What is a swale?
A swale is a broad, shallow ditch dug along a contour line, usually with the excavated soil forming a low berm on the downhill side. Water that runs down the slope is caught, slowed and allowed to soak in rather than rushing off.
The aim is to hold rain on the land, reduce erosion and support plants growing on or near the berm. Designs range from small garden features to larger earthworks.
The idea is related to techniques used for centuries in dry regions, though design differs with rainfall and soil. What works in one climate may fail in another.
Where do swales work and where do they not?
They work best on gentle slopes with soils that absorb water well. On steep slopes, heavy clay or soils near buildings, septic systems, wells or unstable ground, they can cause problems, such as saturated soil, slumping or seepage into places you do not want water.
Before choosing a site, check soil type with the Web Soil Survey and a test hole, and ask your conservation district or NRCS office whether the site is suitable.
Record the date, the weather and what the water did after the first few storms, then adjust the design where you saw trouble.
- Gentle slopes with absorbent soil
- Away from septic systems and wells
- Away from foundations and roads
- Not on unstable or very steep ground
How do I find the contour?
A swale must be level along its length, or water will run to one end and cause erosion. Finding the contour needs a level, a sight level or a simple surveying tool, and care. Mark the line with stakes and check it by eye after rain.
Small errors matter. Ask someone with surveying experience or your conservation district for help, since a mistake can turn the swale into a gully.
Test your line by pouring water along a short length and watching how it moves. If it runs to one end, adjust before digging the whole run.
How do I handle overflow?
Every swale needs a place for excess water during heavy storms. Plan a stable, vegetated overflow point that sends water to a safe place, not onto a neighbor's land, a road or a septic field. A berm that overtops without a controlled spillway can fail.
Check how water will move in an extreme storm and design for it, not for average rain. Qualified technical help is worth having for any large earthwork.
Heavy storms often arrive when soil is already saturated, so a swale that works in a moderate rain may overflow in a big one. Plan for the worst storm you can reasonably expect.
What do local rules say?
Rules on changing drainage, capturing runoff and moving earth are local and vary by state, county and town. Some places regulate water capture, and some require permits for grading or work near streams and wetlands. Water rights differ across regions.
Call your county zoning and building office and your state water resources office and ask what applies. Keep a written record of their answers.
If your land drains toward a neighbor, talk with them before changing flow. Good relations and clear communication prevent most drainage disputes.
What can I plant and how do I maintain it?
Plants on and near the berm help hold soil and use the extra moisture. Choose species suited to your climate and the wetter and drier zones of the swale. Mulch the berm and seed bare areas quickly.
Check after storms, clear debris from the overflow, repair slumps and watch for standing water that lasts long. A swale that stays wet for long periods may breed mosquitoes, so ask your local health or extension office about managing standing water.
Trees planted on a berm need room to grow and should be chosen so roots do not undermine the structure. Ask your extension office about suitable species.
What does it cost and how do I start small?
Cost categories include survey help, equipment or labor, plants, mulch and maintenance. Prices vary by region, so get local quotes. Hand-dug small swales cost mostly time, while larger ones need machinery and a qualified operator.
Start with a small trial on a safe site, watch how it behaves through a season and adjust. Take photos before and after storms and record what you observe.
Compare the cost of a swale with simpler options, such as mulch and ground cover, since these may do much of the same work.
Key takeaways
- A swale is a level channel on the contour that slows and soaks in runoff.
- Soil, slope and distance from wells, septic and buildings decide whether it is safe.
- Plan a stable overflow and check local drainage and permit rules.
- Start small and watch it through a season.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.