Passive Irrigation for Public Food Forests?

As I've mentioned, I'm volunteering to put together some community/public food forests at churches and other places. The land available in some is pretty huge--there's one town that has up to 100 acres that are possibly available. A major limiting factor is irrigation. Around here young trees need irrigation for two to three years to get through our hot, dry summers.

Can anyone recommend a passive watering system? If not, we'll be limited to hand-held hoses.

I may look into growing certain things from seed in the spot, but it's not likely to fly with these people. It's already a big paradigm shift just planting food trees the "normal way"

Can you make contour swales which are periodically flooded from large water tanks?

I think it's a good idea, but I'm not sure it'd be feasible budgetwise or in terms of expertise. And if it fails it will be very public and difficult to restart from there. I may talk to David Ahlgren about putting in earthworks to save water longer term, though.

Submerged buckets with a few small holes in the bottom or big plant pots with most of the drainage holes taped shut. Fill them (manually or automatically) and they will slowly water the tree they're placed next to.

Depending on your climate and soil. Sandy soil limits the usefulness of swales. Raised beds mean more watering. Clay soils in a rainy climate might mean your low spots get too wet for many plants.  Since you have buildings on site, I would say use your roof runoff, but Washington state is known fot weird rules about that. Old hoses can be taped to close holes with electrical tape and drilled to have holes.  I have these around my yard from when I was establishing plants.  Most are mostly buried now, but it did the trick. You could have it on timer, if need be, but I just left it on trickle when I had to go away for work. My climate is, however very wet except for the 2 months a year of watering and we get a discount on our water bill for summer watering.