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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Apr 2020

Submitted as: research article | 03 Apr 2020

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This preprint is currently under review for the journal ESurf.

Inertial drag and lift forces for coarse grains on rough alluvial beds

Georgios Maniatis1, Trevor Hoey2, Rebecca Hodge3, Dieter Rickenmann4, and Alexandre Badoux4 Georgios Maniatis et al.
  • 1School of Environment and Technology, University of Brighton, UK
  • 2Department of Civil and Environmental Engineering, Brunel University London, UK
  • 3Department of Geography, Durham University, UK
  • 4Swiss Federal Institute WSL

Abstract. Quantifying the force regime that controls the transport of a single grain during fluvial transport has historically been proven difficult. Inertial Micro Mechanical and Electrical Sensors (MEMS) sensors (sensor-assemblies that mainly comprise micro-accelerometers and gyroscopes) can be applied to this problem using a smart-pebble: a mobile Inertial Measurement Unit (IMU) enclosed in a stone-like assembly that can measure directly the forces of sediment transport (and consequently metrics such as grain velocities, positions, and kinetic energies). Today, twenty years after this idea was introduced in the literature, it is accepted that there is potential in calculating directly inertial single pebble dynamics for short time scales (after consistent calibration and analysis) despite limitations in the accuracy of MEMS sensors that are suitable for this issue. This paper introduces and tests a theoretical framework that connects the IMU measurements with existing force balance equations for sediment grains on a riverbed. IMUs were embedded in two different grain shapes and used in flume experiments in which flow was increased until the grain moved. The data were then processed to calculate the threshold force for entrainment resulting to the statistical approximation of inertial impulse thresholds for both the lift and drag components of grain inertial dynamics. An ellipsoid IMU was then deployed in a series of in situ experiments in a steep stream (Erlenbach, Switzerland). The inertial dynamics provide a direct measurement of the resultant forces on sediment particles which quantifies: (a) the effect of grain shape; and (b) the effect of varied intensity hydraulic forcing on the motion of coarse sediment grains during bed-load transport. Lift impulses exert a significant control on the motion of the ellipsoid across hydraulic regimes and despite the occurrence of higher magnitude and duration drag impulses. The first order statistical generalisation of the results suggests that the transport of the ellipsoid is characterised by no-mobility states and that the majority of mobility states is controlled by lift impulses.

Georgios Maniatis et al.

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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Georgios Maniatis et al.

Georgios Maniatis et al.


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Latest update: 01 Jul 2020
Publications Copernicus
Short summary
One of the most interesting problems in geomorphology concerns the conditions that mobilise sediments grains in rivers. Newly developed smart pebbles allow for the measurement of those conditions directly, if a suitable framework for analysis is followed. This paper connects such a framework with the physics used to described sediment motion and presents a series of laboratory and field smart-pebble deployments. Those quantify how grain shape affects the motion of coarse sediments in rivers.
One of the most interesting problems in geomorphology concerns the conditions that mobilise...