Environmental Fluid Mechanics

, Volume 16, Issue 5, pp 923–943 | Cite as

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

  • Kabir SuaraEmail author
  • Richard Brown
  • Michael Borgas
Original Article


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.


Eddy diffusivity Turbulence mixing Lagrangian drifter Shallow water Tidal estuary 



The authors thank all people who participated in the field study, those who assisted with the preparation and data analysis, as well as the Queensland Department of Natural Resources and Mines, Australia for providing access to SunPOZ network for reference station data used for RTK post processing of the high resolution GPS-tracked drifter. The authors acknowledge the support Redland City Council for provision of permit to the study sites. The project is supported through Australia Research Council Linkage Grant LP150101172. The authors acknowledge the contributions of Professor Hubert Chanson and Dr. Charles Wang to the work.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Science and Engineering FacultyQueensland University of TechnologyBrisbaneAustralia
  2. 2.Marine and Atmospheric ResearchCommonwealth Scientific and Industrial Research Organisation (CSIRO)AspendaleAustralia

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