Historical Review of Development of Land Subsidence and its Cease in Shitamachi Lowland, Tokyo

Abstract

The land subsidence began in the Koutou Distric developing the Shitamachi Lowland in the eastern par of Tokyo Metropolis at about the end of Meiji Era. Since then it had remarkably increased its degree and spread throughout the Lowland as the advance of the confined groundwater withdrawal. Such heavy land subsidence made the area below sea level almost all over the Lowland, especially the area below ebb tide level called Zero-Meter Region in the estuary of the Ara River. Due to spreading of such area below sea level, the Lowland had a lot of disasters of flooding caused by high tide and typhoons. Then to protect the Lowland area from these disasters, the Tokyo Metropolitan Government has systematically constructed and improved high tide countering facilities such as embankments, pumping stations and water gates. Furthermore in order to stop such land subsidence, the national government has restricted groundwater withdrawal for industrial use since 1961 by the Industrial Water Law, and for air conditional use since 1963 by the Law Controlling Pumping of Groundwater for Use in Building. This paper deals with the historical review of the development of land subsidence and its cease in Shitamachi Lowland to prevent land in the Lowland from subsiding again.