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Thresholds for morphological changes on an exposed Sandy beach as a function of wave height
Abstract
A sandy beach in the south of Portugal (Faro beach, Ria Formosa) was surveyed from the dune crest seaward to 15 m depth 20 times over a period of 26 months. Wave time-series between surveys were analysed to obtain relationships between wave height and vertical profile variations and to define wave thresholds for important morphological changes. Results show that the active zone of the profile lies between 5 m above and 10·4 m below mean sea level, and that there are clear cross-shore differences in the vertical variability of the profile. Based on the pattern of vertical variability, the profile was divided into four cross-shore sectors: A (berm), 20–80 m from the profile origin; B (sub-tidal terrace), 80–170 m; C (long-shore bar), 170–360 m; and D, 360–700 m. The relationship between the modulus of the maximum vertical change in each sector and the 99th percentile of significant wave height between surveys was always significant. Calculated thresholds for significant wave height generating important morphological changes were 2·3 m in sector A, 3·2 m in sectors B and C, and 4·1 m in sector D. Copyright © 2010 John Wiley & Sons, Ltd.
... Maximum recorded values of Hs can reach up to~7 m for W-SW storms (Almeida et al., 2011b). The definition of storm used in this study was provided by Almeida, Ferreira, and Pacheco (2011a) and Almeida et al. (2011b), where storms were defined as events with a significant wave height that exceeds 3 m and a minimum duration above the threshold of 3 hours. ...
... All surveys were performed in fair weather conditions, thereby minimising vertical errors, namely, those induced by wave action. Computed errors related to equipment and field operation comprise a vertical error of up to 610-15 cm, which is within the acceptable error for such surveys (Almeida, Ferreira, and Pacheco, 2011a). Interpolation (kriging interpolation) and grid calculations were performed using Surfer t 9 (Golden Software, Inc., 2009). ...
... Although the maximum Hs of each interval could have been used, a single high value could occur without necessarily inducing important morphological changes. The use of the 99th percentile is a way of expressing the maximum energy conditions for each interval analysed, excluding potential outliers at the same time (Almeida, Ferreira, and Pacheco, 2011a). ...
The morphological variability of a berm-bar system is highly dependent on wave conditions with direct consequences for the evolution of the nearby coast; however, an understanding of this variability based on field measurements is still lacking, in particular with respect to the assessment of both longshore and cross-shore components. In this study, the berm-bar morphological changes were assessed by simultaneously measuring longshore and cross-shore variability as well as the forcing mechanisms (i.e. wave conditions). A sandy beach in southern Portugal (Tavira Barrier Island, Ria Formosa) was surveyed from the dune crest to 20-m depth along six profiles over a period of 16 months. Wave time series between surveys were analysed to obtain relationships between wave conditions, the depth of closure, and berm-bar variations. For the surveyed period, waves approached mainly from the W-SW (78% of the time) and E-SE (18%), and eight moderate storms were recorded. Results show that the active zone of the profiles descends to 6 m below mean sea level (MSL), the maximum depth of closure registered. On the basis of the pattern of vertical variability, the profiles can be divided into three cross-shore sectors: A (emerged beach and berm), B (subtidal terrace), and C (submerged longshore bar). A new index (longshore vs. cross-shore "LvC") is proposed, relating the dominance of longshore or cross-shore processes to volumetric changes resulting from sediment transport. In the study area, cross-shore sediment transfer (LvC ∼ 0) dominated when the largest and longest storms occurred and is associated with storm erosion and poststorm recovery. Longshore dominance (LvC ∼ -1 and 1 for erosion and accretion, respectively) occurred during periods with smaller and shorter storms. The proposed index allows the relative roles of cross-shore vs. longshore processes in coastal areas with berm-bar interaction to be distinguished.
... It was stated at H s ≥ 2.5 m because it represented rare events in Cadiz area with only 10% of total amount in the 44 years (following the methodology of Dorsch et al., 2008). This value reflects the wave height at which erosion started to affect Faro and Cadiz areas, according to data and observations given by Anfuso and Gracia (2005); Rangel-Buitrago and Anfuso (2011b, 2011c); Plomaritis et al. (2009);Almeida et al. (2010); Ribera et al. (2011); Del Río et al. (2012) and Rangel-Buitrago (2013). The minimum storm duration was set at 12 h, since in this way the storm affected the coast at least during a complete tidal cycle (Morton et al., 1997;Dorsch et al., 2008;Rangel-Buitrago and Anfuso, 2013). ...
... Last, following Anfuso and Gracia (2005); Almeida et al. (2010); Rangel-Buitrago and Anfuso (2011aAnfuso ( , 2011b and Ribera et al. (2011), winter season was defined as the October to March period. ...
... Wave height presented seasonal variations (Rodríguez et al., 2003;Anfuso and Gracia, 2005;Almeida et al., 2010) but not a clear trend during the investigated period confirming previous observations from Almeida et al. (2011); Rangel-Buitrago and Anfuso (2011aAnfuso ( , 2011b; Bertin et al. (2013) and Plomaritis et al. (2015). ...
The present work deals with the characterization and classification of storm events affecting Cadiz Gulf, i.e.
the coast including Southern Portugal, SWSpain and Northern Morocco. The general morphology of the gulf and its location determine the exposition and trajectory of storms affecting the zone, producing significant energy gradients alongshore. This study focuses on the frequency and distribution of the different types of storms, in order to estimate their probability of
occurrence. Storm classification was obtained by using wave data records from the HIPOCAS (Hindcast of dynamic Processes of the Ocean and Coastal Areas of Europe) network. The Storm Power Index was used to classify coastal storms. The investigated data sets covered 44 years, between 1958 and 2001. A significant gradient in energy (Storm Power and storm class frequency), approaching direction and storm duration was observed along the gulf, from the most exposed points (Cape San Vicente–Portimão) to the inner, more sheltered ones (Faro–Huelva–Cadiz) and to the southern moderately exposed ones
(Bolonia–Tangier). Themonthly distribution of number of storms, duration and sum of Storm Power were compared bymeans of multiple and independent regression analysis with values of different climatic and meteorological indexes. Multiple linear regression analysis between storminess indices and the teleconnection patterns points out that 45% of the change in monthly storminess indices calculated along the Cadiz Gulf are related to changes in the teleconnection patterns, especially North
Atlantic Oscillation (NAO), Arctic Oscillation (AO) and East Atlantic (EA). Negative NAO and AO phases and positive EA phases correlate with storminess in the zone. Furthermore, when neutral to strong negative NAO–AO and positive EA phases occurred at the same time and/or when an abrupt change of theses indices occurred, then a greater number of storms with longer duration and higher Storm Power Index were recorded.
... It was stated at H s ≥ 2.5 m because it represented rare events in Cadiz area with only 10% of total amount in the 44 years (following the methodology of Dorsch et al., 2008). This value reflects the wave height at which erosion started to affect Faro and Cadiz areas, according to data and observations given by Anfuso and Gracia (2005); Rangel-Buitrago and Anfuso (2011b, 2011c); Plomaritis et al. (2009);Almeida et al. (2010); Ribera et al. (2011); Del Río et al. (2012) and Rangel-Buitrago (2013). The minimum storm duration was set at 12 h, since in this way the storm affected the coast at least during a complete tidal cycle (Morton et al., 1997;Dorsch et al., 2008;Rangel-Buitrago and Anfuso, 2013). ...
... Last, following Anfuso and Gracia (2005); Almeida et al. (2010); Rangel-Buitrago and Anfuso (2011aAnfuso ( , 2011b and Ribera et al. (2011), winter season was defined as the October to March period. ...
... Wave height presented seasonal variations (Rodríguez et al., 2003;Anfuso and Gracia, 2005;Almeida et al., 2010) but not a clear trend during the investigated period confirming previous observations from Almeida et al. (2011); Rangel-Buitrago and Anfuso (2011aAnfuso ( , 2011b; Bertin et al. (2013) and Plomaritis et al. (2015). ...
The present work deals with the characterization and classification of storm events affecting Cadiz Gulf, i.e. the coast including Southern Portugal, SWSpain and Northern Morocco. The general morphology of the gulf and its location determine the exposition and trajectory of storms affecting the zone, producing significant energy gradients alongshore. This study focuses on the frequency and distribution of the different types of storms, in order to estimate their probability of
occurrence. Storm classification was obtained by using wave data records from the HIPOCAS (Hindcast of dynamic Processes of the Ocean and Coastal Areas of Europe) network. The Storm Power Index was used to classify coastal storms. The investigated data sets covered 44 years, between 1958 and 2001. A significant gradient in energy (Storm Power and storm class frequency), approaching direction and storm duration was observed along the gulf, from the most exposed points (Cape
San Vicente–Portimão) to the inner, more sheltered ones (Faro–Huelva–Cadiz) and to the southern moderately exposed ones (Bolonia–Tangier). Themonthly distribution of number of storms, duration and sum of Storm Power were compared bymeans of multiple and independent regression analysis with values of different climatic and meteorological indexes. Multiple linear regression analysis between storminess indices and the teleconnection patterns points out that 45% of the change in monthly storminess indices calculated along the Cadiz Gulf are related to changes in the teleconnection patterns, especially North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and East Atlantic (EA). Negative NAO and AO phases and positive EA phases correlate with storminess in the zone. Furthermore, when neutral to strong negative NAO–AO and positive EA phases occurred at the same time and/or when an abrupt change of theses indices occurred, then a greater number of storms with longer duration and higher Storm Power Index were recorded.
... Recent studies on wave height extreme values, storm distribution and related beach changes along the Portuguese and Spanish coast of the Cadiz Gulf have been carried out by Rodríguez et al. (2003), Menéndez et al. (2004) and Almeida et al. (2010). The aim of this paper is to examine the relationship between different types of storm event and the morphological response of beaches in the Cadiz area (SW Spain). ...
... In order to quantify the impact of storms on morphological and volumetric changes at investigated beach locations, the profiles were sub-divided into different cross-shore sectors according to their morphological variability (Winant et al., 1975;Lee et al., 1998;Almeida et al., 2010). This entailed a detailed analysis of vertical variation of each profile and standard deviations were used to divide the overall profile into sectors and thereby identify the main active zones (Lee et al., 1998). ...
... Opposite behaviour was observed at Faro beach, which generally shows a clear reflective morphodynamic state (x = 1.15, Reyes et al., 1999;Almeida et al., 2010). This results in rapid erosion but quick recovery, in the order of days, this behaviour enhances the importance of storm groupiness on beach erosion. ...
The present work deals with storm classification, using the Storm Power Index, and beach morphological response to storm events in the Gulf of Cadiz (SW Spain). Over the 1958–2001 period, 377 events divided into five classes ranging from ‘weak’ to ‘extreme’ were characterized. Classes I (weak) and II (moderate) accounted for 60% and 23% of events, respectively. Class III (significant), were 9% of the recorded events and Classes IV (severe) and V (extreme) accounted for 5% and 2%, respectively. The probability of storm occurrence per year ranged from 93% for Class I to 15% for Class V. In order to characterize beach response to storm events, 214 beach profiles carried out with a monthly periodicity over the 1996–1998 period along the Chipiona-Rota littoral were analysed, as well as published data. Different beach types were observed: (i) ‘Intermediate’ beaches underwent important vertical relief changes ranging from 0.3 m to 1.33 m associated with average slope changes from tan β = 0.06 to tan β = 0.03; (ii) the ‘dissipative’ beaches were characterized by smaller and homogeneous foreshore vertical changes, from c. 0.36 m to 0.65 m, according to the parallel retreat mechanism characterized by small slope variations (from tan β = 0.025 to tan β = 0.035); and (iii) ‘intermediate with rock shore platform’ experienced small morphological and foreshore slope variations, related to both beach pivoting and parallel retreat mechanisms. The most important morphological changes were due to the impact of usually ‘weak’ and ‘moderate’ events during October and November that produced berm erosion and upper foreshore lowering, and the impact of ‘severe’, ‘significant’ and ‘extreme’ events in December and January which produced dune escarpment, overwash and/or damage to coastal structures. Copyright © 2011 John Wiley & Sons, Ltd.
