Editorial

3 pages, 158 KiB

Open AccessEditorial

by Matteo Postacchini and Alessandro Romano

J. Mar. Sci. Eng. 2019, 7(12), 451; https://doi.org/10.3390/jmse7120451 - 09 Dec 2019

Cited by 8 | Viewed by 2039

The coastal zone hosts many human activities and interests, which have significantly increased in the last few decades [...] Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

Research

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20 pages, 2927 KiB

Open AccessFeature PaperArticle

Beach Profile Evolution towards Equilibrium from Varying Initial Morphologies

by Sonja Eichentopf, Joep van der Zanden, Iván Cáceres and José M. Alsina

J. Mar. Sci. Eng. 2019, 7(11), 406; https://doi.org/10.3390/jmse7110406 - 09 Nov 2019

Cited by 17 | Viewed by 3829

Abstract

The evolution of different initial beach profiles towards the same final beach configuration is investigated based on large-scale experimental data. The same wave condition was performed three times, each time starting from a different initial profile morphology. The three different initial profiles are [...] Read more.

The evolution of different initial beach profiles towards the same final beach configuration is investigated based on large-scale experimental data. The same wave condition was performed three times, each time starting from a different initial profile morphology. The three different initial profiles are an intermediate energy profile with an offshore bar and a small swash berm, a plane profile and a low energy profile with a large berm. The three cases evolve towards the same final (equilibrium) profile determined by the same wave condition. This implies that the same wave condition generates different sediment transport patterns. Largest beach changes and differences in hydrodynamics occur in the beginning of the experimental cases, highlighting the coupling between morphology and hydrodynamics for beach evolution towards the same profile. The coupling between morphology and hydrodynamics that leads to the same final beach profile is associated with differences in sediment transport in the surf and swash zone, and is explained by the presence of bar and berm features. A large breaker bar and concave profile promote wave energy dissipation and reduce the magnitudes of the mean near-bed flow velocity close to the shoreline limiting shoreline erosion. In contrast, a beach profile with reflective features, such as a large berm and a small or no bar, increases negative velocity magnitudes at the berm toe promoting shoreline retreat. The findings are summarised in a conceptual model that describes how the beach changes towards equilibrium from two different initial morphologies. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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17 pages, 7515 KiB

Open AccessFeature PaperArticle

Direct Measurements of Bed Shear Stress under Swash Flows on Steep Laboratory Slopes at Medium to Prototype Scales

by Daniel Howe, Chris E. Blenkinsopp, Ian L. Turner, Tom E. Baldock and Jack A. Puleo

J. Mar. Sci. Eng. 2019, 7(10), 358; https://doi.org/10.3390/jmse7100358 - 09 Oct 2019

Cited by 6 | Viewed by 3341

Abstract

Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses [...] Read more.

Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses coincided with the arrival of uprush swash fronts and high-resolution measurement of swash surface profiles indicated a consistently seaward sloping swash surface with minimal evidence of a landward sloping swash front. The quadratic stress law was applied to back-calculate time-varying friction factors, which were observed to decrease with increasing Reynolds number on smooth slopes, consistent with theory for steady flows. Additionally, friction factors remained relatively constant throughout the swash cycle (except around flow reversal), with a variation of approximately ±20% from the mean value and with only small differences between uprush and backwash. Measured friction factors were observed to be larger than expected when plotted on the Moody or wave friction diagram for a given Reynolds number and relative roughness, consistent with previous field and laboratory studies at various scales. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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16 pages, 19858 KiB

Open AccessArticle

Hydrodynamic Effects Produced by Submerged Breakwaters in a Coastal Area with a Curvilinear Shoreline

by Francesco Gallerano, Giovanni Cannata and Federica Palleschi

J. Mar. Sci. Eng. 2019, 7(10), 337; https://doi.org/10.3390/jmse7100337 - 26 Sep 2019

Cited by 11 | Viewed by 2474

Abstract

A three-dimensional numerical study of the hydrodynamic effect produced by a system of submerged breakwaters in a coastal area with a curvilinear shoreline is proposed. The three-dimensional model is based on an integral contravariant formulation of the Navier-Stokes equations in a time-dependent curvilinear [...] Read more.

