Coastal Morphodynamics

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312).

Deadline for manuscript submissions: closed (29 February 2016) | Viewed by 61517

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Department of Physical Geography, Faculty of Geosciences, Utrecht University, P.O. Box 80.115, 3508 TC Utrecht, The Netherlands
Interests: nearshore waves; currents; coastal geomorphology; nourishments; aeolian processes; remote sensing; climate-change impacts
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Dear colleagues,

Coasts are often beautiful landscapes with high biodiversity and provide a large and rapidly growing proportion of the world’s population with living and working environments, recreation, food, and drinking water. Coasts are also one of the most dynamic natural features on Earth and are also under increasing pressure by human activities and climate change. This Special Issue has been launched to compile the current state-of-the-art and future perspectives in the understanding of coastal morphodynamics, the complex and perpetual interaction between waves, tides, currents, sediment, biota, morphology, and humans. A solid understanding of, and skills in, predicting coastal morphodynamics is critical if we wish to manage our coasts in a sustainable manner.

Contributions are invited that deal with the natural or human-induced dynamics of:

1. Sandy beaches/nearshore and coastal dunes

2. Barrier island systems, including tidal inlets/deltas, and wash-over systems

3. Tidal flats and salt marshes

4. Mangrove shorelines

5. Rock coasts

6. High-latitude coasts

Contributions can be based on field observations, including novel remote-sensing techniques, laboratory experiments, and/or morphodynamic modeling. The focus will be on coastal morphodynamics acting on time scales between days (e.g., a storm) and a century (e.g., human activities and climate-change effects).

Prof. Dr. Gerben Ruessink
Guest Editor

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Published Papers (11 papers)

