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Sizing a Small Tidal Inlet for Restoration
Chan, M.C., 2023. Sizing a small tidal inlet for restoration. Journal of Coastal Research, 39(4), 610–624. Charlotte (North Carolina), ISSN 0749-0208. Coastal inlets located on active shorelines can be vulnerable to shoaling and closure. It is not uncommon for some of these inlets to fall under the category of small tidal inlets with cross-sectional areas <100 m2 and to be transitional in stability characteristics such that neither the classic large-inlet O'Brien-Jarrett equilibrium formulas nor the small-inlet Byrne stability criteria apply fully. The Flax Pond inlet, a dual-jettied small inlet located on the south shore of Long Island Sound, New York, is an example of this class of inlets. The inlet, which connects Flax Pond, a degraded tidal marsh embayment, to Long Island Sound, was analyzed to support a proposed plan to reconstruct the twin jetties and restore the pond's tidal prism to its conditions in the early 1970s to prevent further loss of wetland and ecosystem diversity. The lack of directly suitable stability criteria presented a challenge because an extrapolative use of unsuitable criteria could entail unacceptable risks. The issue necessitated a comprehensive, process-driven analysis of the littoral and inlet conditions to frame a solution. An approach involving multiple stability criteria was followed to determine the inlet dimensions needed to achieve the restoration objectives. It was demonstrated that, with a process-based understanding and informed assumptions, a transitional small inlet can be sized with reasonable confidence.
Journal Article
Modelling double emulsion formation in planar flow-focusing microchannels
Double emulsion formation in a hierarchical flow-focusing channel is systematically investigated using a free-energy ternary lattice Boltzmann model. A three-dimensional formation regime diagram is constructed based on the capillary numbers of the inner ($Ca_{i}$), middle ($Ca_{m}$) and outer ($Ca_{o}$) phase fluids. The results show that the formation diagram can be classified into periodic two-step region, periodic one-step region, and non-periodic region. By varying$Ca_{i}$and$Ca_{m}$in the two-step formation region, different morphologies are obtained, including the regular double emulsions, decussate regimes with one or two alternate empty droplets, and structures with multiple inner droplets contained in the continuous middle phase thread. Bidisperse behaviours are also frequently encountered in the two-step formation region. In the periodic one-step formation region, scaling laws are proposed for the double emulsion size and for the size ratio between the inner droplet and the overall double emulsion. Furthermore, we show that the interfacial tension ratio can greatly change the morphologies of the obtained emulsion droplets, and the channel geometry plays an important role in changing the formation regimes and the double emulsion sizes. In particular, narrowing the side inlets or the distance between the two side inlets promotes the conversion from the two-step formation regime to the one-step formation regime.
Journal Article
Feeding Ecology of a Larval Fish Assemblage During its Passage Through a Coastal Inlet in the Northwestern Gulf of Mexico
Throughout the Gulf of Mexico (GoM), coastal inlets provide vital pathways for marine fish larvae spawned offshore to reach estuarine nursery habitat. While survivorship of fish larvae is dependent on many factors, feeding success has been highlighted as the most important. Currently, little is known about the feeding ecology of larval fish during their passage through coastal inlets. The purpose of this study was to investigate the trophodynamics of fish larvae passing through a GoM estuarine tidal inlet during a fall spawning season. Several trophic niches existed within the δ13C’ and δ15N’ (lipid and baseline corrected values) stable isotope-derived food web of larval fish, with multiple taxa present within most trophic niches. These trophic niches changed throughout the fall season, however. Micropogonias undulatus, an estuarine-dependent species common to the region, was selected for a closer look at dietary shifts through ontogeny and showed an overall shift to higher trophic level prey with size, although there was not yet evidence of a shift towards estuarine prey indicative of settlement. Their diet mainly consisted of Calanoida copepods across all sizes of larvae with significant electivity for only Acartia (Calanoida), and this selection was likely due to a difference in behavior rather than taxonomy or size. This study provides information about larval fish trophodynamics at coastal inlets, advancing our understanding of larval fish survivorship and recruitment to adult fish stocks.
Journal Article
Water Exposure Time Distributions Controlled by Freshwater Releases in a Semi‐Enclosed Estuary
Freshwater diversions manage water shortages, salinity, and control floodwater by redirecting river flows; however, their full ecological and hydrological impact remains unknown. This study examines the Lake Pontchartrain Estuary in Louisiana using a hydrodynamic model and Lagrangian particle tracking to assess how diversion operations (open, closed) and tributary discharge levels (low, median, high) influence water exposure time—the cumulative duration water remains in a domain, including re‐entry. Exposure time was analyzed based on the time required for 50%, 75%, and 90% of released particles (E50 ${E}_{50}$, E75 ${E}_{75}$, and E90 ${E}_{90}$) to leave a defined region of interest (ROI). Results show that when the diversion is open, high tributary discharge reduces exposure times by 51% compared to low discharge. In contrast, when closed, tributary discharge has minimal effect. To identify zones vulnerable to poor water quality due to stagnant water, the spatial heterogeneity of exposure time was evaluated using two metrics: system‐wide (time water remains in a system) and localized (time water remains within a ROI) exposure times. The spatial distribution and magnitude of increased exposure times varied between metrics and tributary discharge, highlighting the complexity of transport dynamics. For example, low tributary discharge led to larger isolated zones with longer system‐wide and localized exposure times. High tributary discharge created direct flow paths of diversion‐sourced water through tidal inlets, short‐circuiting the system and creating flow separation. These findings establish a framework for identifying transport mechanisms that influence exposure time and highlighting areas that may be vulnerable to poor water quality.
