How to Design a Drainage Swale

The purpose of a drainage swale is to remove water buildup from a low-lying area by providing drainage away from the vicinity. Essentially, a drainage swale is an engineered and landscaped shallow ditch that is covered with vegetation, in most cases grass, and is then known as a grassed swale.

Swales are often found along roadways to keep them free of water buildup,
  1. Determine the destination you want the water to flow. This will affect what happens to the water and may have an impact on others. It is important to check the local codes for your area.

  2. Plan the route the swale will take. A straight linear swale to the destination will remove the water most effectively. Mark the path with stakes to both sides.

  3. Determine the grade or slope of the swale. It is recommended that the swale drop about ¼" per foot to achieve a good flow of water. Too big of a drop per foot will allow the water to flow too swiftly and can cause soil erosion.

  4. Remove the sod between the stakes in strips 1 to 1 ½ feet wide and 2 to 3 feet long to be used later in covering the swale. Keep the strips moist to be ready to use.

  5. Dig a V-shaped trench, keeping in mind the desired slope. The swale is meant to be a shallow ditch to aid in the removal of water from a site, so for most residential applications a 6" deep channel is suitable. Smooth the sides of the swale with the shovel as you dig.

  6. Replace the sod or fill with other vegetable content to prevent soil erosion.