One of the challenges with landscaping in the desert is the lack of annual precipitation and the need for supplemental irrigation. Current estimates of annual rainfall for Phoenix average 8.3 inches per year. As you can imagine, water is a very precious commodity here. One of the concepts in landscape design that has always interested me is rainwater harvesting. Having lived in apartment complexes prior to buying the townhouse we live in now, I never had a chance to experiment with different rainwater harvesting techniques.
When we bought this townhouse, there was a hedge of oleanders between our and our neighbor’s driveway that always scratched my car as I pulled into the garage. After living in the home about a month I had the landscapers remove the oleanders and dig up as much of the roots as they could. As you can see, they did a nice job. The grey hose you see in this photo is a flexible “sleeve” that houses the cable feed to our townhouse.
Once the oleanders were removed it occurred to me that the scupper for the roof drain was located directly above this two-foot wide strip and I thought it would be a perfect opportunity to try a rainwater harvesting experiment. My first idea was to install a downspout to the scupper and attach a French drain underground to move water directly from the roof into the narrow planting bed. I even thought about digging a sump pit near the asphalt pavement just in case we got a heavy summer monsoon rainstorm. However, the HOA did not approve the gutter so I had to come up with a plan B.
My plan B was to plant a few arid plants (agave and cactus) that wouldn’t require much water in the planting bed, and then create a swale that would channel the runoff water from the roof, into the planting bed, and to each of the plants. Although it is difficult to see in the photo, I terraced the planting bed with small berms between the barrel cactus so that any larger water flows would back up and percolate into the ground and hopefully not wash the rock mulch into the street.
Once I finished laying out the plants, rough grading, planting, and fine grading, I spread 3/8” sized Madison Gold granite as a ground cover. I estimated that I would need a half a ton, however, the landscape company delivered more than a ton so I spread the granite extra thick so that the berms or the swales wouldn’t be seen. Once the granite was spread, everything was complete. Now I only had to wait for the next storm.
As you can see, a few months after the installation, we had a rainstorm in which we received 6/10” of rain. The scupper drained the rainwater into the swale, watered the plants, and the berms held the water and didn’t wash the decomposed granite into the street. We did have a little wind so I spent the next afternoon raking up the leaves and debris, but over all, my project was a success.
I know this was a small project, but I was excited to see it work and can’t wait to try other techniques on future larger projects. If you’ve had experience with rainwater harvesting and would like to share your story, please leave a comment below or if you’re on twitter, send us a tweet.
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