Quick answer
A swale is a shallow, wide channel that carries runoff across a yard to an outlet, and a berm is a low ridge of soil that slows, blocks or redirects water; the two are often built together across a slope.
PNNL defines a swale as a trapezoidal channel dug to receive storm water and give it a path away from the home. UC ANR says a berm can keep water from draining back toward a foundation or puddling in the wrong place.
Quick facts
The key facts about Swale vs. Berm, with sources:
- Swale
- A trapezoidal channel dug to receive storm water and give it a path away from the home 1
- Berm
- A compacted ridge of earth or gravel that slows the flow of water 1
- Swale grade
- PNNL gives a consistent 2 to 4 percent along the channel; under 2 can pool, over 4 can speed the water too much 1
- Swale sides
- No steeper than 3:1 (three wide for each one high), per PNNL 1
- Berm height
- UC ANR says no more than 18 to 24 inches, since taller berms can erode 2
- Berm shape
- UC ANR suggests making it about four to six times longer than it is wide 2
- Near a foundation
- The model residential code asks swales within 10 feet of the foundation to slope at least 2 percent 4
Key takeaways
- A swale carries water along a path. A berm holds it back or turns it. One is a channel and the other is a ridge.
- Built together across a slope, they slow the downhill flow of water and let more of it soak in 1.
- A swale needs a steady slope. PNNL gives 2 to 4 percent; flatter pools water and steeper speeds it up 1.
- A berm changes where water goes. UC ANR tells builders to think about how it will move water across the site before placing one 2.
- Neither one may send water onto a neighbor. Call 811 before digging and ask your town about rules.
A channel and a ridge: two shapes with opposite jobs
Think of a swale as a gentle ditch with sloped sides, often grassed. PNNL, a laboratory funded by the U.S. Department of Energy, defines it as a trapezoidal channel dug to receive storm water and give it a path to flow away from the home.
Swales slow runoff, filter it and let some soak in. They can also collect water that would pool in a flat yard, or turn water heading toward the house from a sloped yard 1.
A berm is the reverse shape. PNNL describes berms as compacted earth or gravel ridges that slow the flow of water 1.
In a garden, UC ANR says a berm can redirect water, improve drainage, improve poor soil and create planted islands.
It can keep water from draining back toward a house foundation or from puddling in the wrong place 2.
The two are rarely rivals. PNNL says a swale and berm can go together across a slope to slow the downhill flow 1. The berm slows the water. The swale gives it somewhere to go. That is why this page treats them as a pair.
This page owns the swale-and-berm comparison. For the underground tool, see French drain. For the two big families of drainage, see surface vs. subsurface drainage.
How a swale and berm handle a rainstorm
Picture a lawn that slopes toward a house.
- Rain runs downhill in a sheet. On a slope, water moves faster the further it travels.
- The berm interrupts it. A low ridge across the path slows the water and can turn it sideways 12.
- The swale collects it. The water gathers in the channel on the uphill side and moves along the grade.
- Some water soaks in. Grass and soil in the channel slow and filter the flow, and part of it infiltrates 1.
- The rest leaves by the outlet. A safe outlet carries it away from the house, such as a lawn area, rain garden or storm drain where allowed.
- Rain runs downhillFaster on steeper ground
- Berm slows or turns itA low ridge across the path
- Swale gathers itGrade of 2 to 4 percent 1
- Some soaks inGrass and soil filter and absorb
- Outlet releases the restAway from the house and neighbors
Sequence follows PNNL’s description of a swale and berm built together across a slope. Source: [1]
Kinds of swales and berms
| Type | What it is | Typical use | What the sources say |
|---|---|---|---|
| Grassed swale | A shallow trapezoidal channel planted with grass | Carrying lawn runoff to an outlet | PNNL suggests fine, close-growing, water-resistant grass suited to the region 1 |
| Stone-lined swale or dry creek bed | A swale lined with stone | Shady spots where grass will not grow | Michigan State University Extension suggests it for shade 3 |
| Swale with a drain below | A swale with a French drain at its base | Large water volumes that need faster drainage | PNNL says the drain can send water to a drywell or retention area 1 |
| Landscape berm | A low planted mound of fill and topsoil | Redirecting water, improving drainage for plants, screening | UC ANR uses fill for the base and topsoil on top 2 |
| Compacted earth or gravel berm | A ridge built to slow flow | Slowing runoff across a slope | PNNL describes these as ridges that slow the flow of water 1 |
Example: sizing the shape, not the storm
The lot below is invented to show how the published numbers translate to a build. The percentages and heights are from the sources 12; the lot is not real, and a real swale needs a site check.
