[mattferderer]

I don't know of any studies but I would imagine a lot of variables come into play.

Soil Type & how deep of soil effects how much water the ground can soak up & how fast the water will run. All would be slower runoff than concrete.

Also the slope of the land would make a difference.

These are just the obvious ones. Bottlenecks, whether created on purpose or not would have a huge impact. Where I live we have large snowfall in the winter which creates ice jams & flash flooding in the spring.

I personally like the idea of this.