I get the sense that towns built in river beds are pretty universal around the world. Seems to me the human time span does us in every time. We might just remember heavy storms that come in at a pattern of 25 years. But the really big events on a 100 years or more frequency are generally forgotten or dismissed as a singularity in the ordinary bureaucratic mill of today. And that's within a system that has a bureaucratic mill and one properly(?) functioning at that.

Which is why Tokyo probably will be ruined one day. Same goes for LA. Same goes for Napels. And so on...

There were people in the Netherlands that had built their houses in the storm beds of the big rivers and who were then all scorned the river flooded them in the early ninenties. And those houses were built inside the storm bed for the 25 years range.