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, 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,
David Holmgren, 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
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Contour trenching
*
Gutter
*
Keyline design
*
Rain garden
*
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