A three-dimensional numerical study of the hydrodynamic effect produced by a system of submerged breakwaters in a coastal area with a curvilinear shoreline is proposed. The three-dimensional model is based on an integral contravariant formulation of the Navier-Stokes equations in a time-dependent curvilinear coordinate system. The integral form of the contravariant Navier-Stokes equations is numerically integrated by a finite-volume shock-capturing scheme which uses Monotonic Upwind Scheme for Conservation Laws Total Variation Diminishing (MUSCL-TVD) reconstructions and an Harten Lax van Leer Riemann solver (HLL Riemann solver). The numerical model is used to verify whether the presence of a submerged coastal defence structure, in the coastal area with a curvilinear shoreline, is able to modify the wave induced circulation pattern and the hydrodynamic conditions from erosive to accretive. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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15 pages, 3161 KiB

Open AccessFeature PaperArticle

Experimental Observations of Turbulent Events in the Surfzone

by Francesca De Serio and Michele Mossa

J. Mar. Sci. Eng. 2019, 7(10), 332; https://doi.org/10.3390/jmse7100332 - 24 Sep 2019

Cited by 7 | Viewed by 2070

Abstract

In coastal dynamics, large-scale eddies transport and spread smaller turbulent vortices both towards the sea surface, thus contributing to the processes of air-water gas transfer, and towards the sea bottom, inducing sediment pick-up and resuspension. The mechanical role of the breaking-induced vortices to [...] Read more.

In coastal dynamics, large-scale eddies transport and spread smaller turbulent vortices both towards the sea surface, thus contributing to the processes of air-water gas transfer, and towards the sea bottom, inducing sediment pick-up and resuspension. The mechanical role of the breaking-induced vortices to the redistribution of turbulence and turbulent kinetic energy is still unclear and needs a more thorough study, possibly supported by more measurements in this field. Based on this, the present paper aims to investigate the effects of experimental breaking waves in the surf zone. Two regular breaking waves, a spiller and a plunger, which propagate on a fixed slope, were generated in a laboratory channel and were examined shoreward to the breaker line. The measurements of their velocities in the cross-shore plane were assessed by means of a 2D Laser Doppler Anemometer. At the same time and location, elevation data were also acquired using a resistive wave gauge. Here, the principal characteristics are addressed in terms of turbulent intensities, turbulent kinetic energy, length scales and coherent motions. Our results could thus contribute to better define conceptual models used in typical engineering applications in coastal areas. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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19 pages, 3290 KiB

Open AccessArticle

Combining Numerical Simulations and Normalized Scalar Product Strategy: A New Tool for Predicting Beach Inundation

by Matteo Postacchini and Giovanni Ludeno

J. Mar. Sci. Eng. 2019, 7(9), 325; https://doi.org/10.3390/jmse7090325 - 19 Sep 2019

Cited by 11 | Viewed by 2280

Abstract

The skills of the Normalized Scalar Product (NSP) strategy, commonly used to estimate the wave field, as well as bathymetry and sea-surface current, from X-band radar images, are investigated with the aim to better understand coastal inundation during extreme events. Numerical simulations performed [...] Read more.

The skills of the Normalized Scalar Product (NSP) strategy, commonly used to estimate the wave field, as well as bathymetry and sea-surface current, from X-band radar images, are investigated with the aim to better understand coastal inundation during extreme events. Numerical simulations performed using a Nonlinear Shallow-Water Equations (NSWE) solver are run over a real-world barred beach (baseline tests). Both bathymetry and wave fields, induced by reproducing specific storm conditions, are estimated in the offshore portion of the domain exploiting the capabilities of the NSP approach. Such estimates are then used as input conditions for additional NSWE simulations aimed at propagating waves up to the coast (flood simulations). Two different wave spectra, which mimic the actual storm conditions occurring along the coast of Senigallia (Adriatic Sea, central Italy), have been simulated. The beach inundations obtained from baseline and flood tests related to both storm conditions are compared. The results confirm that good predictions can be obtained using the combined NSP–NSWE approach. Such findings demonstrate that for practical purposes, the combined use of an X-band radar and NSWE simulations provides suitable beach-inundation predictions and may represent a useful tool for public authorities dealing with the coastal environment, e.g., for hazard mapping or warning purposes. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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14 pages, 3431 KiB

