A swale is a level, on-contour ditch with a planted earth ridge (the berm) on its downhill side. The pair works together to slow, spread, and infiltrate rainwater into the soil rather than letting it run off and erode your land. For broader context on the design framework that uses swales, see our practical guide to permaculture. Modern permaculture inherited the technique from Bill Mollison in the 1970s, but variants have existed for thousands of years in Indian khadin, Spanish boquera, and the indigenous earthworks of the American Southwest. The reason it endures is simple: a properly placed swale converts a passing rainstorm into months of stored soil moisture for the trees and plants growing on its berm.
This guide gives you the dimensions, the slope rules, the construction sequence, and the planting strategy that turn a sloped backyard into a productive water-harvesting landscape. Every recommendation cites the USDA NRCS Conservation Practice Standards, University of Arizona Cooperative Extension, Pennsylvania Stormwater BMP Manual, Brad Lancaster's Rainwater Harvesting for Drylands, Bill Mollison's Permaculture: A Designers' Manual, or peer-reviewed work.
Key Takeaway
Build a swale only if your slope is between 1% and 15%, your soil drains reasonably well, and you have something useful to plant on the berm. The swale itself is a level ditch on contour; the berm is the excavated earth piled on the downhill side and planted with deep-rooted perennials. A 100-foot hand-dug swale takes 8 to 12 hours of labour, or rent a mini-excavator for $200 to $400 a half-day. Sized correctly, it captures every storm under 2 inches and infiltrates the water within 24 to 48 hours.
A swale is a shallow ditch dug along a contour line so that the bottom of the ditch is perfectly level. Because the bottom is level, water entering the swale spreads sideways rather than running downhill, giving it time to soak into the soil. The earth that comes out of the ditch is piled on the downhill edge to form a berm, which is then planted with trees, shrubs, and herbaceous perennials whose roots benefit from the slow-release water below.
This is fundamentally different from a drainage swale (the kind a civil engineer designs to move water off a property quickly). The Pennsylvania Stormwater BMP Manual covers the engineering distinction in BMP 6.4.8: Vegetated Swale: drainage swales are sloped to convey water away; permaculture swales are level to make water stay. Both are useful; they solve different problems.
Swales are not universal. They excel in three conditions and fail predictably outside them.
| Condition | Build a Swale | Do Not Build a Swale |
| Slope | 1-15% (gentle to moderate hillsides) | 0% (flat: nothing to slow); above 15% (slope failure risk per USDA NRCS) |
| Soil | Well-drained loam or sandy loam | Heavy clay (water stands too long, drowns tree roots) |
| Climate | Arid and semi-arid; uneven rainfall | Already-saturated humid sites where drainage is the problem |
| Property size | Quarter-acre or more for a useful swale | Tiny urban lot (use rain garden instead) |
| Catchment | Adequate runoff source upslope (roof, paved area, hillside) | No runoff to catch (swale stays empty) |
Sources: USDA NRCS Conservation Practice Standard 330: Contour Farming (PDF), USDA NRCS Standard 331: Contour Orchards (PDF), University of Arizona Cooperative Extension: Harvesting Rainwater (PDF)
The standard rule of thumb from Brad Lancaster's Rainwater Harvesting for Drylands is to size the swale to hold the runoff from a one-inch rainfall event over its catchment area. The math:
Runoff volume = catchment area (sq ft) × rainfall depth (inches) × 0.62 gallons per cu ft × 0.95 (runoff coefficient for hard surfaces, less for permeable surfaces).
For a 1,000 sq ft catchment (a small roof or section of hillside) and 1 inch of rain, that is roughly 62 gallons (or 8.3 cubic feet) of runoff. A swale 12 inches wide, 12 inches deep, and 12 feet long holds 12 cubic feet, comfortably handling that storm.
For larger catchments and bigger storms, size accordingly. A 5,000 sq ft hillside in a region that gets a 2-inch design storm needs about 600 gallons (80 cubic feet) of swale capacity, which means roughly 80 linear feet of 18-inch wide, 12-inch deep swale. Most homestead swales run 50 to 200 feet long.
