Morphodynamics of a Nontidal Embayed Beach: The Case Study of Is Arutas (Western Mediterranean (original) (raw)
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Morphodynamics of a wave dominated embayed beach on an irregular rocky coastline
Brazilian Journal of Oceanography
Wave-dominated embayed beaches on irregular rocky coastlines are highly appreciated for their landscapes and tourism potential. Yet our understanding about the interaction of the oceanographic processes with the geological inheritance in this type of beaches still needs further investigation to better understand their natural balance. In this study, we apply the classical approach of morphodynamics to describe for the first time the variations in the Boiçucanga beach morphology, an embayed beach located in São Sebastião City on an irregular rocky coastline that is well known for its beautiful beaches embedded in the valleys of Serra do Mar. Field surveys were performed over 15 months, between April 2008 and September 2009, seeking to evaluate the interactions among the morphology, sediments and hydrodynamic characteristics at Boiçucanga. All data generated during the field surveys have supported the application of the following morphodynamic models: Classification of morphological b...
Morphodynamics of Embayed Beaches. Case Study in Cape Buzios, Rio de Janeiro, Brazil
Cape Buzios is a balneary touristic county located 180 km east of Rio de Janeiro city, Brazil. The geological site is composed by metassedimentary and metavolcanic rocks originated from a Cambrian and Ordovician (530-490 Ma) collisional event named Buzios Orogeny. The main characteristic of Cape Buzios is distinct structurally controlled beaches. The objective of this paper is to present results of morphodynamics of embayed beaches exposed to distinct wave's directions and relate it to the morphological response of beach profiles. Thirteen different beach profiles were monitored during four years in seven embayed beaches using standard topographic methods, resulting in over 250 beach profile data. Wind and wave data statistics; morphodynamic and embayment scale parameters; equilibrium profiles; closure depth; and planform stability were also calculated. Results led to the identification of three different morphodynamic conditions. The first two are low energy reflective and high energy intermediate beaches that are morphologically stable. In the first case beaches are narrow and equilibrated with their transversal profile. Closure depths vary from 3 to 6 meters. In the second case beaches are overfilled with sediments which even in high energy conditions permit rapid morphological recovery, closure depths are up to 20 meters. The third morphodynamic condition refers to unstable beaches that also have two different characteristics: one group of beaches presents permanently erosional profiles, while the other group presents episodic erosional profiles. The differences were in the range of exposition to higher waves and the volume of nearshore sediments available. Estimated maximum wave heights of 1,3; 2,4 and 5,4 meters can be respectively correlated for each one of the morphodynamic conditions described above.
Beach Morphodynamics and Profile Sequence for a Headland Bay Coast
2001
This paper presents a sequence of beach profile for a headlands and bay coast. Shape analyses of the embayed beach, identification of the predominant wave direction, beach and nearshore profiles, sedimentology characteristics, hydrodynamic conditions at the beaches, morphodynamics and morphometric data for 17 beaches on central-north coast of Santa Catarina, Brazil, were obtained. Beaches are classified in three main groups: (1) exposed; (2) semi-exposed; and (3) sheltered. The exposed beaches had an indentation ratio smaller than 0.39 and the dominant south waves are approximately parallel to the coast (angle smaller than 40°). The beaches can be divided into three mainly groups. (a) Reflective beaches have coarse sand (0.59mm-0.94mm) and steeper nearshore slope (1:40) associated with a very narrow coastal plain <1Km). (b) Intermediate beaches with one nearshore bar have medium sand (0.30mm-0.45mm) and gentle nearshore slope (1:100-1:200) and a developed coastal plain-island bar...
Dynamics of single-barred embayed beaches
2011
The dynamics of single submerged sandbars of two artificial embayed beaches (La Barceloneta and Bogatell, Barcelona, NW Mediterranean) has been studied with a video-recorded data set of 4.3 years. The alongshoreaveraged cross-shore migration, the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions, alongshore sediment transport and shoreline variability. In general, the submerged bars follow the general cyclic morphological behaviour observed in natural beaches, switching among the four intermediate morphodynamic states, but the studied beaches can be arrested during long periods of low wave conditions. The dominant up-state transition in Barcelona beaches during storms is the transition toward the rhythmic bar and beach state, the complete morphodynamic reset (longshore bar and trough state) only occurring during extreme wave events. The cross-shore migration of bars is dominated by the weekly and interannual components. The interannual component shows an onshore bar migration trend at both beaches, in contrast with the net offshore migration observed in multibarred open beaches. Bar disposition is located progressively seaward in the dominant alongshore transport direction (i.e., oblique with respect to the shoreline). At La Barceloneta beach, shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found, suggesting that alongshore transport can play a significant role in barline orientation. Finally, bar sinuosity increases during eastern storms in both beaches. This indicates that the formation of crescentic bars occurs for approximately shore-normal waves. Some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves (beach indentation).
