Article

Tracking clast mobility using RFID sensors on a boulder beach in Galicia, NW Spain

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Abstract

Previous studies using unmanned aerial vehicles and remote sensing techniques have provided data on group sediment dynamics and overall mobility of a boulder beach at Oia in Galicia, northwestern Spain. They recorded changes in the location and disposition of hundreds of clasts but were unable to trace the intermittent movement of individual boulders. Radio Frequency IDentification (RFID) sensors were used in the present study to identify and record the long-term trajectories of boulders in this area. Sensors were installed in 80 boulders (mean intermediate axes approximately 55 cm) in September 2016 and were used to locate and record their displacement on five occasions, terminating in December 2019. Although burial and other factors prevented data being collected from every tagged boulder during these periods, recovery rates ranged from approximately 50%–75% of the original population. There was considerable variability in the displacement of the boulders, with maxima of >20 m and mean values >5 m. The distance of travel tended to decrease during the course of this study, despite a corresponding increase in storm frequency and intensity. Patterns of movement, including transport distance and direction were essentially chaotic in nature, reflecting the complex interaction and compound effect of a multitude of controls related to such factors as the location of boulders on the beach, their relationship to surrounding boulders, including the effects of sheltering, interlocking, and burial, and their size, shape, and other physical characteristics. The unpredictable behaviour and high transport thresholds of boulder beaches are in contrast to sand and gravel beaches that are characterized by more uniform and predictable patterns of sediment transport and morphological change.

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... Mega-boulders, those greater than 1 m in length, are frequent sediments on many rock coasts. Although they appear to be motionless, they are in fact able to move during storms (e.g., Fichaut and Suanez, 2011;Paris et al., 2011;Pérez-Alberti and Trenhaile, 2015;Naylor et al., 2016;Erdmann et al., 2018;Kennedy et al., 2019;Hastewell et al., 2020;Oliveira et al., 2020;Scheffers and Kelletat, 2020;Gómez-Pazo et al., 2021) or tsunamis (e.g., Nott, 1997;Marie, 2008;Oetjen et al., 2020). Identifying the type of high energy event that can mobilize boulders on rock coast systems has been a recurring debate among rock coast geomorphologists for about 30 years Trenhaile, 2016). ...
... This technique has recently been used in dynamic geomorphology, first on gravel-bed rivers (Nichols, 2004;Lamarre et al., 2005) and then in coastal environments to study pebble and cobble transport on beaches (Allan et al., 2006;Curtiss et al., 2009;Bertoni et al., 2010;Dickson et al., 2011;Miller et al., 2011;Dolphin et al., 2016;Han et al., 2017) or mega-boulder motion (Neumeier, 2011;Marie et al., 2013;Hastewell et al., 2019Hastewell et al., , 2020Gómez-Pazo et al., 2021). ...
... This made it possible to measure only the net movement over one year, since the boulder may have had multiple transport events during that period. Gómez-Pazo et al. (2021) clearly underlined the limits of this method (insufficient sampling frequency to know the number of transports and their regularity in length and direction, to relate boulder movement to specific events, boulder representativeness). ...
Article
One hundred mega-boulders were tagged to survey their movements (RFID) for five winters (2012–2017) in Sainte-Luce, St. Lawrence Maritime Estuary, where the foreshore is frozen for two to four months per year. In addition, four boulders were fitted with accelerometers to determine the exact periods of motion. It was found that 81% of the boulders moved during at least one of the winters studied. The maximum transport recorded in one winter was 151.87 m for a 3.1 t boulder, but most boulders moved shorter distances (2012–2017 average transport: 9.74 m, standard deviation 23.71). The relationships between length/direction of boulder movements and fast-ice activity as well as weather and oceanic conditions were analyzed. 61% of mobility events took place at the end of the ice period during ice-foot break-up by storm waves or melting, but 37% took place at the beginning of the fast-ice phase during storms and/or high tide, which was unexpected. The length and direction of transport was found to depend on conditions during ice break-up (wind, waves, currents, ice thickness), which have large interannual variabilities. However, a greater proportion of boulders moved landward between 2012 and 2017. Two transport modes occurred: short pushing by ice floes and ice-rafting over longer distances. The first is much more common (70 to 90%) while the second seems to be more frequent during cold winters, when ice is thicker. Moreover, we demonstrated that the geomorphological setting exerts a strong control on boulder transport distance. The longest movements took place near mean sea level, where the ice foot is thicker and the rock platform smooth while cobble and boulder pavements inhibit movements.
