池田湖の水収支に関する研究

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The aim of this study is to clarify the leakage-characteristics of the "Ikeda-Lake" through the surveying of its actual water-balance, for the purpose of utilizing the lake as the reservoir for developing the "Southern Satsuma Project". For the realization of this purpose, several surveys, studies and experimentations have been carried out as in the following : Chapter 1.-General out-line of the features of the lake. Chapter 2.-Records of rain-fall and lake-water-level from 1902 to date. Chapter 3.-Records of water-level in the existing springs and wells around the lake, observed along with the characteristics of underground-water-level. Chapter 4.-Permiability of the soil ascertained in relation to the water-balance-sheet studied by field experimentations. Chapter 5.-Characteristics of the run-off in the area concerned. Chapter 6.-Underground homo-thermal stratum. The water-balance-sheet of the lake was calculated, using the data obtained from the above mentioned studies. From these results, it was confirmed that the quantity of the lateral percolation underground is controled by the variations of the water-level in the lake, especially, by the underground water-level neighboring the intended places seen from the view point of the long period, but seen from that of a shorter term, it seems to be disagreeing with the law of hydraulics, which depends upon the pressure exerted by the sealed air, on the way of rain-fall-percolation and under the resultant influences of other delicate and complex phenomena and effects of rainfall-percolation, experiments were performed in the laboratory, as follows. Using the sieved materials of usual sand and volcanic "Shirasu Sand" existing in the area concerned, an experimentation of vertical percolation was done by pouring water in place of the rain upon the percolating box, while observing the variations of the lateral percolation, which occurred through the foot-part of the box, with the head kept constant. And, to verify the phenomenon the more exactly, experiments using the compressor to press, instead of pouring, water were done in another box similar to the first box except having a coverhead, the head kept constant as stated above. These enabled us to make it sure that the complex phenomena and influences of rain-water-percolation upon the lateral percolation stated before, took place in the laboratory experiments, too. Considering the natural phenomena, and using the results of the experiments, the following conclusions were obtained : i) In case of the vertical percolation, apart of the undergrount-water is expelled instantaneously by the pressure of the confined air, thus in lateral percolation discharge of water is made to be increased and then decreased sharply immediately afterward, gradualy recovering the usual quantity. ii) After the rainfall of heavy intensity, occurring in the last course of percolation, the discharge decreased suddenly through the sudden decrement of the pressure. iii) At the next stage, the discharge increased again. This may be reasonably expained as in the following, namely when the percolated rain water reached the underground-water-table, it was absorbed into the increasing "Storage", resembling a river-storage ; and after having full-filled the discharge will be made increased by the releasing of that storage-water. iv) The exess-water is ponded on to the ground and will confine the air in the soil underneath, and press the water involoed. v) Long after the rainfall, the percolation will almost become ceased, and the underground water-table will begin to get lower. In such condition, the discharge will increase at the beginning, and then decrease afterward for the resons mentioned above. vi) In nature, the relationships among such various factors as the thickness and number of percolation strata, permeabilities of various strata, the length and inclination of lateral percolation, intensity of rain-fall and others are very complex. Hence the necessity for us to take as much care as possible in judging the actual phenomena. In future, much attention should be paid to the following points, practically and technically. A) As to the actual leakage, it has been confirmed that the paths of percolation or leakage are concentrated on a few places, and especially on to the so called "Kyoden" spring, the most prominent one, in which the minimum discharge of water is 0.135m^3/sec, being 68% of the total leakage, observable in case of the lowest lake-level. The total leakage, namely about 30 million tons per year is equivalent to the quantity of water, which is used for one year in "Southern Satsuma" irrigation project ; and the smaller the quantity the lowerer is the water level. Therefore the problem of leakage is one of the most important factors to determine the standard of the lake-water-level, which must be maintained for practical use, and it is very important, also, for the researching of the path of main leakage as well as for the solution of the problem how to develop a special technology most effective to stop the leakage. B) Forecasting of the water-level of the lake in case of rain-fall, is possible in view of the above mentioned facts. C) In this paper, the characteristics of run-off in the volcanic "Shirasu" district in particular have been but under considerations, and they have been applied to the concept of the least discharge in the riverbasin in hydrology, which is composed of surface run-off on that specific day and of the underground run-off resulting from the rains which had been following several months before that day.
鹿児島大学の論文
1972-03-30

著者

阿部雅雄
Laboratory of Agricultural Engineering

池田湖の水収支に関する研究

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