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Wetland Resources of Eastern South Dakota

Results and Discussion

Temporary Basins

The 520,379 temporary basins in eastern South Dakota cover 390,054 ac (157,853 ha) and comprise from 0.7% to 4.3% of the area of eastern South Dakota counties (Table 8). Temporary basins are numerically the most abundant type of basin in eastern South Dakota, and they exert a strong influence on the patterns of basin density described above; however, they affect patterns of basin acreage to a lesser extent because most are small. Temporary basins reach their highest relative densities in eastern South Dakota in the James River Lowland to the limit of the last advances of Late Wisconsin glaciation (Figs 30, 31). In the James River Lowland, small temporary basins tend to occur on broad, smoothly rolling, low subparallel ridges deposited as recessional moraine in the James River Lowland; however, large basins with broad expanses of temporary wetlands occur in the inter-moraine zones, or within the expansion plains of riverine wetlands.

Temporary basins are the most abundant type of basin in the Lake Dakota Plain physiographic region. During glacial retreat, drainage from the northern James River Lowland flowed northward. Because no outlet for this water existed, glacial Lake Dakota formed in what is now Brown and Spink counties. Many temporary basins within this physiographic region represent remnants of initially deeper basins that were partially filled by silt deposited under glacial Lake Dakota.

Temporary basins are less abundant on the Prairie Coteau where terrain relief is typically greater because of more extensive deposition of glacial debris. Greater relief generally results in deeper basins and may result in reduced upland infiltration and increased runoff. Temporary wetland basins also occur at low density on the western slope of the Missouri Coteau and within the dissected Pierre Hills physiographic region where all types of natural basins are uncommon because of a more ancient glacial history.

JPG - Distribution of Temporary Basins
JPG - Distribution of Temporary Basins
Figure 30. Distribution of temporary basins expressed as number of basins/10 mi2. Figure 31. Distribution of temporary basins expressed as acres of basins/10 mi2.

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