... These works provided a first approach to the landscape of these areas and an interpretation of their possible evolution. Since then, new techniques and devices have been applied to understand the evolution of rocky coasts, among which the following are worth highlighting: TMEM (transverse micro-erosion meters) [11,[20][21][22][23][24], TLS (terrestrial laser scanning) [25,26], LiDAR (light detection and ranging) [27][28][29], hardness testers [30][31][32], aerial and satellite images [33][34][35][36], or sensors as RFID (radio frequency identification) [14,[37][38][39] among others ( Figure 2). This improvement in research on rocky coasts has been related to technical and technological advances (Figure 2), which have partly solved the problems associated with measurements in these areas [40]. ...
... It constitutes one of the first areas analyzed with these vehicles. As described in previous works [3,37,47,48], the boulder beach is approximately 20 m wide and 100 m long. This boulder beach is located at the edge of a shore platform and is limited by two rocky promontories to the north and south. ...
... However, size by itself is not sufficient to explain the differences, because in some cases, larger boulders moved while smaller ones remained in place. For this reason, it is essential to understand that the beach environment is key to explaining their dynamics, with a great emphasis on the degree of confinement [37]. Boulder groups could have a more reduced movement capacity, while isolated boulders have a greater degree of freedom to move around. ...
Article
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Rocky coasts represent three quarters of all coastlines worldwide. These areas are part of ecosystems of great ecological value, but their steep configuration and their elevation make field surveys difficult. This fact, together with their lower variation rates, explains the lower numbers of publications about cliffs and rocky coasts in general compared with those about beach-dune systems. The introduction of UAVs in research, has enormously expanded the possibilities for the study of rocky coasts. Their relative low costs allow for the generation of information with a high level of detail. This information, combined with GIS tools, enables coastal analysis based on Digital Models and high spatial resolution images. This investigation summarizes the main results obtained with the help of UAVs between 2012 and the present day in rocky coastline sections in the northwest of the Iberian Peninsula. These investigations have particularly focused on monitoring the dynamics of boulder beaches, cliffs, and shore platforms, as well as the structure and function of ecosystems. This work demonstrates the importance of unmanned aerial vehicles (UAVs) for coastal studies and their usefulness for improving coastal management. The Galician case was used to explain their importance and the advances in the UAVs' techniques.
... A partir de estos resultados se introdujeron sensores RFID en el caso de Oia, este ha sido uno de los primeros usos de RFIDs en ambientes con acumulaciones de bloques, aunque previamente se habían empleado en plataformas costeras y sectores antrópicos (Bertoni et al., 2016;Hastewell et al., 2019). Con el análisis entre 2016 y 2019 se han identificado los principales patrones de movimiento en Oia con variaciones superiores a los 20 m y se han podido conocer en detalle los sectores más dinámicos (Gómez-Pazo et al., 2021b;Gómez-Pazo & Pérez-Alberti, 2017). ...
