Phone answered 24/7 · Sammamish, WA and nearby communities

Call 24/7: (425) 386-5713
Lake Sammamish Water Damage HelpSammamish, WA · Answered 24/7

How Yard Swales and Berms Can Redirect Water From Your Home

Last updated October 25, 2026

Call Now (425) 386-5713

The short answer

What Swales and Berms Do

A swale is a gently sloping channel that collects runoff and moves it away from your house. It is usually planted with grass or native ground cover to slow the water and let some soak in. The slope matters: too flat and water pools, too steep and erosion starts.

A berm is a raised ridge of soil that acts as a barrier. It can block water from reaching your foundation or funnel it toward a swale. Together, they form a simple drainage system that relies on gravity, not pumps or moving parts.

Planning the Layout

Start by watching where water flows during a heavy rain. Look for puddles near the foundation, downspout outlets, and low spots in the yard. The goal is to move water at least 10 feet away from the house, or to a downhill area that drains freely.

Mark the high and low points in your yard. A swale should slope at least 1 percent, which is about 1 inch of drop for every 10 feet. Berms should sit on the uphill side of the area you want to protect, with a gentle slope on both sides to avoid erosion.

  • Use a level and string to check slope.
  • Keep swales at least 5 feet from the foundation.
  • Direct water to a rain garden, dry well, or storm drain.
  • Avoid placing berms where they trap water against the house.
  • Check local rules for drainage changes.

Building a Swale

Dig a trench that is 6 to 12 inches deep and 2 to 3 feet wide. The bottom should be flat or slightly curved, not a sharp V. Slope the sides gently so grass can grow and water can spread out.

Use the soil you remove to build a small berm on the downhill side of the swale. This helps contain the water and slow it down. Compact the soil lightly and seed it with grass to prevent erosion. Test the flow with a garden hose before you finish.

Building a Berm

A berm should be 1 to 2 feet high and 3 to 4 times as wide as it is tall. Shape it with a broad, rounded top so water runs off evenly. Use clean fill soil, then top it with good topsoil and grass seed.

Place the berm where it will block water coming from uphill. It can also be used to create a channel that guides water around your home. Avoid making a berm that is too tall or steep, because it can become a dam and cause flooding on the uphill side.

Maintenance and When to Call Pros

Check swales and berms after heavy rain. Remove leaves, sticks, and sediment that block the flow. Re-grade the swale if it develops low spots or ruts. Reseed bare areas quickly to keep the soil stable.

If water is already entering your basement or crawlspace, a swale alone may not be enough. Local water damage pros can help with interior drying and repairs. For grading work beyond a simple shovel project, a landscaper or excavation contractor can handle the job.

A well-built swale can save you from costly interior water damage, and checking low spots after winter storms helps you catch problems early.

  • Inspect after every major rain.
  • Clear debris from the swale path.
  • Add more soil to berms if they settle.
  • Watch for erosion at the discharge point.
  • Consider a rain barrel to reduce runoff volume.

Water damage does not wait

Every hour counts once water gets into floors and walls. One call starts the response.

Call Now (425) 386-5713

Frequently asked questions

How much slope does a swale need?

A swale needs a slope of at least 1 percent, meaning a 1-inch drop for every 10 feet of length. Too little slope causes standing water, and too much can cause erosion. You can measure with a level and string.

Can I build a swale myself?

Yes, for simple yards with light runoff, you can dig a swale with a shovel or a rented trencher. The work is physical but straightforward. For large yards or complex drainage, a professional landscaper can help design and build it correctly.

What should I plant in a swale?

Choose grasses or native perennials that tolerate both wet and dry conditions. Deep-rooted plants help hold soil and slow water. Avoid trees or shrubs with aggressive roots that could clog the swale or damage nearby pipes.

Call Now (425) 386-5713