Assessment of Geomorphic Impacts of Vegetation Removal on the Colorado River in the Grand Valley, Colorado
Gigi Richard1*
1Fort Lewis College, Durango, CO, USA; garichard@fortlewis.edu
Recent and expanding efforts to remove tamarisk and Russian olive (TRO) from riparian zones may contribute to increased channel mobility and bank erosion, as evidenced by significant bank erosion associated with the 2011 peak flow in areas where tamarisk had been removed along the Colorado River in the Grand Valley, Colorado. The purpose of this study was to assess changes in channel mobility following tamarisk removal along a 51-km reach of the Colorado River in western Colorado via GIS analysis of repeat aerial photos and field surveying of channel cross-sections at vegetation removal sites. The study included field surveys of channel cross-sections at three TRO removal sites (2013-2018), GIS analysis of channel change using repeat aerial photos from 2002 to 2016, and aerial drone surveys of the three study sites in 2017. Results revealed that channel change and bank erosion occur along this reach of river regardless of vegetation removal efforts. During the 2007-2012 time, period erosion sites where TRO removal occurred were significantly wider (nearly 50%, p0.05) than erosion sites where vegetation removal did not occur. The results of this study do not clearly indicate if time after vegetation removal plays a role in changes in rate of erosion. For example, two of the sites experience 10 meters of erosion three to eight years following TRO removal, while three other sites experience decreasing rates of erosion following TRO removal. Method of TRO removal was not included in the analysis but could provide more insights into the variability in erosion rates following TRO removal.