Sensitivity of tidal motion in well-mixed estuaries to cross-sectional shape, deepening, and sea level rise

Abstract

For well-mixed estuaries, key physical mechanisms are identified and quantified that cause changes in characteristics of the semi-diurnal sea surface elevation and lateral velocity due to modifications of the lateral bottom profile, channel deepening, and sea level rise. This is done by decomposing solutions of a new analytical model into components relating to different physical processes. The default geometry and parameter values are representative for the Ems estuary, with a converging width and a reflective landward boundary. The default Gaussian lateral bottom profile is modified to obtain profiles with the same crosssectional area, but with a different skewness or steepness. Results show that a steeper lateral bottom profile leads to amplification of the sea surface elevation. The width convergence is shown to influence the resonance characteristics. Channel deepening and sea level rise result in amplification of the sea surface elevation until a resonance peak is reached. When flooding is incorporated, the amount of sea level rise at which maximum tidal amplification occurs is found to be about two times lower. When using a symmetric Gaussian bottom profile, the lateral tidal flow is determined by Coriolis deflection of longitudinal flow and lateral density gradients caused by differential salt advection. However, an additional lateral tidal flow component incorporating the effect of continuity related to sea level variations and longitudinal gradients in longitudinal flow is shown to become increasingly important for skewed lateral bottom profiles. Furthermore, the lateral flow due to the lateral density gradient is enhanced for bottom profiles with increased steepness.

Effects of sea-level rise on tides and sediment dynamics in a Dutch tidal bay

“…In a convergent basin, the responses of tidal amplitude to SLR is always stronger at the landward than the seaward ends, as found in our study ( Fig. 5b and f) and by Ensing et al (2015). Changing inlet cross-sectional area due to SLR, usually by inlet widening, can also alter tides in the bay due to changed choking effect (Passieri et al, 2016;Talke and Jay, 2020).…”

“…Secondly, in addition to water height, SLR-induced tidal variations in the shelf seas have significant impacts on estuarine and embayment dynamics. Tides in shelf seas exhibit nonlinear and nonuniform responses to SLR (Idier et al, 2017;Pickering et al, 2012), and these effects may penetrate or amplify in estuaries and bays (Ensing et al, 2015). Nevertheless, many previous studies on SLR effects on estuaries simply increased the water level, neglecting changes in the tidal characteristics at their coastal boundary (e.g., Hong and Shen, 2012;Holleman and Stacey, 2014).…”

“…found in a theoretical study that narrowing and deepening of small convergent estuaries tends to increase tidal amplitude and flood dominance, resulting in a hyper-turbid state. Deepening-induced stronger tidal amplitude is reported in the Ems (de Jonge et al, 2014), Hudson (Ralston et al, 2019), and Loire rivers , as well as the Cape Fear River estuary (Familkhalili and Talke, 2016), especially in the upper reach. Tidal responses to deepening also show intra-and intersystem variability due to the various deepening extents and characteristics of estuaries (Talke and Jay, 2020).…”

“…Although challenging, tidal changes due to SLR have been modeled in both idealized and realistic estuaries and bays (e.g., Hong and Shen, 2012;Pelling et al, 2013b;Holleman and Stacey, 2014;Ensing et al, 2015;Passeri et al, 2016;Du et al, 2018). Generally, studies with idealized (simplified) basin shapes cannot fully address the spatially nonuniform shoaling, reflection, and damping in realistic systems.…”

An Analytical Approach to Determining Resonance in Semi-Closed Convergent Tidal Channels

“…On the basis of simplified geometry and flow characteristics, some researchers even derived three-dimensional (3D) analytical solutions to describe the tidal motions in a semiclosed channel [e.g. Winant, 2007;Jiang and Feng, 2014;Ensing et al, 2015], or in a system of connected basins [e.g. Waterhouse et al, 2011].…”