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Research

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6596 KiB  
Article
Sandbar Migration and Shoreline Change on the Chirihama Coast, Japan
by Masatoshi Yuhi, Masayuki Matsuyama and Kazuhiro Hayakawa
J. Mar. Sci. Eng. 2016, 4(2), 40; https://doi.org/10.3390/jmse4020040 - 03 Jun 2016
Cited by 12 | Viewed by 5094
Abstract
Sandy beaches play a key role in regional tourism. It is important to understand the principal morphological processes behind preserving attractive beaches. In this study, morphological variation on the Chirihama Coast, Japan, an important local tourism resource, was investigated using two sets of [...] Read more.
Sandy beaches play a key role in regional tourism. It is important to understand the principal morphological processes behind preserving attractive beaches. In this study, morphological variation on the Chirihama Coast, Japan, an important local tourism resource, was investigated using two sets of field surveys. The objective was to analyze and document the multi-scale behaviors of the beach. First, long-term shoreline changes were examined based on shoreline surveys over the last two decades. Then, the middle-term behavior of multiple bar systems was analyzed based on the cross-shore profile surveys from 1998 to 2010. An empirical orthogonal function (EOF) analysis was conducted to capture the principal modes of the systematic bar migration. The shoreline analysis indicated a long-term eroding trend and showed that the seasonal variation has recently tended to increase. The profile analysis demonstrated that net offshore migrations of bars have been repeated with a return period of approximately four years. This general behavior of the bar system is similar to the net offshore migration phenomena observed at other sites in the world. EOF analysis revealed a relationship between bar configuration and middle-term variations in shoreline location; when a new bar is generated near the shoreline and a triple bar configuration is established, the shoreline tends to temporarily retreat, whereas the shoreline experiences an advance when the outer bar has most evolved. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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11246 KiB  
Article
A Conceptual Model for Spatial Grain Size Variability on the Surface of and within Beaches
by Edith Gallagher, Heidi Wadman, Jesse McNinch, Ad Reniers and Melike Koktas
J. Mar. Sci. Eng. 2016, 4(2), 38; https://doi.org/10.3390/jmse4020038 - 25 May 2016
Cited by 26 | Viewed by 6376
Abstract
Grain size on the surface of natural beaches has been observed to vary spatially and temporally with morphology and wave energy. The stratigraphy of the beach at Duck, North Carolina, USA was examined using 36 vibracores (~1–1.5 m long) collected along a cross-shore [...] Read more.
Grain size on the surface of natural beaches has been observed to vary spatially and temporally with morphology and wave energy. The stratigraphy of the beach at Duck, North Carolina, USA was examined using 36 vibracores (~1–1.5 m long) collected along a cross-shore beach profile. Cores show that beach sediments are finer (~0.3 mm) and more uniform high up on the beach. Lower on the beach, with more swash and wave action, the sand is reworked, segregated by size, and deposited in layers and patches. At the deepest measurement sites in the swash (~−1.4 to −1.6 m NAVD88), which are constantly being reworked by the energetic shore break, there is a thick layer (60–80 cm) of very coarse sediment (~2 mm). Examination of two large trenches showed that continuous layers of coarse and fine sands comprise beach stratigraphy. Thicker coarse layers in the trenches (above mean sea level) are likely owing to storm erosion and storm surge elevating the shore break and swash, which act to sort the sediment. Those layers are buried as water level retreats, accretion occurs and the beach recovers from the storm. Thinner coarse layers likely represent similar processes acting on smaller temporal scales. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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1683 KiB  
Article
Observation of Whole Flushing Process of a River Sand Bar by a Flood Using X-Band Radar
by Satoshi Takewaka
J. Mar. Sci. Eng. 2016, 4(2), 32; https://doi.org/10.3390/jmse4020032 - 04 May 2016
Cited by 6 | Viewed by 3979
Abstract
Morphological changes during a flood event in July 2010 were observed with X-band marine radar at the mouth of Tenryu River, Shizuoka, Japan. Radar images were collected hourly for more than 72 h from the beginning of the flood and processed into time-averaged [...] Read more.
Morphological changes during a flood event in July 2010 were observed with X-band marine radar at the mouth of Tenryu River, Shizuoka, Japan. Radar images were collected hourly for more than 72 h from the beginning of the flood and processed into time-averaged images. Changes in the morphology of the area were interpreted from the time-averaged images, revealing that the isolated river dune was washed away by the flood, the width of the river mouth increased gradually, and the river mouth terrace expanded radially. Furthermore, image analysis of the radar images was applied to estimate the migration speed of the brightness pattern, which is assumed to be a proxy of bottom undulation of the river bed. The migration was observed to be faster when the water level gradient between the river channel and sea increased. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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11801 KiB  
Article
Assessing Embayed Equilibrium State, Beach Rotation and Environmental Forcing Influences; Tenby Southwest Wales, UK
by Tony Thomas, Allan Williams, Nelson Rangel-Buitrago, Michael Phillips and Giorgio Anfuso
J. Mar. Sci. Eng. 2016, 4(2), 30; https://doi.org/10.3390/jmse4020030 - 08 Apr 2016
Cited by 12 | Viewed by 5293
Abstract
The morphological change of a headland bay beach—Tenby, West Wales, UK—was analysed over a 73-year period (1941–2014). Geo-referenced aerial photographs were used to extract shoreline positions which were subsequently compared with wave models based on storm event data. From the 1941 baseline, results [...] Read more.
The morphological change of a headland bay beach—Tenby, West Wales, UK—was analysed over a 73-year period (1941–2014). Geo-referenced aerial photographs were used to extract shoreline positions which were subsequently compared with wave models based on storm event data. From the 1941 baseline, results showed shoreline change rates reduced over time with regression models enabling a prediction of shoreline equilibrium circa 2061. Further temporal analyses showed southern and central sector erosion and northern accretion, while models identified long-term plan-form rotation, i.e., a negative phase relationship between beach extremities and a change from negative to positive correlation within the more stable central sector. Models were then used in conjunction with an empirical 2nd order polynomial equation to predict the 2061 longshore equilibrium shoreline position under current environmental conditions. Results agreed with previous regional research which showed that dominant south and southwesterly wave regimes influence south to north longshore drift with counter drift generated by less dominant easterly regimes. The equilibrium shoreline was also used to underpin flood and inundation assessments, identifying areas at risk and strategies to increase resilience. UK shoreline management plans evaluate coastal vulnerability based upon temporal epochs of 20, 50 and 100 years. Therefore, this research evaluating datasets spanning 73 years has demonstrated the effectiveness of linear regression in integrating temporal and spatial consequences of sea level rise and storms. The developed models can be used to predict future shoreline positions aligned with shoreline management plan epochs and inform embayed beach shoreline assessments at local, regional and international scales, by identifying locations of vulnerability and enabling the development of management strategies to improve resilience under scenarios of sea level rise and climate change. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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1419 KiB  
Article
Dynamics of Small-Scale Topographic Heterogeneity in European Sandy Salt Marshes
by Kelly Elschot and Jan P. Bakker
J. Mar. Sci. Eng. 2016, 4(1), 21; https://doi.org/10.3390/jmse4010021 - 03 Mar 2016
Cited by 4 | Viewed by 4358
Abstract
Heterogeneity can boost biodiversity, as well as increase the resilience of an ecosystem to changing environmental conditions; therefore, it is important to understand how topographic heterogeneity in ecosystems is formed. Sandy tidal marshes have a repetitive pattern of higher elevated hummocks surrounded by [...] Read more.
Heterogeneity can boost biodiversity, as well as increase the resilience of an ecosystem to changing environmental conditions; therefore, it is important to understand how topographic heterogeneity in ecosystems is formed. Sandy tidal marshes have a repetitive pattern of higher elevated hummocks surrounded by lower elevated depressions, representing topographic heterogeneity at the scale of a few square meters. The aims of this study were to determine when this topographic heterogeneity forms, how it is structured, and whether it persists during marsh development. The soil topography of marshes consists of coarse-grained sediment formed before marsh vegetation development, with an overlaying fine-grained sediment layer formed after initial marsh development. To gain insight into the formation of topographic heterogeneity, we studied the underlying soil topography of four European sandy marshes, where topographic heterogeneity at a scale of a few square meters was present. The differences in elevation between hummocks and depressions can either be caused by heterogeneity in the coarse-grained sediment or by heterogeneity in the top layer containing the fine-grained sediment. Our results showed that the largest percentage of elevational differences between hummocks and depressions could be attributed to heterogeneity in the underlying coarse-grained substratum. Therefore, we conclude that the patterns in all four marshes were primarily formed before marsh development, before fine-grained sediment was deposited on top of the coarse-grained sediment. However, a smaller percentage of the elevational difference between hummocks and depressions can also be explained by the presence of thicker fine-grained sediment layers on top of hummocks compared with depressions. This implies that marsh accretion rates were higher on hummocks compared with depressions. However, this result was limited to very early stages of marsh development, as marsh accretion rates estimated on marshes ranging between 15- and 120-years-old showed that depressions actually accreted sediments at a significantly faster rate than hummocks. Eventually, the patterns of heterogeneity stabilized and we found similar marsh accretion rates on hummocks and in depressions in the 120-year-old marsh, which resulted in the persistency of these topographic patterns. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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11499 KiB  
