Development of the Tampa Bay Tidal Current Atlasby Kurt W. Hess, NOAA/Natl Ocean Service, Silver Spring, United States,
Abstract: The NOAA National Ocean Service (NOS) is developing a tidal current and water level forecast atlas for navigation in Tampa Bay, Florida, using the Princeton three-dimensional numerical model of time-varying water levels, currents, and densities. NOS's traditional tidal current charts consist of a set of hourly maps containing plots of instantaneous semidiurnal tidal current vectors at numerous locations where measurements were made and representing a typical tidal cycle. Because the tidal currents in Tampa Bay are mixed, the diurnal inequality may be so large that at the times of maximum lunar declination one of the two daily ebbs can completely disappear. Therefore, a set of charts based on a single typical semidiurnal tidal cycle will not be adequate. A method is tested here that uses three typical tidal current phase categories (semidiurnal flood, ebb, and diurnal flood) as basis functions having standard durations, with all phases referenced to the time of slack water at the Sunshine Skyway Bridge (SSB). The basis functions are the mean modeled currents in each category. The atlas-predicted current for any time is obtained by multiplying the basis function value at the index time by an amplification factor determined from the maximum current speed at the SSB. Mean rms differences between the hourly modeled current and the atlas-based reconstruction of the modeled current were found to be 1.8 cm/s at SSB and averaged 2.6 cm/s for all stations. Mean differences between the hourly observed current and the atlas-predicted current from the NOS tidal current tables were 10.4 cm/s at SSB and averaged 11.9 cm/s for all stations. Possible improvements in the prediction method are discussed.
Subject Headings: Tides | Bays | Ocean currents | Hydrologic models | Floods | Three-dimensional models | Ocean engineering | Water level | North America | Florida | United States | Tampa
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