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).
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.
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
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.
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.
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.
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.