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Swales
& Berms vs Concrete: Low Tech Solutions for Stormwater Runoff
Doug Pushard
Here's a sample of email questions I've been getting lately:
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What can I do with all this rainwater? I have rain barrels, but
they overflow. How can I deal with the overflow?
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I don't have time or money to install rain barrels or gutters,
but I still would like to save rain water, what can I do?
Swales
or berms could be your answer. They are literally as old as the
hills and have been used to control water flow for centuries.
Today they are still used around the world but have been all but
forgotten here in the United States as a way to conserve water.
(This is getting to be a familiar refrain!)
What's
a Swale?
Swales
are simply shallow, low depressions in the ground designed to
encourage the accumulation of rain during storms and hold it for
a few hours or days to let it infiltrate into the soil. Swales
ideally are tree-lined and store water for the immediate landscape
as well as help cleanse the water as it percolates down. Swales
can be installed separately or as part of a larger water rain
catchment system with rain gardens, cisterns and other water conservation
measures.

Swales
are one of the cheapest and easiest water storage methods and
can be installed almost anywhere. If properly built they greatly
reduce storm runoff; thereby reducing the impact of storms on
local storm runoff systems. But more importantly they catch and
preserve fresh rain where it can be used by your shrubs and trees.
Swales are an easy solution that can be effective in homes, commercial
buildings and along street mediums in place of curbs.
What's
a Berm?
Berms
are raised beds that can be used to direct water to swales. They
are the equivalent of the slope in road used to push water off
the middle of the road toward the curbs.

Ideally,
berms and swales should be designed into the landscape where there
is any noticeable slope to slow and capture runoff. They can be
part of the site plan for an individual home or integrated into
the design of an entire multi-unit complex or subdivision development.
Research
Reveals Ancient Truths: Real Benefits
Recent
research in Spokane, Washington, as well as Florida has documented
the storm water quality benefits from swales and low-lying areas
by reducing the flow and allowing slower infiltration into the
groundwater system.
This
is a finding which past generations were aware of. In our hurry
to pave the world wit concrete, we threw our knowledge of swales
and berms out with the stormwater (how's that for a mixed metaphor?).
It
is best when designing the home landscape to preserve low-lying
areas such as wetlands and swales. These low-lying areas retain
storm water, provide water quality filtration and may allow for
some infiltration to replenish groundwater supplies.
Swales
can either be grassed, gravel or rocked. All designed to slow
and retain the flow of runoff. They can also be used instead of
costly curbs and gutters found in most neighborhoods and communities
today.
As an example, at Prairie
Crossing, a 678-acre residential development 40 miles
northwest of Chicago in Grayslake, Ill. adopted conservation designs
to reduce runoff rates and volumes and to reduce pollutant loads.
Storm water is routed into swales, rather than storm sewers. The
swales provide initial storm water treatment, primarily infiltration
and control sedimentation. The prairies diffuse the water and
soils retain contaminants, slowing storm water velocity.
The development expects about 60 percent of the land to be devoted
to open spaces. Residents also employ rain gardens and expect
to retain 65 percent of its storm water onsite and reduce nutrient
loads and reduce heavy metal pollutants by 85 to 100 percent.
Maintenance
costs for storm water controls are expected to drop, downstream
conditions have improved and there's less flooding. A sign of
success has been thriving populations of native fish in the 22-acre
lake.
Considerations
Key
elements to consider when building a swale include:
· Swales are not intended to move water but to hold water
for soil absorption.
· The width of the swale should be covered by the crown
of the mature surrounding trees.
· Soil in the swale should not be compacted or sealed but
should be loose to encourage absorption.
Surprisingly one tree can reduce stormwater runoff by 4,000 gallons
a year thus greatly reducing the need to build costly water treatment
plants. So swales lined with native trees are an extremely-cost
effective, and often overlooked low-tech, water conservation technique.
Swales
with the proper plants and trees help manage runoff and make water
healthy for people, nature and fish.
Swales
are a low-cost win-win solution. Isn't it time we tried them?
More
Info
A
Swale Guide: Permaculture: A Practical Guide for a Sustainable
Future by Bill Mollison
Truly
a wonderful book!
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