swale

In The Land of Little Rain, Mary Austin describes a typical Paiute encampment as being “near the watercourse, but never in the swale.” In constructing his “campoodie,” Austin goes on to say, “the Paiute seeks rising ground, depending on air and sun for purification of his dwelling, and when it becomes wholely untenable, moves.” The swale avoided by the Paiute—and every other knowledgeable camper—is a marshy or moist depression (sometimes mimicking a stream course) in a gently rolling landscape. These elongated hollows were likely created by fingers of glacial ice that melted more slowly than the rest of an ice sheet, depressing the ground beneath them as they did so. (At the same time, the ground between the swales absorbed some of this meltwater and rose.) In Florida, poorly drained swales alternate with beach ridges to form dune-and-swale topography. In the midwestern prairies, a series of swales in an area of little vertical relief, and with only slight rises above the general horizontal line of the glacial plain, is called swale-and-rise topography. Hoosier Prairie, on the southeastern shore of Lake Michigan, is a typical example. With less than a ten-foot change in elevation across its 430 acres, the nearly treeless plain is equal parts dry and wet, its swales harboring ecosystems of great biological diversity. Rich plant communities, including bracken and sweet ferns, originally established thousands of years ago on sand dunes above the prairie, survive today in the protection of the damp swales. Another example of extensive swale-and-swell topography, which disappeared almost completely with agriculture in the late 1880s, is the area around Dallas and Guthrie Counties, Iowa, which was carved during the Wisconsin glaciation. Once a mosaic of wetlands and rolling savanna bordering the Mississippi River, the area must have been a hush of relief to migrating waterfowl.

Terry Tempest Williams