Author(s): Geir Helge Kiplesund; Fjola Gudrun Sigtryggsdottir
Linked Author(s): Geir Helge Kiplesund
Keywords: Dam breach; Rockfill dams; Structure from motion; Video analysis
Abstract: Embankment dams are vulnerable to excess through-flow as well as overtopping. The erosion process that initiates in these cases may ultimately lead to breaching of the dam. Breach parameters are needed to estimate the severity of dam breach outflow. Laboratory investigations into the breaching of embankment dams have mainly related to earthfill dams rather than rockfill dams. The topic of the present study is on laboratory investigations into the breaching of rockfill dam with focus on the instrumentation and the methods of recording of the breaching behaviour. The aim of this research is to enhance the current knowledge on the breaching of rockfill dams and to develop robust methods that can be applied in future research, including future large-scale testing where many of the typical laboratory scale methods and instruments are impractical. The present research is based on a continuous series of laboratory tests combined with some large-scale field tests and other field investigations . The current model, built in a hydraulic flume, represents a full dam profile of a rockfill dam and is a development of earlier models used for investigating stability of rockfill dams and ripraps under throughflow and overtopping situations. Instrumentation of the model includes pore pressure measurements along the dam foundation, water level recording and video recording from multiple angles as well as detailed imagery being collected of the dam before and after testing. The paper describes how still images and video recordings from several cameras are processed in order to develop detailed 3D models of the model before and after testing as well as developing dynamic 3D models of the dam model throughout the entire breaching process. Synchronised video feeds are processed with widely available video processing tools to extract images from different directions at known points in time throughout the breaching process. 3d models of the dam and especially the breach opening are created using the “Structure from motion” and “Multi View Stereo” processing techniques for each timestep, this has been accomplished with widely used software perhaps more commonly associated with drone scanning. This approach allows one to follow the breaching process in greater detail throughout the breach initiation and subsequent erosion process. Examples of the resulting 3D models are presented and the effectiveness of the methodology for investigating embankment dam breaching is outlined.