Swale: A trench dug into the soil, following contour lines, to help capture runoff and the topsoil that it carries.
Berm: A mound of dirt, stone, or other debris laid out following contour lines to slow the movement of water and soil.
Berms and Swales in the Forest Garden:
Berms and swales are one of the most frequently applied earthwork techniques in Forest Gardens. Together, they conserve and protect the water and soil available in a Forest Garden. And while berms and swales can be implemented independently from each other, they make their greatest impact on a farm’s soil health when done together.
Forest Gardeners use an A-frame to mark contour lines across their Forest Garden, always perpendicular to the flow of water. After a farmer digs out soil for a swale, they create the accompanying berms by using the dug out dirt to form a compact mound on the lower side of the swale. Farmers will dig these across their land, starting a new trench several meters down the slope, with the distance between them being dependent on the gradient. The steeper the slope, the closer the trenches.
This technique forces rainwater to slow or stop at each berm and swale. Water then filters underground and deposits the topsoil that it carries. In the absence of these soil and water conservation structures, the majority of rainwater - and the topsoil that it carries - will be taken away from the field, with little value added to the Forest Garden. You can read more about how berms and swales are used throughout the Forest Garden in Chapter 15 of the Technical Manual.