... The possibility to obtain measurements through modern technologies in an interdisciplinary framework represents a development in the reliable understanding of the interactions between complex physical and biological processes occurring in beach environments. [44][45][46][47][48][49][50][51][52][53]; Sedimentology [54][55][56][57][58][59][60][61]; Sedimentology + Biology [17,27,[62][63][64][65][66][67][68][69][70]; Geophysics [71][72][73][74][75][76][77][78][79][80][81][82]. ...
... GPR: Ground Penetrating Radar, SSS Side Scan Sonar; SBP: Sub Bottom Profiler. Geomorphology[44][45][46][47][48][49][50][51][52][53]; Sedimentology[54][55][56][57][58][59][60][61] Sedimentology + Biology[62][63][64]17,27,[65][66][67][68][69][70]; Geophysics[71][72][73][74][75][76][77][78][79][80][81][82]. ...
This study focuses on the analysis of sandy beaches by integrating sedimentological, geomorphological, and geophysical investigations. The beach represents an extremely variable environment where different natural processes act simultaneously with human activities, leading to the gathering of different methodologies of the Earth Sciences to study its evolution in space and time. The aim of this research is to propose a potential procedure for monitoring the morpho-sedimentary processes of sandy beaches by analyzing the textural and compositional characteristics of the sands and quantifying the volumes involved in the coastal dynamics. The study area includes two Apulian sandy beaches (Torre Guaceto and Le Dune beach) that are representative of the coastal dynamics of a large sector of the central/northern Mediterranean Sea involving the southern Adriatic Sea and the northern Ionian Sea. Sedimentological and ecological investigations allowed to describe the textural and compositional characteristics of the beach sands by interpreting their sand provenance and the physical/biological interactions within the beach. The topographic surveys carried out with a Terrestrial Laser Scanner and an Optical Total Station, aimed to quantify the variations of sediment volume over time, whereas the Delft3d software was applied to analyze the effects of the dominant wave motion on the sedimentary dynamics. Lastly, the geophysical techniques which included Sub Bottom Profiler procedures, Ground Penetrating Radar investigation, and resistivity models enabled us to calculate the sand sediment thickness above the bedrock.
... Unfortunately, the survey carried out in 2009 did not cover the submerged beach and thus we lack the underwater profile for 2009. To overcome this limitation, we have extended the profiles by assuming an average underwater profile with support from previous data from Praia de Faro (Almeida et al., 2011). The authors document the cross-shore morphological variability of the profile, identifying zones of change within the active profile based on the pattern of vertical variability: the beach face with the formation and erosion of berms, the sub-tidal terrace with trough/bar generation between 1.5 and 4 m below MSL, the long-shore bar located between 4 and 6 m below MSL and the deeper part of the profile that reaches 10 m below MSL. ...
... For example, the wind model is the simplest possible model that will give a quantitatively reasonable approximation of the slowing down towards the dune foot, acceleration towards the crest and deceleration behind it. The wave-driven model, though relying on a heuristic fix to compensate for unresolved swash processes, now presents behaviour that is in agreement with observations (Almeida et al., 2011) and maintains reasonable profiles over years to decades. In the following we will discuss some important aspects in more detail. ...
A new dune profile model, Duna, is developed and coupled with the existing XBeach model, in which some key improvements allow a much better behaviour of the intertidal beach and the inclusion of structural erosion or accretion through a longshore transport gradient. The model is shown to represent typical behaviour of a beach-dune system in Praia de Faro, Portugal and to be able to simulate processes on a decadal timescale. The model captures a balance between longshore gradients and cross-shore processes in the surf zone, competing effects of moderate conditions and storms in the intertidal area and between build-up by storm waves and aeolian transport on the berm. Vegetation behaviour is shown to play a key role in the development of the shape of the foredunes. The relation between progradation or recession rate and foredune height as often reported in literature is reproduced and explained.
... Potential impacts of storms on beaches have driven researchers to identify thresholds above which forcing conditions trigger significant morphological changes in beach systems, especially over their subaerial portion. These studies are extremely important to coastal management and contribute to improve coastal risk assessment (Almeida et al., 2011(Almeida et al., , 2012Haerens et al., 2012;Burvingt et al., 2017), as loss of the buffer provided by the subaerial beach increases the probability of damage to coastal structures and land nearby. In addition, understanding the timescales and processes of beach recovery contributes to assess coastal resilience (Dodet et al., 2019). ...
Understanding time scales of beach response (erosion and recovery) to extreme storms is particularly relevant for management of coastal land and risk. Observations show that rock-bounded platform beaches are generally remarkably stable and only occasionally respond to extreme storm wave forcing with abrupt morphological changes. The present work aims to understand the conditions leading to the disruption of beach stability (storm thresholds for morphological changes) and to comprehend the conditions of the subsequent recovery.
Results obtained at two rock-bounded beaches of the western Portuguese coast over five years provided the foundations of a new conceptual morphodynamic model. This model explains abrupt beach disruption as a consequence of full inundation of the beach profile during extreme storms, together with strong wave reflection at the rigid landward boundary, causing major erosion of the subaerial beach. We argue that the timescale of post-storm recovery depends essentially on the fate of the sediment transported offshore during the storm event. If sediments remain within the beach sediment cell (underwater beach section) beach recovery to pre-storm conditions is very fast, while recovery is much slower if sediments exit the beach sediment cell. In the latter case, beach recovery depends on external sand sources, which can lead to recovery time scales of several years.
... In Mediterranean coastal regions, floods can be presented as a result of multiple forcings affecting different time scales: ; whereas, the episodic, short-term floods are the results of marine storm surges (Benavente et al. 2006;Bosom García and Jiménez Quintana 2011). A storm surge is the episodic rise in sea level caused by coastal winds, water circulation and atmospheric pressure (Vousdoukas et al. 2018), causing flooding of low-lying coasts, low-lying areas and the movement of sediments from the beaches to the open sea, hence coastal erosion (Almeida et al. 2011). Many studies have been carried out to assess the risk of marine flooding around the world, including Portugal (Ferreira et al. 2016), Spain (Ballesteros et al. 2018), Canada (Simard et al. 2015), United States (Finkl 2000), India (Saxena et al. 2013), Morocco (Niazi 2007). ...
Located in the south of the western Mediterranean, in the central Algerian region, the eastern coast of Cherchell is characterized by its ecological, agricultural, tourist, cultural and patrimonial vocations and by its low topography in many places. It has participated over time in the economic development of the region (agriculture and beach tourism). In recent years, this coast, like all the world's coastlines, has been subject to several coastal hazards such as marine flooding. Flooding is the most frequent and most important threat in terms of induced impacts, and therefore any management plan needs to assess it, noting that no such study has been carried out in the region despite its economic importance. The objective of this paper is to assess the land area flooded by extreme sea levels. Therefore, by combining a high-resolution numerical terrain model with geographic information systems (GIS), the areas at risk of flooding were mapped. The results indicate that most of the flooded land is at the annual return period of extreme sea levels, which is explained by the low topography of the beaches (Hamdania and Bella) and the wadi plains (El Hachem and El Bellaa) near the coast, whereas the extreme marine levels of hundred-year return period do not really exacerbate the flooding risks, due to the mountainous topography of the region which becomes progressively higher when moving away from the coast and the wadi plains. These results represent a basic tool for local managers and decision-makers to adapt planning practices and policies for a better management of these vulnerable areas, and a good adaptation in case of risk.
... Granulometric characteristics of the beach therefore, serve as a valuable information on the coastal processes and evolution (Pradhan et al., 2020;Suvarna et al., 2017;Bhat et al., 2002 ;Edwards, 2001). Many workers have traced the existence of direct relationship between the beach morphology, hydrodynamic conditions of deposition and depositional environment, and the characteristics of the sedimentary deposits (Thanh et al., 2018;Scott et al., 2011;Almeida et al., 2011;Reis and Gama, 2010;Schlacher et al., 2008;Wright et al., 1979Wright et al., , 1985. Every depositional environment is characterized by a specific range of energy conditions, and grain-size characteristics, which is a function of transport agents such as waves, tides and currents that operate in a depositional environment. ...
Beach morphologies, primarily include shape, surface changes/variation, and beach volume along with slope, are very dynamic and believed to be largely controlled by waves and currents (Komar, 1998). Contrary to this general notion, results presented in this paper suggest a strong control of the local morpho-tectonic frame-work on foreshore sedimentation. In the 20 km long study area between Bhatkal on the north and Uppunda in the south, foreshore morphology range from reflective and dissipative to intermediate types, but nearshore hydrodynamic regime is similar. The inland morpho-tectonic frame-work reveals graben and horst-like structures. The foreshores bordering these grabens and horsts are dissipative and reflective respectively, have distinctly different granulometric dynamics and sedimentation processes, whereas an intermediate type between the dissipative and the reflective show a large seasonal variability in terms of beach width and slope. The foreshore profile modification indicated that the reflective beaches remained reflective and the dissipative beaches remained dissipative throughout the year, despite the large variation in the wave energy condition from monsoon through post-monsoon to pre-monsoon. Spit growth is observed only in the dissipative beach. Granulometric dynamics in all the three types of beaches show distinct differences. The reflective beaches show significant fluvial characteristics of sediments in all the seasons, dissipative beaches show minor fluvial characteristics and the intermediate beaches show significant fluvial characteristics only during the monsoon seasons. Sediment transport process in the reflective beaches is dominantly by rolling process, in the dissipative beaches suspension is the dominant mechanism, and in the intermediate type beaches a large range from suspension to rolling is observed. Sediments in the beaches are negatively skewed through symmetrical to positively skewed in reflective beaches, while in dissipative beach negative skewness is dominant. Integration of the tectonic framework, beach morphology and granulometric dynamics suggest that temporal and spatial variations in textural characteristics are related to a strong morpho-tectonic control rather than seasonal variations in wave energy condition.
... e progradação dos cordões dunares verificada na praia da Manta Rota. Os dados mostram ainda que a amplitude da flutuação da largura da praia oscila cerca de 20-30m. Esta oscilação deve ser entendida como a natural oscilação sazonal da praia e é da mesma ordem da verificada noutras praias do Algarve, nomeadamente na Ria Formosa (Teixeira et al. 1989., Almeida et al., 2011. ...
... Ces zones se différencient par de faibles valeurs de l'écart type ou par un palier. Plusieurs, auteurs ont déjà procédé à la segmentation transversale de profils de plage à partir des valeurs de l'écart type (Kuriyama, et al. 2008 ;Almeida et al., 2011 ;Karunarathna et al., 2012). ...
Les plages de poche prennent place le long des littoraux rocheux. Sur la presqu’île de Rhuys, elles forment des cordons sableux protégeant à l’arrière des zones humides basses partiellement connectées au milieu marin. Ces plages subissent un fort marnage de type mésotidal et placées à l’arrière d’une barrière structurale, les houles océaniques y sont fortement atténuées. Le vent local génère une importante mer de vent dont les vagues de courtes fréquences ainsi créées favorisent les plus grands changements morphologiques transversaux et les plus grands transferts de sédiments longitudinaux. Les différentes expériences hydrodynamiques et topographiques menées sur le terrain ont permis de mettre en évidence des déplacements longitudinaux de sédiments favorisés par un vent local modéré et persistant. Avec une plus grande agitation, les transferts sédimentaires s’effectuent transversalement par de plus puissants processus de déferlement et de jet de rive. Les échanges s’effectuent autour d’un point d’équilibre de moindre activité. Le vent et la houle ont un impact hétérogène dans l’espace. Par ailleurs, les variations de volumes indiquent clairement que chaque système de plage est indépendant. Aucun échange de sédiment entre les plages n’est démontré alors qu’une connexion est permise avec le domaine subtidal proche, entre les platiers rocheux. Enfin, le degré d’impact d’une tempête dépend de sa trajectoire et du niveau d’eau. Le volume érodé est par ailleurs rapidement retrouvé par le système. Le budget sédimentaire est conservé. Pourtant, avec la hausse du niveau marin, les cordons dunaires peuvent se briser avec une redistribution longitudinale attendue.
