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

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 tideinducing 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.

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

“…Although the river discharge (figure 2 e) remains small throughout the study, freshwater has a clear impact on the Dee hydrodynamics as periodic stratification was observed (Bolaños et al, 2013), which is consistent with values of the horizontal Richardson number (Brown et al, subm) (this issue).…”

“…However, more detailed studies are still required to better understand the sediment transport patterns and budgets. Bolaños et al (2013) assessed the relative contributions of several physical processes to the overall circulation in the Dee Estuary.…”

Effective energy controls on flocculation under various wave-current regimes

“…The Dee is tidally dominated with a tidal range of about 10 m during spring tides and currents of more than 1 m•s −1 on the surface and nearly 0.5 m•s −1 near the seabed (Bolaños et al, 2013). Tides are significantly distorted due to the shallow nature of the estuary and tidal asymmetry results in flood dominance on sandy and muddy shallow areas, and weaker ebb dominance in the channels (Moore et al, 2009).…”

“…baroclinic behaviour remains important in the estuary, with stratification, tidal straining, wind and friction all having a role in the hydrodynamics of both channels (Bolaños et al, 2013). Nevertheless, the residual spring tide is more important for the circulation of the Welsh Channel, while baroclinicity is more important for the circulation of the Hilbre Channel .…”

Impact of operational model nesting approaches and inherent errors for coastal simulations

“…However, validation has shown it is still capable of simulating the frontal position, although the small scale variability is lost requiring the need for an additional high resolution nest in Liverpool Bay (Bricheno et al, 2014). Numerous studies validating the third 180 m nested model against observations (e.g., Bolaños et al, 2013;Brown et al, 2013;Amoudry et al, 2014;Bricheno et al, 2014;Ramirez-Mendoza et al, 2014;Brown et al, 2015) gives confidence in this 1.8 km to 180 m nested configuration.…”