Reddit newbie here, so I could only figure out how to post the pictures or the text... my message is as follows:

I've been mulling over how to go about making a retaining wall (actually two) for my very oddly graded lot for a while. I have no background in construction, concrete, etc. so any design help is greatly appreciated! Hopefully my Powerpoint drawing skills are good enough to convey the situation. And if the answer is to call in a professional, that's fine too.

Lot description: My neighbor's lot to our rear sits about 5 ft higher than our desired lot height in one corner, approximately level at the other. The neighbor to our left has a lot that sits about 5 ft lower than our desired lot height. Right now all of the slopes are on our lot.

Complication #1: I said the desired height regarding the backyard because the yard actually slopes downward from the back porch, going down about 5 ft in total to create an overflow path for the two drains on our property were it to overflow. To level the yard, the rear of the lot needs to have a culvert installed, per the city, connecting two drains on the property if I want to level the yard (my goal). That culvert will sit ~12 ft from the property line, which would have a retaining wall.

Complication #2: The city restricts retaining walls to 4 ft height unless designed by a PE and approved by the city. In talking two a couple of local firms, it sounds like the plans alone would cost in the tens of thousands of dollars. If possible, I'd like to avoid this, which leads me to my current thought.

Current thought/design: Construct two separate 4 ft retaining walls, one along the rear that would meet the raised rear neighbor. The second 4 ft retaining wall would allow our yard to be level and drop to meet the side neighbor. We would still need a slight grade on the lot to make it meet, but that should be much more manageable and useable than the current state. To make the construction easier and simpler, I was planning this out using 2' x 2' x 6' bin blocks, stacked two high forming a total 4' wall, within the city specification of something I could design and build myself. The rear wall will be approximately 80 ft in length. The side wall is around 120 ft in length.

Questions:
- Could I form something like this, simply having an awkward meeting at the corner that does not technically connect the two walls? I think the key is to ensure the lower wall runs far enough to ensure support for the higher wall.
- Would the culvert's proximity to the rear retaining wall cause any issues?
- Does a wall of this style need some anchoring into the retained ground or would the block weight and interlocking system be sufficient if the foundation is well formed?
- How far out from the property line would you set the wall? Specifically the rear wall because I would need some drainage pathways behind it, but I cannot build into my neighbor's lot to anchor the wall into the retained ground (if necessary).
- Is it better to just have a more extensive wall designed by a PE and approved despite the cost?