THE USE OF UNMANNED AIRCRAFT SYSTEMS TO MONITOR AND ASSESS THE EFFECTIVENESS OF STREAMBANK STABILIZATION PROJECTS IN AN INCISED RIVER SYSTEM

Long-term, post-construction monitoring of streambank stabilization projects has often been neglected, resulting in a poor understanding of project effectiveness. This study utilized unmanned aircraft systems (UAS) over a four-year period to monitor and assess the effectiveness of streambank stabilization projects constructed along the Cottonwood River, an incised river system in east-central Kansas, USA. Streambanks are high priority targets for restoration strategies, particularly in incised fluvial systems, because they have been identified as a major source of sediment to downstream waterbodies. Volumes of sediment eroded over time at 14 streambank stabilization sites were analyzed to compare (1) pre-construction and post-construction periods and (2) stabilized sites and unmodified sites. As monitoring and assessment were not included in the original stabilization project design plans, this study outlines methods to generate appropriate datasets to assess stabilization effectiveness. UAS monitoring results, together with historical pre-construction assessment, indicate that stabilization projects significantly reduced local-scale erosion at the stabilized site. Average reduction in volumes of material eroded at each site range between 51% and 98%. However, the benefits of reduced erosion from stabilization might change over time as evidenced by (1) continued bank erosion after construction, including erosion of the lower bank above installed toe protection, bank steepening, and mass wasting, and (2) evidence of increased erosion immediately upstream and/or downstream at select sites. Overall, this study highlights the viability of UAS surveys for long-term monitoring of streambank stabilization projects along incised river channels.