swale
rhymes with "whale"
A shallow, elongated depression in the landscape — either natural or human-made — that collects and infiltrates water. In permaculture and land management, a swale is a ditch dug along a contour line with a berm on its downhill side, designed to capture rainwater and let it soak into the soil rather than running off. The word applies equally to natural low spots in coastal dunes and to carefully engineered earthworks.
Etymology
Possibly from Old Norse svalr, meaning cool, or Old English swale, a shady place. The word's oldest sense is of a low, damp, shaded depression — a cool place in the landscape.
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