Large-scale flood damage impact assessment in Metropolitan Area

Large-scale flood damage impact assessment in Metropolitan Area
ENTRY DATE: 24 December 2014| LAST UPDATE: 24 December 2014
Categories: Disaster Prevention | Applicable to any disaster (Soft measures)
Technological Maturity: n/a
Technology Owners:

Disaster Management, Cabinet Office

Needs Addressed

The needs to reduce flood risks caused by climate change.

Adaptation Effects

Flood risks reduction through climate change prediction, understanding hazard/vulnerability/risk and systematic adaptaion mesures developing.

Overview and Features

Please see examples below

Considerations (technology transfer criteria, challenges, etc.)


Co-benefits, Suitability for Developing Countries



Reference: Large-scale flood damage mitigation measures in Tokyo Metropolitan Area

  • In Tokyo Metropolitan Area, there was a pressing need to decide on emergency measures, disaster prevention measures and restoration/rehabilitation measures to minimize damage in the event of a major flood. Thus, the Expert Panel on Large-Scale Flood Disaster Countermeasures was established in the Central Disaster Prevention Council in June, 2006 to deliberate on such measures as the first expert panel focusing on large-scale flood disasters. On the basis of the latest knowledge, the expert panel conducted simulations of flooding in the event of a levee break along the Tone, Ara and other rivers or a massive storm surge in Tokyo Bay to gain better understanding of how flooding occurs. As the first attempt of its kind in Japan, the committee also analyzed various risks existing in the metropolitan area based on assumptions about human suffering including the number of deaths and the number of people left behind and other aspects of damage. The committee also deliberated on measures, particularly emergency response measures, to be taken in the event of a major flood in the metropolitan area, taking into consideration the study results mentioned above and past flood disasters. In April, 2010, the committee prepared a report on the results of these deliberations.

    Figure: Flooding simulation results
  • The number of people left behind resulting from levee breach induced flooding of the Tone River caused by a 200-year flood was studied. In the event of large-scale flooding, pump stations may be rendered inoperable by inundation. Even if pump stations are not inundated, the inundation of adjacent areas may hamper refueling, or it may not be possible to operate pump stations, floodgates, etc., because of the need to ensure safety of operation personnel. When considering the number of people left behind, it is important to make appropriate assumptions about the operating status of drainage facilities. The study on the number of people left behind has revealed that if drainage facilities are rendered inoperable and rescue activities are not carried out by the police, fire departments or the Self-Defense Forces, several hundred thousand people will be isolated for a period of several weeks. The study has revealed that in cases where rescue activities are carried out, rescue will be completed in 14 days after a levee breach if drainage facilities are rendered inoperable or in four days if drainage facilities that have not been flooded can be operated.

     Figure: Number of people left behind

  • An analysis of inundation damage caused by levee breach induced flooding of the Ara River taking into consideration the networks of subway and other tunnels has revealed that underground malls and building basements may be inundated through tunnels even when the ground surface is not inundated, and that subway and other tunnels may be inundated earlier than the ground surface.

    Figure: Expansion of inundation through subway and other tunnels