UAS-based assessment of streambank stabilization effectiveness in an incised river system

Long-term monitoring of river restoration and streambank stabilization projects has often been neglected, resulting in a poor understanding of the effectiveness of different types of restoration methods. This study utilized unmanned aircraft systems (UAS) to monitor and assess the effectiveness of streambank stabilization projects in the Cottonwood River valley, an incised river system in east-central Kansas, USA. Streambanks have been acknowledged as a dominant sediment source to downstream waterbodies in incised fluvial systems and are therefore high priority targets of restoration and stabilization strategies. Volumes of sediment eroded at 14 streambank stabilization sites along the Cottonwood River were analyzed to compare: (1) pre-construction and post-construction periods; and (2) stabilized sites and unmodified sites. As monitoring and assessment were not part of the original design plans for stabilization efforts, this paper outlines methods to generate appropriate datasets and models to assess stabilization effectiveness. Results from three years of UAS monitoring, together with historical pre-construction assessment, indicate that stabilization projects significantly reduced local-scale erosion at stabilized sites. However, evidence of continued bank erosion after construction, including erosion of the lower bank above installed toe protection, bank steepening, and mass wasting, suggests that the benefits of reduced erosion from stabilization might change over time. Overall, our investigation demonstrates the viability of UAS surveys for long-term monitoring of streambank stabilization projects along incised river channels.