... The progradational barriers represented by Groups 1 and 4 showed an inverse relationship between dimensionless fall velocity and volume variation (PC 1 ). This relationship could be conditioned by seasonal beach variability (between the winter and summer beach profiles) as shown by Almeida et al. (2010). The dimensionless fall velocity was also correlated to the foredune height (PC 2 from Group 2), which means that the greater the variability in the beach type, the more developed the foredune becomes. ...
This paper investigates the existence of statistical correlations and relationships between geological and oceanographic parameters along a coastal barrier system in southern Brazil. The existence of few statistical studies on coastal barriers motivated the use of multivariate statistical techniques that take environmental parameters such as coastal morphological-sedimentary features and their morphometric measurements into account. The Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were used to assess the spatial variations of fourteen parameters driving the current and past behavior of this coastal barrier system at fourteen locations. Through the application of HCA, these locations were divided into four groups (Groups 1, 2, 3, and 4). The HCA results were analyzed using PCA. The first (PC1) and the second (PC2) principal components together explained at least 76.4% of the variability of all four groups. The most important geological and oceanographic parameters that were correlated to PC1 and PC2 were different in each group. In general, the shoreface slope and shoreface dimensions were common to all groups as PC1-correlated parameters, being the most important ones regarding data variability.
In addition, for the progradational (Groups 1 and 4), retrogradational (Group 2) and aggradational barriers (Group 3) PCA indicated that shoreline orientation (wave exposure) and beach type are secondary, but relevant factors controlling the past and current behavior of coastal barriers in southern Brazil.
... Different researchers have recognized that the height of the extreme waves, number of the storms or their intensity are very important in the changes what happen in the coastal sand systems (e.g. Almeida et al., 2010). Storm is defined as a climatic event during which the wave height exceeds a threshold over a minimum, specific time duration. ...
Coastal sand dune ecosystems are facing threats and pressures across Europe, but the quantification of the exact impacts is not easy, particularly
when natural and anthropic effects are overlapping. In order to tackle this question, during two years sand movement has been measured in pilot
dune plots located in the Northern Spanish coast. We aimed at correlating the waves height, wind velocity and tidal range with the temporal changes
measured in the beach-dune systems. The role of littoral processes on the sand movement is quantified by fitting different regression models using
R, in order to discuss the influence of marine variables, climate change and human activities in the changes identified in coastal sand systems,
which also affects Spanish coasts.
... During the recovery phase, however, no significant correction exists ( Figure 13D), as in the case of post-Irma beach recovery during the 2018 winter season. This is consistent with numerous existing findings that the threshold wave conditions for severe beach erosion can be established from linear, quasi-linear, or probabilistic relationships between incident waves and profile volume loss (Almeida, Ferreira, and Pacheco, 2011;Coco et al., 2014;Gibeaut, Gutierrez, and Hepner, 2002;Splinter et al., 2014). However, no simple model has the capability to predict beach accretion based on incident wave conditions. ...
... The net littoral drift and longshore currents are typically from west to east. Storms are considered as events with significant wave heights (Hs) N 2.5 m (see Oliveira et al., 2018) or 3 m (see Almeida et al., 2011aAlmeida et al., , 2011bCosta et al., 2001), with the SW ones being more energetic, and reaching a Hs of about 8.1 m for a 50 year return period (Pires, 1998). Although no statistically significant linear trends of storm characteristics were identified from the historical reanalysis record (Almeida et al., 2011b), storm variability in the area, both in terms of wave height and surge, is correlated with the North Atlantic Oscillation and the East Atlantic Pattern (Plomaritis et al., 2015). ...
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Storms impact coastal areas often causing damages and losses at occupied areas. On a scenario of increasing human occupation at coastal zones and under climate change conditions (including sea level rise and increasing frequency of extreme sea levels), the consequences of storms are expected to be amplified if no adaptation or further management actions are implemented. The selection of the best possible coastal management measures, considering both costs and effectiveness, will be mandatory in the future, in order to optimise resources. This work analyses the performance of risk reduction measures (beach nourishment and receptors - house and infrastructures - removal), using a decision support system comprised by a morphodynamic numerical model (XBeach) and a Bayesian network based on the source-pathway-receptor concept. The effectiveness of the risk reduction measures is then assessed by a simple index expressing the consequences to the receptors. The approach was tested at Faro Beach by evaluating its performance for a particular storm, Emma (Feb/March 2018), which fiercely impacted the southern coast of Portugal. The output results from the modelling were compared to field observations of the actual damages caused by the storm. The combined use of both measures or the solely use of the nourishment would avoid almost all observed impacts from this storm. The work is pioneer on demonstrating the use of a decision support system for coastal regions validated against observed impacts for a high-energy storm event. The methodology and the proposed index are adaptable to any sandy coastal region and can be used to test (and improve) management options at a broad number of coastal areas worldwide, minimising implementation costs and reducing the risk to the occupation and to the people.
... The coastal response to extreme events is characterized by a significant spatial variability, which depends on the number of incidents events and their intensity (Burvingt et al., 2017). In this process, the most rapid and abrupt changes in the coastal landscape occur, generally, during high energy events (Almeida et al., 2010). However, storm concentration in time (storm groups, regardlles of their mediumlow intensity) has demonstred to be sometimes more effective in eroding the coast at the medium term that the energetic level reached by one single event (Ferreira, 2006). ...
Meteo-oceanographic events are characterized by low-pressure centers and intense winds. These systems are responsible for transferring a huge amount of energy from the atmosphere to the ocean that could cause serious socioeconomics damages to the coastal zones. Some of the consequences of these events propagation are an occurrence of large amplitude waves and an increase in the coastal water level. This study aims to characterize the effects of the extratropical cyclone in southern Brazil that occurred in October 2016, seeking a relationship between this event and the recent erosive episodes. Using satellite images and data obtained by unmanned aerial vehicles (UAV), it was possible to trace the shoreline behavior at time intervals, where occurred actions of extratropical cyclones during the year of 2016. The comparison of the shoreline position data, obtained by the image of July 2016, and the UAV (obtained in September and November 2016) presented an approximated shoreline retraction balance of 5.91 m associated with the cyclone that occurred between October 26th and 27th, 2016. This event was associated with the synoptic patterns, which has feature cyclogenesis in the Southern Uruguayan coast with a displacement to the east and trajectory between 28° and 43°S, with winds of 17.9 m s-1 and SW direction. Associated with the meteorological aspects, erosive process is frequently accelerated or augmented by anthropogenic action, which is mainly related to building construction activities and sometimes contributes to the destruction of dunes. After the passage of cyclone, there was partial or total destruction of 40% of beachfront houses and 65% of coastal protection structures. Therefore, this type of study constitutes a basic tool of general interest in the coastal management, contributing to the understanding of the impacts and risks associated with the coastal dynamics and effects of the meteo-oceanographic events, along the Southern Brazil.
... Additional 0.5 m of protection (Δzprotection) does not have any risk reduction effect. This is due to the low protection standards in place, as the area is known to experience damages almost annually (Almeida et al., 2011a;Almeida et al., 2011b), while the most frequent event analysed here is with return period of 5-years. Δzprotection=1 m results in lower EAD, however after 2040 the damages 20 tend to converge towards the Default case, becoming equal after 2070. ...
An upscaling of flood risk assessment frameworks beyond regional and national scales has taken place during recent years, with a number of large-scale models emerging as tools for hotspot identification, support for international policy-making and harmonization of climate change adaptation strategies. There is, however, limited insight on the scaling effects and structural limitations of flood risk models and, therefore, the underlying uncertainty. In light of this, we examine key sources of epistemic uncertainty in the Coastal Flood Risk (CFR) modelling chain: (i) the inclusion and interaction of different hydraulic components leading to extreme sea-level (ESL); (ii) inundation modelling; (iii) the underlying uncertainty in the Digital Elevation Model (DEM); (iv) flood defence information; (v) the assumptions behind the use of depth-damage functions that express vulnerability; and (vi) different climate change projections. The impact of these uncertainties to estimated Expected Annual Damage (EAD) for present and future climates is evaluated in a dual case study in Faro, Portugal and in the Iberian Peninsula. The ranking of the uncertainty factors varies among the different case studies, baseline CFR estimates, as well as their absolute/relative changes. We find that uncertainty from ESL contributions, and in particular the way waves are treated, can be higher than the uncertainty of the two greenhouse gas emission projections and six climate models that are used. Of comparable importance is the quality of information on coastal protection levels and DEM information. In the absence of large-extent datasets with sufficient resolution and accuracy the latter two factors are the main bottlenecks in terms of large-scale CFR assessment quality.
... Bottom sediment is largely dominated by fine to medium sand down to 10 m water depth; in deeper areas (10 to 15 m) gravel-sized sediments become important representing between 10 to 30 % of the total sediment as well as the presence of mollusc shells that comprises 30 to 45 % (Rosa et al., 2013;Rufino et al., 2008). The depth of closure on this region was estimated to be around 10 m depth by Almeida et al. (2010), while the work of López-Doriga et al. (2015) developed specifically in the study area of the present work revealed a DoC of about 6 m depth below mean sea level. ...
... Storms impact the area every year and wave heights above the defined storm threshold of 3 m are relatively frequent, constituting the major source of threats to the area as they may result in substantial beach erosion and overwash. A major storm occurred in 1941 (Freitas and Dias, 2013) followed by other important events during the 1960s (Almeida et al., 2011), with crucial consequences for the tuna fishing facilities owned by the fishermen communities in the barrier islands (Garnier et al., 2017). During the end of the 1970s, there were also severe storms that affected the human population. ...
This paper illustrates both the potential and challenges of interdisciplinary collaboration amongst researchers from the social sciences/humanities and the natural sciences/engineering in formulating disaster risk reduction measures for coastal regions. The authors aim to share their experiences of working across different scientific and engineering disciplines in the EU project RISC-KIT to co-produce disaster risk reduction measures suitable for specific regional and local contexts, in this case two coastal study areas in Europe (Porto Garibaldi, Italy and Rio Formosa, Portugal).
An overview of the historic-cultural origins of scientific disciplines is first presented, explaining the historical fragmentation of scientific knowledge into natural and social sciences and its associated challenges for prior disaster risk studies – and how the current state of an interdisciplinary approach has emerged. This is followed by an analysis of interdisciplinary collaboration, drawing on the experience and data collected (both quantitative and qualitative) from the two case study areas. The article concludes with suggestions to further overcome the segregation of disciplines within disaster risk studies and projects.
The authors found that qualitative data help to understand knowledge, values and behaviours of institutional and non-institutional stakeholders in formulating appropriate risk reduction measures to increase resilience in a local context – and that such data work “hand in hand” with quantitative information. Furthermore, the collection of qualitative data by researchers of the natural science and engineering disciplines has the potential to build bridges between disciplines and to stimulate further investigations, as in this case, to explain contradictions in human behaviour when managing risk.
... The geologic framework is a decisive factor of landscape formation and coastal dynamics. Despite the fact that during storm events coasts are most strongly affected by wave and storm surge height (Almeida et al., 2011;Gervais et al., 2012), beach responses to storms are more dependent on beach geomorphology than on external driving forces Loureiro et al., 2009). This is especially true regarding coastal erosion and accumulation processes during discrete storms (Fig. 7). ...
The geologic framework is an important factor worth consideration when analyzing the development of seacoasts. The different coastal responses to hydrometeorological and anthropogenic factors depend on the composition and amount of original coast-forming sediments. The impact of sediment composition on morphometric parameters is best observed in areas where sand unrepresentative of the adjacent coastal sectors appears on beaches with a relatively uniform lithological composition. These areas are referred to as lithological anomalies. Large amounts of coarse-grained sand, uncharacteristic of the adjacent coastal sectors of the Curonian spit, accumulated in the area of the strait that existed in the Post-Littorina Late Subboreal (3.7–2.5 ka BP) time south of the Juodkrantė settlement. Due to accumulation of coarse sand, the beach in this sector is narrow and has a higher slope, and the ridge is lower and with a smaller volume of sand than in the adjacent coastal sectors. The specific sand composition and morphology of this coastal sector are responsible for different coastal dynamics during storms. During extreme storms, beach erosion in this coastal sector is minimal (sometimes even accretion takes place) compared with other sectors where beach erosion is rather substantial. Meanwhile, during periods of relatively calm weather, i.e. times of expected regeneration of the cross profile, this sector stands out for active erosion processes.