Article
On the Intersite Variability in Inter-Annual Nearshore Sandbar Cycles
by Dirk-Jan R. Walstra, Daan A. Wesselman, Eveline C. Van der Deijl and Gerben Ruessink
J. Mar. Sci. Eng. 2016, 4(1), 15; https://doi.org/10.3390/jmse4010015 - 25 Feb 2016
Cited by 22 | Viewed by 4485
Abstract
Inter-annual bar dynamics may vary considerably across sites with very similar environmental settings. In particular, the variability of the bar cycle return period (Tr) may differ by a factor of 3 to 4. To date, data studies are only partially [...] Read more.
Inter-annual bar dynamics may vary considerably across sites with very similar environmental settings. In particular, the variability of the bar cycle return period (Tr) may differ by a factor of 3 to 4. To date, data studies are only partially successful in explaining differences in Tr, establishing at best weak correlations to local environmental characteristics. Here, we use a process-based forward model to investigate the non-linear interactions between the hydrodynamic forcing and the morphodynamic profile response for two sites along the Dutch coast (Noordwijk and Egmond) that despite strong similarity in environmental conditions exhibit distinctly different Tr values. Our exploratory modeling enables a consistent investigation of the role of specific parameters at a level of detail that cannot be achieved from observations alone, and provides insights into the mechanisms that govern Tr. The results reveal that the bed slope in the barred zone is the most important parameter governing Tr. As a bar migrates further offshore, a steeper slope results in a stronger relative increase in the water depth above the bar crest which reduces wave breaking and in turn reduces the offshore migration rate. The deceleration of the offshore migration rate as the bar moves to deeper water—the morphodynamic feedback loop—contrasts with the initial enhanced offshore migration behavior of the bar. The initial behavior is determined by the intense wave breaking associated with the steeper profile slope. This explains the counter-intuitive observations at Egmond where Tr is significantly longer than at Noordwijk despite Egmond having the more energetic wave climate which typically reduces Tr. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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6147 KiB  
Article
Natural and Human-Induced Dynamics on Big Hickory Island, Florida
by Tiffany M. Roberts Briggs and Nicole Elko
J. Mar. Sci. Eng. 2016, 4(1), 14; https://doi.org/10.3390/jmse4010014 - 22 Feb 2016
Cited by 2 | Viewed by 6128
Abstract
Big Hickory Island, located in Lee County along the mixed-energy west Florida coast, experiences high long-term rates of shoreline recession, with much of the erosion concentrated along the central and southern portions of the island. In 2013, approximately 86,300 cubic meters of sand [...] Read more.
Big Hickory Island, located in Lee County along the mixed-energy west Florida coast, experiences high long-term rates of shoreline recession, with much of the erosion concentrated along the central and southern portions of the island. In 2013, approximately 86,300 cubic meters of sand from an adjacent tidal inlet to the north were placed along 457 m to restore the beach and dune system. In an effort to combat erosion, seven concrete king-pile groins with adjustable panels were constructed subsequent to the completion of the beach nourishment. Natural and human-induced dynamics of Big Hickory Island are discussed through analysis of shoreline and morphologic change using historic aerial photographs and topographic and bathymetric field surveys of the recent beach erosion mitigation project. Although much of the long-term anomalously high rates of erosion for the area are related to natural interchanges between the sand resources of the barrier islands and adjacent ebb tidal shoals, additional reduction in sand supply is a result of human-interventions updrift of Big Hickory over the last several decades. The coupled natural and anthropogenic influences are driving the coastal processes toward a different morphodynamic state than would have occurred under natural processes alone. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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6744 KiB  
Article
Geometry of Wave-Formed Orbital Ripples in Coarse Sand
by Gerben Ruessink, Joost A. Brinkkemper and Maarten G. Kleinhans
J. Mar. Sci. Eng. 2015, 3(4), 1568-1594; https://doi.org/10.3390/jmse3041568 - 21 Dec 2015
Cited by 12 | Viewed by 5979
Abstract
Using new large-scale wave-flume experiments we examine the cross-section and planform geometry of wave-formed ripples in coarse sand (median grain size D50 = 430 μm) under high-energy shoaling and plunging random waves. We find that the ripples remain orbital for the full [...] Read more.
Using new large-scale wave-flume experiments we examine the cross-section and planform geometry of wave-formed ripples in coarse sand (median grain size D50 = 430 μm) under high-energy shoaling and plunging random waves. We find that the ripples remain orbital for the full range of encountered conditions, even for wave forcing when in finer sand the ripple length λr is known to become independent of the near-bed orbital diameter ds (anorbital ripples). The proportionality between λr and ds is not constant, but decreases from about 0.55 for ds / D50 ≈ 1400 to about 0.27 for ds / D50 ≈ 11 , 500 . Analogously, ripple height ηr increases with ds, but the constant of proportionally decreases from about 0.08 for ds / D50 ≈ 1400 to about 0.02 for ds / D50 > 8000 . In contrast to earlier observations of coarse-grained two-dimensional wave ripples under mild wave conditions, the ripple planform changes with the wave Reynolds number from quasi two-dimensional vortex ripples, through oval mounds with ripples attached from different directions, to strongly subdued hummocky-type features. Finally, we combine our data with existing mild-wave coarse-grain ripple data to develop new equilibrium predictors for ripple length, height and steepness suitable for a wide range of wave conditions and a D50 larger than about 300 μm. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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8077 KiB  
Article
Mesoscale Morphological Change, Beach Rotation and Storm Climate Influences along a Macrotidal Embayed Beach
by Tony Thomas, Nelson Rangel-Buitrago, Michael R. Phillips, Giorgio Anfuso and Allan T. Williams
J. Mar. Sci. Eng. 2015, 3(3), 1006-1026; https://doi.org/10.3390/jmse3031006 - 02 Sep 2015
Cited by 10 | Viewed by 5990
Abstract
Cross-shore profiles and environmental forcing were used to analyse morphological change of a headland bay beach: Tenby, West Wales (51.66 N; −4.71 W) over a mesoscale timeframe (1996–2013). Beach profile variations were attuned with longer term shoreline change identified by previous research showing [...] Read more.
Cross-shore profiles and environmental forcing were used to analyse morphological change of a headland bay beach: Tenby, West Wales (51.66 N; −4.71 W) over a mesoscale timeframe (1996–2013). Beach profile variations were attuned with longer term shoreline change identified by previous research showing southern erosion and northern accretion within the subaerial zone and were statistically significant in both sectors although centrally there was little or no significance. Conversely a statistically significant volume loss was shown at all profile locations within the intertidal zone. There were negative phase relationships between volume changes at the beach extremities, indicative of beach rotation and results were statistically significant (p < 0.01) within both subaerial (R2 = 0.59) and intertidal (R2 = 0.70) zones. This was confirmed qualitatively by time-series analysis and further cross correlation analysis showed trend reversal time-lagged associations between sediment exchanges at either end of the beach. Wave height and storm events displayed summer/winter trends which explained longer term one directional rotation at this location. In line with previous regional research, environmental forcing suggests that imposed changes are influenced by variations in southwesterly wind regimes. Winter storms are generated by Atlantic southwesterly winds and cause a south toward north sediment exchange, while southeasterly conditions that cause a trend reversal are generally limited to the summer period when waves are less energetic. Natural and man-made embayed beaches are a common coastal feature and many experience shoreline changes, jeopardising protective and recreational beach functions. In order to facilitate effective and sustainable coastal zone management strategies, an understanding of the morphological variability of these systems is needed. Therefore, this macrotidal research dealing with rotational processes across the entire intertidal has significance for other macrotidal coastlines, especially with predicted climate change and sea level rise scenarios, to inform local, regional and national shoreline risk management strategies. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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Review

