八ケ岳火山山麓の水理地質学的研究
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概要
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The water resources of a volcanic terrain are generally richer than those of other areas, because this type of land is made up of aquifers with excellant reservation capacity. However, the mechanism of groundwater storage and the groundwater flow process have not been made clear yet. For instance, it is difficult to explain the presence of springs halfway up some volcanoes. To investigate these points, the author studied the Yatsugatake volcanic terrain quantitatively for its groundwater storage mechanism and the relationship between the surfacewater and the groundwater of the terrain and constructed a water balance model of the general volcanic terrain. The Yatsugatake volcanic area is made up of the Yachiho and the Hirose groups which form the independent sedimentary basins each other corresponding to the shift of the volcanic activity center. In addition, each basin form a groundwater basin and a long and wide regional flow system which move from the volcanic body to the piedmont. The unite aquifers constitute the formations in the Yachiho and the Hirose groups. The 5 groundwater zones in the Yatsugatake terrain show different characteristic of groundwater and are divided from the volcanic body to the piedmont. i) Volcanic body recharge zone : This is a recharge zone made by precipitation. There is no base flow into the valley. ii) Middle recharge zone : This zone is located in the upper part at 1,600m altitude, where the spring groups in the valley form a line along the contour line. About 10% of the groundwater flowing from the upper part is discharged along this line. iii) Middle spouting zone : This zone has many springs on the piedmont planation surface. About 40% of the groundwater flows from the discharges of the upper zone. iv) Lower leak zone : This zone is situated on the piedmont planation surface and faces the deep valley which marks the edge of the terrain. The potential of confined groundwater is about 10m lower than the unconfined groundwater in the area. v) Lower spouting zone : This zone is found in the deep valley which marks the edge of the volcanic terrain. All of the recharged groundwater of the terrain is discharged in this area. The water balance of every zone were calculated with the surface water discharge. The result of this calculation showed clearly that the base flows of the rivers of the lower zones rather than the middle recharge zone were supported by the constant discharge of groundwater. The groundwater table draw down rate which supports the base flow was 0.032m/day in the middle recharge zone, 0.017m/day in the middle spouting zone and 0.004m/day in the lower spouting zone. Base flow in the lower leak zone decreases due to the leakage to groundwater, and it increases in the paddy field due to the leakage from surfacewater.
- 信州大学理学部の論文
- 1982-09-30
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