PHYSICAL HABITAT ASSESSMENT OF THE CHEYENNE RIVER WATERSHED

The Cheyenne River in western South Dakota is currently listed as being impaired for total suspended solids (TSS). In 2005, physical habitat assessments were performed at 48 sites thoughout the Cheyenne River Watershed to understand sediment source regions in the Cheyenne River Watershed and the impacts excess sediment loadings have on stream channel morphology. Using metrics calculated from the habitat data, a principal component analysis (PCA) was conducted to describe habitat variability in the watershed. The PCA was used to define regions with similar habitat characteristics. After the completion of the PCA, data gaps were identified in the Badlands and eastern regions of the watershed. For this reason, physical habitat assessments were performed at 16 additional sites in 2007.

The addition of the 16 sites collected in 2007, combined with the original 48 sites, added to the understanding gained from the original PCA. At three sites on different Badlands tributaries, physical habitat data were collected showing geomorphic similarities between the Badlands tributaries and the main stem of the Cheyenne River. Physical habitat data were also collected at sites in the northeast region of the watershed identifying substrate similarities to the Badlands sites, even though the watershed characteristics in the two regions is very different. This similarity indicates that the northeast portion of the watershed may contribute a significant sediment load to the Cheyenne River in the lower reaches. Additionally, the added sites, specifically near the confluence of the Belle Fourche River, solidified a hypothesis that local parent geology has a large influence on channel morphology on both the Cheyenne and Belle Fourche Rivers in the region near the confluence and may override some of the influences of the large upstream sediment load. The analysis of all 64 sites gave a more complete understanding of the watershed, specifically when relating physical habitat characteristics to TSS loadings in the Cheyenne River.