Open AccessFeature PaperArticle

The Influence of Free Long Wave Generation on the Shoaling of Forced Infragravity Waves

by Theo Moura and Tom E. Baldock

J. Mar. Sci. Eng. 2019, 7(9), 305; https://doi.org/10.3390/jmse7090305 - 04 Sep 2019

Cited by 9 | Viewed by 2711

Abstract

Different conceptual models for forced infragravity (long) waves exist in the literature, which suggest different models for the behavior of shoaling forced waves and the possible radiation of free long waves in that process. These are discussed in terms of existing literature. A [...] Read more.

Different conceptual models for forced infragravity (long) waves exist in the literature, which suggest different models for the behavior of shoaling forced waves and the possible radiation of free long waves in that process. These are discussed in terms of existing literature. A simple numerical model is built to evaluate the wave shape in space and time during shoaling of forced waves with concurrent radiation of free long waves to ensure mass continuity. The same qualitative results were found when performing simulations with the COULWAVE model using the radiation stress term in the momentum equation to force the generation and propagation of bound waves. Both model results indicate a strong frequency dependence in the shoaling rate and on the lag of the total long wave with respect to the forcing, consistent with observations in the literature and more complex evolution models. In this approach, a lag of the long wave is only observed in the time domain, not in the space domain. In addition the COULWAVE is used to investigate dissipation rates of incident free and forced long waves inside the surf zone. The results also show a strong frequency dependence, as previously suggested in the literature, which can contribute to the total rate of decay of the incident forced wave after short wave breaking. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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17 pages, 2792 KiB

Open AccessArticle

Downscaling Future Longshore Sediment Transport in South Eastern Australia

by Julian O’Grady, Alexander Babanin and Kathleen McInnes

J. Mar. Sci. Eng. 2019, 7(9), 289; https://doi.org/10.3390/jmse7090289 - 26 Aug 2019

Cited by 8 | Viewed by 3616

Abstract

Modelling investigations into the local changes in the shoreline resulting from enhanced atmospheric greenhouse gas concentrations and global climate change are important for supporting the planning of coastal mitigation measures. Analysis of Global Climate Model (GCM) and Regional Climate Model (RCM) simulations has [...] Read more.

Modelling investigations into the local changes in the shoreline resulting from enhanced atmospheric greenhouse gas concentrations and global climate change are important for supporting the planning of coastal mitigation measures. Analysis of Global Climate Model (GCM) and Regional Climate Model (RCM) simulations has shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in south-eastern Australia, is situated in a region that may experience noticeable future changes in longshore winds, waves and coastal currents, which could alter the supply of sediments to the shoreline. This paper will demonstrate a downscaling procedure for using the data from GCM and RCM simulations to force a local climate model (LCM) at the beach scale to simulate additional nearshore wind-wave, hydrodynamic and sediment transport processes to estimate future changes. Two types of sediment transport models were used in this study, the simple empirical coastline-type model (CERC equation), and a detailed numerical coastal area-type model (TELEMAC). The two models resolved transport in very different ways, but nevertheless came to similar conclusions on the annual net longshore sediment transport rate. The TELEMAC model, with the Soulsby-Van Rijn formulation, showed the importance of the contribution of storm events to transport. The CERC equation estimates more transport during the period between storms than TELEMAC. The TELEMAC modelled waves, hydrodynamics and bed-evolutions are shown to agree well with the available observations. A new method is introduced to downscale GCM longshore sediment transport projections using wave-transport-directional change parameter to modify directional wave spectra. We developed a semi-empirical equation (NMB-LM) to extrapolate the ~3.7-year TELEMAC, storm dominated transport estimates, to the longer ~30-year hindcast climate. It shows that the shorter TELEMAC modelled period had twice as large annual net longshore sediment transport of the ~30 year hindcast. The CERC equation does not pick up this difference for the two climate periods. Modelled changes to the wave transport are shown to be an order of magnitude larger than changes from storm-tide current and mean sea level changes (0.1 to 0.2 m). Discussion is provided on the limitations of the models and how the projected changes could indicate sediment transport changes in the nearshore zone, which could impact the coastline position. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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18 pages, 9128 KiB