Journal Article
Recent Advances in Tidal Inlet Morphodynamic Modelling
Bertin, X.; Mengual, B.; de Bakker, A.; Guérin, T.; Martins, K.; Pezerat, M., and Lavaud, L., 2020. Recent advances in tidal inlet morphodynamics modelling. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1016–1020. Coconut Creek (Florida), ISSN 0749-0208. Tidal inlets connect the ocean to inner water bodies and are present worldwide. Complex interactions between tides, waves and shallow bathymetry often drive fast morphological changes but the underlying processes remain only partly understood. To better understand these processes, the development and application of morphodynamic models represents a unique perspective. This paper evaluates the impact of recent developments in the modelling system SCHISM, which include: a WENO method to solve the Exner Equation, a 3D coupling between waves and currents using a vortex force formalism, an adaptive parameterization for the dissipation of short waves by breaking and improved representations for wave-induced sediment transport. In order to evaluate the relevance of these developments, SCHISM is applied to the Maumusson Inlet, a mixed-energy inlet located on the Western Coast of France. Model-data comparison reveals firstly that complex wave-current interactions take place over the inlet ebb-delta, that include partial wave blocking during the ebb. Compared to classical 2DH approaches, our improved modelling system better reproduces the dynamics of adjacent beaches, inlet migration under oblique waves and sediment infilling of the main channel under storm waves. The relevance of these developments is demonstrated at the mixed-energy Maumusson Inlet (France).
Journal Article
Sediment Bypassing Pathways between Tidal Inlets and Adjacent Beaches
Beck, T.M.; Wang, P.; Li, H., and Wu, W., 2020. Sediment bypassing pathways between tidal inlets and adjacent beaches. Journal of Coastal Research, 36(5), 897–914. Coconut Creek (Florida), ISSN 0749-0208. This study investigated the sediment transport pathways in three sandy barrier, tidal inlet systems through sediment tracking within a numerical model that simulates hydrodynamics and morphodynamics. The three tidal inlet systems, Coos Bay, Oregon, Shark River Inlet, New Jersey, and John's Pass, Florida, represented high-, medium-, and low-wave energy regimes for U.S. inlets (Pacific, Atlantic, and Gulf of Mexico Coasts, respectively). Three methods employed to define sediment pathways from the results of a numerical morphology model were evaluated: (1) morphodynamic interpretation, (2) mean transport vectors across the modeled inlet, and (3) sediment tracer migration. The sediment tracing methodology employed in this study allowed for an evaluation of the sediment transport pathways between the various morphologic features of a tidal inlet, as well as their respective processes that drive the exchange of sediments. Characterizing and correlating the dominant and subdominant, or seasonal, sediment pathways between tidal inlet morphologic features (sediment reservoirs) can improve long-term models of an inlet sediment system. Divergences in pathways to subfeature shoals of a complex tidal inlet shoal, such as the updrift and downdrift shoals of an ebb-tidal delta, can be resolved through tracking sediment migration. The results of this study illustrate the value of including sediment-tracking techniques in simulating sediment bypassing and the potential of this application to inform coastal engineering and design modifications to the sediment reservoirs of tidal inlet systems.
Journal Article
Controls on Shoreline Changes at Pluri-annual to Secular Timescale in Mixed-energy Rocky and Sedimentary Estuarine Systems
Chaumillon, E.; Cange, V.; Gaudefroy, J.; Mercle, T.; Bertin, X., and Pignon, C., 2019. Controls on shoreline changes at pluri-annual to secular timescale in mixed-energy rocky and sedimentary estuarine systems. In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 135-156. Coconut Creek (Florida), ISSN 0749-0208. This article examines the morphological evolution of 27 beaches, including sandy and mixed sandy and rocky beaches, located along a 460 km-long complex shoreline, indented by four incised-valleys. The wave climate, simulated numerically from 1999 to 2017 in front of each beach, allows distinguishing between exposed and sheltered beaches. The morphological changes are quantified at two time scales: the last two centuries, from old maps and aerial photos, and the last two decades, from topographic profiles, aerial photos and satellite images. The first-order parameters explaining most of the spatial variations in the shoreline evolutions are the presence or absence of bedrock outcrops in the foreshore and/or shoreface and the presence or absence of tidal inlets close to the beach. The fastest shoreline changes are observed along exposed sandy beaches close to tidal inlets, whereas moderate to slow evolutions are mainly observed along exposed beaches with rocky foreshore and sheltered beaches. Huge shoreline changes located close to tidal inlets are related to changes in littoral drift orientation and intensity, themselves related to changes in beach orientation. Maximum erosion rates at a decadal time scale are not associated with isolated exceptional storms, but rather with clusters of storms. Beaches evolutions on this indented shoreline are controlled by geological factors (coastal orientation and the basement topography) and display complex patterns that cannot be clearly related to past changes in wave climate and sea level rise, complicating the prediction of their future evolutions.
Journal Article