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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/esurf-2020-27
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2020-27
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Apr 2020

Submitted as: research article | 20 Apr 2020

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This preprint is currently under review for the journal ESurf.

Morphometric properties of alternate bars and water discharge: a laboratory investigation

Marco Redolfi, Matilde Welber, Mattia Carlin, Marco Tubino, and Walter Bertoldi Marco Redolfi et al.
  • Department of Civil, Environmental and Mechanical Engineering, University of Trento, Italy

Abstract. The formation of alternate bars in straightened river reaches represents a fundamental process of river morphodynamics that has received great attention in the last decades. It is well-established that migrating alternate bars arise from an autogenic, instability mechanism occurring when the channel width-to-depth ratio is sufficiently large. While several empirical and theoretical relations for predicting how bar height and length depend on the key dimensionless parameters are available, there is a lack of direct, quantitative information about the dependence of bar properties on flow discharge. We performed a series of experiments in a long, mobile-bed flume with fixed and straight banks, at different discharges. The self-formed bed topography was surveyed, different metrics were analysed to obtain quantitative information about bar height and shape, and results were interpreted in the light of existing theoretical models. The analysis reveals that the shape of alternate bars highly depends on their formative discharge, with remarkable variations in the harmonic composition and a strong decreasing trend of the skewness of the bed elevation. Similarly, the height of alternate bars clearly decreases with the water discharge, in quantitative agreement with theoretical predictions. However, the disappearance of bars when discharge exceeds a critical threshold is not as sharp as expected, due to the formation of so-called diagonal bars. This work provides basic information for modelling and interpreting short-term morphological variations during individual flood events and long-term trajectories due to alterations of the hydrological regime.

Marco Redolfi et al.

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Laboratory experiments on river alternate bars M. Welber, M. Redolfi, and W. Bertoldi https://doi.org/10.5281/zenodo.3746619

Marco Redolfi et al.

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Short summary
Alternate bars are large sediment deposits that tend to naturally form in rivers when the channel width is sufficiently large. Our laboratory experiments on a scaled model reveal that equilibrium properties of self-formed alternate bars highly depend on the water discharge with respect to the relevant theoretical thresholds. This work provides fundamental information for predicting the response of rivers to natural or human alterations of the flow regime.
Alternate bars are large sediment deposits that tend to naturally form in rivers when the...
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