"A swale is a shady spot, or a sunken or marshy place. In particular, in US usage, it is a shallow channel with gently sloping sides. ...
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Such a swale may be either natural or human-made. Artificial swales are often infiltration basins, designed to manage water runoff, filter pollutants, and increase rainwater infiltration – green instances are the subterm bioswales." - (en.wikipedia.org 25.01.2022)