Simulation conditions

The simulation results provided by this Web site show the range of the flood area and the changes in water levels for sections of rivers administered by the state government and the prefectural governments, which were designated as flood forecast rivers or rivers requiring water level reporting, in the event of a breakdown of a levee (flood levee failure) or if river water overflows the levee, etc. (overtopping/overflowing) as a result of rainfall of a certain estimated scale (which, as a rule, serves as basis for flood prevention plans for that river) .

The amount of rainfall estimated is different for each river, but in general it is heavy rain, which occurs once every 30 to 200 years. Web-Based Flood Simulation Search System allows you to search only the rivers, for which flood simulation data is available. Click on the rivers that interest you in the following list to check whether the flood simulation data is available. If you have any questions regarding detailed conditions for flood estimations pertaining to particular rivers (estimated rainfall scale, levee failure points, etc.) please file your inquiries to the offices listed in the list of rivers below.

Please note the following important points:
 ～The actual flood may differ from the estimations～

1. Location of estimated levee failure point, scale of the flood, etc.

The simulation shows the points, in which the river may overflow if a levee breaks down (flood levee failure) due to a rainfall of a certain scale. These are called “estimated levee failure points”. In actuality, a flood may happen with the levee breaking down at points different from the estimated levee failure points. Moreover, if the rainfall scale exceeds the estimations and in some other cases, it is possible for the flooding to originate from points other than those estimated or the amount of overflowing water to increase, resulting in an increase of the areas flooded and an increase in water levels. Accordingly, the spread of the actual flood may differ from the estimations displayed in this simulation.


2. Sometimes unexpected phenomena may happen

The simulation does not cover pluvial floods (phenomenon when water accumulates in a location and cannot flow out to a river or the sea). Please understand that before a river that is covered in the simulation overflows, there is a possibility for a pluvial flooding or a flooding originating in a tributary stream that is not covered in the simulation starting.


＜Contact for inquiries regarding functions, operation, etc. of the system＞
Geographic Department, Geospatial Information Authority of Japan, Ministry of Land, Infrastructure, Transport and Tourism
Please use the inquiry form here if you have any questions