Climate-Driven Flood Effects On Channel Stability, Sedimentation, and Freshwater Mussel Habitat In Rivers Draining The Ozark Highlands

The frequency of intense precipitation events and large magnitude floods in rivers draining the Ozark Highlands has been increasing over the past 40 years due to climate change. The higher energy flood regime can degrade channel habitats due to channel instability, bank erosion, and fine sediment deposition. This study was conducted to assess changes in stream channel morphology along segments of Roubidoux Creek and the Big Piney River on the Fort Leonard Wood Military Reservation, Missouri to address increasing concerns about habitat loss for freshwater mussels and evaluate the spatial distribution and cause of accelerated channel activity. A GIS based assessment of the stream channel geomorphology was conducted using leaf-off aerial photographs from 1995, 2007, and 2015. Stream channel bank and bar features were digitized and classified according to planform change and bar sediment activity. Field surveys were also conducted to assess in-stream channel sedimentation, bank erosion, and sediment and runoff inputs from tributaries. Our results show overall channel widening of 3% on the Big Piney River and 9% on upper segments of Roubidoux Creek during the 20-year study period, with local disturbance zones increasing channel width by over two-times in some cases. Bank erosion rates and bar area increases generally correlated with channel width increases. Over the two time periods (1995-2007 and 2007-2015), bank erosion rates increased in Roubidoux Creek but remained constant in the Big Piney River. Flow regulation by two impoundments on the Big Piney River may be controlling bank erosion rates. Up to one meter of fine sediment from eroding banks and tributary inputs was found in glide units upstream of riffle crests. Low mussel densities were associated with reaches of high channel activity (i.e., bank erosion rates, bar area changes, and fine sediment deposition). This study helps address our understanding of the response of channel morphology and sedimentation to increased climate-driven flooding and effects on freshwater mussel habitats.