Tidal Channels of Skagit Bay: Three-Dimensional Hydrodynamics and Morphodynamic Evolution

2011 ◽  
Author(s):  
Stephen M. Henderson
Keyword(s):  
Three Dimensional ◽  
Tidal Channels ◽  
Morphodynamic Evolution

scholarly journals Intertwined eco-morphodynamic evolution of salt marshes and tidal channels cutting through them

2021 ◽  
Author(s):  
Liang Geng ◽  
Andrea D'Alpaos ◽  
Alessandro Sgarabotto ◽  
Zheng Gong ◽  
Stefano Lanzoni
Keyword(s):  
Salt Marshes ◽  
Tidal Channels ◽  
Morphodynamic Evolution

Sand bars in tidal channels. Part 1. Free bars

2001 ◽  
Vol 440 ◽  
pp. 49-74 ◽  
Author(s):  
G. SEMINARA ◽  
M. TUBINO
Keyword(s):  
Three Dimensional ◽  
Basic Mechanism ◽  
Critical Value ◽  
Suspended Load ◽  
Tidal Channels ◽  
Three Dimensional Model ◽  
Mean Values ◽  
Depth Ratio ◽  
Mean Width ◽  
The Mean

We investigate the basic mechanism whereby bars form in tidal channels or estuaries. The channel is assumed to be long enough to allow neglect of the effects of end conditions on the process of bar formation. In this respect, the object of the present analysis differs from that of Schuttelaars & de Swart (1999) who considered bars of length scaling with the finite length of the tidal channel. The channel bottom is assumed to be cohesionless and consisting of uniform sediments. Bars are shown to arise from a mechanism of instability of the erodible bed subject to the propagation of a tidal wave. Sediment is assumed to be transported both as bedload and as suspended load. A fully three-dimensional model is employed both for the hydrodynamics and for sediment transport. At the leading order of approximation considered, the effects of channel convergence, local inertia and Coriolis forces on bar instability are shown to be negligible. Unlike fluvial free bars, in the absence of mean currents tidal free bars are found to be non-migrating features (in the mean). Instability arises for large enough values of the mean width to depth ratio of the channel, for given mean values of the Shields parameter and of the relative channel roughness. The role of suspended load is such as to stabilize bars in the large-wavenumber range and destabilize them for small wavenumbers. Hence, for large values of the mean Shields stress, it turns out that the first critical mode (the alternate bar mode) is characterized by a very small value of the critical width to depth ratio. Furthermore, the order-m mode being characterized by a critical value of the width to depth ratio equal to m times the critical value for the first mode, it follows that for large values of the mean Shields stress several unstable modes are simultaneously excited for relatively low values of the aspect ratio. This suggests that the actual bar pattern observed in nature may arise from an interesting nonlinear competition among different unstable modes.

Three‐Dimensional Flow Structures and Morphodynamic Evolution of Microtidal Meandering Channels

2020 ◽  
Vol 56 (7) ◽  
Author(s):  
Alvise Finotello ◽  
Massimiliano Ghinassi ◽  
Luca Carniello ◽  
Enrica Belluco ◽  
Mattia Pivato ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Flow Structures ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Meandering Channels ◽  
Morphodynamic Evolution

Dunes and alternate bars in tidal channels

2011 ◽  
Vol 670 ◽  
pp. 558-580 ◽  
Author(s):  
PAOLO BLONDEAUX ◽  
GIOVANNA VITTORI
Keyword(s):  
Eddy Viscosity ◽  
Physical Mechanism ◽  
Three Dimensional ◽  
Critical Value ◽  
Algebraic Model ◽  
Suspended Load ◽  
Tidal Channels ◽  
Second Mode ◽  
Alternate Bars ◽  
Quantitative Results

A simple idealized model is proposed to predict the appearance of alternate bottom forms in tidal channels. The model is based on the linear stability analysis of the flat seabed driven by tidal currents. The hydrodynamics is described by means of the full three-dimensional continuity and Reynolds equations. To quantify turbulent stresses, the Boussinesq assumption is introduced and an algebraic model is used for the eddy viscosity. The morphodynamics is described by the Exner equation and a simple sediment transport predictor. When applied to tidal channels, the model predicts the appearance of alternate bottom forms if the channel width is larger than a critical value. This finding agrees with previous analyses. However, the results obtained show the existence of two different modes. Close to the conditions of incipient sediment motion or when the suspended load is intense, the model suggests the appearance of an alternate sequence of shoals and pools (the first mode), characterized by a wavelength which might be comparable with the horizontal excursion of the tide. However, under such circumstances, to provide accurate quantitative results, the model should be extended to include the effects of the local acceleration and of the possible variations of the depth and width of the channel, which are neglected in the analysis. In all the other conditions, the model predicts the appearance of a second mode, presently termed tidal alternate bars. This mode is geometrically similar to the first mode, i.e. it is characterized by depositional and erosional areas which are found in an alternate arrangement, but it has significantly shorter wavelengths. In this case, the wavelength of the bedforms scales with the water depth. The physical mechanism generating tidal alternate bars appears to be the same as that generating tidal dunes, and it cannot be described by means of a depth-averaged approach.

scholarly journals Tidal, Riverine, and Wind Influences on the Circulation of a Macrotidal Estuary

2013 ◽  
Vol 43 (1) ◽  
pp. 29-50 ◽  
Author(s):  
Rodolfo Bolaños ◽  
Jennifer M. Brown ◽  
Laurent O. Amoudry ◽  
Alejandro J. Souza
Keyword(s):  
River Flow ◽  
High Tide ◽  
Three Dimensional ◽  
Small Contribution ◽  
Residual Circulation ◽  
Tidal Channels ◽  
Tidal Straining ◽  
Macrotidal Estuary ◽  
Resolution Model ◽  
Fine Resolution

Abstract The effect of tides, river, wind and Earth’s rotation on the three-dimensional circulation in the Dee, a macrotidal estuary, are investigated using a fine-resolution model. The interactions of the large tidal amplitude, currents, river, and wind-generated circulation require baroclinic and unsteady studies to properly understand the estuarine dynamics. Assessment of the model skill has been carried out by model–observation comparisons for salinity, which is the main control for density, surface elevation, current, and turbulence. Stationary nondimensional numbers were only partially able to characterize the dynamics in this (real) complex macrotidal estuary. At low water, tidal straining and constrained river flow cause stratification. Large spatial variability occurs in the current and residual patterns, with flood-dominated maximum values occurring within the tidal channels. The tides control residual circulation by modulating stratification through tidal straining and bathymetric constraint on river flow. Tide–stratification–river interaction causes an unsteady pattern of residual circulation and tidal pulses. River-induced pulses are enhanced near low tide–inducing density-driven circulation. Wind effects are concentrated near the surface, mainly occurring at high tide because of increased fetch. Even though Coriolis has, overall, a small contribution it produces tidal pulses modifying the current and salinity distribution.

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