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CAUTION
Exercise 17
Bioswale Construction
OBJECTIVE
The objective of this exercise is to properly construct a
bioswale.
Locate all utilities before beginning
construction.
TEXTBOOK REFERENCE
INTRODUCTION
One application of the concept of stormwater deten-
tion is the bioswale, a gradually sloped drainage chan-
nel with shallow sides that are lined with plant material
and, in certain situations, rip-rap. The bioswale is used
Bioswales
To construct a bioswale, use the following steps:
• Grade a channel with side slopes not exceeding
3:1 (3 feet horizontal to 1 foot vertical) and a
center line slope that is as gradual as the site will
allow (1% is desirable). The cross-sectional shape
of the bioswale can be either parabolic (curved)
Figure 17–1 Bioswale planted with native grasses.
© Delmar/Cengage Learning.
97171_17_ch17_p066-067.indd 66 14/06/10 8:51 PM
Exercise 17 Bioswale Construction 67
or trapezoidal (angled) (Figure 17–1). Ensure an
outlet exists at the end of the bioswale, sized to
allow drainage from the swale during periods of
heavy storms.
• Place an erosion blanket or jute netting over the
area to limit erosion while the plant material cover
is being established. If the swale experiences high
volumes of water, the bottom may be covered with
a 4-inch rip-rap.
The plant material in the bioswale is only periodically
trimmed and is allowed to grow to full height to assist in
trapping sediment and slowing drainage.
PREREQUISITE EXERCISES
• Approximately 25 LF of 8 feet-wide erosion mat or
jute netting
• 10 lbs of seed (plant material will vary by region,
grasses that tolerate inundation with flood water
EXERCISE DESCRIPTION
In the drainage area selected, grade and seed 20 feet
of bioswale using the cross-section shown below
(Figure 17–2).
Plugs (or seed) of flood
tolerant grasses
Erosion blanket
or jute netting
97171_17_ch17_p066-067.indd 67 14/06/10 8:51 PM
