Important point, but there will hardly be a sewage connection there. So install a soakaway pit? Or could a pond be installed at the lowest point of the property to catch surface water? Assumption: Without construction measures in the lower part of the property, it probably won't work
Don't exaggerate. The water also used to run down the slope before. The L-shaped stones rather prevent the water from immediately flowing to the neighbor.
L-shaped stones can't work miracles either; slopes almost always require complex measures (which financially affect the properties higher up). Of course, one wants to stay within reasonable limits, and I also mentioned involving those affected in the planning. It is not necessarily the case that the one on the most expensive property insists on it. Nevertheless, their protection has priority over a pure garden and landscaping discussion.
Didn't get any with elevations, we also had an exemption procedure here, maybe that's why. But it wouldn't help anymore anyway, since strong changes have already been made to the elevations.
Oh, especially when it’s about the waterproof ;-) proof with the exemption, that it was built in accordance with the development plan (and the drainage situation has not worsened compared to the original site).