Salt Flux and Eddy Stresses in a Shallow Estuary of High Tidal Range.
LOUISIANA STATE UNIV BATON ROUGE COASTAL STUDIES INST
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Detailed measurements over a tidal cycle of salinity and current speed were taken across a section of the high-tidal-range 3.0m, shallow 6.5 m estuary of the Rio Guayas in Ecuador. Despite a low freshwater discharge and intense mixing by the strong 1-1.5 msec tidal currents, an ideal well mixed estuary does not develop a weak vertical salinity gradient persists along the channel. A decomposition of the time-averaged salt flux into 18 terms accounting for the mean advective salt flux, changing cross-sectional area, vertical and lateral gradients in speed and salinity, and time deviations from the time means show that 87 of the total downstream salt flux is accounted for by the freshwater discharge but that 61 of the upstream salt flux necessary to maintain the salt balance is produced by upstream turbulent diffusive flux. This high value for the diffusive flux is predicted by the theories of Hansen and Rattray. Gravitational convection and lateral shear effects make unimportant contributions to the salt balance. The role of the time-dependent nature of the cross-sectional area on the structure of the eddy stresses is isolated for the first time.
- Physical and Dynamic Oceanography