Dunk,
You give so much information.
There are websites that will tell you the potential of the mill and of your resources. You will need to assess the cost of getting the thing in operation. You will probably need to get some sort of government approval.
If you have a use for the power, it may be worthwhile to use all you can. If you care to grid-tie, you need to research the 'how' of that.
Once YOU get all of the answers to the questions only YOU can answer, then an assessment of the information, including the social and economic considerations, can be made by YOU.
Good luck. I wish I had the water resources you claim to have. Having a large portion of a water system already built is a bonus, it it can be used.
Ron