Article
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Resumen de la tesis doctoral de Alejandro Gómez Pazo, presentada en la Universidad de Santiago de Compostela con el título "Aplicación de novas tecnoloxías no estudo da costa de Galicia dirixidas a unha nova xestión no contexto do cambio global". Publicado en la sección de tesis doctorales del Boletín de la Asociación de Geógrafos Españoles
... Outro avance no eido tecnolóxico que ten un gran impacto no mundo da investigación é a integración dos sensores RFID nos estudos costeiros. Estes chegaron á investigación por medio dos proxectos en ambientes fluviais e de montaña (Nichols 2004;Liébault et al., 2012;Ravazzolo et al., 2015) e máis recentemente chegaron á costa, en primeiro lugar en ambientes artificiais e máis recentemente, en traballos coma este, empregáronse en praias de bloques naturais (Allan et al., 2006;Benelli et al., 2011;Dickson et al., 2011;Chapuis et al., 2014;Casamayor et al., 2015;Bertoni et al., 2016;Gómez-Pazo e Pérez-Alberti 2017a;Hastewell et al., 2019;Hastewell et al., 2020;Gómez-Pazo et al., 2021b). ...
Thesis
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The aim of this research is to deepen the knowledge of rocky coasts in general, and the Galician coasts in particular. This project carries out an analysis in different scales using the new technologies as the base to improve the coastal knowledge. Devices such as the Equotip are used at the microscale, in the mesoscale this project used RFID (Radio Frequency IDentification) sensors to analyze the displacements in boulder beaches, and lastly, UAV flights data are used in the macroscale to understand the behavior of different coastal typologies, as boulder beaches or cliff areas. Based on the obtained results and from the literature review, we proceed to analyze the risks associated with each type of coast, with particular emphasis in their vulnerability in the global change context. Thus, we developed the necessary recommendations for the existing risks, to improve the coastal management, reviewing the coastal management plans evolution and their possible future.
... The tracing experiment of the Elwha River delta reported by Miller et al. (2011) was notably used to reconstruct volumetric sediment fluxes at two different sites with contrasting angles of breaking waves, showing more intense sediment transport for the site with less oblique angle, a field observation in contradiction with predictions from longshore sediment transport models. More recently, RFID tags have been used to study intertidal boulder transport during storm events, with direct implications for the morphological evolution of rocky coasts in the UK (Hastewell et al., 2019(Hastewell et al., , 2020 and NW Spain (Gómez-Pazo et al., 2021). Field studies reported in the UK notably revealed that very large boulders (more than 10 t) can be transported during contemporary storms of moderate intensity. ...
Preprint
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Boulder transport is an area of growing interest to coastal scientists as a means of improving our understanding of the complex interactions between extreme wave activity and the evolution of rocky coasts. However, our knowledge of the response of intertidal boulder deposits to contemporary storm events remains limited due to a lack of quantifiable field‐based evidence. We address this by presenting a methodology incorporating Radio Frequency Identification (RFID) tagging and Differential Global Positioning Navigation Satellite System (DGNSS) technology to monitor and accurately quantify the displacement of RFID tagged boulders resulting from storm wave activity. Based on preliminary findings we highlight the suitability of the technology and methodology to better understand the spatial and temporal response of intertidal boulders to contemporary storm events. We inserted RFID tags in 104 limestone boulders (intermediate axes from 0.27 to 2.85m) across a range of morphogenic settings at two sites on the intertidal shore platforms at Bembridge, Isle of Wight (UK). Fifteen topographic surveys were conducted between July 2015 and May 2017 to relocate and record tagged boulder locations (tag recovery rate: 91%). The relocated boulder coordinate data from both sites identified 164 individual transport events in 63% of the tagged boulder array amounting to 184.6m of transport, including the displacement of a boulder exceeding 10 tonnes. Incidents of boulder quarrying and overturning during transport were also recorded, demonstrating that despite the relatively sheltered location intertidal boulders are created and regularly transported under moderate storm conditions. This suggests that contemporary storm events have a greater propensity to mobilise boulders in the intertidal range than has previously been realised. Consequently, by documenting our methodology we provide guidance to others and promote further use of RFID technology to enable new hypotheses on boulder transport to be tested in a range of field settings and wave regimes.
