The Cheyenne River in western South Dakota is currently listed as impaired for total suspended solids (TSS) and fecal coliform bacteria. RESPEC initiated a Total Maximum Daily Load (TMDL) assessment study for the Cheyenne River Watershed in western South Dakota the spring of 2007.
Cheyenne River Watershed below Angostura Reservoir (near Hot Springs, South Dakota) to the mouth of the river where it meets Oahe Reservoir was the focus area of this project. A major emphasis of the TMDL project was to identify contributing areas of sediment loadings to the Cheyenne River and to evaluate natural background while linking sediment loading to stream health. The goals were accomplished through four main tasks: design and implement a detailed water-quality monitoring plan; develop a watershed model using the program HSPF, collect and analyze benthic macroinvertbrate biological data, and collect and analyze stream physical habitat data.
The Cheyenne River has a large natural loading of sediment that largely originates from the badlands region of western South Dakota. Four distinct reaches are in the Cheyenne River. The first reach, from Angostura Dam to Cedar Creek near Redshirt Table, has relatively low loading for both TSS and fecal coliforms. The second reach, from Cedar Creek to near Wasta, is a transition reach in water quality for both TSS and fecal coliforms where loading increases dramatically. The third reach, from Wasta to the confluence of the Belle Fourche River, has a shift in stream morphology and sediment transport processes. The final reach, from the Belle Fourche River to the mouth, has consistent increases in both TSS and fecal coliform loading. Biologic condition, based on Index of Biotic Integrity (IBI) scores calculated from benthic macroinvertebrate data, increases upstream to downstream with the highest IBI scores occurring in the lowest reaches of the Cheyenne River.