濃尾平野の地盤沈下の解析

Abstract

The land subsidence in the Nobi Plain, central Japan, was examinined in relation to the withdrawal of ground water and also to the displacement of the basement together with consolidation of subsurface younger sediments. The history of ground subsidence in this area was obtained by the use of bench marks along a surveying line in the southern part of the area for 99 years from 1885 to 1984. The subsidence stage is classified into 5 periods according to its yearly rates. The first period is from 1885 to 1925,the yearly rates of subsidence being 1.5-2.0mm with the withdrawal of ground water of 1000-1640m^3 per day. The second period is from 1926 to 1950,the subsidence rates being 2-5mm with the withdrawal of ground water of (12.0-15.4)×(10)^4m^3 per day. The third period is from 1951 to 1965,the subsidence rates being 1-10cm with the withdrawal of ground water of (15.4-155.2)×(10)^4m^3 per day. The fourth period is from 1966 to 1975,the subsidence rates being 1-18cm with the ground-water withdrawal of (155.2-380.2)×(10)^4m^3 per day. The fifth period is from 1976 to 1984,the subsidence rates being 8-1cm with the ground-water withdrawal of (327.2-210.4)×(10)^4m^3 per day. The major cause of the increasing subsidence is the increasing withdrawal of ground water for industrial, agricultural and other purpose. The ratio of subsidence caused by ground-water withdrawal to that caused by natural factors such as basement displacement and consolidation of younger sediments is found to be from 3 to 20.