Research

27 pages, 10986 KiB

Open AccessArticle

On the Dependency of Bottom Drag and the Eddy Viscosity upon Flow Structure in the Coastal Boundary Layer

by Yao-Zhao Zhong, Hwa Chien, Meng-Yu Lin, Anna Wargula and Jia-Lin Chen

J. Mar. Sci. Eng. 2022, 10(3), 324; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10030324 - 25 Feb 2022

Cited by 1 | Viewed by 1536

The physical processes governing coastal exchange between the surf zone, the inner shelf, and the open ocean is critical for estimating mass exchange and its impact on ecological processes. The present study combined field measurements and theoretical approaches to explore the hydrodynamics in [...] Read more.

The physical processes governing coastal exchange between the surf zone, the inner shelf, and the open ocean is critical for estimating mass exchange and its impact on ecological processes. The present study combined field measurements and theoretical approaches to explore the hydrodynamics in the coastal boundary layer (CBL) in which both bottom drag and shore friction affect the transport and mixing processes. Observed drifter-cluster trajectories in a nearly alongshore-uniform coastal area showed that the occurrence of current reversal varies with cross-shore distance, which confirmed the tidal phase difference between different cross-shore distances predicted by the proposed CBL model. According to the CBL model, tidal phase difference is affected by the bottom drag coefficient and horizontal eddy viscosity coefficient. With the results of three experiments under different wave conditions, this study also discusses the effects of waves on the CBL. Data analysis based on observations indicates that the bottom drag term is closely related to the bottom shear stress induced by the interactions of waves and currents. The bottom drag coefficient under the more energetic wave condition was much greater than that under milder wave conditions during the experiment. The study also suggests that in addition to pressure gradient and bottom drag, flow structure is subject to lateral stress, which reflects the impact of shoreline roughness in the nearshore region and that the estimated eddy viscosity coefficient decreases linearly with distance from the shoreline. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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27 pages, 7346 KiB

Open AccessArticle

The Effects of Tidal Translation on Wave and Current Dynamics on a Barred Macrotidal Beach, Northern France

by Arnaud Héquette, Adrien Cartier and François G. Schmitt

J. Mar. Sci. Eng. 2021, 9(8), 909; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse9080909 - 22 Aug 2021

Cited by 1 | Viewed by 2229

Abstract

Barred macrotidal beaches are affected by continuous horizontal displacements of different hydrodynamic zones associated with wave transformation (shoaling, breaker and surf zones) due to significant tide-induced water level changes. A series of wave and current meters, complemented by a video imagery system, were [...] Read more.

Barred macrotidal beaches are affected by continuous horizontal displacements of different hydrodynamic zones associated with wave transformation (shoaling, breaker and surf zones) due to significant tide-induced water level changes. A series of wave and current meters, complemented by a video imagery system, were deployed on a barred beach of northern France during a 6-day experiment in order to characterize the spatial and temporal variability of wave-induced processes across the beach. Wave and current spectral analyses and analyses of cross-shore current direction and asymmetry resulted in the identification of distinct hydrodynamic processes, including the development of infragravity waves and offshore-directed flows in the breaker and surf zones. Our results revealed a high spatial variability in the hydrodynamic processes across the beach, related to the bar-trough topography, as well as significant variations in the directions and intensity of cross-shore currents at fixed locations due to the horizontal translation of the different hydrodynamic zones resulting from continuous changes in water level due to tides. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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19 pages, 4262 KiB

Open AccessFeature PaperArticle

On the Tidal Prism: The Roles of Basin Extension, Bottom Friction and Inlet Cross-Section

by Marco Petti, Sara Pascolo, Silvia Bosa and Nadia Busetto

J. Mar. Sci. Eng. 2021, 9(1), 88; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse9010088 - 15 Jan 2021

Cited by 6 | Viewed by 2151

Abstract

The prism of the Lignano tidal inlet was approximately constant over the last forty years, although the section width has halved. This has led to questions concerning the factors that most influence the tidal prism, and on the applicability of the well-known A–P [...] Read more.

