How to Create a Swale: Where to Place It & Why It Works

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Direct water runoff and prevent erosion with tips from a pro landscaper
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Digging swales is an excellent technique for rainwater harvesting. Swales capture and transport surface runoff, nourishing plants and reducing erosion. The berms beneath them make great fertile planting beds, and best of all, many swales can be dug by hand, which means they don’t cost anything! We talked to landscape designer Matt Daly to find out everything you need to know about digging your own swale . Keep scrolling to learn more!

How to Dig a Swale: Overview

Use a laser level or A-frame to find a path for your swale that’s level, or “on contour.” Dig a trench along that path that’s 6–12 in (15–30 cm) deep and 3–4 times wider than it is deep. Pile up the excess dirt on the downhill side of the swale to create a berm, then plant the swale and berm to prevent erosion.

Section 1 of 6:

What is a swale?

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  1. Swales are wide, shallow trenches designed to reduce runoff and flooding. They’re usually U-shaped, but sometimes V-shaped. They’re typically placed along a slope to help capture rainwater runoff, allowing the water to seep back into the ground gradually. Multiple swales can be connected to help manage large volumes of runoff. [1]
    • The dirt that’s removed from a swale is typically piled up on the downhill side to create a berm, which helps divert water into the swale. The berms are usually planted, helping prevent erosion.
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Section 2 of 6:

Placing and Marking the Swale

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  1. 1
    Place the swale where water collects or runs off quickly. Daly says, “To really understand drainage problems, don’t just look at the puddles on your land the morning after it rains. Go outside when it’s raining to see what the water is actually doing.” [2] Pay attention to low spots where water pools, but also note where runoff flows quickly—those areas can be subject to erosion, which may be prevented by a swale.
    • While it’s raining, notice the volume of water that moves across your land. If you’re dealing with large amounts of water, you may need to place multiple swales to fully handle the runoff.
    • If there are any dry areas in your yard or spots where erosion is a problem, consider placing the swale just uphill from those spots.
    • Be sure the swale is located at least 10 ft (3.0 m) from building foundations and 50 ft (15 m) from septic systems. [3]
  2. 2
    Use the swale to direct water elsewhere on your property. Don’t direct stormwater runoff onto a neighbor’s property or into a storm drain, street, or another body of water. This can cause flooding and pollution issues, and will likely violate local statutes. [4]
    • Good options for spillways include a rain garden, another swale, or a dry well. [5]
  3. 3
    Reach out to local utilities about digging requirements in your area. Daly says that you should always check with your utility companies—like water/sewer, gas, and electric companies—before you dig in your yard. [6] Additionally, you may need permission from your city officials, county agricultural agency, or even the Army Corps of Engineers to divert surface water.
    • The best place to start researching is your local building or zoning commission. Your city or county public works department may also have the information you need—and if not, they can likely point you in the right direction.
    • If your property is located on a wetland , digging a swale could divert water that damages a fragile ecosystem. In the US, this may be considered a violation of the US Army Corps of Engineers. Reach out to your local Corps office if you’re not sure if this applies to you—you can find a list of them here .
    • In some areas, you may be required to have a professional engineer design the plans for your swale. [7]
  4. Swales should be dug “on contour,” which means they’re level all the way along their length. Hammer a stake where you want the swale to start. Then, use a laser level or line level to find a section of land where the ground is even. Hammer in a second stake at this spot. Keep going all the way down the length of the swale, working in small sections and marking each spot with a stake.
    • Swales need to be level to capture and retain water effectively.
    • Your swale may not be perfectly straight. That’s okay—swales are designed to work with the natural flow of the land.
    • You can also use an A-frame—a triangle-shaped tool fitted with either a plumb line or a spirit level. Just put one leg of the A-frame where you want the swale to start, then rotate the second leg until the level is centered. Hammer in a stake here, then rotate the first leg of the A-frame around to find the next spot.
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Section 3 of 6:

