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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esurf-2019-52
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-52
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: short communication 05 Nov 2019

Submitted as: short communication | 05 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Short communication: Significance assessment of historical surfacic planform changes of mid-sized rivers: A Monte-Carlo based approach

Timothée Jautzy1, Pierre-Alexis Herrault1, Valentin Chardon1, Laurent Schmitt1, and Gilles Rixhon1,2 Timothée Jautzy et al.
  • 1Laboratoire Image, Ville, Environnement (LIVE UMR 7362), Université de Strasbourg, CNRS, ENGEES, ZAEU LTER, 3 rue de l'Argonne, 67083 Strasbourg, France
  • 2Laboratoire Image, Ville, Environnement (LIVE UMR 7362), ENGEES, CNRS, Université de Strasbourg, 1 quai Koch, 67070 Strasbourg, France

Abstract. Remote-sensed data in the fluvial context are extensively used to document historical planform changes. However, geometric and delineation errors inherently associated with these data can result in poor or even misleading interpretation of measured changes, especially (rates of) channel lateral migration. It is thus fundamental to take a spatially-variable (SV) error affecting remote-sensed data into account. In the wake of recent key studies using this SV-error as a level of detection, we introduce a new framework to evaluate the significance of measured channel migration. Going beyond their linear metric (i.e. migration vectors between diachronic river centrelines), we assess this significance through the channel polygon method yielding a surfacic metric (i.e. quantification of eroded, deposited, or eroded/deposited surfaces).

Our study area is an active wandering mid-sized river: the lower Bruche, a ∼ 20 m wide sub-tributary of the Rhine in eastern France. Within our four test sub-reaches, the active channel is digitised using diachronic orthophotos (1950; 1964) and the sub-reach specific SV-error affecting the data is interpolated with an Inverse Distance Weighting (IDW) technique. A main novelty of our approach consists then in running Monte-Carlo (MC) simulations to randomly translate active channels and propagate geometric and delineation errors according to the SV-error. This eventually leads to the production of a Surface of Detection (SoD), which allows evaluating the significance of measured surfacic changes. Putting the SoD into practice in the lower Bruche shows that only 37 % of the total surfacic measured changes are significant. Our results suggest that (i) orthophotos are affected by a significant SV-error, (ii) the latter strongly affects the significance of measured changes and (iii) the significance is strongly dependent on the magnitude of surfacic changes. Taking the SV-error into account is strongly recommended, regardless of the remote-sensed data used (orthophotos or aerial photos), especially in the case of mid-sized rivers (< 30 m width) and/or low amplitude river planform changes (< 1000 m2/yr). We finally insist on the transposability of our approach as we use well-established tools (IDW, MC): this opens new perspectives in the fluvial context (e.g. multi-thread river channels) for robustly assessing surfacic changes.

Timothée Jautzy et al.
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Timothée Jautzy et al.
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