This week, the old "legends" held the key to the story. Monet also said, "Legends are often based on past disasters. They should not be easily dismissed." Upon further investigation, Iwate Prefecture, right next to Monet's hometown of Miyagi Prefecture, also has a "legend" related to river disaster prevention.
Here's a quiz! Tetteren!
This is a legend from Oshu City, Iwate Prefecture (inland part of Iwate Prefecture).During floods (when the river is swollen), the main stream of the river swells up like a tiger's back, and a lot of garbage flows through the river.'
Now, which of the following fits into this ○○?
Difficulty level is ★☆☆☆☆(1/5)!
In Oshu city, Iwate prefecture, there is a saying that "when floods occur, the main stream of the river swells up like a horse's back, and a lot of garbage floats in the river."

*Image taken from the Japan Meteorological Agency website.
https://www.jma.go.jp/jma/kishou/know/tenki_chuui/tenki_chuui_p3.html
There is no scientific basis for this, but it is based on actual experience. This proverb tells us that if the river rises up like a horse's back, it means the water level is high. I hope this will be helpful when evacuating.
By the way, in Monet's hometown of Miyagi Prefecture, there is a saying that goes, "If there's an earthquake, beware of tsunamis." If there's a big earthquake, a tsunami may come. In coastal areas that have experienced many large tsunamis in the past, there are many places where stone monuments with the above words have been placed since ancient times.
You can also see disaster prevention sayings from other regions by clicking the URL below on the Ministry of Internal Affairs and Communications Fire and Disaster Management Agency's website, so be sure to check it out!
[Sources and References]
Fire and Disaster Management Agency website - Publications - Database - National disaster folklore information "Disaster prevention related "traditions""
https://www.fdma.go.jp/publication/database/item/database009_02_02.pdf