Logarithmic Velocity Structure In The Deep Hypolimnetic Waters Of Lake Michigan

Details

• Journal Title:
  Journal of Geophysical Research: Oceans
• Personal Author:
  Troy, Cary ; Cannon, David ; Liao, Qian ; Bootsma, Harvey
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; Sea Grant
• Sea Grant Program:
  ILIN (Illinois-Indiana Sea Grant)
• Description:
  The characteristics of the bottom boundary layer are reported from a Lake Michigan field study carried out in deep hypolimnetic waters (55 m depth) during the stratified period (June–September 2012). The sandy substrate at the measurement site was densely covered with invasive quagga mussels (mean size: 1.6 cm; mean density: 10,000 mussels m−2). The measurements reveal a sluggish, compact bottom boundary layer, with flow speeds at 1 mab less than 5 cm s−1 for most of the period, and a dominance of subinertial energy. A downwelling event caused the largest currents observed during the deployment (10 cm s−1 at 1 mab) and a logarithmic layer thickness of 15 m. In spite of the weak flow, logarithmic profile fitting carried out on high-resolution, near-bed velocity profiles show consistent logarithmic structure (90% of profiles). Flow was dominated by subinertial energy but strong modified by near-inertial waves. Fitted drag coefficients and roughness values are urn:x-wiley:21699275:media:jgrc21583:jgrc21583-math-0001 = 0.004 and urn:x-wiley:21699275:media:jgrc21583:jgrc21583-math-0002 = 0.12 cm, respectively. These values increase with decreasing flow speed, but approach canonical values for 1 mab flow speeds exceeding 4 cm s−1. The estimated vertical extent of the logarithmic region was compact, with a mean value of 1.2 m and temporal variation that is reasonably described by Ekman scaling, 0.07 urn:x-wiley:21699275:media:jgrc21583:jgrc21583-math-0003 / urn:x-wiley:21699275:media:jgrc21583:jgrc21583-math-0004, and the estimated overall Ekman layer thickness was generally less than 10 m. Near-bed dissipation rates inferred from the law of the wall were 10−8−10−7 W kg−1 and turbulent diffusivities were 10−4−10−3 m2s−1.
• Keywords:
  Limnology Quagga Mussel Quagga Mussel
• Source:
  JGR Oceans 121(1): 949-965
• DOI:
  https://doi.org/10.1002/2014JC010506
• Sea Grant Document Number:
  ILIN-R-16-010
• Document Type:
  Journal Article
• Funding:
  Grant no. NAOAR4170095
• Place as Subject:
  Michigan, Lake
• Rights Information:
  Other
• Compliance:
  Library
• Main Document Checksum:
  urn:sha256:ac742c28effcc34cdf4013216c24d8a126d93d4f3e4c6cc70276ed33834ce791
• Download URL:
  https://repository.library.noaa.gov/view/noaa/43836/noaa_43836_DS1.pdf
• File Type:
  [PDF - 2.36 MB ]