... Sediments below 10 m water depth have textural characteristics and a reddish coating suggesting a relict nature as defined by Swift et al. (1971). The depth of closure of this region was estimated to be around 10 m depth by Almeida et al. (2010), while the work of López-Doriga et al. (2015) developed specifically in the study area of the present work revealed a DOC of about 6 m depth. ...
The understanding of the sedimentary links between the beach and the continental shelf is crucial for the evaluation of the coastal sediment budget. However, the comprehension of this dynamics is still poorly understood owing greatly to the lack of direct sediment transport measurement at seasonal and longer time scales. This work aims at evaluating sediment transport just seaward of the closure depth through a sand tracer experiment coupled with wave-current monitoring and modelling. Observations were carried out over 1 year at 14 m depth over a sandy continental shelf offshore Tavira (southern Portugal). The sand tracer experiment was carried out by injecting 400 kg of fluorescent tracer followed by four sediment sampling surveys. Tracer results show a high dispersion of the tracer cloud with a net transport of low magnitude. Time-averaged alongshelf sediment transport rate was estimated in 0.61 m³/m/yr (southwestward) while the cross-shelf transport rate was estimated in 0.31 m³/m/yr (onshore). During the observational period nearbed currents were dominated by the northeastern component, thus flowing in the opposite direction of the tracer displacement. However, when wave-current bed shear stress exceeded the threshold of particle motion, nearbed currents were dominated by a southwestern component which is compatible with tracer displacement. Overall this study showed that seaward the closure depth bottom sediment dynamics is characterized by frequent remobilization but with very low net transport rates.
... Over the past three decades numerous studies have examined short-term coastal change in response to extreme events (Dally et al. 1984;Gallagher et al. 1998;Zhang et al. 2005;Robertson et al. 2007;Stockdon et al. 2007) and seasonal climatic variations in incident wave energy (Aubrey 1979;Wright et al. 1985;Dail et al. 2000;Bernabeu et al. 2003;Haxel & Holman 2004;Miller & Dean 2007;Quartel et al. 2008;Hansen & Barnard 2010;Almeida et al. 2011). The physical dynamics of coastal change at decadal to centennial timescales, however, have received less attention despite being the timescale of greatest relevance to coastal management and planning (Cowell & Thom 1994). ...
Understanding how and why the world’s coastlines are changing is a pressing international concern in a context of rising sea levels, increased climatic variability and intensifying coastal development. Medium to long-term records of coastal change are rare worldwide and often limited to individual beach compartments. This study presents a 70-year (1940–2010) aerial imagery record to compare decadal changes in shoreline position across four high-energy west coast beaches near Auckland, New Zealand/Aotearoa: Whatipu, Karekare, Piha and Te Henga (Bethells). The common exposure of these adjacent mesotidal beaches to changing wind and wave conditions might, if they present the dominant controls on shoreline position, be expected to produce synchronous change. Whatipu (935 m), Piha (32 m) and Te Henga (52 m) showed net overall progradation for the study period, while Karekare retreated slightly (−4.1 m). All except Whatipu underwent periods of beachwide erosion. Shoreline change was not coherent between beaches, despite similar exposure to variations in wind, wave and sea level. Variable sediment supply from northward littoral drift is implicated as the primary control on decadal-scale shoreline change for these beaches, highlighting the importance of local context in influencing shoreline response to changing environmental conditions.
... The oceanic beach often has a low tide terrace exposed during spring low tides and wider at the eastern flank. Sediment exchanges between the beach face and the tidal terrace dominate the cross-shore morphological change at the western flank (Almeida et al. 2011a). ...
The east coast of the Algarve (Olhos de Água –
Guadiana) is a low sandy coast with a high diversity of environments,
including a cliffed coast, sandy beaches, dune
ridges, an estuary, artificial/antrophic sectors and a main, complex,
central morphology: the Ria Formosa barrier islands and
coastal lagoon system. The large majority of this coastal sector
is within the Ria Formosa Natural Park and therefore
protected by Nature conservation laws. Nevertheless, human
activities contributed to some of the most important changes
on coastal behaviour during the last decades, increasing processes
complexity and incrementing furthermore the difficulties
for the already demanding understanding of coastal
evolution.
Full access to the paper (SpringerNature Sharing): https://rdcu.be/6CiU
... The oceanic beach often has a low tide terrace exposed during spring low tides and wider at the eastern flank. Sediment exchanges between the beach face and the tidal terrace dominate the cross-shore morphological change at the western flank (Almeida et al. 2011a). ...
The east coast of the Algarve (Olhos de Água –
Guadiana) is a low sandy coast with a high diversity of environments,
including a cliffed coast, sandy beaches, dune
ridges, an estuary, artificial/antrophic sectors and a main, complex,
central morphology: the Ria Formosa barrier islands and
coastal lagoon system. The large majority of this coastal sector
is within the Ria Formosa Natural Park and therefore
protected by Nature conservation laws. Nevertheless, human
activities contributed to some of the most important changes
on coastal behaviour during the last decades, increasing processes
complexity and incrementing furthermore the difficulties
for the already demanding understanding of coastal
evolution.
... Segundo Vellinga (1982) [7], Ferreira (2005) [8], Silva et al. (2007) [9] e Almeida et al. (2010) [10], as mudanças mais aceleradas e bruscas no cenário costeiro (natural e/ou antropizado) ocorrem durante os eventos de alta energia, como as ressacas do mar. Para Faraco (2003) [11] e Montefalcone et al. (2010) [12], as constantes intervenções do homem na zona costeira têm alterado o balanço sedimentar ao longo das costas, gerando diminuição do suprimento de sedimentos e submetendo as praias a um permanente estado de erosão (caso observado no litoral de Caucaia). ...
Este artigo apresenta resultados de um experimento de campo realizado para avaliar a resposta morfológica de uma praia arenosa durante um evento de ressaca do mar. O estudo foi realizado na Praia do Icaraí, localizada no litoral da Região Metropolitana de Fortaleza. O experimento de campo foi baseado no acompanhamento contínuo de cinco seções de controle a partir de informações topográficas e oceanográficas. Foram realizadas 7 campanhas de campo (28/01/14 a 09/02/14). As respostas morfológicas dos trechos observados foram diferentes em termos de erosão e deposição. A seção limitada por dunas antropizadas (S1) apresentou erosão da berma e da praia submersa. Os trechos costeiros limitados por uma estrutura de proteção costeira (S2 a S4) apresentaram recuo da parte superior do perfil. No trecho de dunas frontais (S5), houve uma erosão generalizada da duna e da berma. De forma geral, a Praia do Icaraí é vulnerável a eventos de ressaca do mar.
... Most rapid and dramatic changes in beach morphology occur during storms, as these events are responsible for short-term erosion. Identifying thresholds above which forcing conditions trigger significant morphological changes is important to coastal management, allowing to further understand beach morphodynamics and contribute to improve coastal risk assessment (Almeida, 2011;Haerens et al., 2012). However, the definition of a storm threshold for any particular beach is hampered by morphological and geological constraints, so it must rely on a site-specific analysis. ...
Most rapid and dramatic changes in beach morphology occur during storms, as these events are responsible for short-term erosion. Identifying thresholds above which forcing conditions trigger significant morphological changes is important to coastal management, allowing to further understand beach morphodynamics and contribute to improve coastal risk assessment (Almeida, 2011; Haerens et al., 2012). However, the definition of a storm threshold for any particular beach is hampered by morphological and geological constraints, so it must rely on a site-specific analysis. This study aims to obtain insights about morphological storm thresholds of high-energy pocket beaches using as case study the Coxos beach, located on Portuguese central-west coast. This is a deeply embayed, reflective sand pocket beach developed over a rock platform (exposed 1 m below mean sea level-MSL), featuring a well-defined berm crest. Systematic surveys were conducted between 2011 and 2014 with a GPS-RTK and terrestrial LiDAR (Diogo et al., 2014), and morphological changes were evaluated through beach profile analysis. Wave forcing was characterized using hindcast wave time-series for the same time period (kindly provided by X. Bertin, University of La Rochelle). Storm events (occurrences with significant wave height (Hs) > 5 m and spaced > 24 hours) were evaluated. During the monitoring period beach revealed considerable stability, disrupted during the first months of 2014 (Figure 1). For the first 3 years seasonal response was restricted to minor berm variations, with a relatively stable and steep beach face. Average beach slope (tanβ), estimated between MSL and maximum swash line, was assumed constant and equal to 0.1. After the early 2014 winter storms, intense/extreme erosion with significant beach surface lowering and shoreline retreat. Offshore wave height analysis (Figure 2) did not allow to establish a direct morphological threshold because the event with maximum offshore Hs (January 19 th 2013) did not promote significant morphological change. To investigate this behavior, the influence of other wave parameters (peak period, Tp) and geomorphological characteristics (tanβ) was analyzed. This was accomplished through the computation of wave run-up parameter, using Masselink and Hughes (2003) formulation: R 2% = 0.36g 1/2 tanβ H s 1/2 T p (Figure 3). Results show that Jan 6 th 2014 storm presented the highest R 2% value. Beach morphology response was consistent with this result, considering the severe erosion recorded (Figure 1 – 16/01/2014 survey). Estimated run-up level suggests that swash reached the cliff base and reflected wave energy may have been responsible for accelerating erosion and beach depleting. After this event, other storms with relatively high R 2% values occurred, promoting significant additional beach erosion. These events were probably enhanced by an inherited lower berm elevation, which facilitated wave reflection at cliff toe. In April and July 2014 some volumetric recovery was recorded, although scarcely matching half of the pre-storm sediment volume. Results show a remarkable stable beach at a multi-annual scale, lacking significant morphological response to seasonal variations in incident wave conditions and typical winter storms. During the monitoring period, beach morphological equilibrium was significantly disrupted at one occasion, related to an extreme storm event. We found that significant storm induced morphological change appears to be more closely related to runup levels, as opposed to wave height alone. In fact, in this case, run-up level provides a suitable tool to quantify thresholds above which the beach experiences significant erosion. However, once this threshold is exceeded, and significant erosion occurs, beach resilience is lowered, allowing further changes to occur under less energetic storm conditions. This shows that storm thresholds cannot be considered as an absolute value and depend on the antecedent beach conditions. Further investigation is needed to evaluate sediment recovery in this embayment, although data collected suggests a long-term sediment loss from the beach system. Morphological changes experienced by Coxos beach over 4 years highlight the importance of a continued monitoring program capable of providing a better understanding of the variables contributing to coastal morphodynamics 73
... Fig. 12 also clearly shows that the condition of TH ¼ 1 m provides consistently better forecast accuracy than the condition of TH ¼ 0 m. Almeida et al. (2011) concluded in their study in Praia de Faro, in southern Portugal, that waves higher than 2.3 m were responsible for the main morphological changes in the berm and beach face and waves higher than 3.2 m were responsible for the changes in the sub-tidal area and long-shore bars. We have found a rather more nuanced picture from our analysis. ...
In this study the medium-term response of beach profiles was investigated at two sites: a gently sloping sandy beach and a steeper mixed sand and gravel beach. The former is the Duck site in North Carolina, on the east coast of the USA, which is exposed to Atlantic Ocean swells and storm waves, and the latter is the Milford-on-Sea site at Christchurch Bay, on the south coast of England, which is partially sheltered from Atlantic swells but has a directionally bimodal wave exposure. The data sets comprise detailed bathymetric surveys of beach profiles covering a period of more than 25 years for the Duck site and over 18 years for the Milford-on-Sea site. The structure of the data sets and the data-driven methods are described. Canonical correlation analysis (CCA) was used to find linkages between the wave characteristics and beach profiles. The sensitivity of the linkages was investigated by deploying a wave height threshold to filter out the smaller waves incrementally. The results of the analysis indicate that, for the gently sloping sandy beach, waves of all heights are important to the morphological response. For the mixed sand and gravel beach, filtering the smaller waves improves the statistical fit and it suggests that low-height waves do not play a primary role in the medium-term morphological response, which is primarily driven by the intermittent larger storm waves.
