Hijiriushi, Japanese Dam Technology from the past.

Hello.
Today we went to learn for Hijiriushi or Seigyuu, a tool which used to hold the drain of the river so the stream wont flood to the residence area in the past. The tool just like the Tetrapod that used in common seashore.

Hijiriushi

Hijiriushi without weighting stones. Looks like a cannon.

In the past, some of Yamanashi area frequently flooded. Then, there is nobody who lived nearby the river due to the danger of the flood. So, the Takeda Clan's warlord, Takeda Shingen did some policy to prevent the stream of Kamanashi river to flood. But nowadays, the river stream is not that much as the past. Maybe it was because of the Hijiriushi. That's all i know.

Thanks for reading.
Pepi.