都市化と水害

Abstract

The urbanization of forest and agricultural areas near big cities is being accelarated with theadvance of the overpopulation from the cities in modern Japan. The urbanization of a watershed, however, is apt to promote the flood potential in the watershed or its down stream areas.This paper discusses the effect of urbanization on the flood potential generally but quantitativelyfrom the view point of engineering practice. The discussion is carried out through the followingitems: Changes in the detention and storage capacity of rain water on the ground surface and inthe surface soil layer; changes in roughness and gradient of the slope surface; changes in theconcentration time, the peak runoff coefficient and the peak dischage of flood runoff; and theground subsidence in an alluvial fan.Moreover, several counter-plans to prevent or mitigate flood disasters due to urbanizations areproposed from the view points of engineering practices and social policies.