... River bank retreat might be triggered and controlled by internal and external forces acting over a wide range of spatial and temporal scales (Almeida et al., 2011;Houser, 2010). This hampers any attempt to identify key contributors to bank erosion processes and to define thresholds marking major changes in bank response. ...
... As mudanças mais rápidas e bruscas na paisagem costeira (natural e antropizada) ocorrem, especialmente, durante um evento de alta energia (FERREIRA, 2005;ALMEIDA et al., 2010). Contudo, a caracterização dos impactos sobre a morfologia costeira e as estruturas urbanas não é fácil, sendo, por vezes, inconclusiva. ...
... The present study also revealed that the 15 m bathymetric seems to be an important turning point in the distribution of most gorgonian species in Lagos Bay, which can be related to higher irradiance above this depth but also to higher surf impact. Indeed, in the Algarve, the lower beach profile limit (closure depth), where wave action is able to disturb the sea bottom, is around 10 m below mean (Dolbeth et al. 2007;Almeida et al. 2011), which is known to influence the patterns of benthic communities (Dolbeth et al. 2007;Carvalho et al. 2011). The turbulence from surf can detach gorgonians but also increase the rates of contact with substrate or neighbouring conspicuous fauna and flora, leading to colony tissue damage due to abrasion. ...
The ecological role of gorgonians for marine rocky bottoms is worldwide recognized, but the information on the distribution patterns of NE Atlantic temperate species is insufficient, considering current global, regional and local threats. To overcome the lack of information on the spatial distribution patterns of gorgonians in south Portugal, in 2009/2010, the occurrence and abundance of gorgonian species in rocky bottoms were quantified over more than 25 km of coast (37.1�N/8.6�W) down to 30 m depth. Eunicella labiata, Eunicella gazella, Eunicella verrucosa and Leptogorgia sarmentosa were abundant and frequent in the studied area, while Leptogorgia lusitanica was less abundant. All species evidenced a similar depth pattern, that is abundance significantly increased with depth below 15 m. At shallower waters (up to 15 m), the distribution of gorgonians may be constrained by abiotic factors and competition with algae. Indeed, the abundance of gorgonians was negatively correlated with the percentage cover of algae along the depth gradient, but gorgonians and sponges coexist. Competition among gorgonian species also seems to be low in this area because of the similarity in the abundance pattern observed for the most abundant species and also their high association. In NE Atlantic shallow temperate rocky bottoms, the distribution of gorgonians seems to be influenced by environmental factors and biological interactions, namely competition (algae) and coexistence (sponges and other gorgonians).
... Storms are considered to occur when the significant wave height (H s ) exceeds 3 m (Almeida et al., 2011b). While the eastern sector of Faro Beach is accreting and vegetated foredune development is evident (Almeida et al., 2011a; Ferreira et al., 2006), the central and western parts tend toward erosion, with much of their natural dune ridge having being destroyed and replaced by urban development (Figure 1). As a result, a part of the ocean front has been artificially stabilized with sea walls, which together with roads and walls are often overwashed during spring tides or under stormy conditions . ...
This study analyses beach morphological change during six consecutive storms acting on the meso-tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep-sloping beaches, since sub-aerial beach volume reductions up to 30 m3/m were followed by intertidal area recovery (–2 < z < 3 m) with rates reaching ~10 m3/m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non-dimensional, morphological parameters. Copyright
... Both SIIs and the pre-defined thresholds are site-specific (Ciavola et al. 2011a) and must be carefully selected on the grounds of existing experience and field data Almeida et al. 2011a;Matias et al. 2008;. For Faro Beach, the selected SIIs were (1) maximum wave runup height during the simulations; and (2) dune-foot horizontal retreat at the end of the simulations (d x,dune crest ). ...
The study aims to calibrate/validate and apply the dune-erosion model, XBeach, in order to predict morphological response to storm events along a meso-tidal, steeply sloping beach. More than 10,000 XBeach calibration runs, including different model parameters and erosion events, were compared with measurements of beach-profile response to storm conditions. Off-shore wave and tidal measurements were used as input for a SWAN wave model, which was used to provide wave conditions to XBeach. The results indicate that using XBeach to predict beach-profile morphodynamic response during storm events on steeply sloping intermediate-to-reflective beaches may be more demanding than for dissipative beaches and that the default model setup can overestimate dune/beach-face erosion. The performance of the model after calibration was satisfactory, with Brier Skill Scores from 0.2 to 0.72. XBeach was found to be more sensitive to input parameters such as the beach-face slope and the surf similarity parameter ξ (especially for values ξ > 0.6). The calibrated XBeach setup was used for simulations of storm scenarios with different return periods (5, 25, and 50 years), and the simulations highlighted the fragility of the dune field and the potential for storm-induced dune retreat, lowering, and overwash in the study area. Finally, the nested SWAN/XBeach models were forced by an existing operational wave-forecast WAVEWATCH-III/SWAN model, operated by the Portuguese Hydrographic Institute to generate daily forecasts of storm impact and serve as a prototype-case for an early warning system for storm hazard mitigation.
Keywords: Beach erosion; coastal storms; XBeach; sediment transport; beach profile evolution; numerical modeling; early warning system
... results presented by Almeida et al. (2011), due to the existence of a nodal point at this level that separates the cross-shore sectors dominated by berm and subtidal terrace changes. ...
Headlands, rock outcrops and engineering structures impact beach and nearshore dynamics of coastal embayments, inducing boundary effects that constrain the lateral and vertical beach variability. This study analyses morphological change in six embayed beaches with diverse levels of exposure to wave action and various degrees of geological control in the mesotidal coast of southwestern Portugal. The aim is to identify whether geological boundaries constrain the morphological behaviour of embayed beaches and assess whether their effects can be decoupled from datasets of morphological change. Topographic data, obtained over a two-year period on each of the six embayments, were analysed using empirical orthogonal functions (EOF) to decompose temporal and spatial variability in the datasets. First and second mode eigenfunctions were explored using time-variable linear correlation analysis with several nearshore parameters that include hydrodynamic variables, sedimentary and geometric characteristics of each embayment in order to derive forcing–response relationships.
... The present study also revealed that the 15 m bathymetric seems to be an important turning point in the distribution of most gorgonian species in Lagos Bay, which can be related to higher irradiance above this depth but also to higher surf impact. Indeed, in the Algarve, the lower beach profile limit (closure depth), where wave action is able to disturb the sea bottom, is around 10 m below mean (Dolbeth et al. 2007;Almeida et al. 2011), which is known to influence the patterns of benthic communities (Dolbeth et al. 2007;Carvalho et al. 2011). The turbulence from surf can detach gorgonians but also increase the rates of contact with substrate or neighbouring conspicuous fauna and flora, leading to colony tissue damage due to abrasion. ...
The ecological role of gorgonians for marine
rocky bottoms is worldwide recognized, but the information
on the distribution patterns of NE Atlantic temperate
species is insufficient, considering current global, regional
and local threats. To overcome the lack of information on
the spatial distribution patterns of gorgonians in south
Portugal, in 2009/2010, the occurrence and abundance of
gorgonian species in rocky bottoms were quantified over
more than 25 km of coast (37.1�N/8.6�W) down to 30 m
depth. Eunicella labiata, Eunicella gazella, Eunicella
verrucosa and Leptogorgia sarmentosa were abundant and
frequent in the studied area, while Leptogorgia lusitanica
was less abundant. All species evidenced a similar depth
pattern, that is abundance significantly increased with
depth below 15 m. At shallower waters (up to 15 m), the
distribution of gorgonians may be constrained by abiotic
factors and competition with algae. Indeed, the abundance
of gorgonians was negatively correlated with the percentage
cover of algae along the depth gradient, but gorgonians
and sponges coexist. Competition among gorgonian species
also seems to be low in this area because of the similarity
in the abundance pattern observed for the most
abundant species and also their high association. In NE
Atlantic shallow temperate rocky bottoms, the distribution
of gorgonians seems to be influenced by environmental
factors and biological interactions, namely competition
(algae) and coexistence (sponges and other gorgonians).
... Faro Beach is essentially a reflective beach (see classification of Wright and Short 1984) with beach-face slopes typically above 10% and varying from 6% to 15%, with a tendency to decrease eastward along the beach where a "low tide terrace" beach state is reached (Almeida et al. 2010). Sediments are medium to very coarse, moderately well-sorted sands (see classification of Folk 1980) with d 50 ∼0.5 mm and d 90 ∼2 mm. ...
Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position of the swash extrema. The generated dataset of 2% wave run-up exceedence values R
2 was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating a best-fit case RMS error of 0.39 m. The R
2 prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η
tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend between R
2 and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravity-to-incident frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E
infra/E
inci > 0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for which η
total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage of the total length ranging from 36% to 75%.
This contribution aims to explore the role of oceanographic parameters on the damage caused by storms at the eastern Cantabrian coast (1996–2016). All wave storms affecting the study area were characterized in terms of several oceanographic parameters; among them, damaging storms (responsible for direct and tangible loss) were identified. Cross-referencing both databases makes it possible to find some thresholds that explain storm conditions associated with property damage. Particularly relevant are those responsible for significant and widespread damage: maximum significant offshore wave height >6.5 m, maximum total water level >6 m, SPI >1700 m2h, and a storm duration >48 h. These values are exceptionally high, mostly exceeding the 95th percentile. A comparison has been made with other thresholds described in the literature. The concurrence of high wave height and high tidal level is crucial as the greatest damage is caused by the combination of wave impact and over-wash, so a long duration of the storm is necessary to coincide with high tide. An empirical Intensity-Duration threshold has also been obtained with the following function I = 248.7 D−0.45. Damage can occur with moderate storms, but with severe effects only with exceptional wave and sea-level values, during long-lasting storms.
Along the tropical coast, there is cyclic variation in wind, wave currents, water and sediment influx, and the coasts experience a monsoonal storm surge that reaches nearly 2–3 times higher than the rest of the year, and foreshores undergo a complex evolution during an annual cycle. Hence, knowledge of foreshore evolution is critical in shoreline management. In this paper, study results on meso-scale foreshore evolution in a low-energy headland bay beach, situated in the Central West Coast of India near Manki, are discussed based on their seasonal and decadal changes in sandy shoreline configuration, wave refraction, sediment movement and depositional process. Decadal changes in the shoreline configuration indicated headland-side erosion and bay growth whereas the southern end grown seawards between the period 1979 and 2001–2002, while the beaches adjacent to the creek present in the area showed accretion and farther south of the creek showed minor erosion, and the trend continued through 2015. Wave refraction patterns for the waves approaching from northwest (NW), west and southwest (SW) for the wave periods 6, 8, 10 and 12 s indicated (a) wave convergence at the central part of the Manki beach; for the waves approaching from NW for wave periods 6 s; (b) wave divergence for the waves approaching from west with wave periods 6, 8, 10 and 12 s and (c) wave convergence at the bay side for the SW as well as NW approach of waves for wave period 10 s. Seasonal beach modification, in general, indicated post-monsoonal to pre-monsoonal (September to April) accretion and May to September erosion. Foreshore is gentle and dissipative (<6°). Sediments in all the seasons are bimodal (at 2ϕ and 2.752ϕ) in nature, and show dominantly saltation to suspension mode of transport. A parabolic shoreline prediction model indicated negative sediment budget in the central and northern parts of the beach (near the headland) and positive sediment budget at the southern end of the beach. Integration of the foreshore profile, sediment movement pattern, results of parabolic shoreline prediction model and decadal changes in shoreline configuration indicated that sediment budget is a critical issue in headland-bounded beaches, and utmost care is needed in the management of such shore line. This paper uses seasonal variations in the foreshore morphology, beach volume, sediment characteristics and wave refraction pattern to understand the sediment movement within the beach.Based on Hsu et al.’s (2004) model shoreline position is predicted.For a finite sediment input beach, shoreline management strategy is suggested. This paper uses seasonal variations in the foreshore morphology, beach volume, sediment characteristics and wave refraction pattern to understand the sediment movement within the beach. Based on Hsu et al.’s (2004) model shoreline position is predicted. For a finite sediment input beach, shoreline management strategy is suggested.
