I cannot even imagine the legal sh!tstorm that would ensue from attempting this here in the PNW, the environmental impact looks quite significant.
No way you'd be able to just DIY it either - some of the permits will require licensed contractors.
- decreasing the amount of water available downstream.
- changing were the downstream water ends up.
- changing the speed of water downstream.
- changing the variability in the stream’s deficit the downstream.
- making it harder/impossible for animals to move along the stream.
I would think this does do the last, and, likely, also the next to last.
It might modify where the wetter parts of the area are, but I don't think that equates to destroying it.
Additionally, there are some definite issues with sedimentation during construction. They excavated the channel to the intake and put all the dirt from the excavation into the stream for it to "carry away"[1]. This would not be allowed in most areas I know of - essentially, fish can't breathe if there's too much dirt in the water. Then several times it overflowed and eroded the channel - more sedimentation. The author even admitted using concrete liner would be the better choice, but opted not to because it was expensive - essentially, this externalized the cost of sedimentation to the ecosystem.
Nature minus humans endlessly causes the same sort of change, but to second an earlier comment this would be a nightmare to try to do in a lot of areas. In my area the most dire thing to touch is the flow of water -- with three layers of government/protection agencies monitoring it with a very close eye.