Garden drainage during heavy rain like recently in NRW

Hello everyone,

I have a question that I unfortunately can only formulate very vaguely. If details are needed, please ask.

We recently had the problem with the heavy rain in NRW that so much water came down that it could no longer infiltrate and after some time the result looked like this:

Here from the garage door



here from the first floor looking at the adjacent kindergarten.



This is the lowest point in the garden, which is why water could accumulate there.

In the end, the water at the garage door was 25 cm high. Fortunately, the door was sealed tight and a pump prevented worse. Nevertheless, we were lucky that the rain subsided overnight, otherwise the level probably would have risen up to the terrace at some point.

The soil unfortunately contains a lot of clay and the water collecting in the kindergarten in picture two naturally did its part because it eventually "connected" with our pond and thus made one large lake out of two.

Tomorrow our landscaper is coming to see how to at least contain this in the future.
Currently, there is no drain, no drainage, no gravel bed, nothing there.
The architect's and the landscaper's idea so far is to tear out the lawn, excavate with a mini excavator and fill with gravel underneath and additionally lay a drainage pipe in the splash protection area to the terrace and connect this with the terrace drain or the roof downpipes.
Does that sound reasonable?
We have to do something there, but of course we don’t want to waste money. It may cost if it helps. We assume that we will more likely have similar weather conditions more often in the future than rarely.

I am grateful for any tip or suggestion, and as I said, if important info is missing, please just ask.

Hole with large pump and connect to roof drainage? With float switch or similar. Thus also "automated".

Hole with a large pump and connect to the roof drainage?
With float switch or similar. Thus also "automated".

Hole just like a hole? Or "underground" under the lawn, like a basin?

With such volumes of water, you don't stand a chance. You would have to prepare for 200 liters per m2. If I assume an area of 100 m2, then you would have to dispose of 20,000 liters.

In my opinion, this can only be done by exchanging the soil from clay to coarse gravel plus a large deep soakaway pit plus an automatic pump connected to the sewer. Estimated costs 10 to 15,000 euros.

With such volumes of water, you have no chance. You would have to prepare for 200 liters per m2. If I assume an area of 100 m2, then you would have to get rid of 20,000 liters.

In my opinion, this can only be done by replacing the soil, clay against coarse gravel, plus a large deep soakaway pit plus an automatic pump connected to the sewer. Estimated costs 10 to 15,000 euros.

Thanks for the assessment. That's what I feared… :(
Man, man… so it probably only remains damage limitation.

with a connection to the channel

when it rains really heavily, the channel is often full and additionally pushes sewage in instead of draining away.
Filling up the property doesn’t help either; then the water stands inside the house.
If you live in such an area, only a small 20-30 cm flood wall helps and pumping and diverting the water over it.