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The role of rocky coasts as depositional environments has been generally neglected by rock- and depositional-coast workers. Although rock coasts can be hostile sedimentary environments, they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles. These deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs, isolated boulders, pocket beaches trapped between headlands, and sand to boulder beaches in shallow bays exposed to strong wave action. The tectonic setting, which is reflected in the degree of geological heterogeneity alongshore, together with the wave regime and other elements of the morphogenic environment, help to determine the amount and mobility of the sediment, and consequently whether it plays an essentially abrasional or protectional role. Many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century. Wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity, and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment. Theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands, or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands.
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Studies of coastal vulnerability due to climate change tend to focus on the consequences of sea level rise, rather than the complex coastal responses resulting from changes to the extreme wave climate. Here we investigate the 2013/2014 winter wave conditions that severely impacted the Atlantic coast of Europe and demonstrate that this winter was the most energetic along most of the Atlantic coast of Europe since at least 1948. Along exposed open-coast sites, extensive beach and dune erosion occurred due to offshore sediment transport. More sheltered sites experienced less erosion and one of the sites even experienced accretion due to beach rotation induced by alongshore sediment transport. Storm wave conditions such as were encountered during the 2013/2014 winter have the potential to dramatically change the equilibrium state (beach gradient, coastal alignment, and nearshore bar position) of beaches along the Atlantic coast of Europe.
Article
Extreme wave events in coastal zones are principal drivers of geomorphic change. Evidence of boulder entrainment and erosional impact during storms is increasing. However, there is currently poor time coupling between pre- and post-storm measurements of coastal boulder deposits. Importantly there are no data reporting shore platform erosion, boulder entrainment and/or boulder transport during storm events - rock coast dynamics during storm events are currently unexplored. Here, we use high-resolution (daily) field data to measure and characterize coastal boulder transport before, during and after the extreme Northeast Atlantic extra-tropical cyclone Johanna in March 2008. Forty-eight limestone fine-medium boulders (n=46) and coarse cobbles (n=2) were tracked daily over a 0.1km2 intertidal area during this multi-day storm. Boulders were repeatedly entrained, transported and deposited, and in some cases broken down (n=1) or quarried (n=3), during the most intense days of the storm. Eighty-one percent (n=39) of boulders were located at both the start and end of the storm. Of these, 92% were entrained where entrainment patterns were closely aligned to wave parameters. These data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions. No statistically significant relationship was found between boulder size (mass) and net transport distance. Graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold, other factors influence transport distance. Paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance - where net transport distances were up to 39 times less where geomorphological control was greatest. These results have important implications for understanding and for accurately measuring and modelling boulder entrainment and transport. Coastal managers require these data for assessing erosion risk. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Article
Gravel beaches occupy a dominantly reflective morphodynamic domain, which has so far been relatively unexplored compared to their sandier counterparts. The dynamics of gravel beachfaces are considered in terms of step and berm evolution and their contribution to profile variation. Extensions of gravel profile types are considered in terms of relative gravel to sand volumes under the profile. The use of sediment assemblages and their association with both process dynamics and microscale morphology are presented via the concept of mosaics, which is considered to be the best approach toward better definition of microscale gravel beach morphodynamic regimes. There are limited morphodynamic links with gravel barrier evolution, though the mosaics as a statement of long-term barrier stability might be considered as a likelihood statement of potential future change.
Article
The critical threshold mass for boulders composing a beach is the mass of the largest stone entrained by the hydraulic forces associated with wave breaking and swash run-up. For any given storm event there is a maximum boulder mass that can be moved and another slightly larger boulder that has the minimum mass necessary to remain stable. Two equations are derived: one to estimate critical threshold mass and another to estimate minimum stable mass for boulders on a beach. The equations incorporate: stone density, beach slope, breaking wave height, water depth, wave period, run-up height, maximum swash velocity and average swash velocity. In both equations the wave force applied to the beach face is scaled relative to the elevation that wave energy raises the water surface. Scaling the wave force relative to the run-up elevation results in a critical threshold formula. This is given as equation (45). Its predictions accurately match field data giving the largest boulder transported on a beach during storm events. Scaling the wave force relative to the breaking wave height at the toe of the beach results in a stability formula. This is given as equation (46). It predicts stable mass in the range defined by the Hudson formula. Equation (46) has an advantage over the Hudson formula by incorporating the physically important parameters of wave period and swash velocity. Both equations could be useful in the initial evaluation and design of dynamic revetments constructed with quarry stone.
