Equilibrium sediment transport by dilute turbidity currents: Comparison of competence‐based and capacity‐based models

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.