When you say "tidal" do you mean that you are near enough to the ocean that when the ocean tide is coming in, the river flow comes to a stop? Then as the tide goes out flow returns?
Before grid electricity became widespread and fairly cheap, I have seen pics of water wheels that used a gear-up to spin an alternator for local power. Perhaps inefficient and not cost-effective if you have to have someone build and install it, but...
When the Romans were under seige and couldn't reach their grain mills to make flour, they put water wheels on barges anchored in a river, worked OK.
If you have a lot of energy and near-free junk, it shouldn't be too expensive to cobble one together to get a few Watts. Might I suggest you take a glance at a "Poncelet" wheel, and compare it to other options? The curved scoops and enclosed sides reduce turbulence and increase energy capture compared to the easier to build flat-paddle wheels (or so I'm told)
http://www.waterwheelfactory.com/history.htm
If you had access to a lot of Roman-trained European slaves, I'd recommend that you Google "noria", but most European slaves these days couldn't build a noria, aqueduct, and hillside gravity-irrigation reservoir if their lives depended on it...
http://en.wikipedia.org/wiki/Noria
