Submerged aquatic vegetation (SAV) provides primary products for the food web, as well as shelter and nursery for many juvenile species. SAV can also attenuate waves, stabilize the seabed, and improve water quality. These environmental services are influenced by the dynamic motion of SAV. In this paper, a consistent‐mass cable model was developed to investigate flow interaction with a flexible vegetation blade. Compared with previous vegetation models, the cable model showed improvements in simulating blade motions in waves with and without currents, especially for “second‐normal‐mode‐like” blade motion. Wave asymmetry would cause blade motion to be asymmetric. However, asymmetric blade motion may also occur in symmetric waves. Results indicate that the asymmetric blade motion in symmetric waves is induced by two major mechanisms: (i) the spatial asymmetry of the encountered wave orbital velocities (wave motion relative to blade) due to blade displacements and (ii) the asymmetric action on the blade by vertical wave orbital velocities. Consequently, the blade motion is asymmetric even underneath symmetric waves unless (i) blade length ( ) is much smaller than the wavelength ( ), (ii) blade length is much smaller than the water depth ( ) in finite water depth waves, or (iii) water depth is much smaller than the wavelength ( ). Peak asymmetric blade motion occurs as increases to a critical value. The peak asymmetry increases with wave height and blade length but decreases with increasing blade flexural rigidity. Blade motion characteristics play an important role in wave‐vegetation interaction, wave‐driven currents, wave‐attenuation capacity, breakage of vegetation and ecosystem services.

Intratidal and fortnightly variability of turbulence at the mouth of a macrotidal estuary is explored in this study. Profiles of turbulent kinetic energy dissipation were estimated from a Vertical Microstructure Profiler, and velocity shear measurements and current velocities were collected with a vessel‐mounted Acoustic Doppler Current Profiler. Gradient Richardson numbers were quantified using density measurements from a Conductivity, Temperature, Depth profiler and squared vertical shear quantified from current velocities. All measurements were collected over one complete semidiurnal tidal cycle in both neap and spring tide conditions. Vertical eddy viscosity (A_z) was quantified from the available data and was used as a proxy for vertical mixing. Results showed intratidal asymmetries in bottom‐generated turbulence during neap with A_z larger during ebb tide (∼10⁻² m²/s) than flood tide (∼10⁻³ m²/s) with the opposite occurring during spring tide with larger A_z during flood (10⁻¹ m²/s) than ebb (10⁻² m²/s). Lateral processes produced elevated near‐surface mixing decoupled from bottom‐generated turbulence at the end of flood and ebb tide during neap and spring. The secondary flows were driven by Coriolis, and these flows either enhanced (neap tide, end of flood) or maintained (spring tide, end of ebb) total shear through slack tides producing near‐surface to midwater column turbulence. These results are the first of their kind to show midwater column mixing from lateral circulation driven by Coriolis in a well‐mixed system, which vary from the lateral processes previously shown to destabilize water columns in estuaries more influenced by stratification.

River plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume, which ultimately impact spreading and mixing rates with the ambient coastal ocean. The degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations. A field campaign was conducted in a river plume in the northeast Gulf of Mexico in December 2013, in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions. Current velocity, density, and Turbulent Kinetic Energy Values, ε, were obtained using an Acoustic Doppler Current Profiler (ADCP), a Conductivity Temperature Depth (CTD) profiler, a Vertical Microstructure Profiler (VMP), and two Acoustic Doppler Velocimeters (ADVs). The frontal region contained ε values on the order of 10⁻⁵ m² s⁻³, which were markedly larger than in the ambient water beneath (O 10⁻⁹ m² s⁻³). An energetic wake of moderate ε values (O 10⁻⁶ m² s⁻³) was observed trailing the frontal edge. The interfacial region of an interior section of the plume featured opposing horizontal velocities and a ε value on the order of 10⁻⁶ m² s⁻³. A simplified mixing budget was used under significant assumptions to compare contributions from wind, tides, and frontal regions of the plume. The results from this order of magnitude analysis indicated that frontal processes (59%) dominated in overall mixing. This emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models.

The impact of a floating oyster aquaculture farm on the intratidal dynamics of a low inflow estuary was investigated using field observations and an idealized numerical model. Measurements of current velocities, temperature, electrical conductivity, and velocity shear were collected around a floating oyster farm during two semidiurnal tidal cycles in a curved portion of the estuary. During flood, farm‐induced friction enhanced the lateral straining of velocity shears, which induced vertical mixing near the surface and extended the farm's frictional footprint. The streamwise flow reduction near the farm limited the development of lateral circulation. During ebb, flows largely bypassed the farm, which resulted in a weaker streamwise flow reduction through the farm and allowed the lateral circulation to develop across the estuary. To capture the farm effects in numerical simulations, a bulk drag coefficient for the farm was calculated as 8.4 × 10⁻³ ± 9.1 × 10⁻⁴, while the drag for a single cage ranged from 0.58 to 0.92. An idealized simulation in the Regional Ocean Modeling System (ROMS) demonstrated that the limited development of lateral circulation during flood was due to farm‐imposed friction rather than the combined influence of channel‐shoal morphology and the natural channel bend. These results showed that even though a farm may encompass a small portion of the estuary, it can affect the momentum and mixing outside of the immediate farm area. Therefore, it is important to consider the hydrodynamic responses of farms in estimates of carrying capacity and siting decisions.

The Damariscotta River in midcoast Maine is a weakly stratified estuary characterized by several constrictions and channel bends that affect tidal asymmetry and material transport. Microstructure and current velocity measurements were collected at a cross‐channel transect in the northern reach of the estuary during spring and neap tidal conditions to study the effects of a channel bend immediately upstream of a constricted sill on intratidal dynamics. During the flood phase, a counterclockwise gyre is formed upstream of the headland, which enhances landward‐directed flow in the channel and is countered by seaward‐directed flow over the shallow shoal. Semidiurnal and quarter‐diurnal patterns of lateral advection and stress divergence emerge in the surface layer because of these secondary flows. Lateral advection effects dominate the dynamics in neap tide, and although they are stronger in spring tide, they are partially obscured by bottom friction forces that are proportional to the along‐channel velocity squared. A novel harmonic decomposition technique is introduced to determine the relative importance of advection and stress divergence on quarter‐diurnal velocity generation, and their implications to neap/spring variability in estuarine water quality are discussed.