You’d need a large drop (148’ IIRC) or you’d have to constrict a wide/deep run into a narrow/shallow run. Either way, it’s practically impossible to legally obstruct or divert a running body of water in the US.
As little as 2 foot head with 450 gpm —> 70W. 10 foot head at 1000 gpm —> 1000W. Power output non-linear based simply on gpm rate.
http://www.microhydropower.com/our-products/low-head-stream-engine/