Have missed this thread by a few days but here goes,
On Australian television saw a setup that was suited to this sort of river. Basically had a catamaran barge, maybe 14ft long, between the hulls was suspended a turbine optimised for low flow speeds. Turbine drove a generator. There was the option of linking several systems together for more power. If you do not like it, it is 100% transportable so that you can sell the unit to someone up or down the river.
The barges are moored in the river and thus go up and down with the river flow. No dams weirs funnels or anything that can be washed away with floods. Sorry I cannot remember the name. They may be out there somewhere and you can buy something off the shelf.
If you cannot find a off the shelf sort of system, you may be able to get a handyman to make something. Make some catamran pontoons out of metal. Put an undershot wheel between teh two hulls. Yes it will go slow but torgue ought to be high. Use some V-belts and pulleys to drive an AC generator. My rough guess for a wheel would be 8ft wide and say 4ft diamteter. Maybe it would go better if scaled up, as this only uses a foot of water level whereas you may have a good 10ft or more. The catamaran hull is very stable, of course you want to keep the c of mass low. So if wheel is 8ft wide then catamran hull maybe 11ft wide by say 22ft long. All this is very rough, maybe bigger is more cost-effective.
Safety is a bit of an issue so the power cables will have to be well insulated. Seems you will need some sort of cut off if the unit breaks down in some respect between the wheel and the generator.
It all looks relatively doable,, as to cost I do not know. You may be spending many thousnads of dollars on petrol for generators already. In theory something what I am proposing seems quite practicable, no doubt development would be a pain but you can always pay someone to do this for you. How you stop people stealing it would be another issue too (alarms and floodlights and small exposives linked to cable cutting? why not?)
As to is all above just nonsense or practical, all I can say is that I have seen full sized models on TV and my gut feeling is that is looks good.
N. Peter Evans