The “Asian Regional Conference of International Association of Hydrogeologists” was held in Tokyo on August, 1971. Taking good advantage of this chance, he summarized the history of IAH which was established in 1956 at Mexican Congress of IUGS. Past conferences and its publications were indicated. He also described the process of Tokyo conference, its significances and member of organizing committee. About three hundreds persons took part in this conference, among these sixty (without ladies) were foreign ones. More than fifty essays were presented, but thirty were read on conference. These were published as IAH Mémoires Vol. 9. Beside announcement, he had exhibition of hydrogeological maps and post-congress tours of Kyushu and Tohoku. He also evaluated this conference from the scientific and cultural stand point of view and pointed out problems to be solved.
Mt. Yotei is a typical conide with the area of 104 km2 and the altitude of 1893 m. It is situated in southern Hokkaido and composed of numerous lava flows and pyroclastics, is called “Ezo Fuji” after its shape because of resembling to Mt. Fuji and one of the well known mountains in Hokkaido. The composed rocks have high permeability so that the rain fall does not stay on the surface to be ground water. Therefore, there are many springs with rich discharge amount, in the piedmont of this conide. The present authors selected 17 springs of which the discharge amount is more than 20 l/second and carried out 7 surveys on the discharge amount and chemical property of those springs from 1969 to 1971. The results are as follows ; 1) Each spring mentioned above is found from an the altitude of 215 m to 270 m and each of them flow out along the basemental plane of Mt. Yotei. As to those 17 springs, there are two, each of which the discharge amount is over 500 l/second and ten of them over 100 l/second respectively. There is no relation between discharge amount and altitude, but is a regional trend on the connection between distribution density and discharge amount. That is to say, there are several rich springs in the eastern piedmont, while many poor ones, but no rich on in the western part. 2) The water shed drawn in a map by the catchment area calculated by the discharge amount of each spring, reveals no relationship to the surface topography of this conide. There are some rich springs of which the catchment area reaches to the western piedmont through under the summit of Mt. Yotei. 3) The maximum discharge amount is recorded in May and the minimum in February. The ratio of the maximum to the minimum is small and 1.1-1.9 in the eastern piedmont, but increases to be 1.6-5.5 in the western piedmont. 4) Spring in the eastern piedmont, of which the water temperature is below 7°C and its concentration of dissolved ion contents is low and less than 2.5 epm, has the property of the river water type. On the contrary, those of the western piedmont of which the water temperature is above 7°C and its concentration of dissolved ion contents is more than 2.5 epm, have the property of the ground water type. 5) The total runoff of all springs is about 1250 mm, the areal rain fall of Mt. Yotei is estimated to be 1700 mm and the evapotranspiration is 450 mm through an average year. Consequently, the water economy is well in equilibrium and the ratio of the runoff is 74 %.
No effective method of surveying the fissure ground water in the base rock has hitherto been found. The writer who has been proceeding the study of surveying the fissure ground water by measuring the natural radioactivity (gamma-ray) since 1950 has established the prospecting method. This method may be applicable not only to the development and utilization of natural ground water, but also to the surveying of artificially recharged ground water. By the performance of the ground water prospecting by this method, the writer has successfully detected some large fissure water zones in thirty water-wanted areas in our country. In these areas where the strong radioactivities were detected deep wells were drilled, from which several hundreds to four thousands cubic meters per day of water obtained. The radioactive dating of these ground waters was done, using tritium. As explained above, the writer's method of prospecting ground water by determining natural radioactivity has been proved to be very effective for the prospecting of fissure ground water.
This report treats of the groundwater condition in Eastern Osaka basin, especially of the problem of water-quality. Analytical works in the 1965-69 period on the artesian groundwater samples taken from the existing wells and test wells were summarized in several maps and diagrams ; a) isogram maps for major constituents, b) profile of chloride content, c) profile of water-quality represented by the shape diagram. The tritium content of 30 water samples was determined. Of these samples, three had less than 0.3 TU, five had less than 3.0 TU. Four main types of water based on alkalinity and chlorinity are described, with subdivision based on tritium content. The water samples characterized by the high chloride with the range of 100 to 300 ppm are distributed in the northern part of the basin. It is confirmed by the isochlor map and profile that the chloride was derived from the ancient saline water entrapped in the sediments deposited in a marine or brackish environments. The water samples of high alkalinity accompanied with nitrogen and phosphorus are found in the central part of the basin. The chemical and hydrological conditions which produce the water are discussed based on the content of the organic materials in the clayey layer. As a result of this study three discontinuous lines of water-quality ware found. One of them coincides with geological structure called Uemachi elevation, and the others lack the geological evidence. The discontinuation lying east and west provides a reasonable interpretation for the groundwater conditions as well as for the distribution of the amount of land subsidence in this area.
In progress of exploration for groundwater resources on the Shirasu areas in Kagoshima Prefecture, it was successful to detect and take fissure water from joints or cracks in andecitic lava-flows getting between tuffacious breccias in deep horizon. The results on electric prospectings and actual water well drillings are shown in this paper.
It was 1912 that the water well drilling by means of a mechanical method was done for the first time in Japan. Since then, various kinds of drilling machines have been designed and developed. 1. Construction methods for water well The purcussion method has gained recently a very high productivity of drilling, e.g.5-6 folds as much drilling speed as that of 20 years ago, by means of using tubular bit '. 2. Screens Many types of screens with various kinds of structure are now being manufactured, especially, the one with a high opening ratio is now widely used. 3. Pumping The main line of pumps for water wells are electro-submersible pump, with which safe-yield and conditions of aquifers are examined by means of draw-down test and recovery test in order to secure a rational discharge of groundwater.