Kinematics and mass flux contribution of migrating multi-scale bedforms
Abstract
Multi-scale bedforms as ripples and dunes of different sizes are ubiquitous surface features in fluvial channels that are observed in both laboratory flumes and natural rivers. Bedforms modulate the flow structure and the bed shear stress distribution, influencing sediment transport rate, which in turn affects bedform morphology and cascade back on the flow. This cyclic feedback loop in river morphodynamics is a key to understand the coupling between bedform scale-dependent migration and deformation, and it is thus a major source of bedform variability. A significant challenge in quantifying bedform variability and estimating bedform mass flux is to define instantaneous bedform characteristics in space and time. In this work, we quantified bedform migration velocity using three methods: i) the bedform tracking that captures migration of individual bedforms in longitudinal bed elevation profiles, ii) two-dimensional cross-correlation function based, image matching technique equivalent to particle image velocimetry, and iii) two-dimensional frequency-wavenumber spectra that does not requires individual bedforms identification. We confirm that bedform migration and deformation are scale-dependent, i.e. highly variable small bedforms migrate faster over slowly moving large dunes. It is also demonstrated that large bedforms shelter downstream smaller bedforms and slow down their migration velocity, leading to bedform splitting and merging processes. In addition, the scale-dependent bedform contribution to mass flux and the direct measurements of sediment flux time signals are compared and investigated with the long term goal to predict mass flux from temporal bed elevation time series.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSY055..04L
- Keywords:
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- 0815 Informal education;
- EDUCATION;
- 9820 Techniques applicable in three or more fields;
- GENERAL OR MISCELLANEOUS;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 1894 Instruments and techniques: modeling;
- HYDROLOGY