Thanks Bev.
Yes, I've done all of the above and contacted everyone people like ANAH can give me contact details for. Without exception, they're full of technical advice but no-one wants to get their hands dirty. Local builders are all frightened off as soon as "l'electricite" hits the conversation, but would be prepared to work alongside an engineer to complete the civil works. And no, it's not a linguistic problem, or even a scientific problem, 'cos I can make myself understood in both milieus.

Navitron, a UK company, has a rep (Marc Asker, who also writes for Connexion) in the Dordogne, but it's going to cost me the best part of 1K Euros just for the site visit.

All I need is a competent local hydro engineer - sob sob ..... lol