Rainwater drainage to the stream - Implementation

O.K., if that doesn't harm the pipes, then that's good. Thank you!

Well, the roots can indeed grow into the plug connections (and they do) and then clog the pipe. It looks like this:

But it somehow looks like a cast pipe...?

And if that happens - so what? You clear it again. If that happened that often, the problem would be widespread, right?

Approval should not be a problem.

Sure? That would be, AFAIK, completely different here.

They write here: A permit according to § 10 WHG is not required if the water flowing off from paved or built-up areas collected from precipitation is discharged into a surface water body, provided that the rainwater is not harmfully contaminated and is not discharged via a joint facility. We will, of course, still obtain consent from the wastewater utility.

As far as the root system is concerned, we laypeople have little idea of how "small" a root system large trees can get by with. Shallow-rooted plants like the rowan bush should not pose a problem anyway. Deep-rooted plants also do not extend meters down... It is therefore advisable to familiarize yourself with the roots of shrubs and then adjust the corresponding plants to the location of the pipe. The pipe will not be everywhere but will only pass through a small area at the property boundary.