Joint mapping of bed elevation and flow depth in microscale morphodynamics experiments

Experiments conducted at very small scales are increasingly being used to study the morphodynamics of sediment beds under the action of flowing water. For such microscale experiments, we propose a measurement approach aimed at jointly mapping the evolving bed topography and distribution of water depth. The proposed measurement system includes a single color camera, a red stripe laser and green fluorescent dye. The stripe laser is scanned back and forth over the experimental surface, while the fluorescent dye is mixed with the flowing water, allowing both the bed topography and water depth to be reconstructed from color images. We present the steps needed for image calibration and processing, including simple models of light refraction and attenuation. The methods are verified using a surface of known geometry, then demonstrated for a challenging groundwater channelization experiment. For this application, co-registered maps of bed topography and water depth are obtained at millimetric resolution for an experimental domain of 650 mm by 650 mm, at a rate of one pair of maps per minute (experimental time). The methods are found to yield accurate results and vividly depict the evolution of a self-formed channel network.