Mark the contour
Use an A-frame level (two wooden legs forming an A, with a string and bob suspended from the apex), a water level (transparent tubing filled with water), or a modern laser level. Place a flag every 5 to 10 feet along the contour. Verify with a second pass that all flags read level relative to one another. This step is the most often skipped and the most consequential.
Dig the swale to dimensions
For a typical homestead swale, dig a level-bottomed ditch 18 inches wide, 12 inches deep, along the entire flagged contour. Use a shovel and pickaxe by hand for short swales (under 50 feet), or rent a mini-excavator for anything longer. Pile every shovelful on the downhill side.
Shape the berm
Compact the piled soil into a continuous ridge 12 to 24 inches tall on the downhill side of the swale. Smooth the top so it is roughly level along its length. The berm should slope gently away from the swale on its downhill face, never directly into the ditch. Walk the berm to compact it; loose berms wash out in the first heavy rain.
Mulch the swale floor
Lay 3 to 4 inches of wood chips or coarse mulch along the swale bottom. The mulch slows surface flow inside the swale even further, prevents erosion of the swale floor, and seeds the system with fungal life that breaks down organic matter into the soil profile.
Plant the berm
Place fruit trees and nitrogen-fixing shrubs first along the berm at appropriate spacing for the species. Underplant with comfrey, yarrow, and white clover. Mulch heavily. The berm becomes the most productive and self-watering planting bed on the property within 2 to 3 seasons.
Inspect after the first three storms
Walk the swale immediately after the first three rainfall events. Look for overflow points, berm erosion, and any places where water is failing to spread evenly. Repair as needed. After year one the system stabilises and needs only annual inspection.
The berm planting strategy is what turns a swale from a piece of earthwork into a productive permaculture system. Choose species that send deep roots into the berm to break up subsoil and pump nutrients to the surface, layered with shorter herbaceous plants that hold soil and feed pollinators.
High stratum (canopy / sub-canopy). Apple, pear, plum, mulberry, persimmon. The slow-release moisture below the berm is exactly what fruit trees want.
Medium stratum (shrub layer). Goumi, sea buckthorn, currant, gooseberry, hazelnut. Nitrogen-fixers in this layer (goumi, sea buckthorn) feed the fruit trees while producing edible berries themselves.
Low stratum (herbaceous). Comfrey 'Bocking 14' (deep taproot to 6+ ft), yarrow (drought-tolerant pollinator), white clover (living mulch, nitrogen-fixer), strawberry, oregano, thyme. The same logic at work in our apple tree guild guide applies on a swale berm.
Ground cover and protection. White clover broadcast across the berm surface stabilises it for the first season. Heavy mulching with wood chips suppresses weeds and feeds the soil life. The full seven-layer food forest framework applies directly to swale berm planting.
For the swale floor itself. The bottom of the ditch sees periodic shallow flooding. Plants that tolerate occasional waterlogging and sometimes-dry conditions: sedges, rushes, swamp milkweed, or simply heavy mulch that decomposes into rich soil over time. Avoid planting fruit trees in the swale bottom; they will drown.
Why This Works: Slow, Spread, Sink
The permaculture mantra for water is "slow it, spread it, sink it" and a swale-and-berm does all three at once. Slowing prevents erosion. Spreading distributes water sideways across the landscape so plants benefit broadly. Sinking moves water from surface (where it evaporates fast) to subsurface (where it stays for weeks). This is the same logic that drives the broader permaculture water strategy in our 12 permaculture principles guide, applied as a single landscape feature.
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Send Me the ChartCommon Mistake to Avoid
Building on a slope steeper than 15 percent. Above 15 percent, the berm itself becomes prone to slumping and the captured water can saturate slope material to the point of slope failure. USDA NRCS Conservation Practice Standard 330 documents the increased erosion risk. On steeper slopes, use terracing instead, which adds a structural retaining edge.
The other failures appear repeatedly in practitioner debriefs:
Not actually level. A "swale" with a 1 percent slope from one end to the other becomes a drainage ditch and erodes its lowest end. Mark the contour twice and verify before digging.
