Tidal dynamics and low-frequency exchanges in the Aransas Pass,Texas

Current, water level and wind data collected from a study site at the Aransas Pass, Texas, during a 45-day period in mid 1977 are used to describe tidal motions and low-frequency, meteorologically-forced exchanges between the inner shelf and a series of intracoastal bays. Analysis of individual tidal constituents indicates a mixed but principally diurnal tide. Tidal constituents move through the Pass as nearly progressive waves. Asymmetry in the co-oscillating tidal motions is explained as a result of unequal frictional forces acting on flood and ebb currents in the Pass. Tidal excursions computed from the tidal harmonic constants and from cumulative net displacements suggest that tidal-period exchanges are not effective in flushing the bays even under tropic tidal conditions. Nontidal water levels are related to the cross-shelf component of the coastal windstress at statistically significant levels. This suggests that low-frequency local meteorological forcing, as a set-up or set-down of coastal water levels, plays a valuable role in assisting tidally-driven exchanges.