Field estimation of the vertical eddy diffusivity: A review

The coastal water is a region receiving an increasing amount of pollution during the past decades. To manage the fisheries, ports and other industrial developments, a knowledge of physical rocesses which govern the dispersion of pollutants is essential. One major mechanism of dispersion is vertical mixing which is mostly formulated by vertical eddy diffusivity. The vertical eddy diffusivity has been estimated in the last 3 decades by using different approaches.This review deals with these approaches from the perspective of field measurements. The methods used or suggested for the field studies such as methods of Cox, Osborn-Cox, Ivey-Imberger and Winters et al. are described and their limitations, advantages and disadvantages especially from the practical point of view are discussed. Some case studies of natural water bodies such as estuaries and ocean are summarised and the results obtained from different methods are compared with those of direct measurements. It is argued that because of the limitation of the existing approaches and the chaotic behaviour of turbulent mixing, even using the most sophisticated instruments, none of the commonly used indirect methods are world widely applicable. These methods only perform well in special cases and mostly overestimate the vertical eddy diffusivity. This review will also improve the future study of pollutant transport and its framework.

Field estimation of the vertical eddy diffusivity: A review Keywords:

eddy diffusivity , turbulent mixing , field study , vertical transport , microstructure measurements , stratified flows