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Mitigation of inundation damage

  • Damage risk of inundation in urban areas has been increasing due to a) urbanized area has been spread into vulnerable areas by inundation, b) recent more frequent occurrence of concentrated heavy rains larger than planned rainfall intensity, c) urbanized utilities of lands like underground shopping moles and underground rooms of buildings.
  • Concerns like increased frequency of heavy rains, stronger typhoons etc were pointed out in the 4th evaluation report of IPCC (November of 2007)
  • In order to minimize inundation damages, integrated inundation measures are carried out, with surely and steadily facilitated measures as effective hardware and combination with software measures and self defensive measures. (Integrated project of mitigation of sewage inundation-supporting project to build strong town against heavy rains)

Recent rainfall intensity and damages

Recently the frequency of stronger rainfalls of which hourly intensity are 50mm or more has been increasing.

Annual frequency of stronger rainfalls of which hourly intensity are 50mm or more (Date source: Material of the Meteorological Bureau of Japan)
Annual frequency of stronger rainfalls of which hourly intensity are 50mm or more
(Date source: Material of the Meteorological Bureau of Japan)
Annually changes of the No. of underground shopping moles and floor areas (data source: Website of Kajima Research Center)
Annually changes of the No. of underground shopping moles and floor areas
(Data source: Website of Kajima Research Center)
Much fallen rain flowing out in a short time caused by urbanization (as an example of Tokyo metropolitan)
Much fallen rain flowing out in a short time caused by urbanization
(As an example of Tokyo metropolitan)
The total of damaged cost in the past 10 years (Data source: The Statistic book of flooding)
The total of damaged cost in the past 10 years
(Data source: The Statistic book of flooding)
Damages of inundation
Damages of inundation

Implementation of the integrated measures

Implementation of the integrated measures
Implementation of the integrated measures

 

Effectiveness of facilities

  • Protection or mitigation of inundation at heavy rainfalls, by construction of storage pipe (Wada Yayoi Trunk Sewer)
Wada Yayoi Trunk Sewer
Wada Yayoi Trunk Sewer
Drastic reduction of the No. of inundation as the same strength of heavy rainfalls by construction of storage pipe
Drastic reduction of the No. of inundation as the same strength of heavy rainfalls by construction of storage pipe