Unified Model of Sediment Transport Threshold and Rate Across Weak and Intense Subaqueous Bedload, Windblown Sand, and Windblown Snow. Issue 4 (9th April 2021)

• Record Type: Journal Article
• Authors: Pähtz, Thomas; Liu, Yonghui; Xia, Yuezhang; Hu, Peng; He, Zhiguo; Tholen, Katharina
• Is Part Of: Journal of geophysical research. Volume 126:Issue 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-09
• Subjects: bedload -- bed slope -- cohesion -- saltation -- sediment transport rate -- sediment transport threshold; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2020JF005859
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Nonsuspended sediment transport (NST) refers to the sediment transport regime in which the flow turbulence is unable to support the weight of transported grains. It occurs in fluvial environments (i.e., driven by a stream of liquid) and in aeolian environments (i.e., wind‐blown) and plays a key role in shaping sedimentary landscapes of planetary bodies. NST is a highly fluctuating physical process because of turbulence, surface inhomogeneities, and variations of grain size and shape and packing geometry. Furthermore, the energy of transported grains varies strongly due to variations of their flow exposure duration since their entrainment from the bed. In spite of such variability, we here propose a deterministic model that represents the entire grain motion, including grains that roll and/or slide along the bed, by a periodic saltation motion with rebound laws that describe an average rebound of a grain after colliding with the bed. The model simultaneously captures laboratory and field measurements and discrete element method (DEM)‐based numerical simulations of the threshold and rate of equilibrium NST within a factor of about 2, unifying weak and intense transport conditions in oil, water, and air (oil only for threshold). The model parameters have not been adjusted to these measurements but determined from independent data sets. Recent DEM‐based numerical simulations (Comola, Gaume, et al., 2019; https://doi.org/10.1029/2019GL082195 ) suggest that equilibrium aeolian NST on Earth is insensitive to the strength of cohesive bonds between bed grains. Consistently, the model captures cohesive windblown sand and windblown snow conditions despite not explicitly accounting for cohesion. Plane Language Summary: Loose sedimentary grains cover much of the wind‐blown (i.e., aeolian) and water‐worked (i.e., fluvial) sedimentary surfaces of Earth and other planetary bodies. To predict how such surfaces evolve in response to aeolian and fluvial flows, one needs to understand the rate at which sediment is transported for given environmental parameters such as the flow strength. In particular, one needs to know the threshold flow conditions below which most sediment transport ceases. Here, we propose a simple model that unifies most aeolian and fluvial sediment transport conditions, predicting both the sediment transport threshold and rate in agreement with measurements and numerical simulations. Our results will make future predictions of planetary surface evolution more reliable than they currently are. Key Points: Unified model simultaneously captures sediment transport threshold and rate data across conditions in water and air within a factor of 2 Model supports the recent numerical result that the threshold and rate of equilibrium aeolian saltation are insensitive to soil cohesion Model challenges the classical prediction that the transport threshold for a longitudinally sloped bed depends on the angle of repose