Upstream Riprap Slope Inspection by Drone

As-built verification and regular inspection of upstream slope protection are important aspects for monitoring dams and levees. Although efficient quantitative methods for design of riprap material exist, including those described by the Bureau of Reclamation [1] and the U.S. Army Corps of Engineers [2], to date, field methods for assessment of riprap have been largely qualitative and subjective. This paper describes a case study using three-dimensional (3D) point cloud data to inspect and evaluate the upstream slopes of two embankments at a reservoir in the northeastern United States. The point cloud data was produced using Structure from Motion (SfM) photogrammetry with images collected from a small unmanned aerial vehicle (UAV), or drone. A measure of the roughness, or variability, of the slope surface evaluated from the point cloud was performed for each embankment following the method described by McGuire et al. (2016) [4] and Shoemaker et al. (2019) [5]. The results of the evaluation and their relevance to riprap performance are provided. The method described has numerous advantages over traditional inspection procedures, including the ability to characterize areas difficult to access by foot or boat, increased time efficiency, and reduced subjectivity than from a traditional visual inspection.