What is a swale?
A swale is a gentle dip in the ground that steers rain on purpose. You may already have one without knowing it.
A swale is a broad, shallow channel, usually grassed, that guides surface runoff along a chosen path. It is not a ditch and it is not a buried pipe. It is a shaped dip in the lawn.
This page prints no prices. It defines the term so you can read a yard, or a plan, correctly.
How it differs from a ditch
A ditch is steep-sided and narrow, and water rushes through it. A swale has soft, wide sides you can mow across. The water spreads out, slows down and soaks in as it goes.
That gentle shape is the whole point. A steep channel scours the soil. A flat one holds water where you do not want it.
Signs your yard already has one
- A long, shallow dip that runs across the lawn.
- Grass that stays greener along one line after rain.
- Water that always follows the same path past the house.
- A faint low line between two properties.
Many lots were graded with a swale on the property line to carry rain toward the street. If you fill or plant over it, the water finds another route, and that route may lead to your wall.
What a swale does and does not do
It moves surface water. It does nothing for water that travels through the soil, and it does not help a basement that is wet because of groundwater. For that case, the curtain drain page compares the options.
It also needs somewhere to send the water. A swale that ends against a fence or a neighbor's patio only moves the problem. Rules about directing runoff onto other lots are local, so ask your building department.
A swale is not a cure-all
Take a position: if gutters spill at the wall and the lawn slopes toward the house, fix those first. A swale cannot make up for a downspout that dumps water at the foundation. The grading and downspouts page covers that order of work.
Going further
Once you know what a swale is, the swale drainage page explains where one fits and where it fails. The yard drainage page helps you choose between a swale and other fixes.
Where to stop and call someone
Do not dig a new channel close to the foundation. Removing soil there can take away support, and that is a question for a licensed structural engineer. An independent one has no repair to sell you.
Frequently asked questions
What is a swale in simple terms?
It is a wide, shallow, usually grassed dip in the ground that carries rain runoff along a path you choose.
Is a swale the same as a ditch?
No. A ditch is narrow and steep and water rushes through it. A swale is broad and gentle, so water slows down and soaks in.
Does a swale help a wet basement?
Only if surface runoff is the cause. It does nothing for groundwater or water moving through the soil.
Can I fill in a swale on my property?
Think twice. Many swales carry water away from houses, and filling one sends the runoff somewhere else. Check local rules first.
Does a swale need an outlet?
Yes. If it ends at a fence or a neighbor's patio it only moves the problem. Runoff rules are set locally.
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