Infiltration of rainwater, which method?

that depends heavily on the soil. What Kf value did you specify? I come up with 14 boxes for a roof area of 140 sqm. It’s due to the not so great Kf value. Your 24 are almost harmless compared to that

We have the peculiarity that we raised the ground by one meter. That means under the system the value would be 0.00009 (hope the zeros are correct). Around it and also somewhat below is gravel and then the gravel bed. That means water drains excellently to the sides, but rather moderately downwards.

So we specified 160 sqm of roof area and only that. Otherwise, it seeps into the ground. So we only need to infiltrate the rainwater from the roof. I hope that is correct.

As mentioned, it also depends on the soil, we specified gravel (it is on a gravel layer), otherwise it would be sand LAGA Z0. Additionally, the region matters; here we use n=0.2 and a factor fz=1.2.

Decided against the tunnel because of?

I hope that’s true

Unfortunately not. You also have to drain the rainwater from the driveway and access path.

Decided against the tunnel because?

Because I would need 16 tunnels instead of 14 infiltration boxes. 16 tunnels mean an area of 15 m², but the infiltration boxes only require about 9 m²,

Around it and also a bit underneath is gravel and then the gravel bed. In other words, water drains very well to the side, but rather moderately downwards.

But then, from my point of view, you would still have an underground "infiltration basin" below the soakaway that stores water in the gravel and releases it from there. You must have specified a value for the soakaway calculation at Graf. The amount for the soakaway looks to me more like 10^-5 (probably taken from one of the deeper layers in the soil survey). I would have a consultation and bring the soil structure into the discussion. With so much gravel, sand, and crushed stone, I can hardly imagine that.

From driveway and access paths?

How is that supposed to work? So how am I supposed to collect the water there and lead it to infiltration?
The soil is permeable.

Our house builder, in the original calculation, since we indicated a basin in the building application, only took the 160 square meters of roof area.

But then, from my point of view, you would have an underground "infiltration basin" below the trench that stores water in the gravel and releases it from there.
You must have specified a value for the trench calculation with Graf. The amount of trenches looks more like 10^-5 to me (probably taken from one of the deeper layers in the soil survey). I would suggest having a consultation and bringing the soil structure into the discussion. With so much gravel, sand, and crushed stone, I can hardly imagine it.

That’s where my concerns came from. The lower water authority calculated a basin size of 50m² for us (3m x 17m x 0.3m depth). I had also written to the Graf consultant that we had built up a meter of crushed stone, but apparently that didn’t get through. I probably should really give him a call.

How is that supposed to work? I mean, how am I supposed to collect the water and direct it to infiltration? The soil is permeable.

Quite simple, with a catchment channel. Wastewater must not be discharged via public roads (I just had to learn that). During heavy rain, your paving won’t infiltrate that quickly, so a channel has to be installed there.

I probably should really call him

Either that or see what companies in the region can provide support for something like this. Possibly also just talk to the building materials dealer that Graf mentioned.