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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 4 | Copyright
Earth Surf. Dynam., 6, 933-953, 2018
https://doi.org/10.5194/esurf-6-933-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Oct 2018

Research article | 25 Oct 2018

Bank erosion processes measured with UAV-SfM along complex banklines of a straight mid-sized river reach

Gonzalo Duró1, Alessandra Crosato1,2, Maarten G. Kleinhans3, and Wim S. J. Uijttewaal1 Gonzalo Duró et al.
  • 1Department of Hydraulic Engineering, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, the Netherlands
  • 2Department of Water Science and Engineering, IHE-Delft, P.O. Box 3015, 2601 DA Delft, the Netherlands
  • 3Department of Physical Geography, Utrecht University, P.O. Box 80115, 3508 TC Utrecht, the Netherlands

Abstract. We apply structure from motion (SfM) photogrammetry with imagery from an unmanned aerial vehicle (UAV) to measure bank erosion processes along a mid-sized river reach. This technique offers a unique set of characteristics compared to previously used methods to monitor banks, such as high resolution and relatively fast deployment in the field. We analyse the retreat of a 1.2km restored bank of the Meuse River which has complex vertical scarps laying on a straight reach, features that present specific challenges to the UAV-SfM application. We surveyed eight times within a year with a simple approach, combining different photograph perspectives and overlaps to identify an effective UAV flight. The accuracy of the digital surface models (DSMs) was evaluated with real-time kinematic (RTK) GPS points and airborne laser scanning of the whole reach. An oblique perspective with eight photo overlaps and 20m of cross-sectional ground-control point distribution was sufficient to achieve the relative precision to observation distance of  ∼ 1:1400 and 3cm root mean square error (RMSE), complying with the required accuracy. A complementary nadiral view increased coverage behind bank toe vegetation. Sequential DSMs captured signatures of the erosion cycle such as mass failures, slump-block deposition, and bank undermining. Although UAV-SfM requires low water levels and banks without dense vegetation as many other techniques, it is a fast-in-the-field alternative to survey reach-scale riverbanks in sufficient resolution and accuracy to quantify bank retreat and identify morphological features of the bank failure and erosion processes. Improvements to the adopted approach are recommended to achieve higher accuracies.

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The challenge to measure three-dimensional bank irregularities in a mid-sized river reach can be quickly solved in the field flying a drone with ground-control points and later applying structure from motion photogrammetry. We tested a simple approach that achieved sufficient resolution and accuracy to identify the full bank erosion cycle, including undermining. This is an easy-to-use and quickly deployed survey alternative to measure bank erosion processes along extended distances.
The challenge to measure three-dimensional bank irregularities in a mid-sized river reach can be...
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