Chapter
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Article
Low altitude flights by a micro-drone were made in 2012 and 2013 over two boulder beaches in northwestern Spain. Geographical information system software was used to map the data. Boulder outlines from the first flight were recorded on 4796 clasts at Laxe Brava and 2508 clasts at Oia. Changes in location were identified by overlaying these outlines on the 2013 images. About 17.5 % of the boulders (mean surface area 0.32 m2) moved at Laxe Brava and about 53 % (mean surface area 0.23 m2) at Oia. Most movement on both beaches was between the mid-tide to about 2 m above the high tidal level. The location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at Laxe Brava and 3324 boulders at Oia. These elevations were compared with the elevations at the same locations in 2013. The occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines. The study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution, micro-drone technology. This article is protected by copyright. All rights reserved.
Article
Since the earliest use of this technology, a growing number of researchers have employed Passive Radio Frequency Identification (RFID) transponders to track sediment transport in gravel rivers and coastal environments. RFID transponders are advantageous because they are inexpensive, durable and use unique codes that allow sediment particle mobility and displacement to be assessed on a clast-by-clast basis. Despite these advantages, this technology is in need of a rigorous error and detection analysis. Many studies work with a precision of ~ 1 m, which is insufficient for some applications, and signal shadowing can occur due to clustering of tagged particles. Information on in-field performance is also incomplete with respect to burial and submergence, especially for different transponders and antennae combinations. The objectives of this study are to qualify and quantify the factors that influence the detection zone of RFID tracers including antenna type, transponder size, transponder orientation, burial depth, submergence and clustering. Results of this study show that the detection zone is complex in shape due to a set of lobes in the detection field and provide a better understanding of transponder detection shape for different RFID transponder/antenna combinations. This study highlights a strong influence of clustering and submergence, but no significant effect of burial. Finally we propose standard operating procedures for tagging and tracking in rivers and coastal environments. This article is protected by copyright. All rights reserved.
Article
This paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high-sediment-load mountain stream typical of alpine gravel-bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38·9-km² degraded catchment. In spring 2008, we deployed 451 tracers with b-axis ranging from 23 to 520 mm. Tracers were seeded along eight cross-sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3-km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right-skewed and heavy-tailed distributions, correctly fitted by a power-law function. This supports the idea that in gravel-bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low-flow channel were characterized by a 15- to 30-fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd.
Article
A mathematical model was used to study the development and dynamics of beaches on shore platforms. The model was based on assumptions that: the gradient of the beachface at its seaward edge must be greater than platform gradient; beach sediment tends to move landwards; and beach occurrence and extent depends upon the amount of sediment available. Equilibrium beachface gradient was related to breaker height, wave period, and sediment grain size. Three grain sizes were used, representing fine and coarse sand and pebble; two deep-water wave sets, representing storm wave and west coast swell wave environments; and two tidal ranges of 9.1 and 3.3 m. Runs were made using linear, concave, and convex platform profiles, with gradients ranging between about 0.6° and 8°. Because platform and beachface gradients are normally quite similar, shore platforms are unable to store much sediment. For a linear platform with a lower gradient than the beachface, sediment first accumulates at the cliff base and then, depending on the sediment available, extends increasingly seawards. Beach development first occurs on the gently sloping seaward portions of concave platforms and on the more landward portions of convex profiles. The amount of available material partly determines the landward and seaward extent of these beaches, respectively, although it is also controlled by beachface and platform gradients. Beaches on shore platforms become thinner and more gently sloping during storms, and they may disappear completely, depending on such factors as: sediment grain size, platform gradient, the amount of sediment that can be stored during calm conditions, wave characteristics, and the duration of the storm. The response of beaches on rocky coasts to rising sea level will be different from those on sedimentary coasts, and will depend, in part, on the morphology of the rocky foundation.
