This paper describes the applications of a model of the two dimensional shallow water equations to the growth of instabilities of the longshore current at SUPERDUCK on October 18th.Simulations are crried out suing two initial current profiles.in the first case the initial longshore current profile results from a balance between bottom friction,the radiation stress gradient and lateral mixing due to turbulence.In the secondf case lateral mixing is neglectede.the shear wave climates resulting from boht simulations are anlayzed and ocmpared to data.In the first case the energy in the shear wave band is udnerpredictd wheras in the second case,it is overpredicted.In both cases,the initial longshore current profile changes due to lateral mixing induced by the shear instabiliteis.The resulting lonshore current profile after shear instabiliteis have reached finite amplitude is found to b4e very similar for both cases.
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