Free ground water is affected by irrigation in paddy field area. The relation between surface and subsurface water can be shown in a water balance formula. The equation of hydrologic equilibrium provides a quantative statement of water balance. For example, repeated use of irrigation water is calculated by this formula. In addition this report referes to the classification of irrigated area from hydrogeologic investigation.
The wells of the shallower natural gas dissolved-in-water in Niigata Plain are mainly household use, and the depth of these wells are mostly shallower than 150m. In about 600km2 area, there are about the 8, 700 wells and the total water volumes discharged from these wells are about 121, 800m3/day. The wells and water volumes are richest in 60-100 depth. Moreover, it is remarkable that the distribution of these wells and the preservation of the shallower natural gas dissolved-in-water harmonize with the condition of Alluvium in Niigata Plain.
The Izumigoshi tunnel was excavated in volcanic rocks belong to the Yugawara volcanic rocks group (pleistocene), Inamura andesite group (pleistocene). During the excavation of thil tunnel many accidents were encountered, were break down of fault zone at 92K 890m from Tokyo, deformation and failure of tunnel suports, tunnel lining due to swelling rocks extended about 360m total long, which from altered volcanic glass, tuff and tuff breccia by hydrothermal alternation. The author analysed clay minerals in the rocks by X-ray diffraction method, concerned the relations between content of clay minerals and value of compressive strength, velosity of super sonic waves, and engineering difficulty occurred in the tunnel. In the results its was found that this clay minerals composed mainly montmorillonite, deformation and failure in the tunnel connected with content of clay minerals. The result of survey and analysis are shown in fig.2-5.
On Sedimentation in Reservoirs, the geologists of Central Research of Electric Power Industry have carried out since 1949 a series of geological investigations on the points of sediments and drainage basins tributary to reservoirs. This paper presents the result of survey on Sediments in the Senzu and the Kuze Reservoirs with the tributary drainage basins consisting of old sedimentary rocks. According to the survey of the impounded water in the Senzu Reservoir, its values of the Secchi-disc readings were from 0m to 3.4 m, its p. H. values from 7.2 to 8. 8, its temperature values from 17.4°C to 21.3°C, for September in 1952, and in the Kuze Reservoir its values of the Secchi-disc readings were from 1m to 7m, its p. H. values from 6.6-8.2, its temperature values from 18.5°C to 25.3°C, for August in 1958. Moreover the p. H. and the temperature distributions of the Senzu Reservoir show the thermocline and the metaliminion, wheres such phenomenons are not clearly seen in the Kuze Re servoir. The sediments in both reservoirs consist of Silt and Sand, with an amount of gravel. Silt is deposited only near the dam, but Sand and Gravel are spread out in the middle and upstream areas of the bottom. The delta with the topset, the fore set and the bottomset beds has been made up in the Senzu Reservoir, wheres such form is not clear in the Kuze Reservoir.