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7216 KiB  
Review
Quantitative Estimates of Bio-Remodeling on Coastal Rock Surfaces
by Marta Pappalardo, Markus Buehler, Alessandro Chelli, Luca Cironi, Federica Pannacciulli and Zhao Qin
J. Mar. Sci. Eng. 2016, 4(2), 37; https://doi.org/10.3390/jmse4020037 - 26 May 2016
Cited by 13 | Viewed by 5100
Abstract
Remodeling of rocky coasts and erosion rates have been widely studied in past years, but not all the involved processes acting over rocks surface have been quantitatively evaluated yet. The first goal of this paper is to revise the different methodologies employed in [...] Read more.
Remodeling of rocky coasts and erosion rates have been widely studied in past years, but not all the involved processes acting over rocks surface have been quantitatively evaluated yet. The first goal of this paper is to revise the different methodologies employed in the quantification of the effect of biotic agents on rocks exposed to coastal morphologic agents, comparing their efficiency. Secondly, we focus on geological methods to assess and quantify bio-remodeling, presenting some case studies in an area of the Mediterranean Sea in which different geological methods, inspired from the revised literature, have been tested in order to provide a quantitative assessment of the effects some biological covers exert over rocky platforms in tidal and supra-tidal environments. In particular, different experimental designs based on Schmidt hammer test results have been applied in order to estimate rock hardness related to different orders of littoral platforms and the bio-erosive/bio-protective role of Chthamalus ssp. and Verrucariaadriatica. All data collected have been analyzed using statistical tests to evaluate the significance of the measures and methodologies. The effectiveness of this approach is analyzed, and its limits are highlighted. In order to overcome the latter, a strategy combining geological and experimental–computational approaches is proposed, potentially capable of revealing novel clues on bio-erosion dynamics. An experimental-computational proposal, to assess the indirect effects of the biofilm coverage of rocky shores, is presented in this paper, focusing on the shear forces exerted during hydration-dehydration cycles. The results of computational modeling can be compared to experimental evidence, from nanoscopic to macroscopic scales. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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Other

