TURBULENT DIFFUSION AND BEACH
DEPOSITION OF FLOATING POLLUTANTS’
1. INTRODUCTION
Some pollutants float on the free surface of the sea; the practically most
important example is perhaps oil, which may be released, e.g., by a shipwrecked tanker. In the Great Lakes, large numbers of alewives (Alosa pseudoharmgus) are regularly killed by thermal shock early in the season
(Stanley, 1969). Masses of these small dead fish (weighing about 25 gm each)
may often be observed floating on the lake surface. They are subsequently
deposited on beaches and create a rather obnoxious nuisance.
The horizontal dispersion of buoyant pollutants exhibits certain peculiarities, on account of the fact that these are confined to a twodimensional
boundary of a threedimensionally turbulent medium. At such a boundary,
convergent and divergent zones occur randomly (Okubo, 1970). Nonbuoyant fluid wells up in divergences and dives down in convergences; floating
particles are prohibited by their buoyancy from participating in vertical
motions, with the result that they congregate in convergences, thin out in
divergences (Csanady, 1963, 1970). The transport, turbulent diffusion, and
beach deposition of such floating particles has received very little systematic
attention in the literature so far.
When a moderately strong wind blows over a water surface, it generates a
characteristic big-eddy field in the winddriven current consisting of “ Langmuir circulations” which are marked by long parallel lines of foam (“windrows”). Such flow structures have been the subject of a number of studies
since the pioneering investigation of Langmuir (1938; for a recent review, see
Scott et ul.. 1969). The windrows are known to form at lines of confluence
parallel with the wind, where the water sinks. They have characteristic spacings of several metres to several tens of metres. They collect not only foam,
’ Much of this work was carried out while the author was on kaveat Woods HoleOceano’ P w s m rrrldrm~t Woods Hole Owatlographic Institution. Woods Hole, Massachusetts.
graphic Institution.
27 t
DEPOSITION OF FLOATING POLLUTANTS’
1. INTRODUCTION
Some pollutants float on the free surface of the sea; the practically most
important example is perhaps oil, which may be released, e.g., by a shipwrecked tanker. In the Great Lakes, large numbers of alewives (Alosa pseudoharmgus) are regularly killed by thermal shock early in the season
(Stanley, 1969). Masses of these small dead fish (weighing about 25 gm each)
may often be observed floating on the lake surface. They are subsequently
deposited on beaches and create a rather obnoxious nuisance.
The horizontal dispersion of buoyant pollutants exhibits certain peculiarities, on account of the fact that these are confined to a twodimensional
boundary of a threedimensionally turbulent medium. At such a boundary,
convergent and divergent zones occur randomly (Okubo, 1970). Nonbuoyant fluid wells up in divergences and dives down in convergences; floating
particles are prohibited by their buoyancy from participating in vertical
motions, with the result that they congregate in convergences, thin out in
divergences (Csanady, 1963, 1970). The transport, turbulent diffusion, and
beach deposition of such floating particles has received very little systematic
attention in the literature so far.
When a moderately strong wind blows over a water surface, it generates a
characteristic big-eddy field in the winddriven current consisting of “ Langmuir circulations” which are marked by long parallel lines of foam (“windrows”). Such flow structures have been the subject of a number of studies
since the pioneering investigation of Langmuir (1938; for a recent review, see
Scott et ul.. 1969). The windrows are known to form at lines of confluence
parallel with the wind, where the water sinks. They have characteristic spacings of several metres to several tens of metres. They collect not only foam,
’ Much of this work was carried out while the author was on kaveat Woods HoleOceano’ P w s m rrrldrm~t Woods Hole Owatlographic Institution. Woods Hole, Massachusetts.
graphic Institution.
27 t