24 Feb 2023
 | 24 Feb 2023
Status: this preprint is currently under review for the journal ESurf.

Spatiotemporal Bedload Transport Patterns Over Two-Dimensional Bedforms

Kate C. P. Leary, Leah Tevis, and Mark Schmeeckle

Abstract. Despite a rich history of studies investigating transport over bedforms and dunes in rivers, the spatiotemporal patterns of sub-bedform bedload transport remain poorly understood. Previous experiments assessing the effects of flow separation on downstream fluid turbulent structures and bedload transport suggest that localized, intermittent, high-magnitude transport events (i.e., permeable splat events) play an important role in both downstream and cross-stream bedload transport near flow reattachment. Here, we report results from flume experiments that assess the combined effects of flow separation/reattachment and flow re-acceleration over fixed, two-dimensional bedforms (1.7 cm high; 30 cm long). A high-speed camera observed bedload transport along the entirety of the bedform at 250 f/sec. Grain trajectories, grain velocities, and grain transport direction were acquired from bedload images using semi-automated particle tracking techniques. Downstream and vertical fluid velocity was measured 3 mm above the bed using Laser Doppler Velocimetry (LDV) at 15 distances along the bedform profile. Mean downstream fluid velocity increases nonlinearly with increasing distance along the bedform. However, observed bedload transport increases linearly with increasing distance along the bedform, except at the crest of the bedform, where both mean downstream fluid velocity and bedload transport decrease substantially. Bedload transport time series and manual particle tracking data show a zone of high-magnitude, cross-stream transport near flow reattachment, suggesting that permeable splat events play an essential role in the region downstream of flow-reattachment.

Kate C. P. Leary et al.

Status: open (until 09 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2023-3', Anonymous Referee #1, 16 Mar 2023 reply
  • RC2: 'Comment on esurf-2023-3', Anonymous Referee #2, 27 Mar 2023 reply

Kate C. P. Leary et al.

Kate C. P. Leary et al.


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Short summary
Despite the importance of bedforms (e.g. ripples, dunes) to sediment transport, the details of sediment transport on a sub-bedform scale are poorly understood. This paper investigates sediment transport in the downstream and cross-stream directions over bedforms with straight crests. We find that the patterns of bedload transport are highly variable on the sub-bedform scale, which is important for our understanding of the evolution of bedforms with complex crest geometries.