We're looking forward to restarting our Superadobe building projects, but the winter break has allowed us to get a lot of other stuff done. One of the most important is installing many water-harvesting earthworks that will help stop erosion of our topsoil and will help build living soil which will enable abundant food production.
Rainwater harvesting can benefit all but the wettest environments, but it is especially beneficial in dry regions like the desert southwest. Soil life has the same needs we have: Food, water, and shelter from the elements. Hot desert sun can bake the life right out of the soil, making it more impermeable. Then when it does rain the drops compact the soil and the water runs off faster. This results in flash floods, soil erosion, and other damage.
Well-made earthworks help to slow and spread water runoff so it has more time to infiltrate into the soil. This allows microbial and plant life to flourish. Living soil sucks up water like a sponge. Plants provide food and shelter for the microbes in exchange for nutrients in an amazing, symbiotic relationship not unlike the relationship we have with our microbiome.
Below I show numerous examples of the earthworks we've been installing, but first let me tell you about a free online class I'm co-teaching on March 23rd that goes into a lot more detail on this topic. You'll get some valuable takeaways you can employ in your own yard. (I'm also co-teaching a webinar on Composting and Soil Building on March 9th and an in-person class in Sierra Vista on 3 Simple Steps to Gardening Success on March 11th - both free.)
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We hope to see you there!
The higher the velocity of water flow, the more erosive it is. One way to combat this is with one-rock dams (at one rock high they are very stable). We have installed more than a dozen of them. They actually reverse soil erosion by slowing the flow of water, allowing it to linger and infiltrate, and capturing fertile sediment above them. Once the soil capture is level with the top of the dam, another dam is built slightly behind and on top of it. As the process continues, the elevation is raised and the water is spread more across the land. Beneficial vegetation further enhances the process by capturing additional soil, stabilizing it, and providing food and shelter for soil life. Soil life, in turn, supports more plant life.
This photo actually shows two boomerang berms installed to capture water for a piñon pine. The berm is the mounded dirt in the form of a half circle. Most of our trees are heavily mulched, but piñon don't like mulch so this made for a good picture of boomerang berms. The smaller berm helps water the sapling and the larger will encourage root growth. Once established our piñons won't require supplemental watering and will provide a wind and privacy screen, shade, and pine nuts, among other benefits!
When we did water infiltration tests before planting a bunch of beneficial trees, we found a few spots with so much caliche that they didn't have good enough drainage for the trees. The water test holes are about 1' wide by 1' deep. So we filled them with wood chips, mulched around them out to the boomerang berm, and planted cover crops to develop the soil. Rabbits decimated the cover crops (we turned the rabbit problem into a solution and enjoyed some forage-fed rabbit soup), but we'll keep working on the spot. I plan to use infiltration trenches, similar to what I just described, near higher-water use trees such as our ponderosa pines.
If you have much space and at least a little slope, running swales and berms on contour can harvest pretty much all the water that falls on it. Swales are essentially a ditch with a berm on the downhill side. So imagine a sunken bathtub without ends that runs across a hill rather than down it, capturing all the water that runs down from above. Of course you would want multiple swales in succession - running parallel to each other. They can be wide and subtle like gently rolling hills or smaller like the ones shown above. In this space we turned the swales into level garden beds and planted cover crops to build soil, and the berms are paths - high and dry. But that can be reversed, it just depends on how you want to use them.
I previously reported on our rain garden so I'm not going to cover that again here. If you missed it, here are the before and after reports about turning an eyesore and erosion hazard into a beautiful resource.
What's cool about our terrace gardens is that they were pretty much already here, so we're making small changes for great benefit. Water naturally flows into them from above. They are relatively level and were filled with sediment, native grasses, and other vegetation. We lined them with rocks, laid cardboard over the grass, and added several inches of wood chips on top. This is called sheet mulching and is a great way to turn grass into soil ready for planting edible, medicinal, and beneficial plants.
When doing water-harvesting earthworks you must always plan for overflow. Otherwise a large rain event can destroy your earthworks and cause additional damage below it. In this picture you can see a mulched swale and berm near the top that will overflow into the boomerang berm below it.
This is just a quick overview of some of our earthworks. If you'd like additional information, I encourage you to attend our free webinar mentioned above.
Dedicated Christian, patriot, family man, founder of Sabbatical Ranch & Resilient Agriscaping, Elegant, Edible Landscape Educator, Facilitator, & Coach
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