The prism of the Lignano tidal inlet was approximately constant over the last forty years, although the section width has halved. This has led to questions concerning the factors that most influence the tidal prism, and on the applicability of the well-known A–P relationship. A conceptual scheme of the sea–channel–lagoon system has been used to perform a sensitivity analysis of different parameters that characterize both the basin and the inlet cross-section. A 2D hydrodynamic model has been applied to evaluate the prism and compare it to the one derived by a static method, which is the basis of the analytical derivation of the A–P linkage. Three regimes have been found in the prism variability as a function of the basin extension: a linear static regime between prism and basin area; an asymptotic regime in which the prism depends only on the basin bottom friction; and an intermediate one. In addition, the roles of the inlet and channel sizes on the prism value have been investigated. The results, compared to the empirical relationships between the prism and the inlet cross-section, show that a variation in the cross-sectional area does not always corresponds to a change in tidal prism. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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17 pages, 2786 KiB

Open AccessArticle

Tidal and Storm Impacts on Hydrodynamics and Sediment Dynamics in an Energetic Ebb Tidal Delta

by Kehui Xu, P. Ansley Wren and Yanxia Ma

J. Mar. Sci. Eng. 2020, 8(10), 810; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse8100810 - 19 Oct 2020

Cited by 4 | Viewed by 2245

Abstract

Bottom-mounted instrumentation was deployed at two sites on a large sandy shoal of an ebb tidal delta offshore of the Port Royal Sound of South Carolina of USA to collect hydrodynamics and sediment dynamics data. One site (“borrow site”) was 2 km offshore [...] Read more.

Bottom-mounted instrumentation was deployed at two sites on a large sandy shoal of an ebb tidal delta offshore of the Port Royal Sound of South Carolina of USA to collect hydrodynamics and sediment dynamics data. One site (“borrow site”) was 2 km offshore in a dredge pit for nearby beach nourishment and the other site (“reference site”) was 10 km offshore. In situ time-series data were collected during two periods after the dredging: 15 March–12 June (spring) and 18 August–18 November (fall) of 2012. Data at the reference site indicated active migrating bedforms from centimeters to decimeters tall, and sediment concentrations were highly associated with semidiurnal and fortnightly tidal cycles. In the fall deployment, waves at the reference site were higher than those at the shallow borrow site. Both Tropical Storm Beryl and Hurricane Sandy formed high waves and strong currents but did not generate the greatest sediment fluxes. The two sites were at different depths and distances offshore, and waves contributed more to sediment mobility at the reference site whereas tidal forcing was the key controlling factor at the borrow site. This study provides valuable datasets for the selection of sites, prediction of pit infilling, and the modeling of storm impact in future beach nourishment and coastal restoration projects. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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23 pages, 3849 KiB

Open AccessArticle

Modeling of Breaching-Generated Turbidity Currents Using Large Eddy Simulation

by Said Alhaddad, Lynyrd de Wit, Robert Jan Labeur and Wim Uijttewaal

J. Mar. Sci. Eng. 2020, 8(9), 728; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse8090728 - 21 Sep 2020

Cited by 8 | Viewed by 2051

Abstract

Breaching flow slides result in a turbidity current running over and directly interacting with the eroding, submarine slope surface, thereby promoting further sediment erosion. The investigation and understanding of this current are crucial, as it is the main parameter influencing the failure evolution [...] Read more.

Breaching flow slides result in a turbidity current running over and directly interacting with the eroding, submarine slope surface, thereby promoting further sediment erosion. The investigation and understanding of this current are crucial, as it is the main parameter influencing the failure evolution and fate of sediment during the breaching phenomenon. In contrast to previous numerical studies dealing with this specific type of turbidity currents, we present a 3D numerical model that simulates the flow structure and hydrodynamics of breaching-generated turbidity currents. The turbulent behavior in the model is captured by large eddy simulation (LES). We present a set of numerical simulations that reproduce particular, previously published experimental results. Through these simulations, we show the validity, applicability, and advantage of the proposed numerical model for the investigation of the flow characteristics. The principal characteristics of the turbidity current are reproduced well, apart from the layer thickness. We also propose a breaching erosion model and validate it using the same series of experimental data. Quite good agreement is observed between the experimental data and the computed erosion rates. The numerical results confirm that breaching-generated turbidity currents are self-accelerating and indicate that they evolve in a self-similar manner. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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18 pages, 10085 KiB

Open AccessArticle

Hydrodynamic Measurements of Propagating Waves at Different Nearshore Depths in Hujeong Beach, Korea

by Jong Dae Do, Yeon S. Chang, Jae-Youll Jin, Weon Mu Jeong, Byunggil Lee and Ho Kyung Ha

J. Mar. Sci. Eng. 2020, 8(9), 690; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse8090690 - 07 Sep 2020

Cited by 2 | Viewed by 1675

Abstract

This paper reports the results of hydrodynamic measurements at two different water depths to observe wave properties in the course of wave propagation, especially during storm periods, in Hujeong Beach, Korea. In addition to hydrodynamic measurements, video monitoring data and satellite images from [...] Read more.

