Migrating bars influence the formation and dynamics of their peers in large sandy‐gravel bed rivers

Abstract

The present study investigates the morphodynamic interactions between migrating bars in a sandy gravel and nearly straight channel of the Loire River (France). From a large dataset collected from field campaigns performed between 2016 and 2020, we analysed the deflection power exerted by bars on flow and sediment transport that influences the dynamics of other bars present in the channel. We also investigated

Statistically derived morphological signatures of large river channels extracted from topo‐bathymetric LiDAR data

“…Three TB LiDAR surveys were performed on the reach S3 between 2017 (S3‐1) and 2019 (S3‐2, S3‐3) to estimate the sensitivity of PDF to hydrological variation. In 2017, the survey was done under low flow conditions (160 m 3 s −1 ) while multiple channels and bars of diverse orders were present (Le Guern et al, 2023). In 2019, the two surveys framed the low flow period of 2019: the first survey was done at the end of the high flow period (S3‐2) at a discharge of 219 m 3 s −1 and the second at the end of the low flow period (S3‐3) at a discharge of 91 m 3 s −1 (hydro.eaufrance.fr).…”

“…Considering the two other surveys (S3‐2 and S3‐3), both show a nearly similar distribution with a slight bimodality for S3‐3. Both can be divided into three parts: the channel network, the first‐order macroforms and the second‐order macroforms (topographically higher bars; Le Guern et al, 2023). After applying the GMM, the S3‐2 survey was composed of three Gaussian curves, each essentially representing the same MU as the visual segmentation of the PDFs.…”

“…The latter are characterized by a higher overall elevation than the LFC, the presence of a fluvial bifurcation including a vegetated island, and slope breaks at the LFC diffluence and confluence of the two channels. Manual bar segmentations (FB) were carried out considering the segmentations previously carried out by Le Guern et al (2023) on the site considered as braided (detrended isoline elevation of the toe of the bar front). Once the segmentation had been completed, the points for each study site were counted in each of the polygons obtained, using the ‘Synthesize ‐ Within’ tool in the ArcGIS Pro suite.…”

“…The Gaussian C is highly superimposed to the Gaussian B, and when represented on the corresponding REM, elevations highlighted are relatively similar especially for the margins of the bars (Figures S3-S5 and S9-S11).Considering the two other surveys (S3-2 and S3-3), both show a nearly similar distribution with a slight bimodality for S3-3. Both can be divided into three parts: the channel network, the first-order macroforms and the second-order macroforms (topographically higher bars; LeGuern et al, 2023). After applying the GMM, the S3-2 survey was composed of three Gaussian curves, each essentially representing the same MU as the visual segmentation of the PDFs.…”

The fate of bars in braided rivers

“…Furthermore, perturbations in flow and sediment supply across multiple scales (e.g., local-, reach-, and system-scale) can influence thread position and mobility, affecting the configuration and kinematics of channel threads and bars in braided rivers. This has been observed in systems where migrating and deforming bars and migrating threads alter local flow paths and network configurations (e.g., Wintenberger et al, 2015;Schuurman et al, 2016;Dixon et al, 2018;Le Guern et al, 2023), or where the configuration and migration behavior of bars and threads in 6 braided networks is altered in response to flooding events and land-use change (e.g., Jarriel et al, 2021;Tejedor et al, 2022;Ghosh et al, 2023).…”