A permaculture swale is a technique for capturing and storing water in a garden. In this article, learn how to build a swale in the home landscape. Oh, and don’t forget to grab your FREE Quick Start Guide: How to Build a Swale to Capture Roof Water at the end of the article.
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A permaculture swale can be an important feature in the productive garden or earth-friendly yard because it helps to slow, store, and spread water. Personally, I discovered it was the perfect solution for creating a low-maintenance, edible landscape in my front yard.
>> Are you wondering what a swale is? If so, check out my article What is a Permaculture Swale: Irrigate the Easy Way for more details.
This article, to clarify, goes into the technical, nitty-gritty details of building a permaculture swale: How to choose an appropriate site/location, and how to build it.
Constructing a Swale in 9 Steps
Step 1: Observe water on your site.
As water flows across a typical surface or landscape, most of it will run off quickly without having a chance to soak into the soil, even on land that appears flat or very gently sloping.
With a swale or another manmade landform such as a rain garden, however, the water flows into a trench or depression, where it percolates slowly into the soil. Consequently, it produces little to no runoff.
To start, collect information about your yard. Where is the water coming from and where does it go?
Write down the following observations.
- Identify where water is wasted.
- Observe drainage patterns.
- Locate steep slopes.
- Determine annual rainfall.
In permaculture design, we call these passive observations, which are made by asking specific questions about the site. You can learn all about them in my article how to use the power of observation in permaculture design, as well as get my free, 13-page worksheet: Making Observations.
Active observations, on the other hand, are another type of observation. They’re made by collecting data about the site and plotting it on physical maps of the property, to get a visual representation of all the data points that can affect design decisions. It’s a good idea to walk through my map exercises for permaculture design if you goal is a whole-system water plan.
Step 2: Identify the ideal site for a permaculture swale.
A swale can help capture water before it’s lost in order to irrigate a planting area.
Most importantly, here are some rules for siting a permaculture swale. It should be:
- 10 feet away from a building (water must drain away from building)
- 18 feet away from the edge of a steep slope or septic drain field
- Uphill from a garden or low spot that doesn’t drain well
- An infiltration test demonstrates an infiltration rate of at least 1 inch per hour.
Note: This may not be an appropriate strategy for areas with a high water table or on extremely steep slopes.
Tired of generic permaculture design advice that you can’t apply to your specific goals? If so, check out my Permaculture Design Program and get the tools and support needed to create and implement your own permaculture design.
Step 3: Mark the contour line.
Mark the contour line every six feet using a contour level and utility flags. The following video shows how to use a simple, homemade A-frame level to mark the contour lines. (Don’t worry, anyone can build one of these!)
It’s essential to mark the contour lines accurately. Swales built off-contour go by other names, such as keyline trenches or diversion trenches.
Step 4: Dig a trench along the marked contour line.
Certainly, swales are unique to the landscape they’re used in, so no two swales will be the same shape or size. But here are some estimated values for swales in residential yards.
- Typical trench depth: six inches to 1.5 feet deep
- Typical trench width: 18 inches to two feet wide
- Length: Varies by your needs, size of the space, and how much water you can catch
As a reminder, the free quick start guide, which you can sign up to download at the end of this article, will help you with more specific calculations.
Step 5: Mound the soil from the trench on the downhill side to create a berm.
Take the soil dug from the trench and place it on the downhill side.
Step 6: Test and adjust the swale.
To test whether your swale trench is level, work the A-frame level along the bottom of the trench, as shown in the video above in Step Three. Fix uneven spots.
Next, observe the swale during a heavy rain event. How did it do? If it overflowed, then make the swale trench deeper, wider, or longer.
Step 7: Plant the swale.
I recommend planting perennials that grow permanent, thirsty roots in order to stabilize the system.
Should you plant in the trench or on the berm? This depends on your climate. In desert areas, plantings are typically placed in the swale trench to take full advantage of the rainfall before it evaporates. Meanwhile, in non-desert areas, it’s typical to plant the berm, as there’s typically more rain that may overwhelm plant roots.
Try these permaculture-based planting techniques on your swale:
(To name a few of my favorite ideas.)
Step 8: Build Redundancy into the Swale System.
Always think about where the water will go if the swale overflows, and then build redundancy in that can handle a 100-year rain event. Are you wondering what that means? In other words, you are the director in your landscape. Therefore, if the swale overflows, you need to tell the water where to go next. Otherwise, it will find its own route.
When I built my front yard swale, for example, I directed the overflow into a rain garden to accommodate any excess water. Likewise, if you have the space, you could direct the water into another swale by using what’s called a spillway—which is simply a trench that directs water somewhere.
Step 9: Add Aesthetic Details (Make the Swale Pretty!)
In residential spaces, aesthetics are often an important consideration. Swales can actually be visually pleasing, although it’s hard to imagine a beautiful setting with a trench running through the yard!
Try filling the trench with gravel or wood chips and you have a walkable pathway. (I prefer filling it with large rocks, followed by gravel, topped with a few inches of wood chips.) If your swale trench doesn’t need to be walkable, however, then consider seeding it with clover or grass, or adding a layer of mulch to reduce evaporation.
Finally, give the berm a pretty border, and you have a raised planting bed.
I don’t recommend filling the trench unless the swale is in a highly visible place where aesthetics are important. That’s because over time, the material in the trench may become compacted from the walking, and you may need to pull it out and replace them over time. In addition, when the trench is filled with material, you can’t see it working, and may not know if there’s a problem.
By observing your system, you’ll be able to notice if a swale berm starts overflowing regularly, or if a swale trench ceases to drain. That’s your sign that it needs a clean-out, re-leveled, or adjusted in size.
Here’s a picture of our front yard before we added a swale and gardens:
The swale system and perennial plantings work to slow the water, spread it, store it, and lock in moisture. The front yard now looks like this:
A permaculture swale can help you store water in the ground and reduce runoff. Nature does it best!
For more details and pictures of swale-building, see:
- Gaia’s Garden by Toby Hemenway
- Rainwater Harvesting for Drylands and Beyond, Volume 2 by Brad Lancaster
- The Suburban Micro-Farm: Modern Solutions for Busy People by Amy Stross (More pictures of swales in my award-winning book. Shameless plug!)
You might question whether using swales to store water in the ground actually works as well as I’m suggesting. This 5-minute video, Greening the Desert, demonstrates how swales used in the right context can turn desert into productive gardens.
Are you digging a swale in your yard?