Article
This paper is the first review of coastal boulder studies; it serves as a peer-reviewed introduction to a special issue on the topic of ‘Boulders as a signature of storms on rock coasts’. Since 2004 and the Indian Ocean tsunami, most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo-tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms. There is growing empirical evidence demonstrating (on inter-annual to century timescales) that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level. Current process studies of how boulders are eroded, transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists. This special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion, transport and deposition. Here, we review the current state of knowledge about boulder dynamics, boulder responses to storms and boulders as sedimentary signatures of storm events. We identify gaps in our conceptual and quantitative understanding. Lastly, we propose means of addressing research gaps, improving consistency between researchers and collecting multi-purpose data. This review and the papers contained within the special issue provide an improved understanding of coastal dynamics; particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material (i.e. boulders or larger), which has hitherto been under represented in the literature.
Article
On 10 March 2008, a particularly high energy storm hit the French Atlantic coast and the western part of the English Channel. This storm did not generate exceptionally high waves: significant and maximum wave heights recorded in the Iroise Sea (Brittany) reached 10.85 and 18.17m respectively, whereas during the 1989–90 winter storms, they had reached 12 and 20m, respectively. The exceptional character of the March 2008 storm event arises from the fact that it occurred during an exceptional spring tide. From a morphogenetic point of view, the effects of this storm in terms of block quarrying, transport and deposition on Banneg Island (Brittany) were significant. This study shows that the weight of the blocks displaced during the event was between 0.07 and 42.64t, with a median value of 0.72t. More than 60% of the blocks were quarried from the wave-scoured cliff-top platform, demonstrating that the favoured zone for supplying material was located inland of the cliff. Two dominant modes of transport were involved depending on the relationship between extreme water levels and cliff height. At the centre of the island, the height of the waves breaking over the top of the cliffs on the western coast resulted in a torrential surge that flowed out towards the eastern coast of the island over a landward-sloping platform. On the western coast of the island, blocks weighing between 0.3 and 1.4 t were displaced between 50 and 90m from the cliff edge by this flow. At the flow outlet on the eastern coast (90m from the western cliff edge), a pit 1.6m deep was excavated at Porz ar Bagou cove and some of the mobilised blocks were deposited in two parallel lobes about 40m seaward of the eastern shoreline. Elsewhere on the island, block transport occurred by airborne projection although wave heights were lower than the altitude of the cliffs. The pressure exerted by breaking waves on the bedrock was sufficient to quarry and displace blocks. A temporal comparison of the changes recorded in the double and triple boulder ridges showed that the most seaward ridges were practically untouched with the most important changes occurring in the second and third ridges. These observations allow us to propose a spatio-temporal model for the accretion of cliff-top storm deposits (CTSDs), with the various stages of CTSD formation being directly related to the morphological evolution of the cliff.
Article
Size and mass of boulders and megaclast deposited from intense wave events of the past coupled with measures of depositional elevation, and transport distance are useful metrics to distinguish between tsunami or storm wave period. This outcome provides for a wave-competence scaling approach to better help distinguish between large storms and tsunamis because wave period for tsunamis and wind driven storm waves differ by an order of magnitude. However, wave-competence equations are simple linear approximations of a complex non-linear processes, hence interpretations of the results need to be taken carefully. At best they may help approximate wave forcing based on size of material transported coupled with other pieces of information gained from stratigraphy, imbrications and morphology of boulder and megaclast deposits, as well as aging techniques for temporal correlation with known storms and/or tsunamis. The focus here is to present a conceptual example of how to apply a wave-competence approach to a beach exposed to both tsunamis and major storm waves and how variance in backshore topography (hills and valleys) and source material (sea cliff erosion and scree slope development) may play into interpreting the mathematical results.