Open AccessArticle

Experimental Analysis of Wave Overtopping: A New Small Scale Laboratory Dataset for the Assessment of Uncertainty for Smooth Sloped and Vertical Coastal Structures

by Hannah E Williams, Riccardo Briganti, Alessandro Romano and Nicholas Dodd

J. Mar. Sci. Eng. 2019, 7(7), 217; https://doi.org/10.3390/jmse7070217 - 13 Jul 2019

Cited by 25 | Viewed by 3735

Abstract

Most physical model tests carried out to quantify wave overtopping are conducted using a wave energy spectrum, which is then used to generate a free surface wave time series at the wave paddle. This method means that an infinite number of time series [...] Read more.

Most physical model tests carried out to quantify wave overtopping are conducted using a wave energy spectrum, which is then used to generate a free surface wave time series at the wave paddle. This method means that an infinite number of time series can be generated, but, due to the expense of running physical models, often only a single time series is considered. The aim of this work is to investigate the variation in the main overtopping measures when multiple wave times series generated from the same spectrum are used. Physical model tests in a flume measuring 15 m (length) by 0.23 m (width) with an operating depth up to 0.22 m were carried out using a stochastic approach on two types of structures (a smooth slope and a vertical wall), and a variety of wave conditions. Results show variation of overtopping discharge, computed by normalising the range of the discharges at a certain wave condition with the maximum value of the discharge in the range up to

10 %

, when the same wave time series is used, but this range increases to

75 %

when different time series are used. This variation is found to be of a similar magnitude to both the one found with similar experiments looking at the phenomena in numerical models, and that specified by the confidence bounds in empirical methods. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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27 pages, 2394 KiB

Open AccessArticle

Effects of Wave Orbital Velocity Parameterization on Nearshore Sediment Transport and Decadal Morphodynamics

by Marcio Boechat Albernaz, Gerben Ruessink, H. R. A. (Bert) Jagers and Maarten G. Kleinhans

J. Mar. Sci. Eng. 2019, 7(6), 188; https://doi.org/10.3390/jmse7060188 - 19 Jun 2019

Cited by 13 | Viewed by 4403

Abstract

Nearshore morphological modelling is challenging due to complex feedback between hydrodynamics, sediment transport and morphology bridging scales from seconds to years. Such modelling is, however, needed to assess long-term effects of changing climates on coastal environments, for example. Due to computational efficiency, the [...] Read more.

Nearshore morphological modelling is challenging due to complex feedback between hydrodynamics, sediment transport and morphology bridging scales from seconds to years. Such modelling is, however, needed to assess long-term effects of changing climates on coastal environments, for example. Due to computational efficiency, the sediment transport driven by currents and waves often requires a parameterization of wave orbital velocities. A frequently used parameterization of skewness-only was found to overfeed the coast unrealistically on a timescale of years—decades. To improve this, we implemented a recently developed parameterization accounting for skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare the effects of parameterizations on long-term coastal morphodynamics. We performed simulations with default and calibrated sediment transport settings, for idealized coastlines, and compared the results with measured data from analogue natural systems. The skewness-asymmetry parameterization was found to predict overall stable coastlines within the measured envelope with wave-related calibration factors within a factor of 2. In contrast, the original parameterization required stronger calibration, which further affected the alongshore transport rates, and yet predicted erosion in deeper areas and unrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up the possibility of more realistic long-term morphological modelling of complex coastal systems. Full article

(This article belongs to the Special Issue Dynamics of the Coastal Zone)

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