Swale drainage
A swale is a wide, gentle dip in the yard that moves rain runoff somewhere safer. It works on the surface, not underground.
A swale is a shallow, wide channel, usually grass-covered, that carries surface runoff away from the house. Unlike a French drain, nothing is buried. Water simply follows the dip across the ground.
This page prints no prices. It explains the idea so you can judge whether a swale suits your yard.
How a swale works
Rain that runs across the yard follows the lowest line. A swale gives it a lowest line that you chose. The channel is broad and gently sloped, so water moves slowly and soaks in along the way. Grass holds the soil and stops the channel from washing out.
The slope has to be steady and gentle. Too flat, and the water sits. Too steep, and it scours the soil.
Where a swale makes sense
- A yard where runoff crosses the lawn toward the house.
- Ground that slopes toward one side with room for a channel.
- A place where water needs a path around the building.
- A property with a safe outlet, such as a lower part of the lot.
If water sits in the yard because the soil is slow to drain, the standing water in the yard page covers that case. A swale only helps when the water has somewhere to go.
Swale or French drain?
A swale handles surface water. A French drain handles water that moves through the soil. They solve different problems, and picking the wrong one wastes effort. Read yard drainage for the overview and curtain drain for the buried option.
The mistakes that make it fail
The first is no outlet. A channel that ends at a dead end is a long puddle. The second is sending the water onto a neighbor. Many places treat that as your problem, not theirs. The third is a channel that runs too close to the foundation, which puts the water exactly where you did not want it.
A swale also needs upkeep. Leaves, mowing clippings and sediment can fill it over time.
Fix the roof water first
A swale does nothing about gutters that dump at the wall. Start with the roof and the slope near the house. The grading and downspouts page covers both. Take a position: for most houses, a swale is a second step, not a first one.
Where to stop and call someone
Do not dig near a foundation wall that is cracked, bowed or leaning. A licensed structural engineer can assess it, and an independent one has no repair to sell you. Rules on grading, runoff and where you may send water are set locally. Ask your building department before you change the lay of the land.
Frequently asked questions
What is a swale?
A shallow, broad, grass-covered channel in the yard that carries surface runoff away from a house.
How is a swale different from a French drain?
A swale moves water across the surface. A French drain is buried and catches water moving through the soil.
Does a swale need an outlet?
Yes. Without a safe place to send the water, the channel just fills up and stays wet.
Can I send swale water onto a neighbor's lot?
Often not. Rules on runoff are local, so check with your building department before you change the grade.
Will a swale fix a wet basement?
Only if surface runoff is the cause. Check gutters, downspouts and slope first.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. What You Can Do to Soak Up the Rain
- US EPA. Soak Up the Rain. Managing stormwater around a property