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Measurements of Form and Frictional Drags over a Rough Topographic Bank Public Deposited

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  • Pressure differences across topography generate a form drag that opposes the flow in the water column, and viscous and pressure forces acting on roughness elements of the topographic surface generate a frictional drag on the bottom. Form drag and bottom roughness lengths were estimated over the East Flower Garden Bank (EFGB) in the Gulf of Mexico by combining an array of bottom pressure measurements and profiles of velocity and turbulent kinetic dissipation rates. The EFGB is a coral bank about 6 km wide and 10 km long located at the shelf edge that rises from 100-m water depth to about 18m below the sea surface. The average frictional drag coefficient over the entire bank was estimated as 0.006 using roughness lengths that ranged from 0.001 cm for relatively smooth portions of the bank to 1–10 cm for very rough portions over the corals. The measured form drag over the bank showed multiple time-scale variability. Diurnal tides and low-frequency motions with periods ranging from 4 to 17 days generated form drags of about 2000 N m⁻¹ with average drag coefficients ranging between 0.03 and 0.22, which are a factor of 5–35 times larger than the average frictional drag coefficient. Both linear wave and quadratic drag laws have similarities with the observed form drag. The form drag is an important flow retardation mechanism even in the presence of the large frictional drag associated with coral reefs and requires parameterization.
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  • Wijesekera, H. W., Jarosz, E., Teague, W. J., Wang, D. W., Fribance, D. B., Moum, J. N., & Warner, S. J. (2014). Measurements of form and frictional drags over a rough topographic bank. Journal of Physical Oceanography, 44(9), 2409-2432. doi:10.1175/JPO-D-13-0230.1
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  • 44
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  • 9
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  • This work was sponsored by the Office of Naval Research in an NRL project referred to as Mixing Over Rough Topography (MORT) and by the BOEM in the project referred to as Currents Over Banks (COB) through the Interagency Agreement M10PG00038. Support for James Moum was provided through ONR Grant N00014-09-1-0280.
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  • description.provenance : Made available in DSpace on 2014-10-09T16:15:47Z (GMT). No. of bitstreams: 1 MoumJamesCEOASMeasurementsFormFrictional.pdf: 3196926 bytes, checksum: a361954d04e3cdbe11af2beaced3cbea (MD5) Previous issue date: 2014-09
  • description.provenance : Submitted by Erin Clark (erin.clark@oregonstate.edu) on 2014-10-09T16:15:29Z No. of bitstreams: 1 MoumJamesCEOASMeasurementsFormFrictional.pdf: 3196926 bytes, checksum: a361954d04e3cdbe11af2beaced3cbea (MD5)
  • description.provenance : Approved for entry into archive by Erin Clark(erin.clark@oregonstate.edu) on 2014-10-09T16:15:47Z (GMT) No. of bitstreams: 1 MoumJamesCEOASMeasurementsFormFrictional.pdf: 3196926 bytes, checksum: a361954d04e3cdbe11af2beaced3cbea (MD5)

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