SOIL EROSION ON THE CHEYENNE RIVER SIOUX TRIBAL (CRST) RESERVATION, SD: NATURAL VERSUS HUMAN

Severe soil erosion of the Pierre Shale has occurred on the old Armstrong Gunnery Range (GR), which was rented at minimum cost from the Lakota Nation during WWII. Erosion is thought to have resulted from prehstoric natural sheet and gully activity, overprinted by erosion from the drought years of the 1930s, overgrazing by non-Indian cattle companies uncontrolled by Bureau of Indian Affairs (BIA), landslide and wave attack along the Lake Oahe impoundment of Missouri and Cheyenne rivers, and subsequent government inattention. Surrounding non-GR tribal lands were thought to be much less eroded, but this is shown to be somewhat inaccurate. This study for the U.S. Army Corps of Engineers (COE) was contracted for assessment of types, locations, and degrees of soil erosion in the GR as part of environmental cleanup of a formerly utilized defense site. Extensive sheet and rill erosion, headcuts and gully erosion, stream incision and increase in sinuosity, wave erosion, slope failures of complex earth fall, topple, slump, and flow, and minor wind mobilization of shale fragments are characteristic. The most effective methods of analysis were GIS manipulation of SCS-mapped soil types (especially shale lands and akaline slickspot complexes), geomorphological mapping of erosion types, and chronology construction of long term soil erosion and alluvial deposition. Spatial and temporal distribution of soil erosion in the area conforms to a complex response by a wide variety of causative factors. Responsibility for soil erosion is spread between natural and human agencies, with BIA, COE and CRST as the main human agents. Environmental justice to CRST indicates that some measured governmental remediation is advisable.