They discuss this in the video, and if you watched it you’ll notice that they’re doing these projects along a major river near the ocean. They only capture 15% or so of what is today run off into the river. Rivers ultimately flow into the ocean. There is no one really downstream depending on that small percent of runoff.
Np I’d also notice the placement along the river and the river proximity to the ocean. They specifically call out not over harvesting the water. I’m pretty impressed as an engineer how well thought out the program is.
