Preprints
https://doi.org/10.5194/egusphere-2025-1080
https://doi.org/10.5194/egusphere-2025-1080
25 Mar 2025
 | 25 Mar 2025

Three-stage evolution of particle shape in headwater streams

Naoya Ono Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane

Abstract. Given the importance of sediments in fluvial morphodynamics, studying how sediment particle shapes change during mass loss is important for understanding the morphology and change rates of fluvial landscapes. Particles of riverbed materials tend to become more rounded and circular downstream, but this trend can often be obscured because it results from processes that increase or decrease shape parameters to various degrees. This study unravels such complex interactions by evaluating the contributions of each process and revealing the factors that determine the rates of change in shape. We investigated changes in the roundness and circularity of basalt and shale particles in headwaters using the automated image analysis software Rgrains. The observed evolution of the roundness and circularity comprised three stages with different rates of increase. Both shape parameters initially increased rapidly, remained nearly constant, and then slowly increased downstream, indicating that the dominant process affecting the particle shape changed during a few kilometers of transport. These punctuated shape changes result from the hillslope sediment supply and the addition of rock fragments produced by chipping and fragmentation, of which finer fragments were found to significantly alter the downstream evolution of the shape. The rate of increase in the roundness and circularity of the particle shape depended on the rock type and grain size. The rates for the shale particles were higher than those for the basaltic particles. Grain size clearly affected the shape change rates of basalt particles but not of shale particles. We interpreted these differences between rock type and grain size to be associated with particle durability, weathering mechanisms and speed, and total residence time in the channel. These findings demonstrate that image-based measurements of shape parameters in headwaters enables a detailed examination of the mechanism and rates of changes in particle shape.

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Journal article(s) based on this preprint

25 Sep 2025
Shape evolution of bulk sediment in headwater streams: effects of rock type and particle size
Naoya O. Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane
Earth Surf. Dynam., 13, 959–980, https://doi.org/10.5194/esurf-13-959-2025,https://doi.org/10.5194/esurf-13-959-2025, 2025
Short summary
Naoya Ono Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee report', Andras A Sipos, 02 May 2025
    • AC1: 'Reply on RC1,', Naoya Takahashi, 08 Jul 2025
  • RC2: 'Comment on egusphere-2025-1080', Anonymous Referee #2, 29 May 2025
    • AC2: 'Reply on RC2', Naoya Takahashi, 08 Jul 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee report', Andras A Sipos, 02 May 2025
    • AC1: 'Reply on RC1,', Naoya Takahashi, 08 Jul 2025
  • RC2: 'Comment on egusphere-2025-1080', Anonymous Referee #2, 29 May 2025
    • AC2: 'Reply on RC2', Naoya Takahashi, 08 Jul 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Naoya Takahashi on behalf of the Authors (08 Jul 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (21 Jul 2025) by Fiona Clubb
RR by Andras A Sipos (01 Aug 2025)
ED: Publish subject to technical corrections (15 Aug 2025) by Fiona Clubb
ED: Publish subject to technical corrections (16 Aug 2025) by Wolfgang Schwanghart (Editor)
AR by Naoya Takahashi on behalf of the Authors (18 Aug 2025)  Author's response   Manuscript 

Journal article(s) based on this preprint

25 Sep 2025
Shape evolution of bulk sediment in headwater streams: effects of rock type and particle size
Naoya O. Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane
Earth Surf. Dynam., 13, 959–980, https://doi.org/10.5194/esurf-13-959-2025,https://doi.org/10.5194/esurf-13-959-2025, 2025
Short summary
Naoya Ono Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane

Data sets

Shape of natural and manually crushed particles collected from a headwater stream in Tsugaru, Japan Naoya Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga Ohta, Yuki Arai, and Yuki Yamane http://doi.org/10.6084/m9.figshare.28424138

Naoya Ono Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, and Yuki Yamane

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Short summary
Changes in sediment mass is accompanied by shape change. We studied downstream changes in particle shape near a channel head using image-based analysis. Although the particles tended to become smoother and more circular, such trend was significantly disrupted by the addition of rock fragment supplied from hillslopes or detached from larger particles during transport. Our findings indicated the dominant process that determine particle shape changes over short distance in headwater streams.
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