Building in heavy clay. Clay holds water for days or weeks. Tree roots planted on the berm rot. If your soil holds standing water in a 2-foot test pit for more than 48 hours, swales are not your first choice; rain gardens with engineered infiltration media work better.
Sizing too small. Undersized swales overflow and cut new gullies on the downhill side. Always size for the design storm and add a 25 percent safety margin.
Skipping the berm planting. A bare berm is a future erosion problem. Plant immediately, or at minimum sow white clover and mulch heavily. Living roots hold the berm together.
Treating one swale as a complete water strategy. Most properties benefit from a system: multiple swales linked with overflow paths, paired with rain barrels, possibly a cistern, possibly a pond. See our permaculture zones guide and the food forest guide for context.
The most cited demonstration of swale-and-berm earthworks at scale is Geoff Lawton's Jordan project, where a degraded desert site was rehabilitated by installing swales on contour, planting berms with hardy perennials, and trapping the rare rain events that did occur. Within a few years the soil had recovered organic matter, native vegetation had returned, and the site was demonstrating water tables rising. Living Earth Africa documents the project; the principle scales from a backyard to a degraded landscape with the same physics underneath.
What is a swale in permaculture?
A swale in permaculture is a level (on-contour) shallow ditch with a planted earth berm on its downhill side, designed to slow, spread, and infiltrate rainwater into the soil. Permaculture swales differ from drainage swales (which are sloped to convey water away) in that they are level so water sits, soaks, and feeds the plants on the berm. The technique was popularised by Bill Mollison in the 1970s and is a foundational permaculture earthwork.
How wide should a swale be?
For most home and small-farm contexts, 12 to 36 inches (30 to 90 cm) wide is typical, with a depth of 6 to 18 inches (15 to 45 cm). Width depends on how much runoff you need to capture and how steep the surrounding slope is. Wider, shallower swales handle larger storms with less risk of berm overflow. Calculate volume needed using the catchment-area-times-rainfall formula, then choose dimensions to match.
How do you build a swale?
Mark a level contour line across the slope using an A-frame level, water level, or laser level. Dig a level-bottomed ditch along the contour to your target dimensions (typically 12 to 36 inches wide, 6 to 18 inches deep). Pile excavated soil on the downhill side as a berm 12 to 24 inches tall. Mulch the swale floor with 3 to 4 inches of wood chips. Plant the berm with deep-rooted perennials (fruit trees, nitrogen-fixers, comfrey, clover). Inspect after the first 3 storms and repair any weak spots.
What is the difference between a swale and a berm?
The swale is the level ditch that captures water; the berm is the raised earth ridge piled on the downhill side that holds the captured water in place and supports plantings. They are two parts of the same earthwork, always built together. The swale stores water and the berm grows the trees that use it.
Can I build a swale on flat ground?
Generally no. Swales work by intercepting water moving across a slope. On truly flat ground there is no overland flow to intercept, so a swale just collects what falls into it directly. On slightly graded land (1 to 2 percent), shallow swales can still gather some runoff. For flat sites, rain gardens, basins, and cisterns are more appropriate water-harvesting tools.
How long does a swale last?
A well-built and well-planted swale lasts decades. The first 1 to 2 years are the highest-maintenance period, with annual inspection of the berm and clearing of any sediment buildup. After year three the berm is typically heavily rooted by perennials, the system is stable, and maintenance drops to occasional annual observation. The Greening the Desert swales installed by Geoff Lawton in 2001 are still functioning in 2026.
What plants grow on a swale berm?
For temperate North American zones 5 to 8: fruit trees (apple, pear, plum, mulberry), nitrogen-fixing shrubs (goumi, sea buckthorn), berry bushes (currant, gooseberry, hazelnut), and deep-rooted herbaceous perennials (comfrey 'Bocking 14', yarrow, dandelion). Cover the entire berm with white clover or another living mulch in the first season. Avoid planting fruit trees in the swale bottom; they will drown during prolonged wet periods.
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