Within a partially mixed estuary both the tidal and the nontidal density-induced circulation exhibits substantial vertical shear. The interaction of this current shear with turbulent mixing across the vertical density gradient contributes to the longitudinal (alongstream) spread of a contaminant introduced into the estuary. A dye tracer experiment conducted in the lower York River Estuary provides abundant evidence for the importance of this "shear effect" to longitudinal dispersion....
Wilson, Robert E., and Akira Okubo. 1978. "Longitudinal dispersion in a partially mixed estuary." Journal of Marine Research 36, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1437