Why the Isère reminds me of a water jet pump

This is what the way to and from the 13-meter-diameter rotating tank in Grenoble looks like (and you should really visit Elin & team’s blog to learn about all the exciting stuff we are doing there!!!)

And the best part is the Isère right next to the bike path:

And one thing that I find really impressive with this river (coming from a much flatter part of the world than Grenoble, where rivers aren’t typically as fast-flowing as the Isère) is how all these return flow pools form everywhere.

Watch the movie below to spot them yourself, or my annotated picture below:


It seems really counterintuitive that a strong current would make water on it’s side flow upstream instead of flushing everything downstream or even just going downstream through stagnant water, doesn’t it? But when I thought about why that is, it reminded me of the way a water jet pump works: You flush water from a tap down through a hose, and that hose is connected with another hose through which you want to suck something (usually some gas out of some container). So there it’s the same: The fast-flowing water pulls things in from the side and takes them with it. Now for continuity reasons, the water that is entrained in the jet needs to come from somewhere, so water has to be brought upstream in order to get sucked into the jet. That’s also similar to playing with Venturi tubes where the thinner the tube, the faster the flow, the lower the pressure… Anyway, riddle solved and I can think about other stuff again ;-)

But it is a really beautiful place to be:


I like water so much better than mountains, but mountains still have their charms, can’t deny that…



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