Application of Three‐Dimensional Lagrangian Residual Transport

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Abstract
Three‐dimensional Lagrangian residual circulation computed from an intratidal hydrodynamic model is used to drive an intertidal water‐quality transport model. The sum of the Eulerian residual and Stokes' drift is used as a first‐order approximation for the Lagrangian residual current. The Stokes' drift approximates residual currents induced by the nonlinear interactions of the tidal currents. Computed residual velocities show close agreement with a two‐dimensional (vertical‐longitudinal) analytical result. The methodology is applied to Chesapeake Bay for the entire year of 1985. Salinity computed with the intertidal transport model (i.e., with Lagrangian residuals) shows good agreement with observed salinity data and that computed with the intratidal hydrodynamic model. The basic effect of the Stokes drift is to transport water mass (e.g., salinity) up estuary. The procedures provide a practical means of interfacing intratidal hydrodynamic model information to water‐quality models for making long‐term, intertidal transport computations for weakly nonlinear tidal systems.