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Learn about vegetated swales


What is a vegetated swales:
Vegetated swales (a.k.a. grassed channel, dry swale, wet swale or biofilter) are constructed open-channel drainageways used to convey stormwater runoff. Vegetated swales are often used as an alternative to, or an enhancement of, traditional storm sewer pipes. They do not pond water for a long period of time and induce infiltration. Vegetated swales generally have a trapezoidal or parabolic shape with relatively flat side slopes. Individual vegetated swales generally treat small drainage areas (five acres or less).

Why consider:
Vegetated swales can be used as an environmentally sensitive alternative to conventional storm sewers in common areas of residential subdivisions and along property boundaries. They can also be used within landscaping islands within parking lots.

Limitations:
There are very few limitations on the use of vegetated swales. They should not be used in steep slope areas and may be difficult to place in very urban settings due to space requirements. Otherwise, they can be adapted for use in most residential commercial and industrial land development projects.

Benefits:
Vegetation in swales allows for filtering of pollutants, and infiltration of runoff into groundwater. Densely vegetated swales can be designed to add visual interest to a site or to screen unsightly views. Broad swales on flat slopes with dense vegetation are the most effective at reducing the volume of runoff and pollutant removal.

Cost:
The cost of a vegetated swale depends on numerous factors including width, depth, length, slope, and plant material, to name a few. Substantial labor and material cost savings can be gained in areas where swales are used instead of traditional piping systems.

Maintenance:
The maintenance requirements of vegetated swales includes periodic inspection for erosion and formation of gullies, removal of sediment buildup and debris from the bottom of channel, and mowing. Grass-lined swales should be mowed regularly to maintain a height of approximately 4-6 inches. Naturalized swales reduce the mowing requirements to only once per season.

Materials:
Native plants and wetland vegetation are preferred to turf grasses as swale liners. Swales planted with native vegetation offer higher resistance to flow and provide a better environment for filtering and trapping pollutants from stormwater. However, turf grass, allowed to remain slightly high, can provide some benefits as well.