In Permaculture, a swale is a method used to harvest rain water. They are long shallow trenches that run along the contour of the land. This means that swales are perfectly level. Swales do not direct water flow, but they collect water. The soil removed from the swale is piled on the downhill side to make a slightly raised bank or berm. When rain falls, the water runs along the surface of the topsoil, and it will collect in the depression of a swale. The water will slowly seep into the soil and collect in underground pockets that will supply the roots of plants through weeks and even months without rain.
- Hugelkultured Swale with Linear Food Forest (permaculturepower.wordpress.com)