Disturbed Rivers & Their Recovery

Abstract (combined): River disturbances can occur at multiple spatial and temporal scales within the same system, and their recovery from disturbance is complicated by these overlapping factors. For example, rivers may be responding to: drainage basin growth and piracy, glaciation, landslides, wood removal, and anthropogenic alterations to baselevel simultaneously. This complexity obscures channel response to a singular change, and can complicate management and restoration decisions. Here, we untangle some of these disturbances and recoveries starting from a larger timescale and working our way in to the present day.

Long timescale (>10 ky) channel disturbances can be hard to recognize if channel recovery is nearly complete; yet, morphologic signatures in valleys walls and tributaries can help identify these disturbances and reveal that channel recovery is still ongoing. A case example in West Elk Creek, central CO, will be presented in which the creek has nearly recovered following a large landslide that caused stream diversion and watershed-scale reorganization. Numerical modeling and tributary morphometrics are used to identify the timescales and degree of landscape and channel recovery.

Over shorter timescales, watersheds and river corridors throughout the temperate latitudes have been extensively altered by human activities. These activities include changes in land cover and channel manipulation, floodplain drainage, and other manipulations within the river corridor. Failure to recognize the historical legacy of activities that no longer occur can skew perceptions of river process and form and the natural range of variability – and restoration options – within river ecosystems. Scientific and management challenges resulting from this situation include (i) recognizing the existence of an anthropogenic legacy that continues to affect river ecosystem process and form, (ii) understanding the source and implications of the legacy, and (iii) designing management strategies that can mitigate the loss of river ecosystem services. This talk uses case studies to explore these issues.

Bio: Dr. Sarah Schanz is an assistant professor in the Geology Department at Colorado College. She received her bachelor’s degree from Western Washington University in geology and her doctoral degree in earth and space sciences from University of Washington. Prior to Colorado College, she was a postdoc at Indiana University Bloomington and a visiting lecturer at California State University Monterey Bay. Dr. Schanz and collaborating students work on bedrock and mountainous rivers to analyze how these dynamic systems respond to disturbances over timescales of millions to tens of years.

Bio: Dr. Ellen Wohl received a BS in geology from Arizona State University and a PhD in geosciences from the University of Arizona. She is a professor in the Department of Geosciences at Colorado State University and a University Distinguished Professor. Her research focuses on physical processes and forms in river channels and floodplains, and how these interact with biogeochemistry and ecological and human communities. She has conducted field work on every continent except Antarctica.