| Check (example lot) | Published rule | What it means on the ground | Result |
|---|---|---|---|
| Swale along a 50 ft run | 2 to 4 percent grade 1 | 1 to 2 ft of total fall over 50 ft (our arithmetic: 2 percent of 50 ft is 1 ft; 4 percent is 2 ft) | A 6 in. drop would be 1 percent and risks pooling |
| Swale side slope | No steeper than 3:1 1 | For a 1 ft deep channel, each side runs at least 3 ft wide | Mowable edges and less erosion |
| Berm of 10 ft width | Four to six times longer than wide 2 | A length of 40 to 60 ft (our arithmetic) | A gentle, natural shape |
| Berm height | No more than 18 to 24 in. 2 | Keep the crest within 2 ft above grade | Taller berms can erode |
The arithmetic is ours and labelled. It shows why “a little dip” is not a swale: without a grade, there is no flow. For tests of your own ground, see the drainage diagnostic.
Where swales and berms show up
In a grading plan. A designer may draw a swale beside a lot line or around a house corner. The model residential code asks for swales within 10 feet of a foundation to slope at least 2 percent 4. Our landscape grading page covers the rule.
In planting beds. A berm often appears in a landscape design as a raised bed for screening or visual interest. UC ANR points out that berms can also improve drainage for plants that need faster-draining soil 2. See landscape design.
On a drainage bid. A swale may be a line item for shaping, soil and turf or stone. Ask how the grade will be checked. The drainage and grading page lists what a complete scope covers.
In a stormwater plan. PNNL lists swales among stormwater control practices for homes 1. Ask your local stormwater office what it accepts.
Strengths and weak points of each shape
What they do well
Where they struggle
- PNNL lists compacted soils, large storms, frozen ground, short grass, steep slopes and fast flow as reducing a swale’s effectiveness 1.
- A swale on a flat lot with too little fall will hold water, as the 2 percent floor warns 1.
- A berm over about 18 to 24 inches tall can erode 2.
- A berm can move water to a new place. UC ANR’s page does not discuss effects on neighbors, so check that yourself 2.
What these sources do not settle
The slope and side-slope numbers are from a DOE laboratory guide written for home builders.
The same guide prints a soil infiltration rate in two units that do not match each other, so we leave that figure out.
PNNL also gives engineering limits, such as a flow cap of 5 cubic feet per second, that are not yard-scale rules 1.
UC ANR is a California extension blog about ornamental berms. It speaks to height and shape, not to storm design. We found no extension guide that gives a berm size for a specific rainfall.
Neither source says how much water a yard swale can carry. PNNL says a swale should be big enough for a six-month, 24-hour storm and suggests contacting the U.S. Geological Survey for local rainfall volumes 1. That calls for a designer.
A swale does not work on every soil. PNNL advises avoiding gravelly or coarse sandy soils that cannot support dense vegetation 1. Always check local rules, because some towns regulate how a lot’s drainage may change.
What drives the price, and how long it lasts
We publish no prices. A swale bid moves with the length, the soil to excavate or fill, the surface (grass or stone), the number of obstacles and the outlet.
PNNL notes that regrading an existing site is difficult and expensive 1, which is one reason swales are often a small shaping job rather than a full regrade.
A berm bid moves with fill volume, topsoil, hauling, edging or a short wall for steep sides, and planting.
UC ANR says a low berm with a gradual slope usually needs no edging, while a taller or steeper one may need a wall 2.
Use the landscaping cost estimator and the cost guide to see what sets a bid.
No source gives a lifespan. Compaction, erosion and debris decide how long either shape works, and both need touch-ups after settling 1.
Who builds them, and how a job runs
A drainage or landscape contractor usually builds both. A designer or engineer should size anything near a foundation or on a steep lot.
- Walk the site during rain and map where the water goes.
- Choose the outlet first. Where will the water end up, and does that place belong to you?
- Call 811 so buried lines are marked before any digging.
- Check local rules and any permit for changing drainage or moving a lot of soil.
- Shape the swale to a steady grade of 2 to 4 percent with side slopes no steeper than 3:1 1.
- Build the berm with fill at the base and topsoil on top, and tamp it as you go 2.
- Plant grass or groundcover and protect the outlet from erosion. PNNL suggests splash blocks or stones 1.