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17113 KiB  
Brief Report
Wave and Hydrodynamic Modeling for Engineering Design of Jetties at Tangier Island in Chesapeake Bay, USA
by Lihwa Lin, Zeki Demirbilek, Donald Ward and David King
J. Mar. Sci. Eng. 2015, 3(4), 1474-1503; https://doi.org/10.3390/jmse3041474 - 01 Dec 2015
Cited by 4 | Viewed by 7181
Abstract
The protection of a boat canal at the western entrance of Tangier Island, Virginia, located in the lower Chesapeake Bay, is investigated using different structural alternatives. The existing entrance channel is oriented 45 deg with respect to the local shoreline, and exposed directly [...] Read more.
The protection of a boat canal at the western entrance of Tangier Island, Virginia, located in the lower Chesapeake Bay, is investigated using different structural alternatives. The existing entrance channel is oriented 45 deg with respect to the local shoreline, and exposed directly to the lower Bay without any protection. The adjacent shoreline has experienced progressive erosion in recent decades by flooding due to severe storms and waves. To protect the western entrance of the channel and shoreline, five different jetty and spur combinations were proposed to reduce wave energy in the lee of jetties. Environmental forces affecting the proposed jettied inlet system are quantified using the Coastal Modeling System, consisting of a spectral wave model and a depth-averaged circulation model with sediment transport calculations. Numerical simulations were conducted for design wave conditions and a 50-year return period tropical storm at the project site. Model results show a low crested jetty of 170-m length connecting to the north shore at a 45-deg angle, and a short south spur of 25-m long, provide adequate wave-reduction benefits among the five proposed alternatives. The model simulation indicates this alternative has the minimum impact on sedimentation around the structured inlet and boat canal. Full article
(This article belongs to the Special Issue Coastal Morphodynamics)
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