An upscaling of flood risk assessment frameworks beyond regional and national scales has taken place during recent years, with a number of large-scale models emerging as tools for hotspot identification, support for international policymaking, and harmonization of climate change adaptation strategies. There is, however, limited insight into the scaling effects and structural limitations of flood risk models and, therefore, the underlying uncertainty. In light of this, we examine key sources of epistemic uncertainty in the coastal flood risk (CFR) modelling chain: (i) the inclusion and interaction of different hydraulic components leading to extreme sea level (ESL), (ii) the underlying uncertainty in the digital elevation model (DEM), (iii) flood defence information, (iv) the assumptions behind the use of depth–damage functions that express vulnerability, and (v) different climate change projections. The impact of these uncertainties on estimated expected annual damage (EAD) for present and future climates is evaluated in a dual case study in Faro, Portugal, and on the Iberian Peninsula. The ranking of the uncertainty factors varies among the different case studies, baseline CFR estimates, and their absolute and relative changes. We find that uncertainty from ESL contributions, and in particular the way waves are treated, can be higher than the uncertainty of the two greenhouse gas emission projections and six climate models that are used. Of comparable importance is the quality of information on coastal protection levels and DEM information. In the absence of large datasets with sufficient resolution and accuracy, the latter two factors are the main bottlenecks in terms of large-scale CFR assessment quality.
Abstract Coastal communities are threatened by the impact of severe storms that may cause significant loss of life and damage to properties. Among the main processes behind such impacts on coastal barriers are the occurrence of overwash and breaching during storm events. In order to estimate potential losses associated with a particular event, the above processes must be properly parameterized. Here, we propose a novel methodology to estimate overwash and breaching hazards suitable for a regional scale analysis (Ø 100 km). For the overwash hazard assessment, the method is based on the application of the approach developed by Donnelly (2008) that allows the parametrisation of the overwash hazard considering both flow velocity and flow depth. Moreover, the inland extension of the associated hazard, which is critical to assess subsequent vulnerability, can also be estimated following this methodology. The proposed method requires the selection of a runup formula validated for the study area, a storm beach profile, a runup lens angle, and a percolation constant for infiltration. To assess the breaching, hazard, a new multivariable evaluation is proposed that allows ranking the potential of breaching. The multivariable evaluation combines overwash and erosion hazards as well as their extensions with the main morphological characteristics of the barrier, resulting in the breaching hazard index, that ranks from 0 to 5 (no breaching to inlet formation). Inland breaching extension is also relevant for the vulnerability assessment. The breaching extension can be estimated using historical or contemporary analogues of the nearest flood deltas. The developed approaches were applied to Ancão Peninsula (Algarve, Portugal) as a demonstration example. The advantages of the present approach are: adaptability to various environments where overwash and/or breaching processes are important, time efficiency on evaluating overwash and breaching hazards, and the assessment of hotspot areas at a regional scale.
Coastal communities are threatened by the impact of severe storms that may cause significant loss or damage of property and life. The main processes causing such impacts at sandy coastlines and nearby coastal communities are storm erosion, overwash and inundation. Coastal response under present conditions and under predicted climate change has been frequently assessed on the basis of numerical models, which in turn can be also used to evaluate the effectiveness of Disaster Risk Reduction (DRR) measures to mitigate the response of the coast to the imposed conditions. However, detailed morphodynamic models are computationally expensive and not commonly used by coastal managers. The present work proposes the construction of a probabilistic Bayesian Network (BN) as a surrogate for the numerical simulations. This BN is trained with a large number of morphodynamic simulations, under a variety of storm conditions and DRR measures, in order to serve as a front-end platform for visualising, analysing and evaluating combined results of the numerical modelling. The BN introduced in an early warning system will be able to serve both, as a predictive and as a working tool to determine impacts and evaluate risk reduction after measures implementation.
This study investigates the medium-term (months to years) morphodynamic variability of embayed beaches in contrasting geomorphological settings, combining two years of topographic and sedimentary monitoring in six embayments on the southwestern Portuguese coastline (three on the west coast and three on the south coast) with hydrodynamic forcing data explored using statistical and modelling techniques. From a broader, embayment-wide scale, towards a focused, process-oriented scale, the thesis addresses the following points: (i) the classification of morphodynamic state in embayed beaches, (ii) assessment of geological boundaries as constraints on the morphological variability of embayed beaches, (iii) the identification of morphodynamic mechanisms responsible for non-uniform alongshore behaviour in high-energy embayed beaches, and (iv) the development of megarips and their role in enhancing erosion during storm groups.
This study demonstrates that: (i) geological control significantly influences embayed beach morphodynamic behaviour; (ii) beach morphodynamic parameters have limited ability to adequately differentiate beach types, particularly within the intermediate domain; (iii) geological boundaries constrain morphological change and promote conspicuous alongshore variability in embayed beaches; (iv) beach rotation processes in south coast embayments and topographically-controlled rip circulation in the west coast embayments are the primary drivers of alongshore non-uniform variability; (v) under high-energy conditions topographically-controlled rips evolve to megarips, which promote significant beach erosion; (vi) the persistence of megarips during storm groups leads to extreme beach erosion, and maintenance of megarip circulation following storms inhibits post-storm beach recovery. Further research is still necessary to improve the present understating of embayed beach morphodynamics, particularly involving detailed field studies of nearshore circulation and morphologic change. Embayed beaches frequently present site-specific behaviour and knowledge of their dynamics is fundamental to improve both beach safety and management
Mediterranean beaches experience major modifications in their morphology and grain size features mainly during intense storms and extreme meteo-marine events. The assessment of beach response to storms can be useful in the evaluation of coastal hazards, and in relation to the efficiency of management projects such as artificial nourishment. This paper aims to establish the subaerial morphological response of a beach located in western Sardinia (western Mediterranean) during the period of a year. Both experimental and numerical approaches were adopted to investigate the beach system. In particular, beach profiles, acquired by means of Differential Positioning System were used to analyze the morphological changes of the beach and wave parameters and current velocity data were collected by means of an Acoustic wave and current meter (ADCP). Numerical techniques were also applied to investigate the hydrodynamics in the area of study. Coupled wind wave - 3D hydrodynamic finite element model were used to reproduce the wave propagation and the wind, tide and wave induced 3D water circulation along the coastal areas, and it displayed a good accuracy. During the year, the beach experienced intense morphological changes in the area where submerged beach is not occupied by rocky outcrops and the model was also able to reproduce the related observed periods of strong wind wave events. The interdisciplinary approach allowed an evaluation to be made about the response of the beach morphology in respect to meteo-marine forcings.
Three embayed beaches exposed to energetic wave conditions along the south‐western Algarve coast were
regularly monitored over two years. Throughout this period, storms of variable characteristics, ranging from
extreme single storms to storm groups, impacted the coast, promoting widespread beach erosion. On the three beaches, Arrifana, Monte Clérigo and Amoreira,moderate erosion observed during individualstorms was generally linked to the development of large‐scale rip currentsystems(megarips) and associated feeder channels. Extreme erosion, however, occurred when megarips and feeder channels became persistent during storm grouping, promoting continued erosion and offshore sediment export. The combined analysis of profile morphological change with megarip and feeder channel influence highlights the close association of megarips and feeder channelsto erosion in embayed beaches exposed to high energy wave conditions. Differences within and between beaches were found to be related to embayment geometry and orientation, which determine megarip location by inducing alongshore variations in breaking wave height and gradients of radiation stress. By exploring nearshore circulation and embaymentresponse to storms, the present work provides new insightsinto the morphodynamics of embayed beaches. Although megarip activity has long been recognized as an important morphodynamic mechanism, its impact in the erosion of embayed beaches is still poorly understood and further research is required.
Along the southwestern coast of Portugal, a high-energy, swell
dominated environment with a markedly seasonal wave climate, morphologic
change in three embayed beaches was regularly monitored over a two year period.
While a general seasonal pattern was identified, the occurrence of a storm group
induced dramatic beach response, producing marked interannual variability.
Significant spatial variations in behaviour emerged during the monitoring period,
inducing alongshore non-uniform beach change within each embayment. Megarips
were the prevailing mechanism responsible for the extreme erosion experienced in
all three beaches, and their specific location (controlled by topography) contributes
to the variability observed within each beach. Despite severe beach erosion, dunes
were unaffected, which suggests long-term stability of these high-energy,
dissipative, embayed coastlines.
Despite the considerable research that has sought to describe past and predict future shoreline change, little consensus has emerged on the best methodology for forecasting future shoreline positions. While a certain degree of heterogeneity in approach is warranted given the variability in coastal geomorphology and sediment-transport processes, the prediction error associated with each method has not been evaluated in great detail. In this study, measured shoreline positions from Delaware and New York were used to calculate long-term erosion rates and make predictions to subsequent, known positions. Rates were calculated using end-point and linear-regression methods, including and excluding storm-specific shorelines. Those rate computations that included storm-specific shorelines yielded consistently poor predictions (average factor-of-three increase in error) compared with non-storm erosion rates, regardless of rate-calculation method. Linear-regression predictions, on average, performed better than end-point rate predictions, reducing error by over 70% in New York and 34% in Delaware for rates including storm shorelines, and between 4 and 31% for non-storm data (DE and NY, respectively). Predictions (hindcasts) were also made to 19th century shoreline positions using rates computed with modern, non-storm data. The positions predicted along relatively undeveloped stretches of the coast were within the 95% confidence interval associated with the prediction. Hindcasts made in areas characterized by heavy development and/or beach nourishment projects were poor, as would be expected given the recent alteration of the natural sediment-supply system. For all locations, inclusion of 19th century data reduced uncertainty in forecasts of 21st century shoreline positions by roughly 44%. These results show that forecasts derived from linear-regression rates using non-storm, 19th and 20th century data produce the lowest prediction error and uncertainty in the long-term trend.
A linear regression (studentized) residual analysis was used to identify potential shoreline position outliers and to investigate the effect of the outliers on shoreline rate-of-change values for transects along the Outer Banks, North Carolina. Results from this analysis showed that, over a 134 year period, storm-influenced data contribute statistically significant information to the long-term signal. Consequently, storm-influenced data points do not appear to be temporal outliers and thus, do not need to be excluded from a long-term analysis of shoreline changes. Furthermore, projections of the upper and lower confidence intervals (CIs) for the regression line to the year 2010 (24 year extrapolation) showed that including or excluding outliers had minimal effects on shoreline position predictions.
Analysis of ground conditions and meteorological and oceanographic parameters for some of the most severe Atlantic and Gulf Coast storms in the U.S. reveals the primary factors affecting morphological storm responses of beaches and barrier islands. The principal controlling factors are storm characteristics, geographic position relative to storm path, timing of storm events, duration of wave exposure, wind stress, degree of flow confinement, antecedent topography and geologic framework, sediment textures, vegetative cover, and type and density of coastal development. A classification of commonly observed storm responses demonstrates the sequential interrelations among (1) land elevations, (2) water elevations in the ocean and adjacent lagoon (if present), and (3) stages of rising water during the storm. The predictable coastal responses, in relative order from high frequency beach erosion to low frequency barrier inundation, include: beach erosion, berm migration, dune erosion, washover terrace construction, perched fan deposition, sheetwash, washover channel incision, washout formation, and forced and unforced ebb flow. Near real-time forecasting of expected storm impacts is possible if the following information is available for the coast: a detailed morphological and topographic characterization, accurate storm-surge and wave-runup models, the real-time reporting of storm parameters, accurate forecasts of the storm position relative to a particular coastal segment, and a conceptual model of geological processes that encompasses observed morphological changes caused by extreme storms.
