Excess Flood Event in Tokyo East Lowland (below sea level) and Defense Measure (II)

Abstract

The suggestion about ways of protection for flood exceeding the designed level in the eastern part of Tokyo Lowland（below sea level area）. The East Tokyo inundation area will be seriously damaged if once the dyke is destroyed because there is densely populated with highly economically activated. In order to increase the safety against the flood, super dyke would be the most effective countermeasure, which aims to achieve the protection of dyke from the excessive flood. The super dyke would be enough strong for the excessive flood and seepage failure as the width would be 30 times of its height. At the same time, this dyke with soil improvements against liquefaction could be enough strong for the earthquake and would be possible to protect the low land below sea level from flood. Furtherer more, the dyke could produce the safe high land as an evacuation area to protect human lives and properties from flood and high tide. From these characteristics, the main effectiveness and objective of the super dyke can keep the evacuation area for the citizens in the east lowlands in Tokyo. Nakagawa river is the most urgent area to equip the super dyke among East Tokyo basin because it is located at the lowest elevation with highly dense populations. Therefore, the author would like to propose to Arakawa river let to increase flood through capacity enough to use the space of Nakagawa for construction the super dyke. This plan would be the only way to protect human life and properties in Edogawa district from the coming excessive flood and high tide.