Last weekend we hosted a group of 19 students for a class about catching rainwater in the landscape. We set a record for the number of people in our basement, and we ran out of chairs! We accomplished a lot, except that the tour outside to see the front yard rain catchment system was canceled due to the garden being buried under ice and snow.
Catching rainwater in the landscape can be an efficient way to irrigate and improve soil quality at the same time. Swales are one method for capturing rainwater in the residential landscape. In this post I discuss what a swale is and why you should have one.
If you’re ready to get started building a swale in your yard, see my article how to construct a swale in the residential landscape.
If you’re managing a larger landscape, see my article What is a Swale? geared toward larger land holdings.
What is a Swale?
A swale is a shallow trench dug along the land’s contour, with a berm on the downhill side.
All points along a contour line are exactly the same height above sea level. Therefore, a trench along the contour slows the water and spreads it across the contour line. This slowing and spreading of water reduces erosion, retains more water where it is needed, and does a bunch of other cool stuff, too!
In the above picture, the contour lines are shown in pink. These indicate that all points along a single pink line are the same height above sea level, so in this picture you can see that the hillside slopes downward toward the bottom right corner of the image.
Potential swale trenches are drawn in blue. When constructing a swale, the soil from the trench is mounded on the downhill side to form a berm, which is usually planted with perennials (shown in green).
Without the swales, the water rushing down the hill in the above picture would form gullies, taking precious topsoil and nutrients with it.
Since swales are a permaculture technique, the goal is usually the production of edible-producing plants. For that reason, the berms are often planted with fruit tree guilds or a diverse blend of edible trees, shrubs, and herbs. They can also be planted as hedgerows for privacy or windbreak.
Now, the above picture is showing large swales on a large farm field. Lucky for us that swales are also applicable on a residential scale, and–when constructed in the appropriate location–our environment desperately needs more of them.
More good news: We don’t need a hillside for a swale to be useful! A gentle slope or flat land can also benefit from a swale.
Why you should have a swale in your yard
- Swales mitigate stormwater runoff.
- Swales are way easier than catching rain in a tank or barrel.
- Swales are more efficient than tanks or barrels.
- Swales build self-sustaining ecosystems.
Let’s elaborate on each of those points.
1. Swales mitigate stormwater runoff.
Stormwater runoff is a huge problem in most cities. Water is seen as a liability (flooding) so the modern mindset is that we need to send it away as fast as possible. This has resulted in horrible breaches of environmental stewardship every time it rains, when we send 13 million gallons of raw sewage into local waterways each year in my city alone, because the overtaxed sewer system combines stormwater with sewage during heavy rain events.
We think stormwater is a problem that only governments, institutions, and experts can solve. In reality, there would be no problem at all if citizens did their part.
“Though the problems of the world are increasingly complex, the solutions remain embarrassingly simple.” – Bill Mollison, father of permaculture, and author of Introduction to Permaculture and Permaculture: A Designers’ Manual
For example, our 1200 square-foot house catches 30,525 gallons of rain from the roof each year. How much water does your roof collect? We capture 75% of that, or almost 22,900 gallons in our landscape. What if we all caught tens of thousands of gallons of water in the landscape–assuming a site assessment proves a swale to be feasible?
It would mean that the millions of dollars of taxpayer money currently going to fixing the sewer problem wouldn’t be necessary. Quick everyone! Dig a free swale!
2. Swales are way easier than catching rain in a tank.
I wish I had building and engineering skills. Alas, with all of skills I hope to learn in the life I have left, engineering isn’t going to be one of them. Catching rainwater in tanks or barrels means that you have to buy a bunch of parts. You have to connect the downspout to the container, you may have to connect more than one container together, and you have to connect the overflow either back to the sewer, or run the overflow elsewhere.
You also have to be able to clean out the barrel frequently and add mosquito dunks, and you need a spigot for filling up a watering can or running a hose. Plus, all of these parts are going to eventually degrade with sun and weathering and will need fixing or replacing.
And finally, there is very little water pressure from rain barrels, so using the water is quite frankly a pain in the ass. Believe me, watering takes a REALLY long time without water pressure. The solar pump I tried didn’t work very well. I think the inventors know that because it isn’t on the market anymore.
Look at all of that engineering and purchasing of parts, when–in the end–we could dig a trench and let nature slow the water, spread it, and store it for us. Easy-peasy (after the trench is dug)!
One more thing: If you’re going to have rain catchment containers, the overflow must be planned. Water is powerful and it is both irresponsible and a waste to send thousands of gallons of water to nowhere in particular.
While we have a swale in the front yard edible landscape, we do also have rain barrels in the backyard, which overflow responsibly to irrigate the yard. I begrudgingly use the water they collect to water potted plants. Our in-the-ground solutions work better, last longer, and save me time.
This is one reason why local municipalities haven’t been proactively encouraging rain catchment: It takes just one person to flood their neighbor’s basement or start a mosquito pond to ruin it for the rest of us.
So let’s catch rain in the landscape responsibly and use it to our advantage!
3. Swales are way more efficient than tanks.
Good soil is thirsty. Organic matter acts like a sponge, easily holding several times its weight in water. Toby Hemenway in Gaia’s Garden tells us that three quarts of dry soil can easily hold one quart of water. When we translate that to the soil in our yard, if our yards were covered in one foot deep of rich, moist soil, it would hold as much water as a 3-inch-deep lake the size of the yard. It would be cost-prohibitive to install a container that could catch that much water. But the soil will hold it for free.
Here are a couple of other strategies that will maximize the benefit of a swale by minimizing evaporation and your time in the garden:
- add organic matter (compost) and mulch to your swale berms regularly
- shade the soil on swale berms with dense plantings
4. Swales build self-sustaining ecosystems.
Swales catch water and direct it to where it’s needed, which is in the soil. Instead of water running off or pooling above ground, swales direct it downward into an underground reservoir.
Nature has its own built-in, self-regulating system. When water is needed, it is naturally released. No work on our part after the swale is built!
This underground reservoir attracts microorganisms. Suddenly the soil is alive and the “micro herds” begin eating and pooping and procreating (perhaps not in that order) and voila–we’re generating organic matter and fertilizer right in the place where we need it.
This means fewer inputs, which saves you money and time. The more the organic matter builds, the more moisture it holds. With more organic matter, the system can better withstand both floods and droughts.
As the water reservoir and nutrients in the soil build, gardening will become a breeze for you.
Now your ready to learn how to build a swale!
Have you built a swale on your property? What benefits have you noticed?