Resumo

ALVAREZ, LG. Bottom boundary layer properties in the Upper Gulf of California derived from velocity profiles. Cienc. mar [online]. 2010, vol.36, n.3, pp.285-299. ISSN 0185-3880.

The vertical structure of currents in the Upper Gulf of California was studied using velocity profiles observed at a site in 25 m water depth during one fortnightly cycle, in order to determine the development of a logarithmic bottom layer and to estimate parameters derived from the law of the wall. The velocity data included two neap-tide periods in which gravity currents have been shown to develop. The currents were dominated by tidal forcing, and were oriented along-gulf, with the main axis towards 323.8°. Spring tide velocity amplitude was 0.5-0.9 m s^-1, decreasing to less than 0.30 m s^-1 during neap tides. A logarithmic layer structure was observed within the lower half of the water column during spring tides. This layer was less than 5 m thick during neap tides, and was not observed under low velocity conditions, around the times of current reversals. The seabed shear stress values were typical of macrotidal environments, reaching ±2.5 Pa under spring tide conditions and decreasing by a factor of 2-3 during neap tides. Mean values of the bottom drag coefficient and seabed roughness parameter were 10^-2 and 0.05 m, respectively. These relatively high values were attributed to the influence of near-bed stratification. During the two neap-tide periods, two gravity current events were observed within 4-5 m from the seabed, reaching 0.30 m s^-1, intensified by the ebb tidal flow. The near-bed velocity profiles were markedly modified during these events that persisted for about three days.

Palavras-chave : Gulf of California; bottom boundary layer; tidal currents.

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