Multi-camera measurements of free surface topography and velocity for water flows past sediment deposits

We describe the development of a multi-camera system tailored for small-scale hydrodynamic and morphodynamic experiments. The system includes four precisely synchronized stationary cameras, together with a laser scan traverse. Prior to water flow, this allows precise camera calibration and topography measurements. The calibrated cameras are then used to acquire stereo views of the flow free surface (Fig.1), seeded with fluorescent particles (to avoid light reflection). The 3D positions of the particles are determined to sub-millimeter accuracy, and their trajectories obtained by particle tracking (Fig.2). This allows measurements of channel topography, surface topography and surface velocity to be acquired in a common frame of reference. The methods are validated using pure water flows over 3D-printed topography, then applied to experiments involving flows past live sediment beds, including debris fans and slackwater deposits. In addition to measurements, preliminary comparisons with hydrodynamic model results will also be reported.

Keywords: multi-camera imaging; stereo imaging; three-dimensional topography and velocity measurements.

Fig.1 Flood flow past a debris flow fan in a small-scale laboratory channel, stereoscopic views.

Fig.2 Flood flow past a debris flow fan in a small-scale laboratory channel. Top: surface velocity map (up to 60 cm/s); bottom: particle trajectories.