Kinematic analysis of sea cliff stability using UAV photogrammetry

13 Erosion and slope instability poses a significant hazard to communities and 14 infrastructure located is coastal areas. We use point cloud and spectral data derived from close 15 range digital photogrammetry to perform a kinematic analysis of chalk sea cliffs located at 16 Telscombe, UK. Our data were captured from an unmanned aerial vehicle (UAV) and cover a 17 cliff face that is about 750 m long and ranges from 20 to 49 m in height. The resulting point 18 clouds had an average density of 354 points m. The models fitted our ground control network 19 within a standard error of 0.03 m. Structural features such as joints, bedding planes, and faults 20 were manually mapped and are consistent with results from other studies that have been 21 conducted using direct measurement in the field. These data were then used to assess differing 22 modes of failure at the site. Our results indicate that wedge failure is by far the most likely 23 mode of slope instability. A large wedge failure occurred at the site during the period of study 24 supporting our analysis. Volumetric analysis of this failure through a comparison of sequential 25 models indicates a failure volume of about 160 m. Our results show that data capture through 26 UAV photogrammetry can provide a useful basis for slope stability analysis over long sections 27 of coast. This technology offers significant benefits in equipment costs and field time over 28 existing methods. 29