You need height to get ‘serious’ hydro power. In the Netherlands, the Rhine water drops by less than 20 meters across the entire country (ballpark 100km), so I think a 1 m drop already would be optimistic.
So let’s take that 7000m³ and drop it by a meter. That’s dropping 7 million kg of water by one meter, or (if my math is right) about 70 MW of potential energy. You might get somewhat more out by decreasing the speed at which the water flows, but I doubt that would be much (the more you slow the water down, the larger the river downstream has to be)
Also, that’s if you dam the entire river. The Waal is a major river for shipping, so you can’t do that.
Finally, I think 7000m³/s is an outlier. Google gives me 1500m³/s flow rate for the Waal (and, consistent with that, 2000m³/s for the Rhine). So, on average, a system damming of the whole river, requiring all ships to go through locks, would produce about 15MW.
And I think my math is at least in the right ballpark. https://en.wikipedia.org/wiki/Beauharnois_generating_station generates “up to 1,903 MW of electrical power”, but it has a water drop of 24 meters, and runs in a river that has an average discharge about equal to that peak of that of the Waal (https://en.wikipedia.org/wiki/Saint_Lawrence_River: “The average discharge at the river's source, the outflow of Lake Ontario, is 7,410 m³/s”), and, I would guess, is designed for somewhere around that average discharge, dropping surplus water over an overflow system. So, that would account for a factor of 24 (times the height) × 5 (flow rate)