This paper reports the results of hydrodynamic measurements at two different water depths to observe wave properties in the course of wave propagation, especially during storm periods, in Hujeong Beach, Korea. In addition to hydrodynamic measurements, video monitoring data and satellite images from Sentinel-II were employed to compare the temporal changes in shoreline positions and shallow water bathymetry during the storms. Through combination of a variety of observational data sets, the accuracy of analysis could be enhanced by preventing possible misinterpretation. Two significant storms were observed from two experiments conducted at different times and locations of the beach. The hydrodynamic conditions were similar in both of the periods in terms of wave and current conditions as well as wave nonlinearity such as skewness. However, the response of shoreline during the two storms was the opposite because it was eroded during the first storm but advanced during the second storm. This suggests that other controlling factors such as storm duration need to be investigated to support the analysis of cross-shore sediment transport and consequent shoreline evolution for future studies. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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15 pages, 5177 KiB

Open AccessArticle

Data-Driven Analysis of Stratified Flow Effect on Suspended Sediment Concentration in an Estuary

by Heui-Jung Seo, Minsang Cho and Hyun-Doug Yoon

J. Mar. Sci. Eng. 2020, 8(8), 606; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse8080606 - 14 Aug 2020

Cited by 2 | Viewed by 1909

Abstract

An estuary is an area where a complex circulation pattern appears due to various hydrodynamic parameters such as tides, river discharge, salinity and water density. Especially during a flood, a large amount of freshwater discharge from a river can cause stratified flows due [...] Read more.

An estuary is an area where a complex circulation pattern appears due to various hydrodynamic parameters such as tides, river discharge, salinity and water density. Especially during a flood, a large amount of freshwater discharge from a river can cause stratified flows due to the difference in density between freshwater and seawater. This makes it difficult to understand the mechanism of behavior of the suspended sediment concentration in an estuary. To elucidate this problem, we investigated field observation data in the Gyeongin Port area in South Korea during the rainy period. It was found that there were stratified flow features of flow velocity, salinity and temperature between the upper and lower layers due to the abruptly increased amount of freshwater from a river in the rainy period. An artificial neural network (ANN), one of the data-driven modeling techniques, was applied to inductively analyze the hydrodynamic factors affecting the suspended sediment concentration in the estuary. The ANN model showed the best performance when including river discharge, and flow velocity and salinity measured at the surface and bottom layer. This shows that stratified flow is important to understand the behavior of suspended sediment concentration in the estuary. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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23 pages, 9002 KiB

Open AccessFeature PaperArticle

Estimation of Longshore Sediment Transport Using Video Monitoring Shoreline Data

by Jung-Eun Oh, Yeon S. Chang, Weon Mu Jeong, Ki Hyun Kim and Kyong Ho Ryu

J. Mar. Sci. Eng. 2020, 8(8), 572; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse8080572 - 30 Jul 2020

Cited by 4 | Viewed by 2425

Abstract

Video monitoring systems (VMS) have been used for beach status observation but are not effective for examining detailed beach processes as they only measure changes to the shoreline and backshore. Here, we extracted longshore sediment transport (LST) from VMS in order to investigate [...] Read more.

Video monitoring systems (VMS) have been used for beach status observation but are not effective for examining detailed beach processes as they only measure changes to the shoreline and backshore. Here, we extracted longshore sediment transport (LST) from VMS in order to investigate long- and short-term littoral processes on a pocket beach. LST estimated by applying one-line theory, wave power, and the oblique angle of incident waves were used to understand shoreline changes caused by severe winter storms. The estimated LST showed good agreement with the shoreline changes because the sediments were trapped at one end of the pocket beach and the alongshore direction of transported sediments was corresponded to the direction of LST. The results also showed that the beach that was severely eroded during storms was also rapidly recovered following the evolution of LST, which indicates that the LST may play a role in the recovery process while the erosion was mainly caused by the cross-shore transport due to storm waves. After the beach was nourished, beach changes became more active, even under lower wave energy conditions, owing to the equilibrium process. The analysis presented in this study could be applied to study inhomogeneous beach processes at other sites. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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