from the operation procedures which put importance on water supply sectors rather than flood control sector.In Japan, release in advance of flood depend on the prediction of rainfall becase of the narrow basins of reservoirs.However, under the existing conditions of the unprecise prediction, it is difficult to satisfy the interests of these two kinds of sectors with the release in advance of flood.
4).This kind of difficulty should be taken into consideration for the establishment of flood control operation plans.

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It was aimed to build up the rural improvement image on each rural type, using the integrated rural improvement plans in 350 rural districts and setting out questionnaire to these districts. The movement of population in the decade in each district was used to classify rural areas. There are five types of rural areas, that is, urbanized rural area, the rural area increasing in population, the rural area decreasing in population, the rural area rapidly losing population and mountainous area. We analyzed the needs and the level of improvement in each rural type.The data used for this analysis are restricted by the existing system in the rural improvement, but it has been definitely shown by this research study that each rural type has the specific character in the above-mentioned items.

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In case of taking water out of rivers, we must realize the character of rivers. Since Dr. Kinoshita discovered ‘Sarekitai’(Alternating sand bar or Transverse bar in English) originally, the research on the relation between river bed forms and flood flows has made the rapid progress in Japan. But in the field of agricultural engineering, his research is not yet adopted sufficiently.
Reinvestigating diversion weirs from this point of view, the formation of Sarekitai, we can find out a nice technique.That is a curved oblique weir.Modern weirs are built making a right angle with river channels, but·old ones, mostly constructed during the 17 th or 18 th century, crossed rivers obliquely and curvedly.
The author discovered the following advantages of those curved oblique weirs through the fieldwork and his experimental studies.(1) Safety of weirs against flood flows.(2) Easy construction.(3) Deep digging does not occur in the downstream of the weirs.(4) Safety of intake gates.(5) Small change in the form of river bed after construction.
Thus the author clarified the rationality of curved oblique weirs, especially against flood flows, on the basis of the conception of ‘Sarekekitai’

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Some features on the longitudinal dispersion process of a solute matter in open channel flow are described based on the fundamental properties of the turbulent advective diffusion equation. Moment equations were obtained by applying Aris's moment transformation to the two dimensional advective diffusion equation.These moment equations are solved numerically to the third order, under the condition of instantaneous line source of a solute and the assumptions of logarithmic velocity distribution law, 1/6 power law and Reynolds analogy for turbulent diffusivity.The mean displacement or the central position and spreading of a solute and the distortion of solute distribution in flow were investigated with the statistical quantities, such as mean value, variance and skewness factor.The distribution of the mean displacement and variance with water depth increases with dispersion time, and reaches an equilibrium state at dispersion time t=5.0. h/u_*, here, h is water depth and u_* is shear velocity.On the other hand, the distribution of skewness factor with depth tends to become uniform with the increasing dispersion time.The mean overall variance in depth direction varies linearly with the increasing dispersion time, and overall skewness factor approaches zero gradually with time.The dispersion coefficient E proposed by Taylor's one dimensional dispersion theory was estimated with the calculated variance.When E is expressed as E=C·u_*·h, the constant value C depends mainly on the velocity distribution. Especially, when the velocity distribution is given by 1/6 power law, the constant C is a function of U/u_*, here U is mean velocity. Generally, it seems that the value of C is between 1.0 and 13.0 in the ordinary two dimensional open channel flow.
The characteristic time scale T_* and velocity scale V in a flow field were introduced to represent the results from the general point of view. The time scale T_* is defined as the intersection of the asymptote to the time-variance curve with the time axis, and the velocity scale V is defined with eq.(61), which represents the magnitude of nonuniformity of velocity distribution. The dispersion parameter E, similar to the dispersion coefficient E was expressed as E'=T_*·V² in terms.of T_* and V, according to the analogy of turbulent diffusion theory. The value of T_* is same order as h/u_* in the two dimensional flow.As the value of E' is almost same as that of E, E' seems to represent E, which may be estimated easily by experiments even in general flow fields.Also, it was shown that the Taylor's one dimensional dispersion theory is valid at the dispersion time of more than 5 times of T_*.

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The results of experimental study about subsidence and stress wave propagation in case of the repeated loading on semi-infinite cohesive soil and the relation between them are reported. The laboratory experiment and field experiment were carried out using clay soil and silty-loam soil as samples.The following matters were clarified.
Direct proportionality existed between the accumulated subsidence and the frequency of repetition of loading regardless of surface and inside.However, the absolute values of the former varied appreciably with the kinds, and water content of the sample soils and the experimental conditions.
The ratio of the cumulative volume of subsidence at 5 cm depth to that on the surface was in direct proportion to the frequency in logarithm of loading, but the absolute values were different remarkably according to the water content of the sample soils.
The front line of yield, which is the boundary of the subsided region and no subsidence region, moved forth both vertically and horizontally as the number of repetitive loading increased.
At any depth in the samples, the magnitude of stress wave propagation was reduced greatly by first several times of loading, then became nearly constant with a few exceptions.
The above results indicate that the dimensions of a subsided region can be estimated on the basis of the relation between precompression load and the propagation of stress waves.

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