Channel Morphologic Changes Associated with Invasive Vegetation Removal
Celeste Wieting1*, Sara Rathburn2, Lindsay Reynolds3, Jonathan Friedman4, Derek Schook5
1,2Colorado State University, Fort Collins, CO, USA;,
3Bureau of Land Management, Denver, CO, USA;
4US Geological Survey, Fort Collins, CO, USA;
5Department of Forest and Rangeland Stewardship, Colorado State University, Fort Collins, CO, USA;
Invasive vegetation poses a great threat to riparian ecosystem diversity in Western North America. Invasive species such as tamarisk (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) dominate much of the riparian corridor of American Southwest rivers. In addition to altering riparian ecosystems, the spread of invasive vegetation causes channel morphologic changes including channel narrowing and incision. Over the past decades, various methods of river restoration have been applied at different scales to remove invasive species along river corridors to benefit native vegetation, local wildlife, and restore channel morphology. As widespread removals become more prevalent in river restoration projects, it is critical to understand how channels will respond. Comprehensive post-removal channel morphologic response studies are lacking, largely because post-removal monitoring generally focuses on vegetation or wildlife response. Our work will help fill this knowledge gap through i) a literature review of channel morphologic changes resulting from invasive species removal throughout the Southwestern US; ii) ongoing reach- to segment-scale field monitoring of channel geometry changes resulting from different types of vegetation removal; and iii) explicitly linking vegetation characteristics to channel and floodplain surfaces through flow and sediment transport dynamics. Some of the broader questions related to channel-vegetation feedbacks include: What are the fundamental controls that govern the suite of probable channel responses following invasive vegetation removal? How do different removal methods compare in terms of resulting stream morphologic changes? Does mechanically removing the whole plant lead to the greatest stream restoration benefits? Which invasive species impart the greatest fluid drag and promote deposition and channel narrowing? This research will involve a coarse-scale analysis of channel geometry changes following removal of invasive species on rivers with ongoing research. Examples of variables to be noted include vegetation type, method of vegetation removal, time since removal, number of high flows since removal, and major channel changes such as avulsions. Additional analyses will utilize satellite imagery and existing data from remote sensing applications. Stream channel response to invasive vegetation presence and removal will be analyzed on a smaller scale at Canyon de Chelly National Monument (CACH) and Big Bend National Park (BIBE). Work within CACH will include repeat Unmanned Aircraft System (UAS) flights for high-resolution terrain data and digital elevation models (DEM), and repeat channel cross-section surveys building on previous work. Identifying controls on incision versus widening will be important at CACH because the channel has been actively incising, putting cultural resources within the canyon at risk. At BIBE, there are complex channel-vegetation interactions with tamarisk, giant cane (Arundo donax), and willows and past and future vegetation management practices along the Rio Grande River. Existing terrestrial laser scans (TLS) will be used to map invasive vegetation extent and changes that alter hydraulics and sediment transport characteristics. Our research results will be useful to federal land managers addressing ongoing invasive vegetation issues and will assist in predicting future post-removal channel change to protect the time and financial investments of large-scale invasive species removal projects.