- Return after the first rainy season to fill and regrade settled spots 1.
Keep water off the neighbor, and call 811 first
A berm or swale that sends water toward a neighbor can cause damage and disputes. Michigan State University Extension warns that redirecting runoff without soaking it in can hurt neighboring properties 3. Call 811 before digging. Large grading or a berm near a foundation or lot line may need a permit or an engineer.
Keeping them working
Upkeep tasks are listed here without fixed dates.
- Fill and regrade after settling. PNNL suggests a site visit after the first rainy season 1.
- Keep the swale clear. Organic debris can fill a swale 1.
- Mow grass at a suitable height. PNNL lists short grass among factors that reduce effectiveness 1.
- Do not compact the channel. Avoid driving on it, since compacted soil lowers performance 1.
- Check berms for slumping. UC ANR says tamping helps prevent erosion and slumping 2.
- Protect the outlet. Use stone or a splash block where water leaves 1.
Warning signs, and when to call a pro
- Standing water in the swale after rain. The grade may be under 2 percent, or the outlet may be blocked 1.
- Bare, cut-out soil in the channel. Flow may be too fast; PNNL warns grades over 4 percent can cause excessive velocity 1.
- A berm that is slumping or washing out. It may be too tall or too steep, or not tamped 2.
- Water collecting at the foundation. A berm or grade may be sending water toward the house.
- A neighbor reports new water. Stop and review the outlet.
Ask a drainage contractor or civil engineer to look at any berm or swale near a foundation, on a steep lot or near a property line. See choosing a landscaping company for what to ask.
Codes and local rules that touch swales and berms
Model residential code. Section R401.3 of the International Residential Code, as reproduced by Maricopa County, says lots shall be graded to drain surface water away from foundation walls.
The grade falls at least 6 inches within the first 10 feet.
Where barriers prevent that, the ground slopes at least 5 percent and water goes to drains or swales, and swales within 10 feet of the foundation slope at least 2 percent 4.
The county page names no edition, and your town’s adopted code decides.
Stormwater ordinances. PNNL tells readers to follow local stormwater ordinances 1. Some towns require permits for changes to drainage or grading.
Property lines. Rules on water that crosses a lot line vary by place. We did not find one national rule, so ask your town.
Utility easements. A swale or berm may not be allowed across a utility or drainage easement. Check your plat or title.
Swale and berm vs. related terms
| Term | What it is | How it differs | Read more |
|---|---|---|---|
| Swale | A shallow channel | Carries water along a grade 1 | This page |
| Berm | A low ridge | Slows or turns water 12 | This page |
| French drain | Perforated pipe in gravel | Works underground, below the surface | Channel drain vs. French drain |
| Rain garden | A planted depression | Holds roof or yard runoff to soak in 5 | Stormwater runoff management |
| Landscape grading | The overall slope of the yard | Sets where water goes before any swale | Landscape grading |
Common myths about swales and berms
- Myth A swale is just a ditch you dig anywhere.
- Reality PNNL gives a consistent 2 to 4 percent grade; under 2 percent can pool and over 4 percent can run too fast 1.
- Myth A bigger berm is a better berm.
- Reality UC ANR says a berm should not be taller than 18 to 24 inches, since higher berms can erode 2.
- Myth A berm solves a drainage problem on its own.
- Reality A berm moves water. It must go somewhere. PNNL pairs a berm with a swale for that reason 1.
- Myth Any soil works for a swale.
- Reality PNNL advises avoiding gravelly or coarse sandy soils that cannot support dense vegetation 1.
- Myth A swale needs no upkeep.
- Reality PNNL says debris can fill a swale, and settling needs a return visit 1.
The regional variable: rainfall, soil and local rules
Rainfall depth, soil type and frozen ground change what a swale or berm can do.
PNNL says frozen ground is among the factors that reduce a swale’s effectiveness, and it advises sizing a swale for a six-month, 24-hour storm using local rainfall data from the U.S. Geological Survey 1.
The NRCS Web Soil Survey maps your soil 6, and many towns publish their own stormwater rules.
Our research page covers specifics, and the soil pages in this glossary explain how soil passes water.
When to choose each, and your next step
Choose a swale when water needs a path. Choose a berm when it needs to be slowed, held back or turned. Choose both when a sloped yard sends fast runoff toward a house or a low spot.
If the main problem is soaked soil rather than moving water, neither shape is the answer. See yard ponding and standing water.
