Monitoring River-Channel Change Using Terrestrial Oblique Digital Imagery and Automated Digital Photogrammetry
Annals of the Association of American Geographers
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Imagery acquired using a high-resolution digital camera and ground survey has been used to monitor changes in bed topography and plan form, and to obtain synoptic water-surface and flow-depth information in the braided, gravel-bed Sunwapta River in the Canadian Rockies. Digital images were obtained during daily low flows during the summer meltwater season to maximize the exposed bed area and to map the water surface on the days with the highest flows. Images were acquired from a cliff-top 125 m above and at a distance of 235 m from the riverbed and used to generate high-resolution orthophotos and digital elevation models (DEMs) at a ground resolution of 0.2 m, within an area 80 times 125 m. The creation of DEMs from oblique and nonmetric imagery using automated digital photogrammetry can be difficult, but a solution based on rotation of coordinates is described here. Independent field verification demonstrated that root mean square accuracies of 0.045 m in elevation were achieved. The ground survey data representing riverbed topography were merged with photogrammetric DEMs of the exposed bars. The high-flow water surface could not be surveyed directly because wading was dangerous but was derived by ground survey of selected accessible points and photogrammetry. The DEMs and depth map provide high-resolution, continuous data on the channel morphology and will be the basis for subsequent two-dimensional flow-modeling of velocity and shear stress fields. The experience of using digital photogrammetry for monitoring river-channel change allows the authors to identify other potential benefits of using this technique for fluvial research and beyond.