Application of enhanced SfM photogrammetry to medium-scale earthen embankment breaching experiments

This study presents the application of structure-from-motion (SfM) photogrammetry to monitor breach evolution in medium-scale experiments on non-cohesive sand embankments (median grain size 0.61 mm, dike height 1 m) conducted at the Hydraulic Research Laboratory of SPW-MI, Châtelet, Belgium. Breach development caused by overtopping was captured using a close-range, static multi-camera SfM system, providing high-resolution reconstructions of dike topography. The accuracy of the 3D reconstructions was assessed through root-mean-square reprojection errors of ground control and check points, and by comparison with dense point clouds obtained from a FARO LiDAR scanner and an iPhone LiDAR sensor, both confirming centimetre-scale precision. Key challenges when applying photogrammetry concern the submerged bed and dynamic water surface; these were addressed in two ways in the present paper. First, limitations from poor texture, reflections, and water motion were mitigated using floating tracers and synchronized imaging. Second, embedding coloured balls within the dike enabled tracking of breach deepening, improving the accuracy and completeness of SfM photogrammetry reconstructions. The resulting detailed experimental data are made available to the scientific community.