Vertical structure of tidal flows at the entrance to Guaymas Bay, Mexico

Abstract

A 144-day bottom-mounted ADP experiment at the entrance to Guaymas Bay was used to examine the vertical structure of the tidal flows of a small basin (33.6 km2) located in a semiarid region. Harmonic analysis techniques were used to extract the tidal ellipse parameters of the time series of ADP and to determine amplitude and phase of the tidal components of additional time series of tide height from two sites on the inner side of the bay taken before the experiment. The K1-current and the M2-current were the tidal currents of foremost importance; they were aligned with topography and showed amplitudes of 7.8 ± 0.2 cm s-1 and 7.4 ± 0.3 cm s-1, respectively. The M4-current was the principal shallow water tidal current with amplitude of 1.0 ± 0.2 cm s-1. Because of the small embayment condition, the main tidal motions showed characteristics of a standing wave. The vertical structure of the tidal currents was parabolic, which suggests that the barotropic tidal currents were affected by boundary layer process, furthermore, the mean current profile confirmed previous indication of an inverse estuarine circulation. The diurnal currents rotated anticlockwise in the upper layer and clockwise in the lower layer, which suggests that they were modulated by stratiflcation.