Near yearlong time series measurements of water level elevation from seven stations along the Suwannee River, Florida, were used to characterize, observationally and analytically, the propagation of tidal and subtidal signals along the estuary resulting from tide‐river interactions. Tidal amplitudes and phases were obtained from least squares fits to observed values and used to compare to an analytical model. Subtidal amplitude and phases were characterized by Hilbert empirical orthogonal functions (HEOFs), obtained through complex principal component analysis, and compared to an analytical solution. The landward attenuation of the tidal signal was replicated analytically. The subtidal signal (periods > tides) was also described analytically with an oceanic wave moving landward and a seaward river pulse. The subtidal analytical solution reproduced the competition between the landward and seaward waves and the zone where each wave dominated over the other. Depending on the phase of these landward and seaward subtidal waves, the resulting subtidal signal amplitude could either (a) attenuate landward to a certain location and then increase or (b) amplify landward up to a certain zone and then decrease.

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Estimates of turbulence properties with Acoustic Doppler Current Profiler (ADCP) measurements can be muddled by the influence of wave orbital velocities. Previous methods—Variance Fit, Vertical Adaptive Filtering (VAF), and Cospectra Fit (CF)—have tried to eliminate wave-induced contamination. However, those methods may not perform well in relatively energetic surface gravity wave or internal wave conditions. The Harmonic Analysis (HA) method proposed here uses power spectral density to identify waves and least squares fits to reconstruct the identified wave signals in current velocity measurements. Then, those reconstructed wave signals are eliminated from the original measurements. Datasets from the northeastern Gulf of Mexico and Cape Canaveral, Florida, are used to test this approach and compare it with the VAF method. Reynolds stress estimates from the HA method agree with the VAF method in the lower half of the water column because wave energy decays with depth. The HA method performs better than the VAF method near the surface during pulses of increased surface gravity wave energy.

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<p>A 10-year time series of surface salinity values along an estuary-river transition documents their spatial structure and their temporal variability. Decomposition of detided time series into empirical modes indicates that the first mode, explaining almost 95% of the overall variance, has the typical sigmoid spatial structure found in estuaries. The temporal variability of mode 1, referred to as <em>salinity index</em>, displays annual and semiannual signals that are modulated from year to year. A fit of the <em>salinity index</em> to harmonics associated with luni-solar orbital motions and solar activity explain more than 70% of the <em>index</em> variance. This suggests that a) gravitational forcing from moon and sun, and b) the thermodynamic influence of solar activity, both impact salinity intrusions into rivers. The mechanistic linkage is unknown, but it is likely that it develops through atmospheric pressure, winds, air temperature, and water level. These variables are influenced by gravitational forcing and solar activity as observed elsewhere. The main finding is that the salinity variability at an estuary-river transition is influenced by gravitational forces and solar activity, i.e., saltwater intrusion could be determined by the modulation of astronomic influences. Similar variability may be found for mixing processes in coastal regions.</p> <p> </p>