"Instant" hügelkultur in a desert climate?

After the weekend Permaculture Properties Summit, I'm particularly creative but not very practical. So I'm wondering about the following "design" concept:

Goal: create a 5x10 hügelkultur garden in sloped and rocky, infertile roadside space.

Proposed construction:

1. Dig a 12" deep pit (or a short contour trench and berm)
2. line it with plastic to retain water up to the wood layer height or former surface level, and surround it with a 24" wide woodchip path, slightly dug in and lined with plastic as an extra rain catchment area draining into the pit/trench..
3. Layers: (from bottom to top)
    a. 12: Pack logs and wood slash mingled with dirt for the tightly packed and recessed bottom 12" of the pit/trench.
    b. 6" Raw compost feedstock plus dirt/biochar mix
    c. 6" half decayed compost plus dirt/biochar mix
    d. 6" finished compost plus dirt/biochar mix
4. Plant a permaculture-informed, layered, edible and ornamental garden or landscape

The result will be a circular hill/bump or a normal hügelkultur berm shaped garden. Rain catchment will be optimized but manual watering will be available and logged. Theoretically, the wood layer will increase the time gaps between watering, but this is one reason for the project. The idea is to do a one-time garden installation that lasts several years with no-till planting methods and mulching. The hügelkultur structure is the easy part, in some ways, as the plant selection and layering will require a lot of ongling "design effort".

The primary goal is to transform unproductive space into a garden that needs minimal intermittent watering and care. The trench and berm could extend indefinitely along the land contour or be repeated as circles wherever space is available.

The project is to test out disaster relief gardens for families rebuilding homes after earthquakes or other natural disasters or for refugees from conflicts. The assumption is that survival food is rice or other "aide" provisions but that nutritionally dense foods must be grown.

I am not in a desert climate, but have some thoughts.

I think that the plastic sounds like a good idea to absorb as much water as possible, but I would worry about the buried wood floating and tearing the bed apart. It may be worth trying though.

I think that digging a trench then building a hugelkultur bed up to the surface or above would work well. Being buried, the wood should hold on to more moisture than if it was built above ground. This is what I would try. If it didn't work well enough, then I would consider plastic.

I hope someone from a dry climate chimes in