That's great if the entire river system is continually receiving decent amounts of rain. In most real world scenarios there's a rain-rich area in the top of the watershed, then a less rain-rich but flood-prone area, then a bit more rain closer to the seashore, then the river delta.

In Australia for example there's a practise of "flood water harvesting" where you build large earth walls along your property boundary, and collect all the water that falls on your land. Combined with irrigation downstream this means the river dries up in the space of a hundred kilometres.

There's very little water released back into the river, since that's basically wasting water as far as the agriculture industry is concerned.