RECORDS OF ANTHROPOGENIC LAND USE PRESERVED IN FILL TERRACE STRATIGRAPHY OF LOWER DRY CREEK, IDAHO

Understanding erosion rates and processes is crucial for assessing the impacts of anthropogenic land use on stream morphology in streams of the western United States. In Idaho, the Boise River and its tributaries experienced a major base level fall from the draining of ancient Lake Idaho approximately three mya; this change in base-level is recorded in fluvial terraces and channel incision of tributaries of the Boise River. Lower Dry Creek has been established as one of these major tributaries experiencing recent channel incision. Since the 1800s, Lower Dry Creek has a history of beaver trapping, logging, dredge mining, and grazing. These anthropogenic activities further correlate with the timing of recent major down cutting events that have resulted in well-exposed stratigraphy in cut banks within Lower Dry Creek. The objective of this study is to use terrace stratigraphy to investigate how anthropogenic land uses have influenced the aggradation and incision of Lower Dry Creek. Through observations made in the stratigraphic columns observed along different terrace heights, conclusions can be drawn about previous aggradation rates and lead to a better understanding of creek behavior in western streams today.

Stratigraphic columns of three terrace heights display the anthropogenic effects on the middle section of Lower Dry Creek. The five-meter terrace sits the farthest upstream on the northeast side of modern Lower Dry Creek next to what is currently used as grazing land. The three-meter terrace sits on the southwest side of the stream below a previous dredge mining site and current grazing land. The half-meter terrace creates a wider flood plain around modern Lower Dry Creek and displays trampling due to modern grazing cattle. By correlating the older five-meter and three-meter terraces to the more recent half-meter terrace, the anthropogenic effects upon the stream aggradation in Dry Creek can be better understood and related to other tributaries throughout the western United States.