This study examines the local, intratidal effects of suspended sediment concentrations (SSCs) on the hydrodynamics and vertical mixing in the Ems Estuary, located on the border between Germany and The Netherlands, during summer and winter seasons when the estuary turbidity maximum (ETM) is located upstream and adjacent to the study site, respectively. Measurements of density, SSCs, turbulent kinetic energy dissipation, and current velocity were collected and analyzed over a semi-diurnal tidal cycle in August of 2018 and January of 2019 as part of the collaborative Ems-Dollard Measurement (EDoM) campaign. During August, the estuary turbidity maximum was located 25 km upstream from the measurement site and local SSCs were low. Results revealed that under these conditions, suspended sediment minimally impacted vertical mixing by stabilizing density near-bottom during flood tide, while typical salinity-induced tidal straining patterns dominated. During January, the ETM was located only 5 km upstream of the measurement site leading to higher local sediment concentrations. Salinity-induced straining of the density occurred on early flood tide, creating stratification that suppressed vertical mixing. The suppression was enhanced by the contribution of vertical gradients in SSC to density, as signified by the gradient Richardson number. Suppression of vertical mixing by sediment-enhanced stratification was most significant within the hour following maximum flood currents when elevated velocity shear occurred. The variability observed between the local dynamics during August and January were attributed to greater sediment concentrations due to the ETM proximity in January. The intratidal asymmetry of vertical mixing observed under higher SSCs likely has implications for sediment transport. ... Read more

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. ... Read more