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A swale is a low tract of land, especially one that is moist or marshy.〔Merriam-Webster. ("Swale." ) ''Online Dictionary.'' Retrieved 2009-09-21.〕 The term can refer to a natural landscape feature or a human-created one. Artificial swales are often designed to manage water runoff, filter pollutants, and increase rainwater infiltration.〔U.S. Environmental Protection Agency (EPA). Washington, DC (1999). ("Storm Water Technology Fact Sheet: Vegetated Swales." ) EPA Document No. 832-F-99-006. September 1999.〕 The swale concept has also been popularized as a rainwater harvesting and soil conservation strategy by Bill Mollison, Geoff Lawton and other advocates of permaculture. In this context it usually refers to a water-harvesting ditch on contour. Another term used is 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), facilitating runoff infiltration into the soil. This type of swale is created by digging a ditch on contour and piling the dirt on the downhill side of the ditch to create a berm. In arid climates, vegetation (existing or planted) along the swale can benefit from the concentration of runoff. Trees and shrubs along the swale can provide shade which decreases water evaporation, however, they increase transpiration, so their net effect on the hydrologic cycle is probably to reduce infiltration. 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.〔Michigan State University Extension.("Wetlands of the Great Lakes Open Shoreline and Embayed Wetlands." ) Retrieved 2009-09-21.〕 ==See also== *Bioswale *Gutter *Keyline design *Rain garden *Surface runoff *Stormwater ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Swale (landform)」の詳細全文を読む スポンサード リンク
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