PREDICTING CUTOFF LOCATIONS ALONG MEANDER BENDS ON THE EAST RIVER IN CRESTED BUTTE, COLORADO

The East River is a snow-melt dominated, meandering, mountain river that flows through Crested Butte, Colorado. Lidar and Worldview 2 multispectral satellite imagery collected in 2015 revealed approximately 100 abandoned channels in our 10 kilometer long study reach that occupy approximately 25% of the floodplain. Abandoned channels preserve the shape of former river meander bends. The imagery was also used to identify headcuts on several bends that could erode to become chute cutoffs under the proper flow conditions. Linear regression was used to extend discharge data along the study reach to 1934 using a USGS gauge station at the East River in Almont, Colorado. Fifteen satellite and aerial images spanning 60 years were used to count the number of cutoffs in each image and relate it to the peak and mean discharge for that time period. Field measurements are being collected at current bends with and without headcuts and chute channels to provide information for an empirical model to identify the probability of cutoff formation.

Our preliminary model incorporates soil depth, grain size, meander neck length, bend orientation, peak and mean discharge, slope, erosion rates, and sinuosity to predict at which bends a cutoff will likely form. The slope along the meander neck and the orientation of the neck relative to the valley slope could influence the surface flow direction and likelihood of a chute cutoff. Beaver activity along the East River complicates cutoff prediction if water is re-routed over a dam or along a beaver trail that intersects a meander bend. The only cutoff to occur between 2013 and 2015 formed along a bend containing a beaver dam and additional past cutoffs have occurred where beaver dams were present in historical imagery. One cutoff formed between 2009 and 2011, three cutoffs formed between 2005 and 2009, and three cutoffs formed between 1990 and 2005. This study is made possible by the temporal data sets it combines, and reflects the evolution of cutoffs in the river landscape over time.