Modeling Tidal Hydrodynamics of the Montrose Tidal Inlet System: Ebb Jet and Eddy Formation at a Tidal Inlet with a High-Angle Half-Delta
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 150, Issue 6
Abstract
Montrose Bay’s coastline in Scotland is experiencing the most severe erosions, especially in its southern section, interfacing with the Montrose Tidal Inlet System. This inlet system could induce a distinct ebb tidal jet and eddy when ebbing, influenced by its high-angle half-delta, and the understanding of jet and eddy formation at this type of inlet is still limited. This paper presents the results of a numerical modeling study conducted using Delft3D FM to characterize tidal hydrodynamics at the Montrose Tidal Inlet System, emphasizing the flow features at its seaward side. Acoustic Doppler current profiler measurements captured an asymmetry between peak ebb and flood flow induced by the interaction between the residual of an ebb jet and the alongshore tidal current, which later was successfully replicated by the model, especially after a satellite-derived topography was applied to the Montrose Basin. The observed jet and eddy formation at the Montrose System is unique compared to what has appeared at other inlets with different delta shapes. At spring tides, the jet develops a pair of main and frontal bodies that extend more than 2 km from the inlet and experiences a sharp deflection after interacting with cross current. This jet is accompanied by only one transient eddy with about 1 km diameter at the landward side of the jet frontal. Analysis of residual flow revealed a strong residual going toward the harbor channel at adjacent beaches, which could be contributing to the ongoing sedimentation at the channel.
Practical Applications
This study is about a unique coastal current formation at the southern end of Montrose Bay, Scotland, United Kingdom, visualized through numerical modeling. The main feature of this current is a strong outflow, known as the ebb (tidal) jet, which forms during the ebbing phase. This ebb jet expands in the offshore direction before being strongly deflected to the North by the ambient current and simultaneously forming a counter-clockwise eddy within a region between the ebb jet and the beach. This unique coastal current formation is strongly influenced by the configuration between shoreline features, inlet positioning, and the ambient tidal current. This study further explores the potential relevance of this ebb jet and eddy to the ongoing erosion and sedimentation in and around the inlet. Furthermore, this research provides insights into various ebb jet and eddy formations observed at other inlets around the world and highlights the value of utilizing satellite-derived topography data for numerical modeling.
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Data Availability Statement
Data in this study are available from the corresponding author upon reasonable request.
Acknowledgments
This research was funded by the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Partnership. The Delft3D Flexible Mesh Suite used in this research is under the Deltares Beta Testing Program. ADCP measurements are provided by Angus Council and Partrac Ltd. This research also used data from Edina-Digimap, UKHO Admiralty Seabed Mapping, NatureScot, Dynamic Coast, SEPA, NRFA, Copernicus Dataspace, and Microsoft Bing Map Services. The authors thank Jack Poleykett and Martin Mannion for the helpful discussion. The authors also acknowledge the insightful comments provided by the two anonymous reviewers.
Notation
The following symbols are used in this paper:
- C
- Chezy coefficient (m1/2/s)
- Csmag
- Smagorinsky coefficient (−);
- d50
- median grain sizes (μm);
- f
- Coriolis parameter (s−1);
- g
- gravitational acceleration (m/s2);
- H
- total water depth (m);
- M
- modeled data (−);
- N
- number of data (−);
- O
- observed data (−);
- P
- pressure (Pa);
- q
- contribution of external discharges sinks/sources per unit area (m3/s/m2);
- r
- Pearson correlation coefficient (−)
- t
- time (s);
- U, V
- depth-averaged velocity components in x- and y-directions (m/s);
- v
- kinematic viscosity (m2/s)
- vback
- background viscosity (m2/s);
- x, y
- Cartesian coordinate axes (m);
- ΔS
- characteristic length scale (m);
- ρ
- water density (kg/m3); and
- τb,x, τb,y
- bed shear stress in x- and y-directions (N/m2).
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Information
Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 150 • Issue 6 • November 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Feb 8, 2024
Accepted: Jun 21, 2024
Published online: Sep 2, 2024
Published in print: Nov 1, 2024
Discussion open until: Feb 2, 2025
ASCE Technical Topics:
- Analysis (by type)
- Bodies of water (by type)
- Coastal engineering
- Coastal processes
- Coasts, oceans, ports, and waterways engineering
- Continuum mechanics
- Eddy (fluid dynamics)
- Engineering fundamentals
- Engineering mechanics
- Fluid dynamics
- Fluid mechanics
- Hydraulic engineering
- Hydraulic structures
- Hydrodynamics
- Hydrologic engineering
- Hydrologic models
- Inlets (waterway)
- Models (by type)
- Numerical analysis
- Numerical models
- Ocean currents
- Structural engineering
- Structures (by type)
- Tides
- Water and water resources
- Water management
- Waterways
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