Eddy diffusivity: a single dispersion analysis of high resolution drifters in a tidal shallow estuary

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• 作者：Kabir Suara ; Richard Brown ; Michael Borgas
• 关键词：Eddy diffusivity ; Turbulence mixing ; Lagrangian drifter ; Shallow water ; Tidal estuary
• 刊名：Environmental Fluid Mechanics
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：16
• 期：5
• 页码：923-943
• 全文大小：2,025 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Environment
  Environmental Physics
  Mechanics
  Hydrogeology
  Meteorology and Climatology
  Oceanography
  
• 出版者：Springer Netherlands
• ISSN：1573-1510
• 卷排序：16

文摘

In an estuary, mixing and dispersion resulting from turbulence and small scale fluctuation has strong spatio-temporal variability which cannot be resolved in conventional hydrodynamic models while some models employs parameterizations large water bodies. This paper presents small scale diffusivity estimates from high resolution drifters sampled at 10 Hz for periods of about 4 h to resolve turbulence and shear diffusivity within a tidal shallow estuary (depth <3 m). Taylor’s diffusion theorem forms the basis of a first order estimate for the diffusivity scale. Diffusivity varied between 0.001 and 0.02 m2/s during the flood tide experiment. The diffusivity showed strong dependence (R2 > 0.9) on the horizontal mean velocity within the channel. Enhanced diffusivity caused by shear dispersion resulting from the interaction of large scale flow with the boundary geometries was observed. Turbulence within the shallow channel showed some similarities with the boundary layer flow which include consistency with slope of 5/3 predicted by Kolmogorov’s similarity hypothesis within the inertial subrange. The diffusivities scale locally by 4/3 power law following Okubo’s scaling and the length scale scales as 3/2 power law of the time scale. The diffusivity scaling herein suggests that the modelling of small scale mixing within tidal shallow estuaries can be approached from classical turbulence scaling upon identifying pertinent parameters.