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.     

The suitability of routine weather data for estimating local estuarine heat energy fluxes

Meteorological data and water temperatures from a 98-day period during the summer of 1980 are used to examine the suitability of routine weather observations for quantifying the heat energy budget of a shallow lagoon on the Atlantic coast of Florida. Hourly cloud-cover observations are used to calculate incoming solar radiation, and results are compared with pyranometer readings. The standard error of the estimate is 26% of the mean daily accumulation for simulations of one day, but this decreases to only 0.3% of the total accumulation for simulations of 21 days. Wind speeds recorded at a weather station 4 km from the study site must be modified by a site-specific wind ratio before they can be used to calculate latent and sensible heat fluxes. Even with site-specific corrections to routine weather data, the standard deviation of simulated temperatures is 2 to 3 times that of observed temperatures. Cloud cover and wind speed are the two variables most difficult to incorporate into the simulations.     

Tidal and nontidal flushing of Florida’s Indian River Lagoon

The flushing of Florida’s Indian River Lagoon is investigated as a response to tidal and low-frequency lagoon-shelf exchanges in the presence of freshwater gains and losses. A one-dimensional computer model uses the continuity equation to convert water-level variations into both advective transport within the lagoon and lagoon-shelf exchanges. The model also incorporates transport by longitudinal diffusion. Flushing is quantified by calculating the 50% renewal time, R₅₀, for each of 16 segments. R₅₀ is calculated for tidal exchanges enhanced by 0–30 cm nontidal fluctuations in coastal sea level, then for a range of rainfall rates. In both series of simulations, results suggest that in the northern sub-basin, R₅₀ increases dramatically with distance from the inlet due to relatively weak tidal and nontidal exchanges. A 50% renewal occurs in about one tidal cycle just inside Sebastian Inlet; at the northern end of the northern sub-basin, R₅₀ is over 230 d, and only coastal sea-level variations on the order of 30 cm and/or dry season rainfall rates decrease R₅₀ to less than 1 yr. R₅₀ is 1 wk or less throughout the central and southern sub-basins, where lagoon-shelf exchanges occur through two inlets. Simulations involving seasonal variations in precipitation and evaporation indicate that maximum and minimum rates of freshwater input lead minimum and maximum salinities by time periods on the order of 2–3 wk for the lagoon as a whole and in the northern sub-basin. The central and southern sub-basins respond in 1–2 wk.     

A comparison of winter and summer temperature variations in a shallow bar-built estuary

Bihourly water temperatures from two, 110-day study periods are compared for a study site in the Indian River Lagoon, along the Atlantic coast of South Florida. Results of a summer study include the annual maximum temperatures in July and August, and reveal low-frequency variations of ±1–2°C superimposed onto the annual curve. The winter study shows the annual minimum temperatures in late February and low-frequency variations of ±3–4°C superimposed onto the annual curve. At the very long and the very short periodicities, thermal activity is consistently higher during the winter study. At the diurnal period, however, the temperature range during the summer study is twice that recorded during the winter study, and the time of warmest water in the diurnal cycle is shifted back between two and three hours toward mid day in the summer months. This is attributed to the relative increase in importance of heating by insolation at that time of year. Sensible and latent heat fluxes appear to damp the diurnal cycle in both records.