When the crop rotation is carried out in sloping paddy field areas, the groundwater table often rises with the seepage from the surrounding paddy fields. Consequently, it becomes one of the most important problems to lower the groundwater table and to improve the drainage conditions of such a rotational field. In this study, we have considered the groundwater table in the rotational field in sloping paddy field areas, when drain pipes were buried at the toe of the levee.
At first, the flow region bounded by an impervious boundary at a finite depth was considered. After the groundwater table was transformed into a straight line using the Zhukovsky's function as shown in Fig. 1, the flow problem was analyzed to obtain a theoretical equation of groundwater table by the theory of conformal mapping. And as a particular solution, a theoretical equation when the impervious boundary was infinitely deep was also derived.
Next, the results calculated from these theoretical equations were compared with the observed data at the Higanden test field in Okayama Prefecture, and the results have shown a good agreement with each other (Fig.3).
From the above calculations, it was found that the groundwater table is affected by the depth of the impervious boundary, namely, the groundwater table would fall deeper as the impervious boundary became shallower. However, the effect was not so large that the results obtained from the assumption that the impervious boundary was infinitely deep were applicable well for practical purposes.
The results of discussion are shown in Figs.4 and 5. In order to lower the groundwater table of the rotational field, the drain pipes were to be buried along the toe of the levee of upper paddy fields as near as possible. Moreover, they must be buried as deep as 1 m, which is rather deeper than in the case of level land.
The groundwater table was much affected by the slope as shown in Fig.6. In the sloping areas steeper than 1/20, the groundwater table could be lowered by only one drain pipe at the toe of the levee. In a more moderate slope, mpre than two drain pipes were necessary to lower the groundwater table.

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The water quality and load were investigated in 8 rivers flowing into Lake Kasumigaura in May. In the manuring period fertilizers are intensively used for paddy fields of the basin. The concentrations of NH₄-N, PO₄-P and COD in May are higher than those in winter. But, contrary to expectation, the specific loads in May are not higher than those in winter, resulting from significant decrease of discharge of the rivers by the intake of irrigation water into paddy fields (Fig.1). Changes of load in the downstream of the Rivers Sakura and Sonobe (Fig.3) show similar results. On the other hand, the load in the River Ichinose into which irrigation water enters from Lake Kasumigaura is not decreased in May (Fig.4). This is due to the load of irrigation water which in turn increases the load in the River Ichinose. Furthermore, the same tendency is observed by comparing the water quality and load in May with those in April; the concentration of nitrogen in May is higher than that in April (Fig.6), but the total load in the 8 rivers is not higher than that in April (Fig.7). Nevertheless, in some rivers the load of inorganic nitrogen is increased. The load flowing into the lake from the rivers is influenced by circumstances such as the method and water volume of irrigation.

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In the study of underground water, it is nessesary to know the conditions of the container, that is, the underground geological structure in which the underground water exists, and the boundary conditions of the container, and moreover, to grasp the quantity of water that goes into and goes out from the underground. Of course, this quantity varies in accordance with the conditions of area, such as farm and paddy fields, industrial and residential zones and mountaineous area.
We make some devices in dealing with the underground water. For example, to calculate the permeability-coefficient (p. c.) of the complicated underground layers, we use the formula “Σk_i·h_i=k_m·h”, where ‘k_i’ means the respective p. c. of layevs, ‘h_i’ the respective thicknesses of layevs, ‘k_m’ the p. c., and ‘d’ the total thickness of the layers.
And, in the mountaineous area, we adopt relatively smaller values of the porosity and the p. c.
We applied the method mentioned above to the Echigawa Delta Area.
First, we divided the area into 4 parts as shown in Fig.4, the lake-side and river-sideareas indicated by ‘A’, the mountaineous area by ‘B’, the industrial and residential zones by ‘C’, and the farm and paddy fields by ‘D’.
The permeability-coefficient was changed between 10^-4 m/secand 10^-8 m/sec and the porosity between 0.15 and 0.30, in accordance with part A, B, C and D.
Assuming that 60-30% of the rainfall (varies with parts A-D) and 60-20% of the irrigation water (also varies with parts A-D) go into the under ground and the amount of evaporation is 1-5 mm/day (varies with theseason), and the amount of pumping up for the industrial and drinking water is 1-3mm/day (varies with the season and parts A-D), we obtained good results for practical use, judging by comparing the calculated and the measured values of the undefground water level as shown in Fig.6 and 7.

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In this paper, the relationship between water and soil compaction has been studied. In considering the surface of soil particles, it is possible to deal with the water in soils as the thickness of absorbed water around the soil particles. The thickness of absorbed water is obtained by dividing the water quantity in soils by the surface area of soil particles.
The soil compaction tests were carried out on a soil sample of which the surface of the particles was known and the experimental results were considered on the basis of the thickness of absorbed water.
The results obtained from these experiments are as follows:
1) In soil compaction, it was found that the relationship between the thickness of absorbed water (t) and the molding water content (w) was linear.
2) The change rate of the thickness of absorbed water with the change of molding water content (dt/dw) was in inverse proportion to the specific surface of soil particles (S_w).
3) Near the optimum moisture content, it was clear that the change rate described above was almost constant for various soils used in this experiment.
4) It became possible to analyze the shape of the compaction curve of soils and the analysis showed that fine soil-that is, soil that had a large quantity of the surface area of soil particles-had a gradual slope.

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Structures are generally required to be stable even in a state of accumulated random effects of environmental changes in the history of their assigned service duration. These effects are expected to be of many kinds in change and influence. A problem of such kind in which the cause of change is known but the influence of it can only be statistically estmated is treated here.
When a highway is planned to constructon the crest of an earth dam in a service state, it is necessary to check the stability of it because the dam is going to be subjected to an additional load effect due to vehicular running. Traffic flow has a typical stochastic character so that the effect can only be estimated statistically.
In this study, on the assumption taht the effect of vehicular traffic causes fatigue of dam material, the rate of stability degeneration by the effect of simulated traffic flow is analyzed with the aid of FEM. A design method to keep recommended safety is proposed, in which the effect of vehicular running is mostly taken into account.
The paper consists of three parts and the outlined contents of them are: 1) examination of dynamic characteristics of earth dam by actual vehicular running, 2) determination of design load by simulation of traffic flow, and 3) establishment of a method of design and of traffic control rules.
A blief description of the conclusion arrived at in this part of the paper is that an impulsive load effect is observed due to vehicular running in the earth dam and its effect is intensified by existing roughness on the surface of highway.

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