Digging the Swale

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  1. Start by digging a trench the depth you want the swale to be—you’ll come back and widen it later. Most swales are about 6–12 in (15–30 cm) deep, and they’re usually 3–4 times wider than they are deep. So if your swale is 1 ft (30 cm) deep, it should be 3–4 ft (0.91–1.22 m) wide. [8]
    • If you’re digging a small swale, you may be able to excavate the trench with hand tools, like a pickaxe or a shovel. But for larger jobs, it’s probably best to rent an excavator or hire a professional.
    • Go with a level slope for irrigation or a graded slope for drainage. Learn more in our section on leveling vs. grading swales .
  2. 2
    Pile excess dirt on the downhill side of the swale. As you’re digging, scoop the loose dirt onto the downhill side of the swale, heaped up into what is called a "berm." Daly says, “The berm will help channel the water in the direction you want it to go.” [9] It also makes a great planting bed.
    • Try to make the berm level. That way, if the swale overflows, the water will crest the berm evenly, rather than rushing through a single low point and eroding the berm. [10]
    • If you want a larger berm, Daly says, “you can put larger organic material in there to fill up space.” [11]
    • If you’re using a swale somewhere like a front lawn, you might not want to include a berm. In that case, use the excess dirt to fill in low areas in your lawn or arrange to have the dirt hauled away. [12]
  3. 3
    Shape the sides of the swale into a gentle slope. After you’ve excavated the initial trench, go back through the swale, leveling the bottom and widening the sides. Swales usually have gently sloped sides, around 25–30%. [13]
    • Having a shallow slope makes the sides of the swale easy to mow. It also makes it less obvious, especially once it’s overgrown with grass.
  4. 4
    Run water through the swale to test it, or wait for it to rain. Use a hose to pour water into one end of your swale. Watch the way the water moves—if your swale is level, the water should spread evenly along the bottom. If it’s graded, the water should gently flow toward the deeper end.
    • The best way to test a swale is to wait for it to rain, but if you need to finish up the project and there’s no rain in sight, a hose can give you a rough idea of how well the swale is working.
    • If water sits in your swale for more than 24–48 hours, you may need to amend the soil with sand or compost to facilitate drainage. [14]
  5. If you need to slow heavy stormwater or you want to retain water longer in a dry climate, it might help to add a layer of crushed stone or gravel along the bottom of the swale. This may help slow down erosion, and it can even be used as a walking path. [15]
    • Keep in mind that sediment will eventually build up in the rocks. You’ll need to remove that sediment with a shovel 2–4 times a year and after heavy storms to prevent the swale from being blocked.
    • Some people fill their berms with a layer of natural matter like leaves, straw, and pieces of wood. This can help prevent erosion. Also, as it decays, it will enrich the soil in the swale. [16]
  6. 6
    Plant the berm and the sides of the swale to prevent erosion. Adding plants to the swale will help stabilize the soil. Ideally, choose native plants like shrubs, grasses, and groundcovers—these are already well-adapted for your climate, so you won’t have to spend much time watering or fertilizing them. Choose plants that can thrive in both wet and dry conditions, since the swale and berm may dry out completely in a drought. [17]
    • Some people prefer to plant foods like vegetables and small fruit trees along the berm. This can be a good way to help irrigate crops in a dry climate.
    • For a subtle look that fits into any landscape, plant the swale with grass. The gently sloped sides should be easy to mow.
    • Daly says planting the berm is especially important: “The root system will help hold the soil in place. Otherwise, when a storm hits, the berm is going to erode like a sandcastle.” [18]
  7. 7
    Regularly check the swale and remove obstructions. Every 3–4 months, walk the length of the swale. Use a shovel or rake to remove any dirt, limbs, leaf litter, or other buildup that could block the flow of water through the swale. [19]
    • It’s also a good idea to check your swale after heavy storms.
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Section 4 of 6:

Should my swale be level or graded?

