Science Fiction: Post-industrial, forest planet, retainment dam?

I'm searching for a book which I read in german (I think) but is most definitely from a UK/US author. The story takes action on a planet which is (possibly) post-nuclear, forested and the main actor maintains/builds a retainment dam (?) with his father (?). There's also a girl who reads scientific and/or alchemy books and lives in a tree house. I belive to remember that these books were old and from a time where mankind had more knowledge about science. The girl was described as 16-18 I think. The boy mocked her about these books being useless. These informations were given early in the book, I did not read it past the first 30 pages and now it bugs me.

Any hints are highly appreciated!

some of this reminds me of LeGuin's The word for world is forest, but that's not quite it.

just possibly the second chapter of Brightness Reef but the first chapter is about Alien characters

The Brightness Reef it is! I could not remember where I read it and now I know why: it is an eBook stored on my PC.

Thank you so much for contributing!