Last weekend we hosted a group of 19 students for a class about catching rainwater in the landscape. It was cozy – we set the record for the number of people in our basement at one time, and we ran out of chairs. Though we tried to keep Molly the social cat outside so as not to bother any non-cat people, she just ran back in with every new visitor. After all, it was cold outside, and all the people were inside! Non-cat people were very patient with her weaving her way through the crowd and running in front of the screen, and we love you for it. Darn it if we didn’t get any pictures. If you got any, we’d love a copy!
We hope to be able to invite everyone back in the summer to see the front yard rain system working, when it’s not buried under ice and snow.
The class focused on two ways to hold rainwater in the landscape: Swales and rain gardens.
In this post, I’m going to elaborate on swales: what they are and why you should have one.
In part 2 (coming next week) we’ll discuss how to build one.
What is a Swale?
Easy enough: a swale is a shallow trench dug out dead level along the land’s contours, with a berm on the downhill side.
In the above picture, the contour lines are shown in pink. These indicate that everything along the same pink line is the same height above sea level, and in this picture, the hillside slopes downward toward the bottom right corner of the image. Without the swales, the water would form gullies and rush down the hillside without sinking in, taking precious topsoil and nutrients with it.
Swales are dug along the (pink) contour lines and are shown in blue. The soil from the trench is mounded on the downhill side of the trench and planted (shown in green). The important function that swales perform is to slow down the water, spread it along the contour, and let it slowly sink in underground, rather than above ground as in runoff.
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 our environment desperately needs them. We can all do our part with this simple technique.
Also lucky for us, we don’t need a hillside for a swale to be useful.
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.
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 combined overflow 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
For example, our 1200 square-foot house catches 30,525 gallons of rain from the roof each year. See Gaia’s Garden: Chapter 5, p.108 to calculate how much water your roof collects. We capture 75% of that, or almost 22,900 gallons in our landscape. What if we all did caught tens of thousands of gallons of water in the landscape, assuming a site assessment proved 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, I do not (though I’m always up for learning – Vince humors me). 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 have to have 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. Unless you want to buy a pump, which is fine, but look at all of this engineering and purchasing, 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. This is the reason why government and experts haven’t been proactively encouraging rain catchment: It just takes one person catching water irresponsibly to flood their neighbor’s basement or start a mosquito pond to ruin it for the rest of us.
So let’s catch it in the landscape responsibly and use it to our advantage.
Inside scoop: We do have rain barrels in addition to a swale and two rain gardens on our homestead. But truthfully, I find it difficult to use the water in the rain barrels in a timely manner because in doing so, I’m spending my precious time hand watering. Our in-the-ground solutions work better, last longer, and save me time.
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 benefits of the swale, minimize evaporation, and minimize your time in the garden:
- add organic matter (compost) and mulch to your beds and swale berms continuously
- 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 our own organic matter and fertilizer. This means fewer inputs on your part, 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.
Tune in next week when I detail how to build a swale!
Have you built a swale on your property? What benefits have you noticed?