Hi Mark:
I also recommend Brad Lancaster's excellent books on
Water Harvesting. Essentially, in drylands, you need to plant water along with the trees. You didn't mention if you were on a large property or an urban/suburban property, but Brad's Vol 2 has a chart on what the best types of
earthworks are for you in your situation (p. 42). For example, if you're on sloped
land, swales on contour are great. If you're on flat land (like most urban lots), infiltration basins are the way to go. Planting trees right in the basins/swales as opposed to on the berm/earthmound of a swale is also a dryland adaptation. Plants that have lower water needs are planted up the sides or at the top of swales/infiltration basins (cacti and succulents, for example - although not all of these are low water). Brad also includes edible and other useful plants that are low water in the appendix of Vol 1.
Here in downtown Phoenix, my property is FLAT! And some areas are very narrow. So I've chosen infiltration basins for rain and graywater, sunken veggie beds to keep water in the bed, as well as some French drains for some narrow areas.
I also recommend finding out what your "water budget" is (how much rain and graywater you have access to) before you begin your design. I truly wish I had! It would have saved me loads of time and money.... Live and learn! (over and over and over again!). You can determine your water budget at Brad's website here:
http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/rainwater-harvesting-online-calculator/
Please keep us updated on how things are going with this
project!
Best,
Jen in Phoenix