FAQ/ Building a wall on a river (wall erection calculation)¶
Is it possible to set the river so that it does not overflow at certain points (so-called "wall erection calculation")?
response¶
It's possible.
Figure: Virtual wall setup screen.
You can erect walls on any section of the river.
The height of the walls is endless. Therefore, by erecting a wall, it will not overflow from that section.
You can erect a wall on either the left bank, the right bank, or both of the specified sections.
However, even sections with walls can be broken.
In addition, sections with walls can be set to return or not return to the river from the floodplain.
In addition, in the guide for creating flood estimation maps for small rivers Reiwa June 2, wall erection calculation is required.
Guide to Estimating Flooding of Small Rivers, June 2 Reiwa p. 43
Technical Reference 5: Maximum water level calculated by wall water level calculation for target flow rate
The maximum flow rate calculated by the target flow rate (4.3) shall be given to the existing river channel, and the maximum water level shall be calculated by calculating the water level under the condition that floods do not overflow from the river channel (see Fig. 5).
The river channel shape and roughness coefficient are the values set by the longitudinal survey data of the river channel (3.1) and the roughness coefficient of the river channel (3.2).
As the water level calculation method, the water level calculation method (one-dimensional, quasi-two-dimensional unequal flow calculation, equal flow calculation, etc.) adopted in river planning studies, etc., or the calculation method suitable for the characteristics of the river is used. 
For more information, please refer to the Technical Reference River Model - Virtual Wall.