Equilibrium sediment transport, grade and discharge for suspended-load-dominated flows on Earth, Mars and Titan

Amy, Lawrence; Dorrell, Robert

Abstract

© 2020 The Authors Recent surface observations have emphasised the importance of bedload transport by rivers and streams on Mars and Titan. Previous “hydraulic” analysis, however, has also shown that transport as suspended load should be possible, if not more prevalent due to lower critical shear stresses, under reduced gravity conditions compared with Earth; where the dominant mode of sediment flux by rivers is as suspended load. A new suspended-load equilibrium condition (zero net erosion and deposition) constraint is advanced, using a flux-balance model applicable to transport (capacity) limited alluvial channels. The theory unifies Gilbert's relation for slope and flow capacity model with the Shields criterion for incipient motion. Shields-stress analysis shows that sediment transport thresholds on Earth, Mars and Titan are dynamically similar. Thus, despite large differences in dimensional shear stresses, variations in the critical slopes and flow depths required for threshold and equilibrium conditions are comparatively modest. Under reduced gravity conditions, there exists a slightly higher potential for sediment transport as suspended load; except for systems involving high particle-fluid density ratios, as may apply to the transport of organic particles on Titan. Critically we show that graded suspended-load channels should develop gentler slopes under reduced gravity, and not steeper slopes as previously inferred based on generalized hydraulic geometry relationships of terrestrial river and submarine channels. We further argue that the use of submarine channels as analogues for channels formed under reduced gravity is not physically justified. Finally, compared with bedload channels, suspended-load channels should also have markedly higher discharges, with implications for mechanistic-based discharge predictions and precipitation models.

Citation

Amy, L., & Dorrell, R. (2021). Equilibrium sediment transport, grade and discharge for suspended-load-dominated flows on Earth, Mars and Titan. Icarus, 360, Article 114243. https://doi.org/10.1016/j.icarus.2020.114243

• Journal Article Type: Article
• Acceptance Date: Nov 30, 2020
• Online Publication Date: Dec 8, 2020
• Publication Date: May 15, 2021
• Deposit Date: Dec 9, 2020
• Publicly Available Date: Dec 17, 2020
• Journal: Icarus
• Print ISSN: 0019-1035
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 360
• Article Number: 114243
• DOI: https://doi.org/10.1016/j.icarus.2020.114243
• Keywords: Geomorphology; Equilibrium; Grade; Mars;Titan
• Public URL: https://hull-repository.worktribe.com/output/3673041
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0019103520305716?via%3Dihub