SUBSIDENCE OF THE NOBI PLAIN

Abstract

The Nobi plain underlain by younger sediments is situated in the central part of Japan and is about 1300 km^2 in area. The yearly rates of subsidence in this area were 1.4-1.8 mm before 1925, 2-5 mm during the period from 1925 to 1950, 10-20 mm during the period from 1950 to 1960, 20-40 mm during the period from 1960 to 1965 and more than 100 mm at places having severe subsidence recently. The major cause of this increasing subsidence is the increasing withdrawal of ground water for industrial, agricultural and other purposes. As a result of such subsidence, an area of 250 km^2 subsided below the mean sea level. The drainage during and after heavy rainfalls has been becoming difficult day by day, and the potential danger' of tidal flood under a typhoon has been increasing year by year. Against such subsidence of the Nobi plain, investigations are being done by officials of central and prefectural governments and professors of universities in this area. Based on the investigations, withdrawal of ground water in this plain is now being controlled by regulations of the authorities concerned.