Georgia Magazine - March 2018 - 44
(Continued from page 42)
anders across the landscape in a
pleasing, curved shape.
The bottom of the depression
must be essentially flat so that the
stormwater runoff is not directed one
way or another; instead, the swale
should fill up like a bathtub when it
rains. In the process, any soil particles or bits of organic matter washed
off of the landscape uphill are deposited at the bottom of the swale, which
over the years fills up with fluffy, fertile loam.
When digging a swale, pile the
excavated soil on the downhill side
of the depression to form a low
mound. This serves as a convenient
raised bed, from which plants can access the moisture that collects at the
bottom of the swale without being
drowned by it. The bottom of the
swale can be planted with species
that tolerate wet soil or simply lined
with a thick layer of mulch.
The swale and adjacent planting
bed should be broad, with gently tapered edges, not sharp cuts into the
soil. A typical swale is 6 to 8 inches
deep and 24 to 30 inches wide. The
mound should be as high as the
swale is deep, and equal in width.
Note that swales are suitable only
for moderate slopes. Steeper slopes
require terraces, flat areas where the
earth is supported by a retaining wall.
These also force stormwater to slow
down, spread out and sink into the
It is often more feasible to collect
rainwater on relatively flat ground,
rather than building swales or terraces
on a slope. Rain gardens operate on
the same principle as swales but are
not restricted to a long, skinny shape.
They can be round, oval, kidneyshaped-any shape, really, as long as
the bottom is flat and the sides are
sculpted in such a way that the depression fills up and prevents water
from flowing away when it rains.
Rain gardens typically feature
wetland plants that thrive in a saturated depression, while a swale holds
the water slightly away from the planting area in order to accommodate
species that need better drainage.
A rain garden can be a beautiful
landscape feature. But if you don't
like the idea of a visible depression in
your yard, fill it with fine gravel and
cover the top with a decorative mulch.
You can plant tough wetland species-like those listed in the sidebar
below-directly into the gravel. Just
be advised that you will have to irrigate them during dry periods for the
first two years so the roots can grow
into the soil below.
Rain gardens are typically between 8 and 12 inches deep, with a
surface area that reflects the amount
of water flowing in; one-tenth the size
of the area draining into it is a good
rule of thumb.
You also can use corrugated piping to route water from your downspouts directly into a rain garden.
Don't worry if you can't build it big
enough to catch all the water in a
heavy downpour; the excess will
seep slowly over the edges.
This is the simplest earthwork for
catching runoff and the only one that
is almost invisible. Dry wells have
one major drawback: They are ineffective at providing moisture to small
plants. They do collect water at a
depth where it is available to deeprooted trees, however, and help to
restore groundwater, which keeps
streams and rivers flowing whenever
it is not raining.
A dry well is nothing more than a
big hole in the ground-typically
much deeper than wide-that is filled
with coarse gravel. Rather than rely
on surface runoff to fill a dry well,
water usually is brought there via
pipes from downspouts or surface
drains. Dig the well as deep as you
can manage, and cover the surface
with mulch to make it blend in with
Brian Barth is a freelance writer
living in Ontario, Canada.
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10 plants for rain gardens and swales
Cardinal flower, Lobelia cardinalis
Common buttonbush, Cephalanthus
Jewel weed, Impatiens capensis
Marsh marigold, Caltha palustris
River oats, Chasmanthium latifolium
Sedges, Carex spp.
Swamp hibiscus, Hibiscus coccineus
Swamp sunflower, Helianthus
Sweet flag, Acorus gramineus
Wild white indigo, Baptisia alba
For more information on installing swales and rain gardens, download a free rain-garden
app from the University of Georgia's EcoScapes Sustainable Land Use program at
More online at www.georgiamagazine.org