MONITORING BLUFF EROSION RATES USING TERRESTRIAL LASER SCANNING AND STRUCTURE-FROM-MOTION PHOTOGRAMMETRY ON MINNESOTA'S NORTH SHORE STREAMS

Excess turbidity from increased fine sediment can degrade water quality and be harmful to fish and other aquatic life. On Minnesota’s North Shore of Lake Superior, there are several streams impaired by turbidity, often driven by erosion of stream bluffs. We have been quantifying rates of erosion on North Shore bluffs, starting in 2011, using terrestrial laser scanning (TLS). TLS allows for creation of 3D point cloud datasets that result in cm-scale resolution models of topographic surfaces, which can then be compared over time to quantify geomorphic change on bluffs. This project adds to earlier monitoring data, by providing bluff erosion rates on both natural and stabilized bluffs. We also use a technique called Structure-from-Motion (SfM) to create point cloud datasets from photographs collected with an unmanned aerial vehicle (UAV). This method may provide a faster, more cost-effective way to collect high-resolution topographic data of bluff surfaces. Results will include quantitative analysis using CloudCompare, a 3D point cloud processing software, to determine geomorphic change associated with erosion of bluffs and deposition on bluff toes and constructed bankfull bench features. We will also compare the TLS and UAV methods to determine if SfM is a viable low-cost alternative for monitoring bluff erosion rates. Future work will include a geotechnical assessment of slope stability with the goal of developing a predictive model for stable slope angle. The results from this work will assist in determining appropriate construction of bluff stabilization structures, and may better inform stream restoration activities along the North Shore.