Load-bearing capacity of L-stone and water drainage at 45° slope

Thank you for the hints, I will take a look at them in a quiet moment. Pictures 5-7 show the currently still existing original site. (Everything is more difficult to present and visualize in 2D).

You apparently have a monetary problem.

That’s probably what you have to call it…

I would keep the terrain a bit lower than the wall.

That would mean we’d have to plan a 3m staircase to get from the house to the garden.

Connect the overflow to the canal. That was allowed for us.

Unfortunately, that’s not allowed for us.

We have a 76,000-liter cistern.

What!?!?!?!? Is your cistern in the garden called a dam and your pond a reservoir!? (You have about 70,000 liters more volume than we planned.)

I fear you were poorly advised and nobody told you what the earthworks and garden landscaping will cost…

You are definitely right there, but I wouldn’t like to accuse us of laziness here, absolutely everyone tells us every time that we are too early, we worry too much, etc. The house is supposed to come next spring, the basement in November/December and we thought it would make sense to do the retaining wall beforehand. That we already want to talk about the garden now caused the next eye roll again…

Are you planning with a basement? Why not excavate more and have daylight in the basement as well. That way you wouldn’t have such a steep slope.

The little tip on the bottom right is almost exactly at 302m and is the floor of the basement, so half of the south and east side is thus open.

Alternatively to the overflow, you could also use the cistern pump to pump water into a higher-lying canal from a certain fill level. Wilo has suitable pumps, controls, etc., but please don’t ask about the prices.

As I said, we are not allowed to go into the canal.

Without a connection to the sewer, draining the wall becomes difficult, since the cistern needs to be emptied somehow. Some data regarding rainfall amounts and feedback from the soil survey concerning the slope / groundwater are probably needed in order to calculate / estimate an amount here. The worst thing that can happen (I mean my Higher Regional Court example) is a slow undermining of the wall over years due to lack of drainage. You say the neighbors above you also have 2m L-shaped stones? Do you know how they solved the drainage? If everyone on the slope has to drain on their own property, the lower properties almost always have more load (as mentioned, depending on how much slope / groundwater flows here). Have you planned a drainage above your house? Sort of as "protection" from the upper neighbor?

Then you have planned the cistern far too small if you really want to use it to water the garden.
Lawn, for example, requires 15-20 liters per m2 per week. Then there are hedges, bushes, trees, beds...
Let’s assume you have 200m2 of lawn. That amounts to 12,000-16,000 liters per month. In summer, it might not rain for a month. So after 1-2 weeks you either start wasting valuable fresh water or your freshly and expensively created garden partly dies. Water can be saved by plant and grass seed selection but only up to a certain extent. I don’t understand planners who think a 6,000-liter cistern is large.

We have no pond, only a pool. But it is self-sufficient.
Then think about rainwater use inside the house. That is allowed to go into the sewer ;) But they never calculate it.
Or you have to build a large soakaway. Here an appropriate infiltration capacity must be proven/established.
Building the wall in front of the house makes sense. How else will you get large equipment there?
If you dimension the cistern large enough, the overflow shouldn’t be an issue. Here you have to consider precipitation amounts and areas

emptying can also be done by pump. But I agree with you that a sewer connection would be very sensible. I would seek a conversation with the authorities. With a large cistern, the overflow will hardly ever be used. Therefore, approval for the sewer connection is probably to be expected.

You are definitely right about that, but I don’t want us to be accused of laziness here, everyone, absolutely everyone tells us every time that we are too early, that we think too much, etc. The house is supposed to come next spring, the basement in November/December, and we thought it would make sense to do the retaining wall beforehand. The fact that we already want to talk about the garden caused yet another eye roll…

You have to plan the garden together with the house to get something reasonable out of it. However, many home construction companies prefer a quick completion, since the outdoor landscaping is ultimately left to the builder and therefore not their problem ;)

For example, lawn needs 15-20 liters per m2 per week. Add to that hedges, bushes, trees, flowerbeds…

Golf lawns maybe. One can also let the whole thing grow a bit more naturally. The only thing that absolutely must be watered is the vegetable garden. Trees and shrubs only during their initial growth phase. The grass at my parents’ place was never watered but still withstood 3 playing children and also provided 2 rabbits with homemade hay ;)

That is then meadow;) not lawn. Golf course turf requires more care and effort.