Close-Range Photogrammetry Application to Monitor Levee Erosion in Case of Wave Overtopping

Coastal and riverine levees are prone to wave and steady-flow overtopping, which can result in breaching and consequential flooding of the hinterland. Full-scale field experiments on a levee are a sound approach to understanding of the underlying physical processes without suffering from scale effects, provided that accurate and valuable data can be collected. This paper outlines how close-range photogrammetry was applied to monitor a levee’s morphological evolution continuously and intermittently during wave overtopping. High-resolution spatial topographical models were obtained from which erosion rates could be quantified. Two camera setups—a system of multiple stationary synchronized cameras and a single mobile camera—were used for photo acquisition. The first configuration enabled reconstruction of the target zone as a dynamic scene and reduced photogrammetric analysis time through simultaneous processing of several frames [four-dimensional (4D) processing]. The second configuration applied the structure-from-motion (SfM) technique using multiple overlapping photographs to obtain three-dimensional (3D) elevation models at specific moments. Both approaches resulted in high-resolution digital elevation models (DEMs) with low mean absolute errors (MAEs) on the order of a few centimeters. Furthermore, photogrammetry proved to be highly flexible and could be applied to different types of levees with various cover layers, hydraulic loads, and meteorological conditions.