GEOLOGIC CONTROLS ON EROSION AT COW CREEK ENGINEERED STREAM IN STILLWATER, OKLAHOMA

Stream erosion can cause extensive damage to adjacent structures that were previously thought to be well sited. The erosive behavior of Cow Creek in Stillwater, OK had removed 4 feet of streambank in 18 months and was jeopardizing structures such as the Highway 51 bridge, Oklahoma State University service roads, local utilities, as well as the Oklahoma State Botanical Gardening Studio. A $2M project, largely funded by the ARRA, engineered a solution to limit the erosion of the stream. The design for combatting erosional destruction included engineering specific slope gradients and planting certain species to stabilize streambanks and creating riparian wetlands and a spillover path or “short circuit” for flooding. It is still unclear in this system why the banks were so erodible in the area. The purpose of this study is to identify the geologic causes for stream erosion and better understand how lithology, grain size, and grain shape affect them at Cow Creek. The area of investigation contains an engineered segment of Cow Creek, which is a highly erosive, pre-oxbow cut off, meander in the south-central portion of the Botanical Gardens. A direct push sampling tool (Geoprobe) and grain size analysis were used to obtain and analyze the fine-grained sediment from the riparian zone of the stream to better understand the geologic controls on erosion. Preliminary results show that one zone near the stream bed elevation had low shear strength and was evaluated for soil properties.