Assessing the Influence of Installed Stabilization Structures on the Upstream and Downstream Reaches on Cedar River, Nebraska
Matthew Russell, Aaron R. Mittelstet, Tiffany Messer and Jesse Korus
Riverbank erosion rates have seen dramatic increases in recent decades, thus requiring the implementation of stabilization practices in riverine ecosystems. However, little to no pre- or post-stabilization research has been conducted to address the potential impacts of these structures at or adjacent to the stabilized reach. The objective of this study was to: 1) Measure the amount of riverbank loss/gain at designated intervals upstream and downstream of each reach and on the opposite bank from 1993 to 2005 (pre-stabilization), and 2005 to 2018 (post-stabilization) on Cedar River using ArcGIS and historical NAIP imagery. Cedar River is located in Central Nebraska on the eastern edge of the Nebraska Sandhills. The river originates as the groundwater fed Cedar Creek and outlets into the Loup River south of Fullerton, Nebraska. Cedar River is a meandering river with sparse woody vegetation on the riverbanks, and has historically been free to move across the landscape, unimpeded by property lines and pivot pumps. In 2004, the Cedar River Corridor project, funded by the Nebraska Environmental Trust and headed by the Loup Basin RC&D Council, provided matching funds to citizens living or farming the area in order to install bank stabilization practices on their property. Some of the stabilization practices implemented include wooden and tree jetties, rock vanes, reinforced concrete walls, sloped gravel banks, and root wads. Today, human impediments are present, and concerns for their protection and safety continue to increase with increased incidents of peak flow events (i.e. historic 2010 and 2018 flood events) in the area. Previous studies have been conducted for the Cedar River Corridor Project to assess streambank stabilization effectiveness, cost effectiveness, and quantifying deposition at and near wooden jetty structures in the river. For this study, riverbank boundaries were drawn over NAIP images for 1993, 2005, and 2018 at each study site (24 total) for 10 meters up/downstream, 25 meters up/downstream, and 50 meters up/downstream. This process was repeated on the opposite bank of the reach, and all values were recorded for analysis. Cedar River, like many other streams and rivers in the state of Nebraska, is facing increasing rates of flooding and erosion, leading to losses of property and arable land. Historically, the solution for increased flooding in the area was to cut and channelize the river, directing high flows away from a landowner’s property. This short-term solution not only has an impact at the point of channelization, but also impacts the changing geomorphology of downstream river sections. Understanding how stabilizing riverbanks impacts changing geomorphology and riverine ecosystems allows for improvements in stream restoration design as well as informed decision making for future stabilization practices in similar streams and rivers.
Keywords: Erosion, stabilization, GIS, stream restoration, riverine ecosystems