The importance of exchange flows through channels or straits,which are interconnecting water bodies of different densities,lies in the fact that water mass characteristics in sub-basins aredetermined by these flows, extend of which depends on the exchangerate between the interconnected water bodies. The knowledge ofvertical diffusivity, κ, along a channel/strait istherefore crucial as this gives us an idea about the amount ofheat, mass and dissolved solids transported across it and provideparameterisations for circulation models. From comparison withnumerical results of an exchange through a channel at variousvalues for Gr, Pr and aspect ratio, we infer the effectivevalue for κ as it appears in the Grashof number.