did you post this on the main board Natasha? I think swales could lead to trouble with land slip and the answer to your gardening may be "no dig" in raised beds.
I suggest you post for a wider input.
It's 2.5 acres. From what we've heard from the previous owner, when it does rain, the rock is permeable and everything will soak through and out pretty quickly. I have watched the "Greening the Desert" videos - very good info. We're not at the bottom of an ancient river bed, we are a short distance from a steep cliff that overlooks the current riverbed. I like the idea of building the swales upward, and this seems like it will be a LOT more feasible than digging into the rock across the whole property! Phew, centuries! I wonder if we can still grow food in the meantime . . .
I would need more detail. How much land? Is the rocky portions permeable to water? I watched a video called "Greening the Desert" on youtube. That might be a good place to start. If the whole ground is rocky as in the bottom of an ancient river bed, then I think I might consider mulching up raised beds several meters hight to create the swale and planting areas. "Top soil" only need to be about 12" so you could use biomass or fill dirt to create the beds. Trees need the deeper structure. Instead of building the insides of the swales downwards, you may have to build the outside of them upwards if the rock is too deep. Consider planting something creeping or clinging that will go between the rocks and start creating a biomass there and start breaking down the rock (this will take centuries so don't hold your breath). I hope this helps.
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