Abstract
AbstractEquilibrium sediment transport is the condition of zero net entrainment and deposition by sediment‐transporting flow (i.e. grade or regime). Here criteria for equilibrium sediment transport, or those used as proxies for equilibrium (for example, onset of erosion, onset of particle setting or suppression of turbulence) for dilute, suspended‐load‐dominated, turbidity currents, are tested against laboratory and natural data. The examined criteria are restricted to those describing flow over a bed of loose particulate material involving non‐cohesive sediment. Models include both monodisperse and polydisperse formulations that represent sediment non‐uniformity by using a single characteristic grain size or discretization of the grain‐size distribution, respectively. Analysis shows that a polydisperse‐type flux‐balance model, that equates erosional and depositional fluxes and where erosion is related to the power used to lift sediment mass from the bed (the ‘Flow‐Power Flux‐Balance’ model) provides predictions most consistent with observational data. Other equilibrium models tested, monodisperse or polydisperse, fail to predict realistic bed slopes and/or flow durations for concentrations, velocities and depths within limits for natural flows. Results of the Flow‐Power Flux‐Balance model are used to quantify sediment transport fields, equilibrium Shields numbers and slopes for turbidity currents of variable flow and particle properties.
Highlights
Turbidity currents are an important agent of downslope sediment transport in submarine and lacustrine environments, representing some of the most far-travelled and voluminous sediment transport events on Earth (Meiburg & Kneller, 2010; Talling et al, 2013; Azpiroz-Zabala et al, 2017; Wells & Dorrell, 2021)
Channel bed flow erosion equilibrium slope flow channel bed equilibrium slope channel bed flow deposition equilibrium slope sensitive to deposition and erosion: deposition may result in collapse of the flow as it loses its driving force, whilst erosion may lead to the flow becoming increasingly erosive or ‘ignitive’ as its driving force increases (Parker, 1982; Parker et al, 1986; Pantin et al, 2011; Halsey et al, 2017)
Model results using the flow-power flux-balance model illustrate the sensitivity of equilibrium Shields number and slope to the standard deviation of the particle size distribution, σ, flow concentration, c, and depth, h (Fig. 5). (Here and for subsequent presented results of the flow-power flux-balance model, particle size distribution is specified in the model a priori by a log-normal distribution discretized into N size classes with a phiscale bin size of 0.01, truncated to the central 99% region of the probability function to avoid overly small and large particles in the analysis.) The parameters σ, c and h impose an order of magnitude variation on equilibrium Shields number comparable or larger than the variation caused by median grain size over À2 < φ < 8
Summary
Turbidity currents are an important agent of downslope sediment transport in submarine and lacustrine environments, representing some of the most far-travelled and voluminous sediment transport events on Earth (Meiburg & Kneller, 2010; Talling et al, 2013; Azpiroz-Zabala et al, 2017; Wells & Dorrell, 2021). Assuming an erodible bed of loose sediment, equilibrium describes the condition of zero net erosion and deposition (Smith & Hopkins, 1973; Garcia & Parker, 1991, 1993; Garcia, 2008; Dorrell et al, 2013, 2018; Amy & Dorrell, 2021), and critically defines the boundary between erosional and depositional regimes. This sediment transport state represents the minimum condition for complete sediment bypass, or ‘bypassing flow’ sensu Stevenson et al (2015). These have received limited validation, largely due to a lack of suitable observational data and, as noted by Stevenson et al (2015), a validated model for accurately predicting equilibrium (or sediment bypass) remains lacking
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
