Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

H (Human Geosciences) » H-CG Complex & General

[H-CG23] Turbidity current: from triggers for the generation to the depositional and morphological processes

Mon. May 21, 2018 3:30 PM - 5:00 PM 102 (1F International Conference Hall, Makuhari Messe)

convener:Miwa Yokokawa(Osaka Institute of Technology), Norihiro Izumi(Faculty of Engineering, Hokkaido University), Takeshi Nakajima(産業技術総合研究所地圏資源環境研究部門, 共同), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Chairperson:Nakajima Takeshi, Naruse Hajime

4:15 PM - 4:30 PM

[HCG23-10] Characteristics of the equilibrium basal driving layers of turbidity currents

★Invited Papers

*Rossella Luchi1, S. Balachandar2, Giovanni Seminara3, Gary Parker1,4 (1.Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA. , 2.Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, USA. , 3.Department of Civil, Environmental and Architectural Engineering, University of Genova, Genova, Italy., 4.Department of Geology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.)

Keywords:turbidity current, steady state, driving layer

We use a numerical model to describe the temporal evolution of a turbidity current toward steady state. At the beginning of the simulation, the effect of turbulence-driven upward mixing prevails over sediment settling, producing an upward dispersion of the sediment and an increased thickness of the current. The settling velocity limits the increase in thickness and dissipation. As a result, the turbidity current asymptotically partitions itself into two layers as it flows over a constant bed slope under condition of zero net sediment flux at the bed.

The lower ‘driving layer’ approaches an invariant flow thickness, velocity profile, and suspended sediment concentration profile within which nearly all of the suspended sediment is sequestered. The upper ‘driven layer’ carries a highly dilute suspension of sediment. This partition is a likely candidate for the mechanism by which the driving layer is able to run out long distances, keeping confined within a leveed subaqueous channel of its own creation.

The thickness of the driving layer provides a scale for channel characteristics. We show that this thickness and the average velocity of the driving layer mainly depend on two parameters: the dimensionless settling velocity and the shear Richardson number, that is a measure of the degree of stratification. Increasing dimensionless fall velocity and shear Richardson number result in a steady state solution characterized by concentration profiles that are more biased toward the bed, with the bulk of the volume of the suspended sediment confined within an ever thinner layer. The average velocity of the driving layer decreases for higher values of fall velocity and increases for lower values of shear Richardson number.