The effective rainfall in the paddy field during the irrigation period was studied from the viewpoint of determining the storage capacity of the rainfall. The results of this study, are as follows:
1) The maximum storage capacity of the rainfall was estimated. As the measurement of the storage capacity for the rainfall is very difficult for a large number of paddy fields, the simulation technique was employed. For this purposes, the statistical properties of the undulation of paddy field surface and hight of the outlet sill were investigated at the Wadayama test field.
2) Taking into consideration the ponding conditions of the paddy fields, the storage capacity at that time was also estimated with the aid of statistical data concerning the heights of the surface of paddy fields and the level of the formed pond.
3) This method was applied to Wadayama test field in Hyogo Prefecture. According the results, it is expected that the storage capacity and the amount of storage rainfall was rather small compared to the effective rainfall standards for paddy fields which were already applied.

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Measurement of daily evapotranspiration from peanuts by a weighing lysimeter during the summer, 1976, in the Tottori sand dunes showed a maximum daily value of about 10 mm/day. Considerably more energy was consumed for evapotranspiration than was available from net radiation during growth in mid-season. The multiple correlation coefficient in the multiple regression equation for estimating evapotranspiration by air temperature, net radiation, wind speed, relative humidity and the leaf area index was 0.92 as a result of evapotranspiration on crop growth, while the coefficient in the case where the leaf area index was not used as the predictor variable was 0.80.The crop coefficient for potential evapotranspiration estimates, from predicting methods for a reference crop, was determined and the pan evaporation method and the combination method were compared with regard to the estimating accuracy.The former was unexpectedly superior to the latter which seemed to have resulted from the use of relative humidity at 9 a.m.instead of the mean values owing to data inavailability. The daytime latent heat flux exceeded the difference between net radiation and soil heat flux.This was due to the downward flux of sensible heat which was verified by the measurement of air temperature profiles. The downward flux of sensible heat in the daytime has been considered to be evidence of advection which is popularly observed in the irrigated fields in arid land, and evapotranspiration in a sand dune area might be influenced by this effect to a great extent.

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Dispersed housing areas had been effective in maintaining adequate rural road networks prior to the introduction of land consolidation projects.
As more and more farm households have found it necessary to use vehicles, they have in turn demanded better roads for the rural areas. The municipal governments in these areas are making all-out efforts to improve the road networks on behalf of the people.
In order to find the best way to rationalize the road networks in dispersed housing areas, we made a comparative case study on methods of road improvement between two cities Tonami and Oyabe, in Toyama prefecture which are typical dispersed housing areas in Japan.
In the case of Oyabe, to satisfy the demands of the inhabitants the city paved all the farm roads by without broadening them. As a resut of this, the roads were not wide enough to allow for the clearing of snow, nor were they wide enough so that vehicles could pass each other.The paving of the roads help farmers better mechanized their farms, but road maintenance became very costly for the local gevernment.Tonami, on the other hand, took a more futuristic approach, not only paving their trunk roads but widening them as well.Therefore, the amount of roads which they were able to pave and widen was small in comparison to Oyabe's, but in the longrun this method will be better able to satisfy the demands of the inhabitants using them.
The differences in the way in which the roads were improved upon was the result of the way in which they are to be used.

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The paddy fields in the Makake and Yogoiri areas, which are two representative paddy fields along Lake Kasumigaura, have been investigated with respect to water balance and material balances during times of irrigation.The amount of the area in Makake and Yogoiri to be irrigated are 35 ha and 233 ha, respectively.
The Makake area is irrigated and surfacedrained using the same pump, and usually the surface-drained water is used again as irrigation water.In Yogoiri area, irrigation water is naturally let in by intake gates and drainage operations are carried out by pumps.
Results of investigation:
1) The total amount of water used for irrigation in Makake is 1, 338mm (rainfall, 861mm;water taken from the lake, 314mm;reused surface-drained water, 163mm), with the amount of water being drained off totaling 565 mm.
Therefore, the irrigation system in this area is a type which economizes on water.
In contrast, in the Yogoiri area, there is a large quantity of water, with the amount of water for irrigation totaling 3, 840 mm and drainage water amounting to 3, 270mm (Fig.2).
2) T-N concentrations of irrigation water from Lake Kasumigaura are slightly higher in Yogoiri than in Makake.This is probably due to the fact that the intake gates for Yogoiri are nearer to the mouth of the Ono river.However, T-N concentrations of drainage water are higher in Makake.
3) The T-N load taken from Lake Kasumigaura in Makake is 8.5 kg/ha and the T-N load drained into the lake is 9.0kg/ha.In Yogoiri, these values are remarkably higher (the load taken in, 44kg/ha; the load drained, 41kg/ha).
4) In Makake, the T-P load taken in is 0.11 kg/ha and the load drained is 0.29kg/ha. In Yogoiri, the former is 0.74kg/ha and the latter is 0.72kg/ha.
5) May is the time when the T-N and T-P loads drained into the lake are the highest, when manure used for planting is made.Therefore, it is important that the manure utilization technique be improved.Moreover, it has become clear that proper circulating irrigation and economization of water are two effective means to reduce the unnecessary drainage of manure to outside areas.

