Rainwater Flooding and Its Counter Measures in Urban Area of Mega-Underground Mall

Abstract

Frequency of rainfalls over the capacity of drainage system is increasing and underground inundations occurred in some Japanese cities in recent years. It is an urgent matter that managers of underground spaces plan for safe evacuation of users. In order to make the plan, they should know when and from which entrances the rainwater will flow into there. In this paper, inflow discharge was calculated by using 1D-2D urban drainage model in a drainage basin where one of mega-underground mall is located. And appropriate counter measures were investigated. From the results, it is found that peak discharge of inflow appears behind the rainfall peak and that the delay time is from 0.5 to 2.5 hours and depends on the rainfall conditions. It means that several rainfalls should be considered for planning of counter measures and evacuation.