A swale is a shady spot, or a sunken or marshy place. In US usage in particular, it is a shallow channel with gently sloping sides. Such a swale may be either natural or human-made. Artificial swales are often
infiltration basin
An infiltration basin (or recharge basin) is a form of engineered sump or percolation pond that is used to manage stormwater runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. I ...
s, designed to manage water
runoff, filter
pollutants
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
, and increase rainwater
infiltration.
Bioswales
Bioswales are channels designed to concentrate and convey stormwater runoff while removing debris and pollution. Bioswales can also be beneficial in groundwater recharge, recharging groundwater.
Bioswales are typically vegetated, mulched, or xer ...
are swales that involve the inclusion of plants or vegetation in their construction, specifically.
On land
The use of swales has been popularized as a
rainwater-harvesting and
soil-conservation strategy by
Bill Mollison
Bruce Charles "Bill" Mollison (4 May 1928 – 24 September 2016) was an Australian researcher, author, scientist, teacher and biologist. In 1981, he was awarded the Right Livelihood Award "for developing and promoting the theory and practice ...
,
David Holmgren
David Holmgren (born 1955) is an Australian environmental designer, ecological educator and writer. He is best known as one of the co-originators of the permaculture concept with Bill Mollison.
Early life
Holmgren was born in Fremantle, Western ...
, and other advocates of
permaculture
Permaculture is an approach to land management and settlement design that adopts arrangements observed in flourishing natural ecosystems. It includes a set of design principles derived using Systems theory, whole-systems thinking. It applies t ...
. In this context a swale is usually a water-harvesting ditch on contour, also called a ''contour
bund''.
Swales as used in permaculture are designed by permaculturalists to slow and capture runoff by spreading it horizontally across the landscape (along an
elevation
The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotenti ...
contour line
A contour line (also isoline, isopleth, isoquant or isarithm) of a Function of several real variables, function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a ...
), facilitating runoff infiltration into the soil. This archetypal form of swale is a dug-out, sloped, often grassed or "ditch" or "lull" in the landform. One option involves piling the soil onto a new bank on the still lower slope, in which case a bund or
berm
A berm is a level space, shelf, or raised barrier (usually made of Soil compaction, compacted soil) separating areas in a vertical way, especially partway up a long slope. It can serve as a terrace road, track, path, a fortification line, a b ...
is formed, mitigating the natural (and often
hardscape-increased) risks to slopes below and to any linked watercourse from
flash flooding.
In arid and seasonally dry places, vegetation (existing or planted) in the swale benefits heavily from the concentration of runoff. Trees and shrubs along the swale can provide shade and mulch which decrease evaporation.
On beaches
The term "swale" or "beach swale" is also used to describe long, narrow, usually shallow troughs between ridges or
sandbar
In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or ...
s on a beach, that run parallel to the shoreline.
See also
*
Contour trenching
Contour trenching (a.k.a., Continuous Contour Trench or CCT) is an agricultural technique that can be easily applied in arid sub-Sahara areas to allow for water, and soil conservation, and to increase agricultural production.
Between two trench ...
*
Gutter
*
Keyline design
Keyline design is a landscaping technique of maximizing the beneficial use of the water resources of a tract of land. The "keyline" is a specific topographic feature related to the natural flow of water on the tract. Keyline design is a system o ...
*
Rain garden
Rain gardens, also called bioretention facilities, are one of a variety of practices designed to increase rain runoff reabsorption by the soil. They can also be used to treat polluted stormwater runoff. Rain gardens are designed landscape sites t ...
*
Stormwater
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed lan ...
*
Water-sensitive urban design
References
External links
Fact Sheet: Dry and Wet Vegetated Swalesfrom
Federal Highway Administration
The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...
Wetlands of the Great Lakes: The Beach Swale & Dune and Swale Typesfrom
Michigan State University
Michigan State University (Michigan State or MSU) is a public university, public Land-grant university, land-grant research university in East Lansing, Michigan, United States. It was founded in 1855 as the Agricultural College of the State o ...
Video showing swales used to rehabilitate desert terrain
{{Wetlands
Environmental engineering
Landforms
Landscape
Sustainable gardening
Sustainable design
Water
Water pollution
es:Zanja