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Of rate, demand for industrial and city water has remarkably increased, and the effective utilization of available water resources and a large scale development covering multiple river systems for supplying water are some of the urgent subjects to be executed.
In this study, the annual minimum moving average rainfall of n days (R_j (ⁿ)) was obtained based on the observations from the principal observatory points in Kochi Prefecfure and some review were given to obtain the results stated below:
a) R_j⁽ⁿ⁾at the principal observatory points in Kochi Prefecture shows a nearly linear distribution in the Weibull probability paper.
b) No tendency change can be observed in the secular change of R_j⁽ⁿ⁾.However, within such short, period of ten (10) years, its average values indicate variation and are not always constant.
c) R_j⁽³⁰⁾ shows nine (9) years of periodicity in the level of significance of 1% while seven (7), nine (9) or sixteen (16) years of periodicity in the level of significance 5%. Other R_j⁽ⁿ⁾does not show any periodicity.
d) In the correlation coefficients between R_j⁽ⁿ⁾ and minimum discharge per year, drought discharge and low water discharge, the coefficient at the time of n=30 is maximum and is about 0.7 However, in the correlation coefficient between R_j⁽ⁿ⁾ and discharge corresponding to n days of the moving average when daily discharges are ordered according to quantities starting small quantity, it has been found to indicate an extremely similar variations within the range up to n=100.

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The temperature of irrigation water is an important factor affecting rice yields.As the snow melts water is obtained for irrigation and is stored in reservoirs for agricultural use in Hokkaido. As the temperature of water is directly related to rice yields, sufficient attention must be given to the water temperature in the reservoir.
In this paper, we have described about the characteristics of water temperature in the Tsukigata Reservoir.The results are summarized as follows:
1) When the amount of the water entering the reservior is low, during the time when the fields must be irrigated, then the water level of the reservior will suddenly drop, influencing the temperature of the epilimnion and thermocline.
2) The drift current resulting from valley winds of over 2.5m/sec in the daytime will cause the water temperature of the surface water around the intake tower to fall rapidly.
3) If the cold water is discharged from the lower layer before irrigation operations are started, the water temperature of upper layer is formed quickly and the water temperature of lower layer becomes high.Therefore, the water temperature in the reservoir increases by about 20% when compared to the water being discharged from the spillway.

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Several features on the dispersion process in the open channel flow are investigated, solving numerically the two-dimensional advective diffusion equation. The results, obtained for turbulent flow with a logarithmic velocity distribution, show that the longitudinal distribution of the solute concentration is a skewed asymmetric pattern at the initial time stage and Taylor's dispersion model is inadequate at this time stage. However, the longitudinal dispersion coefficient can be estimated, as the statistical variance of distribution varies almost linearly as dispersion proceeds. The dispersion coefficient is expressed as E=8.19u_*·h, under the hydraulically rough boundary condition (U/u_*=14.5) here, h represents the depth, u_* the friction velocity and U the discharge velocity.

