Author(s): Ana Margarida Bento; Lucia Couto; Teresa Viseu; Joao Pedro Pego

Linked Author(s):

Keywords: Local scour; Underwater processing tools; Scoured bed profiles; Submersible cameras; Continuous monitoring

Abstract: In experimental tests on scour around bridge foundations, the current approaches for scour monitoring rely mainly on visual point-wise measurements, which may provide less accurate estimates of scour and its effects. Meanwhile, methods for characterizing scoured hole surfaces have been developed. More recently, approaches making use of three-dimensional (3D) point cloud and digital elevation models (DEMs) have shown the ability to describe the scour hole geometry at bridge foundation models (piers or abutments) with high accuracy levels. However, the available methods are intended for the characterization of the scour hole patterns under drained conditions, i.e., without the effect of flowing water. Thus, the need to develop a system capable of continuously monitoring the evolution of scour at bridge foundations, without interruption of the flow, emerged. Few studies have been devoted to the continuous monitoring of the scouring process, consisting of: (i) photogrammetry-based methods, by using a pair of cameras and algorithms for camera calibration, image rectification and stereo-triangulation; and (ii) laser-based approach with a laser source and a camera. The results obtained from these investigations shed light on the need for further studies to better monitor the scouring process around bridge foundation models, taking advantage of the increasing development of the technology of submersible cameras and underwater processing tools. A new methodology was developed in the present study to obtain two-dimensional (2D) scoured bed profiles for a continuous/non-stop monitoring of the scouring process. Four submersible action cameras (Action Cam NK 3056 Full HD, waterproof with remote control, 12 MP resolution) were used for the acquisition of synchronized underwater images of the scour holes developed and surrounded affected areas. Since the cameras’ disposal is not universal, several preliminary tests were conducted in order to ensure that the selected structure did not unduly disturb the scouring process. A data set of large field views was produced using the cameras, not only due to their ultra-wide-angle lenses but also owing to their strategic displacement around the bridge pier model. The tests were performed in the Portuguese National Laboratory of Civil Engineering (LNEC). By processing each sequence of images and running a python code to detect the sand-pier border line for certain instants of the scouring experiment, it was possible to obtain the scour hole evolution in the form of 2D bed profiles. The developed algorithm has been verified as accurate by comparing its results against the point-wise scour depth measurements. The results allowed the temporal characterization of the scouring process taking advantage of the increasing development of the technology of submersible cameras and processing tools. Thus, the proposed methodology has delivered promising results for studying the phenomenon in the vicinity of bridge pier models in an experimental environment.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022623

Year: 2022