What are Grassy Swale Drainage Systems?

Grassy Swale Drainage Systems

We often get asked “What are grassy swale drainage systems?” A swale is an area of your lawn which is carefully graded to direct water. A swale may not be visibly noticeable. This is because it can be as little as a 1 inch drop of every ten feet to provide enough flow for it to be effective. It helps dissipate water over a larger area, or directs the water to a bog planting or a drain.

What are Grassy Swale Drainage Systems?

A grassy swale drainage system is a graded an engineered landscape feature appealing as a linear, shallow, open channel with trapezoidal or parabolic shape. Flood tolerant, erosion resistant plants vegetate the swale.

In addition, the design of grassy swale promotes the conveyances of storm water at a slower, controlled rate and acts as a filter medium removing pollutants. It also allows stormwater infiltration.

Agscapes Landscaping can effectively design your grassy swale drainage system to accommodate a predetermined storm event volume. This results in a significant improvement over the traditional drainage ditch in both slowing and cleaning of water.

Applications of Grassy Swale Drainage Systems

Grassy swales are ideal for stormwater management practice in most regions of North America. These drainage systems are a low cost maintenance option to remove sediments, nutrients and pollutants. Grassy swales also increase stormwater infiltration and add a visually aesthetic component to your property.

Additionally, installing a grassy swale is a potential solution wherever stormwater requires transportation from impervious surfaces and slowing down to allow it to infiltrate into soils. Grassy swales are typically an environmental preferential solution. The linear structure of swales assists in the treatment of runoff from the following:

  • highways
  • residential roadways
  • residential sub-divisions
  • property boundaries
  • parking lots

Typically, grassy swales treat relatively small drainage areas of five acres or less. We don’t recommend grassy swales in highly urbanized ares or other highly impervious areas, unless constructed in a series or function as pre-treatment for other stormwater management practices.

Benefits of Grassy Swale Drainage Systems

The following are a few advantages of both dry swale and wet swale drainage systems.

Dry Swales

Dry swales offer the following benefits:

  • Traps and removes sediments and other pollutants, which improves the water quality
  • Reduces peak runoff velocity and promotes infiltration
  • With proper design, provides for some groundwater recharge
  • Because of their linear structure, they are ideal for use in treating highway and residential road runoff
  • Ideal for use in low to moderate density developments
  • Helpful as a means of disrupting impervious pavement in parking lots
  • Has ponding of water for only a short time with little increase in water temperature, which makes it useful in watersheds containing cold-water trout streams
  • In comparison to a traditional curb or gutter system, they are less expensive to build and maintain

Wet Swales

Wet swales offer the following benefits:

  • Functions as a linear wetlands
  • Reduces peak flows and runoff velocity and promotes infiltration
  • Reduces erosion
  • Has easy design process to build in relatively impervious soils or in seasonally saturated soils or intersection water table
  • Traps and removes sediments and other pollutants with increased efficiency, which improves water quality
  • Creates visually appealing and beneficial habitat between uplands and surface waters
  • In comparison to a traditional curb and gutter system, they are less expensive to build and maintain
  • Provides effective pre-treatment of stormwater passing through for further processing by additional stormwater management practices


These are just the basics of grassy swales. Contact Agscapes Landscaping with the link below for more information or to get started on you about grassy swale drainage system project today!

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