I wonder if you want a portable system to drop into the bywash channel at the lock, with a longish cable to get back to the boat (you wouldn't want to moor on the lock landing, would you ....). Or else you could hide a couple of batteries behind a bush, to shorten the cable run.
yes a portable system, ideally an alternator in a waterproof housing with a turbine inside a cage so it can be lowered into spill weirs with an armoured cable back to the boat.
getting the thing to spin fast enough, I wonder if you could adapt a sturmey-archer 3 speed hub to give you something to tune the rpm