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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. It i ...
s, designed to manage water
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock marke ...
, filter
pollutants A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...
, and increase rainwater
infiltration Infiltration may refer to: Science, medicine, and engineering *Infiltration (hydrology), downward movement of water into soil *Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings *Infiltration (me ...
.
Bioswales Bioswales are channels designed to concentrate and convey stormwater runoff while removing debris and pollution. Bioswales can also be beneficial in recharging groundwater. Bioswales are typically vegetated, mulched, or xeriscaped. They con ...
are swales that involve the inclusion of plants or vegetation in their construction, specifically.


On land

This swale concept has also been popularized as a rainwater harvesting and
soil conservation Soil conservation is the prevention of loss of the topmost layer of the soil from erosion or prevention of reduced fertility caused by over usage, acidification, salinization or other chemical soil contamination. Slash-and-burn and other uns ...
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 o ...
,
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, Weste ...
, 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 whole-systems thinking. It applies these principl ...
. In this context it is usually a water-harvesting ditch on contour, also called a ''contour bund''. Swales as used in permaculture are designed to slow and capture runoff by spreading it horizontally across the landscape (along an elevation
contour line A contour line (also isoline, isopleth, or isarithm) of a 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 plane section of the three-dimensional gra ...
), facilitating runoff infiltration into the soil. This archetypal form of swale is a dug-out, sloped, often grassed or reeded "ditch" or "lull" in the landform. An option is to pile the spoil on to 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 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 border/ separation ...
is formed, mitigating the natural (and often hardscape-increased) risks to slopes below and 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 sandbars on a beach, that run parallel to the shoreline.


See also

* Contour trenching *
Gutter Gutter may refer to: Water discharge structures * Rain gutter, used on roofs and in buildings * Street gutter, for drainage of streets Design and printing * Gutter, in typography, the space between columns of printed text * Gutter, in bookbind ...
* Keyline design *
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 ...
* Stormwater *
Water-sensitive urban design Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design to minimise environm ...


References


External links


Fact Sheet: Dry and Wet Vegetated Swales
from Federal Highway Administration
Wetlands of the Great Lakes: The Beach Swale & Dune and Swale Types
from Michigan State University
Video showing swales used to rehabilitate desert terrain
{{Wetlands Environmental engineering Landforms Landscape Sustainable gardening Sustainable design Water Water pollution es:Zanja