ᐅ Carport Drainage: Calculating Water Volume

Hello, the rainfall amount is clear; here we have 209 liters per second per hectare (l/s ha) according to Kostra - DWD 2010R.

I don’t want a ready-made infiltration trench; I plan to dig the pit myself.

This raises some questions: How large, how deep at most, how far from the property boundary, etc. I can’t really find any clear information online!

The wastewater authority requires a site development plan / building plan showing the size and depth of the infiltration system we intend to build.

They don’t provide any guidance themselves and refer you to an architect, which I personally find a bit excessive.

As large as necessary. As deep as the permeable layer begins. Not at the boundary but possibly directly beneath the carport.

The carport will be placed on an already paved area. At the rear, there is a 2 x 7 m (6.5 x 23 ft) unpaved space next to the neighbor's property, and on the side, there is an additional 2.5 x 12 m (8 x 39 ft) area.

Well, then keep a distance of 1-2m (3-7 feet) to prevent the paved area from sinking while digging.

But how much excavation do I need to do now...?

How deep do you mean? Your soil report will tell you, or you will find out during the process.