The shoreface (Barrell, 1912) is a relatively simple and easily distinguished coastal environment. It appears as a concave upward surface with a slope on the order of 1:200 and is just seaward of the surf zone. This slope decreases seaward until the shoreface blends into the continental shelf with a slope on the order of 1:2000 (Figure 8-1).
Monitoring beach volume changes of the Texas Coast following a major hurricane reveals the impact of storms on sand dispersal and shoreline movement at spatial and temporal scales encompassing tens of kilometers and decades. Beach volume histories at profile sites show the interdependence of sand exchange among adjacent sites and the spatial autocorrelation of sand movement. Beach volume histories also indicate periods when either longshore or cross-shore transport predominate and illustrate the long-term effects of coastal structures on beach mobility. This study confirms that net losses of sand from updrift barriers may not be directly linked with net gains of sand on adjacent downdrift barriers. Instead, sand dispersal within a coastal compartment may depend partly on the dynamics of shoals and temporary sand storage at the intervening tidal inlet. In our study, sand eroded from the updrift barrier (Galveston Island) is deposited in a terminal sand flat of the barrier, whereas sand accreted to the downdrift barrier (Follets Island) is derived from the intermediate ebb-tidal delta (San Luis Pass). Unlike continuous sand bypassing on some microtidal, wave-dominated coasts, sand bypassing at San Luis Pass is episodic, event driven, and inefficient, and sand is not transferred directly from one barrier to the next. Because storms rapidly redistribute beach sediment, they can be the most important factor controlling short-term (< 10 yr) shoreline movement where natural replenishment of beach sand depends entirely on updrift erosion. Large-volume, nearly instantaneous sand transport during storms can locally accelerate rates of shoreline change or reverse the trend of beach movement, thereby significantly altering projected shoreline positions even ten years into the future. Future storms will probably have even greater impact on coastal sand budgets and beach mobility as natural sources of beach sand are eliminated or become unavailable to replenish beaches.
The subtidal macrobenthic community of a temperate beach in southern Portugal was studied along a depth gradient (1.3 to 32 m deep), which was long enough to comprise both highly hydrodynamic and calmer areas, to assess the influence of the spatial and temporal differences in hydrodynamic impact at the seafloor on the organization of a macrobenthic community. These differences were assessed by studying the variations in wave climate, depth of closure and extension of the mixed profile. A spatial zonation was detected from highly hydrodynamic shallow depths, 7.2 m deep shorewards, to the calmer deeper areas, from 8.4 m seawards. Accordingly, in the shallowest depths, species richness and densities were lower, with the inhabiting species, mainly crustaceans and surf clams, adapted to the environmental severity. Both species richness and densities increased along the depth gradient, and the community became dominated by polychaetes, nematodes and nemerteans. Seawards, within the relict sediments (deeper than 25 m), species richness and abundance decreased again. The community patterns also changed in response to the occurrence of strongly hydrodynamic episodes (such as storms), which had a higher impact than the seasonality. It was concluded that harsh physical environmental conditions reduce species richness, both spatially and temporally. With respect to density, other parameters related to life cycle characteristics, recruitment success and biotic interactions may also have some impact.
A synthesis of some results obtained over the period 1979–1982 from a study of beach and surf zone dynamics is presented. The paper deals with the different natural beach states, the process signatures associated with these states, environmental controls on modal beach state, and the temporal variability of beach state and beach profiles.Hydrodynamic processes and the relative contributions of different mechanisms to sediment transport and morphologic change differ dramatically as functions of beach state, that is depending on whether the surf zone and beach are reflective, dissipative or in one of several intermediate states. Depending on beach state, near bottom currents show variations in the relative dominance of motions due to: incident waves, subharmonic oscillations, infragravity oscillations, and mean longshore and rip currents. On reflective beaches, incident waves and subharmonic edge waves are dominant. In highly dissipative surf zones, shoreward decay of incident waves is accompanied by shoreward growth of infragravity energy; in the inner surf zone, currents associated with infragravity standing waves dominate. On intermediate states with pronounced bar-trough (straight or crescentic) topographies, incident wave orbital velocities are generally dominant but significant roles are also played by subharmonic and infragravity standing waves, longshore currents, and rips. The strongest rips and associated feeder currents occur in association with intermediate transverse bar and rip topographies.Long-term consecutive surveys of different beaches with contrasting local environmental conditions provide the data sets for empirical—statistical assessment of beach mobility, direction of change and response to environmental conditions. Conditions of persistently high wave energy combined with abundant and/or fine grained sediment results in maintaining highly dissipative states which exhibit very low mobility. Relatively low mobility is also associated with persistently low-steepness waves acting on coarsegrained beach sediments. In such cases, the modal beach state is reflective. The greatest degree of mobility is associated with intermediate but highly changeable wave conditions, medium grained sediment and a modest or meager sediment supply. Under such conditions, the beach and surf zone tend to alternate among the intermediate states and to exhibit well-developed bar trough and rhythmic topographies. A good association is found between beach state and the environmental parameter where Hb is breaker height, is mean sediment fall velocity and T is wave period. Temporal variability of beach state reflects, in part, the temporal variability and rate of change of Ω, which, in turn depends on deep-water wave climate and nearshore wave modifications.
The main objective of the CROP (Cross-shore Process on Contrasting Environments) project is to enhance the understanding of cross-shore processes over different time scales. With respect to morphodynamics, studies will focus mainly on closure depth, movement of submerged bars, beach profile changes and erosion and accretion time scales. To achieve this, a monitoring program involving periodic topography and nearshore bathymetric surveys is planned. The shore surveying is undertaken using a total station while the nearshore bathymetry is surveyed using a boat mounted bathymetric survey system that consists of a RTK- DGPS (Real-Time Kinematic Differential GPS) and echo sounder. The results of testing of the bathymetry survey system show that the system is capable of providing good quality morphology data with reasonably high accuracy. The system and general method developed is functional and accessible and could be easily used at other sites.
O Instituto Hidrográfico (IH) iniciou, em 1979, com o apoio de várias instituições nacionais, um programa de medição de dados de agitação marítima, o programa ONDMAR, com o objectivo de contribuir para o conhecimento do clima de agitação marítima na costa portuguesa. Em 1987, conseguido o apoio da OTAN através do seu programa “Science for Stability “, deu-se início ao projecto PO-WAVES, o qual veio permitir aumentar a rede inicial de estações ondógrafo e sistematizar a aquisição e o processamento dos dados. No relatório final do projecto (1994) foi apresentado um resumo da informação obtida a partir do processamento
de todos os dados colhidos no âmbito do projecto.
Nesta comunicação apresenta-se, com base num maior volume de dados, uma caracterização sumária do clima de agitação marítima, de reconhecido interesse para o projecto e dimensionamento de estruturas e instalações costeiras. Usando toda a informação relativa às estações da Figueira da Foz, Sines e Faro, desde 1980 até ao corrente ano, são caracterizadas as condições médias globais, as condições médias sazonais e as condições extremas, na costa oeste e na costa sul de Portugal. As condições de temporal nas duas áreas referidas são tipificadas de acordo com as situações meteorológicas dominantes no Atlântico Norte.
An 11-year time series of high-resolution beach profile surveys made on an Atlantic Ocean beach was analyzed for spatial and temporal characteristics of beach profile change. Approximately 300 profile surveys, most extending from the dune to 8-m depth, were available for the analysis on each of four cross-shore lines, together with electronically recorded and statistically processed wave time series from a nearshore gage located seaward of the survey site. The profile survey data set was analyzed for such quantities as depth change, frequency of depth change, general seasonal shape of the profile, seasonal depth change, and change in the profile produced by extreme storms. The morphodynamics of an inner and outer longshore bar were also examined, including depth to bar crest, bar height and length, and speed of bar movement onshore and offshore. Several properties of depth change were related to wave characteristics. Representative results were: average profile elevation change from +4 m to -4 m was symmetric about the mean sea-level shoreline; the average spring and autumn profile shapes were almost identical and occurred as transitional states between the summer and winter profile shapes; the depth of active profile movement (within survey accuracy of about 0.025 m) was 4 m for the summer and 6 m for the winter; and the 10-year frequencies of maximum absolute depth change in depths of 2, 4, 6, and 8 m were 1.64, 1.38, 0.22, and 0.12 m, respectively. A surprising result was that typical large storms transported sand into the nearshore from the seaward end of the profile (from a depth of about 6–8 m).
The quantity of coastline retreat resulting from storm erosion is one of the most important phenomena that needs to be accurately quantified to facilitate effective coastal management strategies. Historically, the volume of storm erosion (and coastline retreat) accommodated for coastal planning decisions has been directly linked to the storm (usually defined by considering wave height and duration only) with a certain pre-defined return period, known as a Synthetic Design Storm (SDS) (e.g. I in 100 year storm). The SDS method of estimating storm erosion volumes for coastal planning thus assumes that, for example, the 1 in 100 year storm event also results in a I in 100 year erosion event. This communication discusses the physical reality of this assumption and demonstrates the improved performance of a new method, based on joint Probability Distributions (JPD) for estimating storm erosion volumes proposed by Callaghan et al. [Callaghan, D.P., Nielsen, P., Short, A-D. and Ranasinghe, R., 2008. Statistical simulation of wave climate and extreme beach erosion. Coastal Engineering, 55(5): 375-390] using one of the world's longest beach profile surveys from Sydney, Australia.
Cambridge Core - Oceanography and Marine Science - Coasts - by Colin D. Woodroffe
The barrier system moves as a whole, so that the sediment balance is relative to the moving shoreline (Lagrangian grid). Application of a continuity model to the budget suggests that, in places, the barrier system is supplied with sand from the shelf. -from Authors
Storms are the main mechanism responsible for coastal erosion on open coastlines. There is a vast amount of literature on the consequences of extreme single storms, however the knowledge of the consequences of storm groups is recent and scarce. This study compares the predicted effect of single storms with an associated return period and the cumulative effect of average storm groups on the Portuguese west coast. This comparison is made through the use of the convolution model. It was found that storm groups with relatively small return periods induce average erosion volumes as significant as a single storm with a much longer return period. For coastal areas with frequent storm groups the use of the predicted effects of extreme single storms with associated return periods is, therefore, not correct for defining design storm conditions or to take management decisions. A conceptual approach for design storm conditions is presented, where the determination of global erosion volume return periods should be made, incorporating both consequences from individual storms and storm groups, with the latter ones considered as a single large individual event. This procedure would allow to obtain better results and to minimise underestimations.
The constituent processes (waves, currents, sediment transport) and their interaction with the bottom topography changes (morphodynamics) are considered at various space and time scales. Mathematical modelling has much to add to the analysis and interpretation of large-scale coastal dynamics, especially if it can be integrated with laboratory and field measurements. -from Author
Beach erosion is one of the most significant impacts of coastal storms because beach width is a measure of coastal vulnerability for beachfront houses. Storm tide, wave energy, and duration are three major factors determining storm erosion potential. Several authors have proposed erosion indexes for large storms in terms of storm intensity measured by wind speed or wave energy and duration, but the role of the storm tide has not been fully incorporated into previous analyses. It has been found that the erosion potential of severe nor'easters is more dependent on storm tide than wave energy and duration. Thus, we propose a quantitative index of storm erosion potential that includes storm tide based on hourly water level measurements. Our storm erosion potential index (SEPI) is the sum of the products of hourly storm surge and corresponding storm tide water levels, and it correlates well with observed erosion.
Spectral analysis of the 1962 great Atlantic coast storm penetration (overwash) along the Outer Banks of North Carolina and Fenwick Island, Maryland, reveals along-the-coast periodicities ranging in wavelength from 14 km to 15 km. Periodicities with similar wavelengths exist in long-term mean rates of change of the shoreline and storm-surge penetration line. This suggests the location and magnitude of storm deposits and storm hazards along the Atlantic coast are systematically distributed.