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  1. 1
    Dig your swale so the bottom is level if your main goal is irrigation. If you want to capture rainwater runoff and disperse it evenly across a land, you’ll need a level swale. The water will fill the swale evenly, so all of the land along the swale will have equal access to the water after a rain. [20]
    • Level swales can be especially beneficial in dry climates, since they’ll help you use the rainwater most effectively.
  2. 2
    Dig your swale at a 1–2% grade if your main goal is drainage. If you want to dig a swale for the purpose of moving water away from a foundation or other structure, add a slight slope. A 1–2% grade will help direct the water in the direction you want it to go. Avoid higher slopes, which can cause erosion—especially during storms. [21]
    • For example, let’s say you’re building a 50 ft (15 m) swale and you want to direct water away from your home. Dig the far end of the swale 6–12 in (15–30 cm) deeper than the end of the swale that’s closest to your home.
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Section 5 of 6:

Why are swales beneficial?

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  1. Swales can help you effectively manage stormwater on your property. They can help redirect runoff from heavy rains, slowing erosion on your property. They can also help hold rainwater to irrigate the soil in dry climates. Moreover, the plants in a swale and berm system help filter pollutants and contaminants from water, improving the groundwater quality—not just on your property, but in neighboring areas as well.
    • Swales are a low-cost drainage solution compared to installing storm drains or other options.
Section 6 of 6:

Frequently Asked Questions

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  1. 1
    Do you need a permit to dig a swale? It’s always a good idea to double-check whether you need a permit. You don’t want to get all the way through the project and then discover that you’re in violation of a city ordinance or the Army Corps of Engineers. Start by reaching out to a local authority, like your city or county building, zoning, or public works department.
  2. 2
    Can I build a swale on a steep slope? Don’t build swales on slopes greater than 15%. Slightly sloping land (between 3–15%) is ideal, since water will run down into the swale. But the swale isn’t likely to be effective on steeper slopes, and digging could potentially destabilize the area, especially during heavy rains. [22]
  3. 3
    Should I hire a professional to dig a swale? If you’re only building a small swale—and a professional engineer isn’t required by your local government—it’s probably fine to dig your own swale. But for longer swales that would be difficult to dig by hand, you’ll need to rent equipment or, if you’re not comfortable using heavy dirt-moving equipment, hire a professional.
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Community Q&A

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  • Question
    There is a grassy rut on my property which handles runoff on mountain-side land with a gentle pitch that is mostly dry. Is a swale appropriate for this situation where the land runs down?
    Community Answer
    Yep, that's the best. No maintenance, replacement or back-flushing of anything, and it can be both widened or deepened to handle more, if you have a home gutter system that you want to tie into it with pipes or another swale.
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      References

      1. ↑ https://www.susdrain.org/delivering-suds/using-suds/suds-components/swales-and-conveyance-channels/swales.html
      2. ↑ Matt Daly. Landscape Designer. Expert Interview
      3. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      4. ↑ https://treecanopybmp.org/uploads/files/Hobby+Farm+BMPs/Section+6./Fact+Sheet+6.3+Vegetated+Swales+-+CEI.pdf
      5. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      6. ↑ Matt Daly. Landscape Designer. Expert Interview
      7. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      8. ↑ https://www.bitesizedgardening.co.uk/how-to-build-a-swale/how-to-dig-for-victory/
      9. ↑ Matt Daly. Landscape Designer. Expert Interview
      1. ↑ https://www.bitesizedgardening.co.uk/how-to-build-a-swale/how-to-dig-for-victory/
      2. ↑ Matt Daly. Landscape Designer. Expert Interview
      3. ↑ https://youtu.be/L5JbD0vCgTI?t=267
      4. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      5. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      6. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      7. ↑ https://www.greener.land/swales/
      8. ↑ https://conwayma.gov/files/vegetated-swales.pdf
      9. ↑ Matt Daly. Landscape Designer. Expert Interview
      10. ↑ https://www.greener.land/swales/
      11. ↑ https://www.grit.com/farm-and-garden/do-it-yourself/how-to-build-a-swale-for-drainage-zm0z23jazawar/
      12. ↑ https://www.epa.gov/system/files/documents/2021-11/bmp-grassed-swales.pdf
      13. ↑ https://www.greener.land/swales/

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