Many tidal basins are connected to the open sea by multiple inlets. An example is the Guana-Tolomato-Matanzas (GTM) estuary (see Fig. 1), a 60 km long back-barrier estuarine system extending from Palm Valley to Palm Coast, Florida, US. A large area of this estuary ( 300 km2) is part of the GTM–National Estuarine Research Reserve with a great bio–diversity. This estuary is connected to the open sea by two inlets, the northern inlet is St. Augustine Inlet, located in St. Augustine, and the southern one, Matanzas inlet, is located 25 km southward. Hydrodynamics at the GTM estuary are primarily driven by the tidal propagation, although density driven flows might be relevant after major rainfall events (e.g. Sheng et al., 2008). Using parame- Figure 1. Guana–Tolomato–Matanzas estuary. ters characteristic for the GTM–estuary, the existence of morphodynamic equilibria of two–inlet systems is investigated using a width–averaged idealized morphodynamic model, and their sensitivity to parameters is assessed. @en

The Grand LAgrangian Deployment (GLAD) used multiscale sampling and GPS technology to observe time series of drifter positions with initial drifter separation of O(100 m) to O(10 km), and nominal 5 min sampling, during the summer and fall of 2012 in the northern Gulf of Mexico. Histograms of the velocity field and its statistical parameters are non-Gaussian; most are multimodal. The dominant periods for the surface velocity field are 1–2 days due to inertial oscillations, tides, and the sea breeze; 5–6 days due to wind forcing and submesoscale eddies; 9–10 days and two weeks or longer periods due to wind forcing and mesoscale variability, including the period of eddy rotation. The temporal e-folding scales of a fitted drifter velocity autocorrelation function are bimodal with time scales, 0.25–0.50 days and 0.9–1.4 days, and are the same order as the temporal e-folding scales of observed winds from nearby moored National Data Buoy Center stations. The Lagrangian integral time scales increase from coastal values of 8 h to offshore values of approximately 2 days with peak values of 3–4 days. The velocity variance is large, O(1)m2/s2, the surface velocity statistics are more anisotropic, and increased dispersion is observed at flow bifurcations. Horizontal diffusivity estimates are O(103)m2/s in coastal regions with weaker flow to O(105)m2/s in flow bifurcations, a strong jet, and during the passage of Hurricane Isaac. The Gulf of Mexico surface velocity statistics sampled by the GLAD drifters are a strong function of the feature sampled, topography, and wind forcing@en

A tidal-cycle study at Destin Inlet, Northwest Florida, investigated intratidal and residual flow structures for the first time across the inlet. Underway current velocity profiles were combined with hydrographic station profiles at neap tides to document the appearance of tidal fronts, the distribution of tidal currents across two cross-sections, and the residual, or non-tidal, flow structure at the same cross-sections. Intratidal variations of water density and velocity showed the presence of fronts both in 1) late ebb-early flood and 2) late flood-early ebb tidal stages. Late ebb-early flood tidal intrusion fronts brought about depth-independent changes in water density >10kg/m3 in <2h. Their counterparts, late flood-early ebb plume-like fronts, produced similar magnitude of variations in density but were depth-dependent. Diurnal tidal current distributions across the inlet followed a general behavior of a damped wave with strongest currents appearing near the surface and near the deepest part of the cross-sections (thalweg). However, curvature effects seemed to modify this behavior locally by shifting the maximum tidal current away from the thalweg. Frictional and curvature effects on the diurnal flows were confirmed by an analytical solution for tidal currents. The observed density gradients drove residual flows that were vertically sheared, with outflow at the surface and inflow near the bottom. Such residual flow distributions were reproduced by an analytical solution that diagnosed the flow structure as inherent of a dynamically narrow inlet with relatively weak frictional effects.@en