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The backsand phenomenon in a steep slope straight riverwith a compound section was experimentally studied and the following facts were found:
1) In the compound section of a straight and winding rivers, the eddy region appears at the connecting position of rivers and reservoirs, that is on the high-water channel of the direct downstream station of the jump. Owing to this phenomenon, the backsand mechanism differsfrom the rectangular section case and backsand occurs only with the undular type. The beginning of deposition moves more rapidly in the straight river case with a rectangular section and its speedlessens in order of the winding river case and the a straight river case with a compound section. And reversely, the front of the delta moves slowly in the former order. This order is same as the order for the area of the eddy region.
2) The vaious sedimentation characteristics are similar to thosein the case of the rectangular section except that the sedimentation begins at the downstream station separated from the jump in case of a large eddy area owing to the existence of the eddy region.
Assuming the formation rule for delta sedimentation based on thetest results, the movement at the beginning point of deposition and the front of the delta with a lapse of time were theoretically estimated.
3) The area of the eddy. region was affected mainly by dr (dr=d/h₁, d: The difference of the elevation between high-water and low-water channel beds, h₁: the depth of the low-water channel at the upstream station of the jump) When dr is less than the critical value, the eddy region disappears, and when dr is larger than the critical value, the eddy region expands its area with an increase in dr.
This critical value is shown by the equation that is strictly the function of the Froude number.And then, the mean width of the eddy region was theoretically estimated by the momentum equation.

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The authors studied the water characteristics of organo-volcanic ash soils by using the pressure plate and centrifuge methods for undisturbed soil samples.
In this paper, the authors compared the pF-soil moisture curves with both methods mentioned above, and investigated the effect of soil compression by centrifugal force on the pF-soil moisture curve when the centrifuge method was used.
Soil samples, four of organo-volcanic ash soil, one volcanic ash soil, one heavy clayey soil and one alluvial type soil were used (Table 1).
The results obtained are summarized as follows:
(1) The pF-soil moisture curves by the centrifuge method differed from those by the pressure plate method. And water retention by the centrifuge method was lower than that by the pressure plate method.above pF 2.5 for the volcanic ash soil (Fig.2 and 3).This can be explained by the excess drainage due to soil compression when the centrifuge method was used for water retention measurements.
(2) The volume change of the soil samples by using the centrifuge method was much larger in comparison with that by the pressure plate method, especially for organo-volcanic ash soils which are commonly called KUROBOKU SOIL (Fig.5 and 6).The decrease in the volume of soil samples was mainly due to the soil compression by centrifugal force, and a part of that was due to shrinkage resulting from drainage when the centrifuge method was used.
(3) The volume change by using the pressure plate method agreed with the shrinkage curve for undisturbed soil samples (Fig.7).And according to the experiments, the turningpoint at which the structural shrinkage changes to normal shrinkage on the shrinkage curves for undisturbed soils, was equivalent to about pF 3 in case of the pressure plate method (Fig.7)
(4) The decrease in volume by using the centrifuge method at above pF 3 for KUROBOKU SOIL, and pF 2.5 for volcanic ash soil and non-volcanic ash soil, was much larger than the volume change due to shrinkage by air drying.(Fig.7).
(5) The degree of water saturation of the soil samples by the centrifuge method increased with increasing pF value when the pF value was higher than pF 2.5 (Fig.8).It seems that the drainage by consolidation owing to centrifugal force may occur in that pF range mentioned above.
(6) The experimental data show that the centrifuge method should not be used above pF 2.5 for water retention measurements of KUROBOKU SOIL.

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Most of the hydraulic structures are made of concrete and are easily susceptable to deterioration due to acidic water and so on.If concrete is left in acidic water for long periods of time, the properties of the concrete will deteriorate.Therefore, to show the influence of acidic water on the durability of concrete, a large number of concrete test pieces were submerged in a small stream in which acidic water flowed. The location of this stream is at Arakane, Iwami-Cho, 30km from Tottori University. The mean pH value of the water in this stream is about 3.2 for last six years. The first experiment (series 1) was carried out from January, 1973 to July, 1976 and second (series 2) has been carried out continuously since October, 1976. The test pieces were 10×10×40cm, and both test pieces were of different weights. The first had a unit cement content of 250 and 300kg/m³, and the second 200 and 400kg/m³.
The following factors were measured and analyzed, respectively, every 6 months.
a.Volume and weight
b.Bending and compressive strength
c.Dynamic modulus of elasticity
d.Surface roughness of concrete
The results so far obtained are summarized as follows.
1.Concrete was deteriorated to a great extent by acidic water with a pH of about 3.2, and so, concrete which had a cement unit weight content of less than 300kg/m³ was almost reduced to zero after one or two years.
2.After one or two years, it is assumed that the volume of the test pieces increased due to the infiltration of acidic water into the test pieces, resulting in internal corrosion, and so, the rate of corrosion decreased rapidly for concrete which had a cement unit weight content of less than 300kg/m³.

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