Faculty of Engineering


Flow and depositional processes of clay-rich turbidity currents

The focus of this research is the investigation of the effect that clay has on turbidity current flow structure and deposit textural variation.

Turbidity currents are thought to be the primary agent for transporting sand, silt and clay particles from the continents to the deepest oceans, forming giant subaqueous rivers that eventually deposit their loads as turbidites. An understanding of turbidity flow is important as many of the world’s largest petroleum reservoirs are hosted within turbidites, they are often the location of subsea infrastructure such as cables, pipelines and hydrocarbon installations, and they may be linked to tsunamis.

 

Key focus areas/issues


Clay types will match those observed within Waitemata Basin sediments sampled from turbidite beds.The principal aim being to investigate the effect that clay has on turbidity current flow structure and deposit textural variation.

A series of experiments are being conducted, with the following objectives:

  1. To investigate if different clay types produce a change in flow behaviour and deposit style at a range of concentrations.
  2. Examine the critical threshold value between turbulent and laminar flows for different flow concentrations.
  3. Sampling of experimental turbidite deposits, to allow detailed quantification of deposit characteristics.
  4. Confinement study - use of a turbidity basin and turbidity flume.

 

Current major developments


The initial funding (The University of Auckland, CFRIF) allowed the start of collaboration between the Faculty of Engineering and the Faculty of Science to set up the facilities to undertake experimental turbidity related research. Two students are currently undertaking Masters studies in turbidity related research, as part of this collaboration between the Faculty of Engineering and the Faculty of Science. Theo Sangster (ME student) studies the effect of confinement on the depositional evolution of laboratory turbidity currents. Sophie Milloy (MSc student) studies turbidite lobe development on an aggrading basin floor, combing experimental and field investigation of Waitemata Basin clay rich turbidities.  New funding (The University of Auckland, FRDF) has been obtained to expand the present work, and NIWA is joining the project.

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Key achievements


The project is ongoing. Videos of the experimental study can be seen here.

Side view of turbidity current evolution.
Front view of turbidity current evolution

Key people


Contact


Heide Friedrich
Email: h.friedrich@auckland.ac.nz
Phone: +64 9 373 7599 extn 86912

Selected publications


Sangster, T.W.H., Friedrich, H. and Strachan, L.J. (2010) Evolution of Unconfined Turbidity Current Deposits: an Experimental Study. Paper submitted to 17th Australasian Fluid Mechanics Conference.

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Experimental setup


Laboratory experiments are conducted using a hydraulic flume, 0.4m wide and 6m long, and a basin 2m wide and 2.4m long, in the Fluid Mechanics Laboratories of the Faculty of Engineering. Ranges of different sand/clay concentrations are mixed with clear water, ranging from roughly 3-8% volumetric clay concentration. A measurement section is positioned downstream from the flume inlet. Qualitative and quantitative information of the shallow (water depth approx 15-20 cm) turbidity current is obtained.

Measurement equipment

Different measurement equipments are used:

  1. Instantaneous streamwise flow velocities are measured with Ultrasonic Doppler Velocity Profilers (UDVP). The UDVP equipment was provided by The University of Leeds and Dr. Gareth Keevil from Leeds participated in the project. The UDVP equipment, shown below, is a well tested and designed system to measure velocities in oblique und non-Newtonian flow conditions.
  2. Acoustic Doppler Velocimeter (ADV) probes from the Civil Engineering Department are used to compare with UDVP measurements.
  3. Camera footage is used to document the behaviour of the clay-rich turbidity currents from different view angles.
  4. For selected experiments deposits are allowed to dry and impregnated with resin. It is then used to obtain an image from a Scanning Electron Microscope (SEM).
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cl-udvp-probe

Ultrasonic Doppler Velocity Profilers

Each UDVP probe can obtain simultaneous velocity data along a profile of 128 points along the axis of the ultrasound beam. A vertical array of ten 4 MHz UDVP probes is utilized to measure the streamwise component of flow velocity at regularly spaced dimensionless depths. For some selected runs th UDVP probes were positioned in such a manner that velocity distributions across the flume can be compared and the flume wall effect can be studied.

Scanning Electron Microscope (SEM)

The SEM photographs show dry ballotini (sand substitute) and clay close-ups. The image to the right is an SEM photograph of a slice through the deposit layer of the settled turbidity current. The spherical shape of the ballotini helps to easily distinguish clay particles from sand particles and thus image analysis can be used to analyse changes in clay-sand distribution for varying flows and concentrations for the settled turbidity current.

cl-iande-sem-photographs