Medium time-scale behaviour of adjacent embayed beaches: Influence of low energy external forcing
Medium term (decadal) beach profile response to external forcing was assessed on two adjacent embayed beaches (North and South Sands) in Pembrokeshire, West Wales. Both have contrasting physical and geological characteristics: a headland bay backed by dunes and a constrained embayment backed by geological promontories, promenades, walls and rock revetments. Paired t-tests showed significant changes at all cross-shore profile locations (95% confidence), with south and north shores respectively exhibiting falling and rising beach levels. South to north sediment transport was revealed by volumetric variation (r ¼ 0.83), and longshore sediment distribution (r ¼ 0.91). North Beach level variations lagged behind South Beach by one-year (r ¼ 0.85). A reduction in high wind speed frequency, coincidental to spring tides, was correlated with falling South Beach levels (r ¼ 0.87) and rising North Beach levels (r ¼ 0.92). Heavily refracted Atlantic swells also have contrasting effects on these systems. Multiple regression models applied to beach level change for both systems showed high correlation (R2 ¼ 0.93 and 0.85 respectively), suggesting that swell wave period and strong north-westerly winds that occur during high spring tides had cumulative effects. Furthermore, variations in the North Atlantic Oscillation (NAO) index were correlated to cumulative changes in mean sea level, wind wave height and south-westerly winds (R2 ¼ 0.75). While NAO variations were linked to variations in South Beach morphology, it was insignificant on North Beach (r ¼ 0.72 and 0.14 respectively). Cross-correlation analyses showed that North Beach morphological changes lagged behind NAO Index variation by oneyear with much improved correlation (r ¼ 0.77). A similar scenario existed when comparing Mean Sea level and beach level differences (r ¼ 0.54 and 0.32 respectively). Similar behaviour should be exhibited at other worldwide embayments, and it is suggested that this work is repeated to establish specific responses, to will underpin intervention or no active intervention strategie
Morphodynamics of Fetch-Limited Beaches in Contrasting Environments
2009
Sandy beaches can be found in fetch-limited environments that are protected from ocean generated waves, as estuaries, lagoons, and backbarriers, and where fetch characteristics allow local wind-generated waves to develop and maintain a beach. The morphodynamics of these low-energy beaches present a peculiar behaviour and general open-ocean models are inappropriate for their study. The main objective of this work is the development of a fetch-limited beach classification scheme based on the relative importance of wave, tidal and river flow forcing. This objective was pursue through the study of the evolutionary pattern of two fetch-limited beaches located in two different Portuguese systems, Alfeite (in Tagus Estuary) and Ancão backbarrier (in Ria Formosa barrier system). Results show that both beaches display a typical fetch-limited profile, with a narrow reflective beach face and a wide dissipative tidal flat, and that profile shape exhibits small changes without a seasonal pattern typical of ocean beaches. At Alfeite, profile changes are restricted to the beach face and result from low-frequency extreme events (strong wind generated waves, Hs>0.5m). At Ancão, although major morphologic changes are also related to the beach face, which is typical behaviour of wave dominated beaches, sediment transport, mainly driven by tidal currents, extends through the entire profile. A tentative fetch-limited beach classification, based on the relative importance of wave and tide effects, is presented.
Geological control of beach morphodynamic state
Marine Geology, 2005
The concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid-1980s and expansion in the 1990s. Much of the pioneering work was undertaken in Australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3-dimensional morphology and the Dean's parameter (H b /W s T) was established. Subsequently, the Relative Tidal Range parameter (H b /TR) was extended to beaches of all tidal ranges.
Morphological Response of a Macrotidal Embayed Beach, Porsmilin, France
Journal of Coastal Research, 2016
Morphodynamics of sandy, macrotidal, embayed beaches is complex because of the numerous physical processes interacting at the same location over a wide range of temporal scales. As most of these processes are controlled by beach morphology, dynamic feedbacks are generally observed between hydro-and morphodynamics. Investigating short-term processes is essential in order to improve long term morphological prediction. A key question is to understand how beach slope reacts to forcing conditions, in particular the response time of the beach profile, how long the transient state lasts. This study deals with the spatial and temporal responses of beach morphology to varying incident conditions. Here we report main observations, preliminary results and ongoing investigations on the DYNATREZ1 field campaign, which was conducted in the framework of the National Observation Service Dynalit. Beach profiles are shown to adapt rapidly to forcing conditions, within two days, with more intense variations observed in the high tide swash zone. The presence of infragravity waves and their dissipation on the beach is highlighted. It is likely that the very large variability in beach slope observed over a single neap-spring cycle is responsible for the accordingly large variability in wave skewness, asymmetry and breaking processes, and thus in sediment fluxes and morphological changes.
Morphodynamics of Embayed Beaches Case Study in Cape Buzios
Cape Buzios is a balneary touristic county located 180 km east of Rio de Janeiro city, Brazil. The geological site is composed by metassedimentary and metavolcanic rocks originated from a Cambrian and Ordovician (530-490 Ma) collisional event named Buzios Orogeny. The main characteristic of Cape Buzios is distinct structurally controlled beaches. The objective of this paper is to present results of morphodynamics of embayed beaches exposed to distinct wave's directions and relate it to the morphological response of beach profiles. Thirteen different beach profiles were monitored during four years in seven embayed beaches using standard topographic methods, resulting in over 250 beach profile data. Wind and wave data statistics; morphodynamic and embayment scale parameters; equilibrium profiles; closure depth; and planform stability were also calculated. Results led to the identification of three different morphodynamic conditions. The first two are low energy reflective and high energy intermediate beaches that are morphologically stable. In the first case beaches are narrow and equilibrated with their transversal profile. Closure depths vary from 3 to 6 meters. In the second case beaches are overfilled with sediments which even in high energy conditions permit rapid morphological recovery, closure depths are up to 20 meters. The third morphodynamic condition refers to unstable beaches that also have two different characteristics: one group of beaches presents permanently erosional profiles, while the other group presents episodic erosional profiles. The differences were in the range of exposition to higher waves and the volume of nearshore sediments available. Estimated maximum wave heights of 1,3; 2,4 and 5,4 meters can be respectively correlated for each one of the morphodynamic conditions described above.
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)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(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 (R 2 = 0.59) and intertidal (R 2 = 0.70) zones. This was confirmed qualitatively by OPEN ACCESS J. Mar. Sci. Eng. 2015, 3 2 time-series analysis and further cross correlation analysis showed trend reversal timelagged 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.