Basins were classified by water regime and other factors following protocol described in the methods section. Basin coverages were created from NWI-mapped wetlands to complement existing data on basin distribution, hydrology, and biota. Although terminologies for wetland and basin water regimes are the same, acreage of NWI-mapped wetlands and basins are not comparable because basins are composite features comprised of one or more wetlands. Number and acres of eastern South Dakota basins by water regime. Most eastern South Dakota basins are small potholes.
Deeper basins tend to be larger than shallower basins.
That is, high densities of temporary, seasonal, and natural semipermanent basins tend to occur in discrete regions of eastern South Dakota, in part reflecting the manner in which they were formed during and following glacial retreat. The advancing glaciers split into two lobes, the James, that flowed down the James River Lowland, and the Des Moines, that flowed through northeastern South Dakota into southern Minnesota and Iowa. Because eastern South Dakota has a recent glacial history, much of the landscape has unintegrated drainage. That is, surface runoff flows into insular depressions or basins that formed from the melting of ice blocks deposited with the glacial till. The thickness of the ice mass and the amount and manner of deposition of glacial debris determined the modern topography and characteristics of basins.