Wouldn’t it be perfect if we all could all use rainwater even after the rain ends? Unfortunately, we can’t all build a well in your backyard as they are expensive and hard to make. What you can do, however, is utilise the power of swales in your backyard.
Swales can be the perfect fit for your garden, as they’re fairly fast to make and come with a lot of perks. So, the Fantastic Gardeners team is here to bring you the know-how of building a swale and how one can be perfect for your garden.
What is a swale drain?
A swale in gardening is a ditch used to harvest and distribute rainwater along a horizontal plane. The basic anatomy of a swale consists of a shallow channel on a slight slope lined along with a mound on the downward side – called a berm – to keep the water in. Both sides of the swale must be covered in plant life to prevent soil erosion.
How can a swale help your garden?
- Swales can be used in conjunction with other permaculture techniques to capture runoff and spread it across the landscape to improve water infiltration in the soil.
- The quality of water will improve as a result of this since it will first percolate through the soil. This improves the water’s mineral and microbial content which in turn provides better nutrition for your garden.
- Vegetation planted in and around the swale will benefit from the concentration of runoff. Trees and shrubs planted there will provide shade and natural mulch which will make evaporation slower and thus improve the amount of water absorbed. This is doubly useful for arid climates.
- Swales can also act as a filter for urban pollutants that rainfall absorbs, because of the fact water seeps through the soil before reaching your plants’ roots.
- Naturally, all of this will result in optimum water efficiency, especially if you are building a xeriscape.
- Swales are really cheap to construct and require no maintenance once set up, which leaves you more money for other gardening supplies. With a small enough garden or big enough smartly situated swale, you can potentially completely eliminate the need for supplemental watering.
How to build a swale drain
Building a swale drain is actually not that hard, so we've provided detailed instructions on how to do it yourself!
1. Observe your plot
To manage rainwater properly you want to hold it at maximum height in your landscape. This will provide maximum absorption efficiency. Typically runoff quickly escapes flat surfaces and barely any of it sinks in the soil. The swale will hold the water inside the trench and help it soak deep in the soil, minimising water loss due to runoff.
Additional observation tips:
- To build one properly you need to observe how water flows in and out of your yard. Pay attention to the following things: Where are the steepest slopes in your yard? These are instrumental, as swales need an incline to be build upon. Of course, if a slope isn’t present in your yard you can create it artificially by piling soil in your desired spot.
- Learn the drainage pattern of your property. This is easily done by sitting in good view of your garden with a cup of tea during rainy weather and just paying attention where water gathers and where it flows out.
- Consider how much water your home’s roof captures and where your gutters deposit that water. This is helpful to have in mind when building the swale as this can be integrated into your planning stage to make the most out of rainfall. Think of your roof as one big funnel for rainwater.
2. Choose the perfect spot
Here are a few things to have in mind when choosing the site for your swale:
- Keep it at least 3 meters away from your house. Water must drain away from your home, otherwise, you may have some problems with moisture, especially in your basement.
- The swale has to be at least 5 meters away from steep slopes or septic drain fields
- The soil at the spot you choose or the soil you use to create an artificial slope for your swale must have good drainage to make sure water absorbs properly.
3. Mark the land
Mark the contour line of your swale. You have to make sure it’s properly levelled so it will hold water without spilling it. The swale’s maximum capacity is as big as its shallowest end. This is why you want to make the depth and width as uniform as possible.
4. Dig the swale
Now it’s time to get digging. You don’t want to make the swale too deep. A maximum of half a metre in depth is enough. You’d want your swale to be wider than its depth. This will make it easier for water to sink in the soil and enrich a wider area.
Mound the soil you’ve dug up from the trench on the downhill side to create the berm. Make sure it’s at least as high as the other side to hold water properly.
5. Testing and adjustments
Once you’re done building the swale you have to test if the bottom is level. If there are uneven spots fix them. The surest way to see if your swale is working properly is to observe it during rainy weather. If you can’t wait for such an event you can always test it by manually filling it with your garden hose. Although this option may not be entirely trustworthy as you can’t exactly replicate rain conditions with it.
If the swale overflows you can either make it longer, deeper, or wider. Another option is to dig another swale further down and make a spillway in the top one’s brim. Lining this spillway with rocks will prevent soil erosion. This way the overflow will be captured in the second tier. Figure out which option is most applicable to your garden.
6. Start planting!
Once your swale is complete and you are sure it won’t overflow you can start planting on it. The berm is the best place to do that. You can either use it for decorative vegetation or crop yielding plants. Perennials are the best choice. Fruit-bearing trees are a great option as their foliage will shade the swale and slow down evaporation, as well as provide mulch and organic matter for it.