Subaqueous silt ripples measured by an echo sounder: Implications for bed roughness, bed shear stress and erosion threshold
Journal article
Zhang, Shaotong, Zhao, Zixi, Nielsen, Peter, Wu, Jinran, Jia, Yonggang, Li, Guangxue and Li, Sanzhong. (2023). Subaqueous silt ripples measured by an echo sounder: Implications for bed roughness, bed shear stress and erosion threshold. Journal of Hydrology. 626, pp. 1-15. https://doi.org/10.1016/j.jhydrol.2023.130354
Authors | Zhang, Shaotong, Zhao, Zixi, Nielsen, Peter, Wu, Jinran, Jia, Yonggang, Li, Guangxue and Li, Sanzhong |
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Abstract | Bedforms like ripples are widely distributed in the coastal zone. They influence the bed roughness thus the estimation of bed shear stress and associated sediment transport. An echo sounder was mounted on a bottom-supported tripod intended to measure the erosion and deposition of seabed in the subaqueous Yellow River Delta, China. However, variations in bed elevation are found to be not the net erosion or deposition at the observation site, but the migration of silt ripples which were generated by waves and pushed back and forth or flattened off by the tidal currents. Ripple heights were observed to be within 0.1–0.7 cm and were used for testing the model of Nielsen (1981). The model overestimated the height of silt ripples as it was developed for sands, but the deviation can be well addressed by incorporating a linear modification (R-squared = 0.79). Alternatively, a new model specifically for silt ripple height was regressed from the field data with R-squared up to 0.78. The existence of silt ripples increases the bed shear stress by 4 times due to the additional bed roughness. A “fluffy layer” overlies the consolidated seabed, therefore, net seabed erosion occurs after the “fluffy layer” is resuspended. A representative critical bed shear stress for net seabed erosion in the study area was found to be 0.8 Pa. The echo sounder can be an alternative tool for observing silt ripples in coastal regions like the Yellow River Delta where the water is too turbid for underwater videos. The proposed model infers silt-ripple features from bed grain size and flow condition and provides a quick estimate for bed roughness improving the understanding on sediment transport. |
Keywords | Bed elevation; Ripple height; Waves and currents; Tripod platform; Field observation; The yellow river delta |
Year | 01 Jan 2023 |
Journal | Journal of Hydrology |
Journal citation | 626, pp. 1-15 |
Publisher | Elsevier Science BV |
ISSN | 0022-1694 |
Digital Object Identifier (DOI) | https://doi.org/10.1016/j.jhydrol.2023.130354 |
Web address (URL) | https://www.sciencedirect.com/science/article/pii/S0022169423012969 |
Open access | Published as non-open access |
Research or scholarly | Research |
Page range | 1-15 |
Publisher's version | License All rights reserved File Access Level Controlled |
Output status | Published |
Publication dates | |
Nov 2023 | |
Publication process dates | |
Accepted | 05 Oct 2023 |
Deposited | 19 Aug 2024 |
Additional information | © 2023 Elsevier B.V. All rights reserved. |
Place of publication | Netherlands |
https://acuresearchbank.acu.edu.au/item/90wy2/subaqueous-silt-ripples-measured-by-an-echo-sounder-implications-for-bed-roughness-bed-shear-stress-and-erosion-threshold
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