Dispersion of matter in homogeneous, time-dependent nearly-horizontal flows

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Summary

In this report the dispersion of a solute in a time-dependent nearly-horizontal flo~ is considered. The velocity field is horizontally homogeneou

and non-stratified, but the horizontal velocity vector may rotate in the

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vertical. Such Flo~s may occur at sea as caused by tidal action or ~ind. The also occur in shallow lakes where the circulation is caused by wind only. Because of the time-dependent flow the dispersion tensor is time-dependent as well. In the case of instantaneous release of a solute a semi-analytical solution is derived for its spreading. In the case of release at sea it is shovn that the initial behaviour of the concentration iSVfi~ry variable and depends on the instant of release and on the dispersion transverse to the mean velocity. The "Breeveertien" experiment (North Sea) is analyzed in

terms of the theory presented.

In addition similar calculations are made for a dye release experiment executed in a shallow Dutch lake, the IJsselmeer, in which the flow field is generated by wind only. These calculations are hampered by insufficient knowledge about the velocity profiles, both in the vertical and in the horizontal plane.

Finally some attention is payed to the influence of incomplete mixing in the vertical directly after release of the solute.

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