Your next step is to find the outlet. A swale with nowhere to go is a long puddle. Then confirm local rules and ask a drainage pro to check the grade.
- If Runoff needs a path along or past the house
- Then Swale on a 2 to 4 percent grade 1
- If Fast water crosses a slope and needs to slow
- Then Berm and swale together 1
- If Water drains back toward a foundation
- Then Berm may help, with a safe outlet 2; also check grading
- If Soil stays soaked with no moving water
- Then Neither. See subsurface options
- If There is no safe outlet
- Then Stop. Ask your stormwater office
Look downhill first
Before you shape anything, walk to where the water would end up. If that place is a neighbor’s yard, a foundation or a septic area, redesign the plan.
Questions about Swale vs. Berm
What is the difference between a swale and a berm?
A swale is a shallow channel that carries water along a grade. A berm is a low ridge that slows, blocks or turns water.
PNNL defines a swale as a trapezoidal channel that gives storm water a path away from the home, and describes berms as compacted earth or gravel ridges that slow the flow of water.
Can a swale and a berm be used together?
Yes. PNNL says a swale and berm can be installed together across a slope to slow the downhill flow of water. The berm slows or turns the water, and the swale carries it to an outlet. Both need a safe place for the water to end up.
How steep should a swale be?
PNNL recommends a consistent grade of 2 to 4 percent along the channel. Slopes under 2 percent can lead to pooling, and slopes over 4 percent can cause excessive water speed. Side slopes should be no steeper than 3:1. Check your local rules and ask a pro to confirm the numbers for your lot.
How tall should a landscape berm be?
UC ANR says a berm should not be more than 18 to 24 inches tall, because a higher berm may erode. It also suggests making a berm four to six times longer than it is wide, with fill at the base and topsoil on top. Taller or steeper berms may need a short retaining wall.
Will a berm fix a yard that floods the house?
It can help, but not by itself. UC ANR says a berm can keep water from draining back toward a foundation. Water still needs a place to go, so a swale or other outlet is usually part of the plan. Grading, downspouts and soil also matter, and a pro should look at it.
Do swales work in clay soil?
They can carry water in clay, but they do not soak it in quickly. PNNL notes that swales soak water into the ground on site, and lists compacted soil as a limit. A swale on clay may need a longer path to an outlet. Soil tests and local advice help here.
What is the minimum slope near a foundation?
The model residential code, section R401.3, asks for a fall of at least 6 inches in the first 10 feet away from the foundation.
Where barriers prevent that, it asks for a 5 percent slope with water directed to drains or swales, and swales within 10 feet should slope at least 2 percent. Your town’s code governs.
Do I need a permit for a swale or berm?
It depends on your town and the size of the change. Moving a lot of soil, altering drainage near a property line or building near a foundation can trigger a rule. Ask your local building or stormwater office before you start, and call 811 for utilities.
Can I send swale water onto my neighbor’s property?
No. Redirecting runoff in a way that harms a neighbor can cause damage and legal trouble. Michigan State University Extension warns that sending runoff without soaking it into the soil can hurt neighboring properties. Choose an outlet on your own land, and ask your town what is allowed.
How do I keep a swale working?
Keep debris out of it, avoid compacting it, and fix settled spots. PNNL suggests visiting after the first rainy season to fill soil and finish grading, and notes that organic debris can fill a swale. Use stone or a splash block at the outlet to control erosion.
Sources
- Pacific Northwest National Laboratory, Building America Solution Center, Swales, Drains, and Site Grading for Stormwater Control (updated 2020-09-27), retrieved .
- UC Agriculture and Natural Resources, The Real Dirt, Landscaping with Berms (2023-06-30), retrieved .
- Michigan State University Extension via Ask Extension, answer on a wet yard and drainage options, retrieved .
- Maricopa County, Building Elevation Plan Requirements (reproduces International Residential Code R401.3, no edition named), retrieved .
- U.S. EPA, Soak Up the Rain: Rain Gardens, retrieved .
- USDA NRCS, Web Soil Survey, retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Swale slope, side slope, soil cautions, maintenance and the swale-berm pairing are from the PNNL Building America guide (DOE laboratory).
Berm height, length ratio and construction are from one UC ANR blog article and are California gardening advice.
The code figures are the model residential code R401.3 as reproduced by Maricopa County, with no edition named. The PNNL infiltration figure was left out because it prints two non-matching units.
The arithmetic in the example is ours and labelled. No prices or lifespans are given.
Suggest a correction. We fix errors and say what changed.