Comprehensive Flood Control Measures
Tokyo Metropolitan Torrential Rain Measures Basic Policy
Recently, local torrential rains occur frequently in part of the Tokyo metropolitan area. The
extensive flood damage of approx. 6,000 houses occurred due to the torrential rain
exceeding 100mm per hour centered on Suginami Ward and Nakano Ward on September
4th, 2005.
Responding to these, we established the Tokyo Metropolitan Torrential Rain Measures
Examination Committee comprised of the academic experts in May 2006, and consulted
with respect to the measures for torrential rains in Tokyo in the future.
As a result, we received the recommendation of the following two items as a frameworkfrom the committee.
(1) To further promote the disaster mitigation countermeasures such as “River BasinMeasures” not to directly run rain water into a river which is used as a sewer and“Housing and Urban Development Measures” to mitigate the flood damages, from aviewpoint of the promotion for self-help and mutual-help, as well as “River Improvement”
and “Sewage Improvement” as public-help.
(2) Designation of “Countermeasure Promotion Areas” based on the frequency of thetorrential rains and flood damage occurrence
Based on the recommendation from the committee, we compiled its directions
focusing on the countermeasures for the torrential rain which has been increasing
recently, out of the whole flood control measures the Tokyo Metropolitan Government
conducts, and instituted “the Tokyo Metropolitan Torrential Rain Measures Basic Policy”
in August 2007.
Specifically, it was to show the directions of the objectives and efforts the Tokyo
Metropolitan Government should realize in ten years in “the Countermeasure
Promotion Areas” where torrential rains and following flood damages occur frequently.

【Objectives to Realize in Ten Years】①

To prevent the damages of the inundation above the floor level against rainfall up
to approx. 55mm per hour and of the basement flooding② To secure the safety of human lives even in case of the record high rainfall【Directions of Efforts】●River Improvement
・To address rainfall exceeding 50mm per hour using the whole river facilities by theimprovement of the river channel and the regulating reservoir for the time being.
・To address rainfall exceeding 50mm per hour combined with the river channel by theimprovement of the regulating reservoirs based on the basin and thecharacteristics of the area.

●Sewage Improvement
・To address rainfall of corresponding to 50mm per hour using the whole seweragefacilities by introducing the new design method which can take into account thecharacteristics of the area and improving the river channels (culvers) and retention
facilities (regulating reservoirs).
・The partial improvement of the facility in advance which can address rainfall of 75mm
per hour in the high risk areas of flood damages such as underground shopping
complexes.
●River Basin Measures
・The promotion of the infiltration by the public rainwater infiltration inlet and the deliveryof subsidies for the rainwater infiltration inlet installation to private houses.
・To incorporate the water-holding capability of green land into the River BasinMeasures●Housing and Urban Development Measures
・The creation of the mechanisms so that the flood records can be explained at the realestate transactions
・The expansion of the subsidy programs to the construction of the raised floor structure
and the installation of a water stop, and the promotion of the countermeasure
implementation by the guidelines and the ordinances
・The formulation of the Tokyo Metropolitan version of the underground space flood
countermeasure guidelines which shows the areas that need the countermeasuresand the examples including the simple flood fighting methods by water bags, and theformulation of the underground flood countermeasure plans by facility (undergroundshopping mall, subway)●Implementation method for Evacuation
・The study of the implementation method for the evacuation to the upper floor
・The preparation of the chart for the flood hazardous area and the hazard map, and theprovision of the information for the highly accurate local heavy rain occurrence

Torrential Rain Countermeasure Plan by BasinIn the countermeasure promotion basin, principally the Council for Comprehensive FloodControl Measures instituted the Torrential Rain Countermeasure Plan by Basin which shows
the torrential rain measures to be implemented by the fiscal year 2017, for “the Kanda-River,Shibuya-River, Furukawa-River basin” in March 2009 and for “the Shakujii-River,Meguro-River, Nomi-River, Nogawa-River, Shirako-River basin” in November 2009.

Emergency Torrential Rain Measures
Furthermore, triggered by the flood damage due to the torrential rain exceeding 100mmper hour occurred in the Shakujii-River basin in July 2010, the Tokyo Metropolitan
Government newly instituted the Emergency Torrential Rain Measures to pursue the swift
damage mitigation by the intensive emergency improvement for the flood damage high risk
area in cooperation with the related municipal governments and the citizen of Tokyo in
November 2010.
①To promote the establishment of the retention facilities utilizing public facilities
・Projects in fiscal year 2013: to schedule junior high schools in Musashino Ci
ty and three housing complexes owned by the Tokyo Metropolitan Government.
・To approach the 28 municipal governments especially related to seven basins to promote the flood damage measures such as Shakujii-River and each
Bureau of the Tokyo Metropolitan Government to promote the establishmentof the facilities.
②To take water into the underground regulating reservoir from other basin
・To study to take water into the Shirako-River Underground Regulating Reser
voir from Shakujii-River・To shorten the construction period of the Shirako-River Underground Regulati
ng Reservoir now under construction by approx. one year
③To expand the measures for large-scale underground shipping complexes
・To promote the formulation of the evacuation plan
(to schedule Tokyo Station Yaesu Entrance in fiscal year 2010, Shinjuku St
ation West Entrance, Ikebukuro Station West Entrance, Kabuki-cho and Shibuya in fiscal year 2012, Keio Line Shinjuku Station, Shinjuku Station East E
ntrance, Ikebukuro Station East Entrance and Shimbashi Station East Entran
ce in fiscal year 2013)
・To move up the schedule of the improvement of the sewerage facilities (rainwater storage pipe) as the underground shopping complex measures.
(Moving up the schedule of the improvement of the sewerage facilities (rainwater storage pipe) in the three basins of Kanda-River, Shakujii-River and Shirako-River)④To provide the information to protect human lives and livelihood
・In case there is a threat of the overflow stream, we newly implemented theprovision of the flood prevention information which can be immediately reac

hed to the citizen of Tokyo at Shakujii-River in cooperation with the Ward in the basin
・To promote the efforts to raise the public awareness among the citizen of Tokyo incooperation with the Tokyo Fire Department