Quantification of bedform dynamics and bedload sediment flux in sandy braided rivers from airborne and satellite imagery |
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Authors: | Robert J.P. Strick Philip J. Ashworth Gregory H. Sambrook Smith Andrew P. Nicholas James L. Best Stuart N. Lane Daniel R. Parsons Christopher J. Simpson Christopher A. Unsworth Jonathan Dale |
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Affiliation: | 1. Division of Geography and Geology, School of Environment and Technology, University of Brighton, Brighton, BN2 4GJ UK;2. School of Geography, Earth, Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, BL5 2TT UK;3. Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ UK;4. Departments of Geology, Geography and Geographic Information Science, Mechanical Science and Engineering and Ven Te Chow Hydrosystems Laboratory, University of Illinois at Urbana-Champaign, 1301 W. Green St, Urbana, IL, 61801 USA;5. Institute of Earth Surface Dynamics, Faculté des Géosciences et de l’Environnement, Université de Lausanne, Bâtiment Géopolis, CH1015 Lausanne, Switzerland;6. Geography, School of Environmental Sciences Faculty of Science and Engineering, University of Hull, Hull, HU6 7RX UK |
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Abstract: | Images from specially-commissioned aeroplane sorties (manned aerial vehicle, MAV), repeat unmanned aerial vehicle (UAV) surveys, and Planet CubeSat satellites are used to quantify dune and bar dynamics in the sandy braided South Saskatchewan River, Canada. Structure-from-Motion (SfM) techniques and application of a depth-brightness model are used to produce a series of Digital Surface Models (DSMs) at low and near-bankfull flows. A number of technical and image processing challenges are described that arise from the application of SfM in dry and submerged environments. A model for best practice is presented and analysis suggests a depth-brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low-turbidity and shallow (< 2 m deep) water. The aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18 km reach and three ~1 km long reaches respectively. Dune and unit bar migration rates are highly variable in response to local variations in planform morphology. Sediment transport rates for dunes and unit bars, obtained by integrating migration rates (from UAV) with the volume of sediment moved (from DSMs using MAV imagery) show near-equivalence in sediment flux. Hence, reach-based sediment transport rate estimates can be derived from unit bar data alone. Moreover, it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2D imagery, including from satellite images, so long as informed assumptions are made regarding average bar shape and height. With recent availability of frequent, repeat satellite imagery, and the ease of undertaking repeat MAV and UAV surveys, for the first time, it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low-turbidity rivers that currently have sparse information on bedload sediment transport rates. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. |
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Keywords: | sandy braided rivers UAV drone CubeSat digital surface model bedforms bedload transport South Saskatchewan |
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