My friends have a [broken-down] dam that was built in the 1940s. Those techniques that pump concrete underground to shore up building foundations would effect repair. The flow is seasonal but even in summer it's substantial.
I'm working on them to install a gravity vortex waterwheel as above, to test the flow. I have a Fisher-Paykel washing machine motor that's ~750w/1hp and a design that keeps it up out of the water for easy maintenance. I think they are paralyzed by fear of success.
I came back to see how broad the topic is. Does it include auto recycling?
https://www.youtube.com/channel/UCUS...able_polymer=1
Apocalypse Auto, home of War Child, the Zombie Plow bus.