What is an Infiltration Swale?
Swales are shallow, landscaped open channels running along the contour of the land; built to infiltrate, convey and slow down rain water flow. They are constructed to reduce runoff volume and improve water quality. Swales are widely used in combination with other water quality and quantity (volume) practices in a storm water system or treatment train.
On this project the swales are designed to receive the overflow from the pervious pavement and provide water quality treatment prior to the water overflowing into a drainage way to the north.
How does it work?
When rain falls, the water runs along the surface of the landscape swale, collecting in the depression of a swale (which intakes them like a linear rain garden), slowing down the water and allowing it to seep into the soil. The soil will hold the water in underground pockets that supply the roots of plants and/or trees and replenishes ground water which is the source of many of our streams.
The swale acts as a conveyance of rain water in a treatment train from or to other water quality or quantity practices, and as a natural water quality treatment for the pollutants that the rain water might carry into the swale from roads, parking lots, roof tops, etc., such as oil, gas, heavy metals and excess nutrients. Enhancing the soil in the swale with filtering materials (sand and organic matter) provides additional water quality treatment. Planting deeper-rooted native vegetation in the swale, rather than regular turf grass, will enhance the infiltration capability of it and the native vegetation will require less watering during dry period.
A swale can be more aesthetically pleasing than a rock-lined drainage system and is generally less expensive to construct.
How is a Swale Created?
Swales can be very large or very small. The key to making swales is keeping the swale level or having a check dam to hold back the water so it can infiltrate into the ground.
Larger swales should be designed by an engineer so that proper stabilization to keep the water from eroding the swale is assured. This keeps the swale from becoming a source of- pollution. Swales can be stabilized with sod, river stone, or environmental blankets.