A 2-yr set of profile data from Torrey Pines Beach, California, measured at monthly intervals has been statistically analyzed by using empirical eigenfunctions. The analysis separates the temporal and spatial dependence of the data, this separation permitting beach changes to be described objectively by a linear combination of corresponding time and space functions. Most of the variation in profile configuration can be accounted for by three eigenfunctions corresponding to the three largest eigenvalues. The largest eigenvalue corresponds to an eigenfunction called the'mean beach function,' which represents an average profile. A second eigenfunction, the 'bar-berm function,' has a large maximum at the location of the summer berm and a minimum at the location of the winter bar, indicating its relation to the seasonal onshore-offshore movement of sand. The third eigenfunction, the 'terrace function,' has a maximum at the location of the low-tide terrace. Results of this study indicate that the eigenfunctions are useful in the analysis of beach profile data and provide objective insight into the nature of the variations of the profile configuration. sent the variation of the beach profile configuration in terms of distance from. fixed data points and in terms of temporal changes in profile configuration over the period of study. No standard set of terms exists for describing beach profile features. However, certain features are sufficiently common in their occurrence to be recognized on most beaches and have been given names that are ill defined but are in general usage. Figure I (Inman, 1971) shows the morphological definition of some important beach features. This study will be concerned primarily with three of these features which are the basic parts of the beach profile; the berm and beach face, the terrace, and the bar. Movement or change in these three features accounts for most of the changes in beach profile configuration and con sequently is most significant in describing profile changes. Since these three features are so important in the profile changes, the morphologic term has also been applied to the appropriate statistical function.
Many coastal engineering problems require an estimate of the seaward limit of sediment transport, defined as the minimum depth at which no measurable change in water depth occurs. A procedure to estimate this limit depth was evaluated using measurements collected at the Coastal Engineering Research Center's Field Research Facility located on the Atlantic Ocean. The data consisted of measured wave characteristics and accurate repetitive nearshore surveys which extended out to a depth of 30 ft (9 m). Ten unique data points were used in the evaluation with measured limit depths ranging from 18 to 21 (3.9 to 6.4 m). These depths were overpredicted by an average of 4.6 ft (1.4 m). This difference could be reduced to 1.3 ft (0.4 m) by adjusting the coefficients in the equation. A reasonable correlation was also obtained using a simple multiple of wave height.
The paper addresses the possible role of mathematical models in the analysis of large-scale coastal behaviour (LSCB). The constituent processes (waves, currents, sediment transport) and their interaction with the bottom topography changes (morphodynamics) are considered at various space and time scales.The overall conclusion is, that mathematical modelling has much to add to the analysis and interpretation of large-scale coastal dynamics, especially if it can be integrated with laboratory and field measurements.
An analysis of storm-driven sedimentary changes on the shoreface of a low-wave-energy cuspate delta on the southern coast of Spain is examined. Bathymetric surveys, ranging from 1- to 40-m depth, were collected 2 days before and 9 days after a high-magnitude Levante storm. The storm lasted only 36 hours, with peak wind gusts of 100 km/h (28 m/s) and maximum wave heights of 7.4 m. Storms of similar magnitude have only been recorded four times in the last 20 years along this coast. The deltaic nearshore and shoreface was divided into three main morphologic and morphodynamic zones based on process-response mechanisms following the storm event. The eastern section, characterised by a steep and concave shoreface, only had minor erosion and deposition as a result of the storm. The area seaward of the river mouth, an intermediate zone where the coastline changes orientation, is characterised by a widening surf zone and an irregular shoreface out to 10-m depth before dipping steeply to 40-m depth. Poststorm changes along this transitional area resulted in the deposition of a thin veneer of sediment over a 3 km(2) area from 10- to 40-m depth. The western section, a shallow and wide delta front with a double-bar, a trough, and shore-oblique topography, was modified the most by the storm, with significant upper shoreface erosion and shore-oblique erosional scars in 5-7-m depth. Results of spectral wave modelling of wave-induced force match well with observed morphological change; force is minimal along the east coast, more pronounced along the steep shoreface opposite the river mouth, and at a maximum along the west coast. It is suggested that coastal orientation, shoreface morphology (topography, gradients), and storm parameters (wave and wind direction) generated contrasting wind and wave-induced currents on the delta shoreface, resulting in spatial differences in storm response.
Sand characteristics and annual wave statistics at a site are used to determine two water depths bounding a shoal zone on the beach profile. This zonation is based on two thresholds of wave-induced sand agitation, so that expected waves during a year have neither strong nor negligible effects on the sand bottom within the shoal zone. The calculation procedure and representative results for the shoal zone bounds are presented to supplement techniques for estimating a seaward limit of significant sand transport given in the Shore Protection Manual (SPM). A calculator program is provided. (Author)
A series of field studies were carried out on three Portuguese beaches (Garra˜o, Faro and Culatra) to assess sand-mixing depths under a range of wave heights (0.34–0.80 m), wave periods (5.1–7.0 s) and mean grain sizes (0.26 and 0.38 mm). All the studied beaches had a reflective profile with a steep upper foreshore (tanβ of 0.10–0.14) and a more gentle low-tide terrace. In all experiments, plunging waves were breaking on the beach face. The study has identified a linear correlation between significant wave height at breaking (Hb), and average sand-mixing depth (Zm), whereby Zm = 0.27Hb. The empirical relationship is ten times larger than a previous one proposed by other authors working on gentle-slope dissipative beaches, and confirms previous findings on similar reflective beaches carried out in the USA. It was also confirmed that Zm is related to wave period, but does not seem to be a function of mean sand size.
Coastal sediment transport and associated morphological change can be examined at many spatial and temporal scales. These scales range from instantaneous movement of single grains on a time scale of the local turbulence to seasonal and long-term movement of large sand bodies such as longshore bars and tidal deltas. Researchers have begun to recognize that a first-principles (microscale) approach to calculating long-term and large-scale (megascale) coastal change may not be possible or even adequate. Therefore, new approaches are being sought to advance quantitative understanding and prediction of large-scale coastal behavior. The present paper opens with a discussion of compatible spatial and temporal scales for calculating sediment transport and morphology change. Motivation is given for the need to calculate morphologic change at scales greater than the typical one of microscale. Example calculations are made at different scales, showing the assumptions and approximations of each. The main conclusion is that calculations at different scales can be related and reconciled if limitations in prediction of initial and boundary conditions and in the fluid forcing are recognized.
This paper presents results of experimental and mathematical modelling of beach and dune erosion under storm events. Re-analysis of the experimental results on dune erosion in small-scale and large-scale flumes shows that the dune erosion for extreme conditions is somewhat smaller than that based on earlier analysis results.Dune erosion caused by wave impact has been modelled by a cross-shore profile model (CROSMOR-model), which is based on a ‘wave by wave’ modelling approach solving the wave energy equation for each individual wave. The model has been applied to the recent Deltaflume experiments on dune erosion. The three main processes affecting dune erosion have been taken into account: the generation of low-frequency effects, the production of extra turbulence due to wave breaking and wave collision and the sliding of the dune face due to wave impact. The calibrated model can very well simulate the observed dune erosion above the storm surge level during storm events in small-scale facilities, large-scale facilities and in the protoype (1953 storm in The Netherlands) using the same model settings. The mathematical model results have been used to develop a new simplified dune erosion rule.
Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.
The US Army Corps of Engineers' Field Research Facility (FRF) at Duck, North Carolina, has collected approximately biweekly beach-nearshore profile data to 8-m depth and associated wave data since 1981. Sediment budget analysis was used to examine the medium-scale (years to a decade) variability of the beach-nearshore profile from 1981 to 1991. Significant changes occurred during four groups of energetic storm events during February/March of 1983, 1987, 1989 and December 1989. Each group was comprised of at least two storms within a period of less than 39 days both with Hmo > 4 m. During each storm group, offshore sediment movement caused a distinct outer bar to migrate offshore and grow in size resulting in an abrupt increase in the volume of sediment on the upper shoreface. The net profile changes were much larger than the changes due to single storms and the cumulative effect of the storms can be considered as one ‘event’. During these events, the first storm appears to have a destabilizing effect on the profile which has insufficient time to recover before the second (and subsequent) storm (s). As a result, several storms in quick succession are able to have a large impact on the morphology. The intervening periods between the groups of storm events (termed fairweather conditions) lasted up to 4 years. They are characterized by slow, but steady sediment redistribution (averaging 33 m3 m−1 year−1) from the upper shoreface (> 5 m depth) toward the shore, while the total sediment volume was effectively constant. The onshore feed of sediment was not significantly affected by individual storms during the fairweather conditions. These two processes of (1) morphologic change during groups of storm events and (2) the steady onshore feed of sediments from the shoreface during fairweather conditions appear to play an important role on medium- and long-term profile evolution at least at Duck.
Determination of inlet hazard areas (IHAs) is important for the management of barrier island systems such as the Ria Formosa. An IHA is an area of natural importance that can be easily destroyed by inlet-related processes and covers the land adjacent to inlets [CAMA, 2004. Handbook for Development in Coastal North Carolina. Division of Coastal Management from the North Carolina State Department of Environmental and Natural Resources. http://www.nccoastalmanagement.net/Handbook/contents.htm, (accessed 07.04)]. One parameter is defined in order to quantify the extension of the inlet-associated hazards within a barrier island system. This parameter, the minimum inlet hazard area (IHAmin), represents the extent of the minimum area that should be taken into account when analysing inlet-associated hazards and is determined using the following criteria: (a) inlet maximum width; (b) inlet migration path and (c) existence of frequently overwashed areas that can be related to present or historic inlets. The calculation of the IHAmin was applied to the Ria Formosa barrier island system (southern Portugal) for a time scale of decades. For the Ria Formosa the IHAmin represents approximately 45% of the total length of the system. Most of the occupied areas within the barrier chain are located inside the IHAmin. Changes in the configuration and number of inlets of the system would modify the total IHAmin calculated for the entire area. However, assuming that the typical migration patterns identified for the system do not change, the herein proposed methodology can still be applicable to calculate the new associated IHAmin. This study showed that other studies should be considered in future work including: (i) quantifying buffer distances on both sides of the IHAmin and (ii) analyses of the inland extent of the hazardous areas. The IHAmin is an easy-to-use parameter that could be quantified for other inlets located in other parts of the world.
In an earlier paper a particular discrete wavelet transform (DWT) was used to study the complex variation of beach profile changes. However, use of the DWT requires that the sequence of spatial and temporal resolution is fixed as a dyadic sequence, which means that the variability over longer intervals is not characterised well. Here we introduce the discrete wavelet packet transform (DWPT) that uses an adaptive scaling to partition the data variance, according to an entropy cost function. The advantages of this approach are demonstrated by its application to the study of temporal variability of a 22 year record of beach profile data from the Field Research Facility (FRF) at Duck, North Carolina, USA. Time series of beach elevations at three locations across a particular profile are investigated in detail. We conclude that the DWPT provides a superior analysis of non-stationary time series to that of the DWT, with improved resolution of the scale intervals of the variability. The beach elevation around the shoreline is shown to respond at both sub-annual and interannual scales, but variability at an annual scale is weak. Moving seaward into deeper water, the variance is partitioned into fewer and longer scales. It is confirmed that elevation changes around the inner bar at Duck exhibit a strong interannual variation consistent with Plant et al. (Plant, N.G., Holman, R.A. and Freilich, M.H., 1999. A simple model for interannual sandbar behaviour. Journal of Geophysical Research 104(C7), 15755–15776). Around 23% of the variance around the inner bar is explained at the temporal scale of 64–128 months, which is consistent with the bar behaviour of 6 years found by Ruessink et al. (Ruessink, B. G., Wijnberg, K. M., Holman, R. A., Kuriyama, Y. and Van Enckevort, I. M. J., 2003. Intersite comparison of interannual nearshore bar behaviour. Journal of Geophysical Research, 108 (C8): 1–12). A significant new finding is, however, that about 26% of the variance is attributable to temporal scales of 16–21.3 months. Reconstruction of the wavelet packet components for individual temporal scales is shown to provide a means for identifying the impact and scale of non-stationary events, such as storms, on the beach response. This provides further information that can be used to interpret the morphological changes in terms of the forcing processes and also serves to inform morphodynamic modelling.
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