CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

Paper No. 7
Presentation Time: 9:35 AM

NEW INSIGHTS FROM EXPERIMENTAL DATA INTO THE CONCEPT OF EQUILIBRIUM IN COMPOSITE SUBMARINE CHANNEL-LEVEE SYSTEMS AND CHANNEL DEPOSIT CHARACTER


HUNTER, Katrina1, KEEVIL, Gareth1, KANE, Ian2 and MCCAFFREY, William1, (1)School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom, (2)Statoil ASA, Research Centre, Bergen, P.O. Box 7200, Bergen, NO-5020, Norway, mccaffrey@earth.leeds.ac.uk

Sinuous submarine channels are significant conduits for the transport of sediment from rivers into deep marine basins. Channel systems can vary greatly in width and length but are major morphological features. Turbidity currents transport terriginous sediment within submarine channels. Due to the nature of turbidity currents, direct measurements are difficult to obtain in active channels and therefore the interaction between turbidity currents and sediment transport is poorly understood.

The relationship between the evolution of turbidity currents and sinuous channels is investigated through scaled experiments using a channel model with 15 bends. Physical modelling allows examination of velocity distribution, inner channel and overspill flow properties, alongside their associated deposits. Nominally identical particulate turbidity currents were created using a known initial mass concentration of silica flour. Current understanding of flow development predicts that the turbulence of the flow would decrease as the axial slope decreases. Preliminary data show an unexpected trend in the results: turbidity current turbulence decreases between 3 degree and 2 degree slope and increases between 2 degree and 1 degree slope, indicating a low at the mid slope angle. The initial findings question the present understanding of the development of an equilibrium flow state and turbulence propagation through a sinuous channel system.

Flow morphology evolves and adjusts to the channel form throughout the system. Velocity and overspill is greatest in the proximal bends forming coarse grained levee deposits. In the distal bends the deposit becomes progressively finer, until the final five bends, as flow velocity decreases and overspill is predominantly confined to the outer edge of the bend apex stripping the flow of the coarse grains. The intra-channel deposit grain size decreases down channel and remains finer grained than the levee deposits.

The flux in overspill seen along the model channel indicates that the rate at which the channel levees are built alters throughout the system. The overspill continues to occur through the system but decreases distally. This matches the observed decrease in channel width and height in natural channel systems.

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