Article
In this paper we examine the sedimentological properties and morphodynamic evolution of a boulder beach at Huayanpeng Cape on Putuo Island off the southeast China coast. Focus is given to the formation of the boulder beach (256–2000mm diameter) and resulting morphology in relation to high-energy storms and seasonal typhoon. Holocene sea level rise to the present position at ca. 7000–6000yrs BP provides a long term window for the formation of the beach. The beach is primarily characterized from east to west by: 1) the convex to concave beach morphology, 2) reduced longest axis of the skeleton boulders, 3) decreased flatness of the skeleton boulders, and 4) greater sphericity of the skeleton boulders. Infilling cobbles/pebbles in the beach demonstrate a bi-modal distribution, corresponding to dominant sizes of 100–250mm and 50–100mm in diameter, on the eastern beach and western beach, respectively. This reflects changed intensity of storm waves alongshore. Multiple-peaks of the distributions of infilling clasts for the western beach (supratidal) probably reflect storm and calm weather sedimentation. Statistically, both the skeleton boulders and infilling clasts follow a β-distribution, reflecting the high-energy control of beach formation and the dominance of crushing in boulder size reduction. A boulder transport model applied in the present study further reveals that boulders with an a-axis length of 500–1000mm (the dominant component on the beach) move under a wide range of wave conditions depending on wave height and wave period with a cluster of critical wave heights in the range 2–6m and wave periods of 5–15s.
Article
Field observations from previous studies of boulder movements were compiled to augment our own work on boulders that have been displaced by storm waves during recent typhoon events in the Okinawa Islands, Japan to elucidate the ability of storm waves to move boulders. Our observations reveal that recent storm waves displaced by sliding and overturning 100-ton boulders emplacing them on the reef or high cliff tops and that storm waves might also be capable of displacing 200ton boulders on the reef. The weights of storm wave boulders at the Okinawa Islands are of comparable order to those boulders displaced by historical tsunami origins. Consequently, boulder weight alone is an inappropriate parameter to discriminate between tsunami or storm wave processes. However, these heavy storm wave boulders are close to the reef and cliff edges, while tsunami boulders can be deposited much further inland. Hence, horizontal displacement distance of boulders could be a useful parameter to discriminate boulders deposited by the tsunami and storm waves on the wide fringing reef. The storm wave boulders were characteristically concentrated on the southeastern (Pacific Ocean) sides of each island but large boulders are rarely found on the northwestern (East China Sea) side. This is probably because the storm wave intensities are generally stronger at the southeastern side than at the northwestern side, although differences of reef strength and initial condition of boulders should also be taken into account. Consideration of the high frequency of typhoons at the area suggests that effects of the storm waves and the consequent displacement of boulders on the reef might have contributed to the formation of the reef-moat framework that typifies the Okinawa Islands especially, if the moat is located within the transport limit of the storm wave boulders (approximately 300m from the reef edge at the islands).
Article
Few large-scale field measurements of longshore sediment transport have been undertaken on beaches composed of coarse sediments, in part owing to difficulties associated with measurement in energetic swash zones in which large clasts are moving. Here we present results from a field experiment in which Passive Integrated Transponder tags were used to investigate patterns of cobble transport over 8months on a mixed sand and gravel beach on the east coast of New Zealand. The study objectives were to document rates of alongshore transport, and measure rates of cobble abrasion under field conditions. Cobble recovery rates were highly variable over the study period with 30–60% recovery at site 1 compared to much lower (0–20%) recovery rates at sites 2 and 3. Consistent uni-directional patterns of net alongshore sediment transport were observed. The median cobble transport rate was approximately 500m over 207days, indicating long-term net northward transport rates on the order of 2–2.5m/day. Results highlight a number of factors, in addition to longshore energy flux, that are important for understanding the observed patterns. In particular, across-shore sediment transport during storms may have been smaller at site 1 than the other sites owing to lesser wave exposure. This is partly responsible for higher cobble recovery rates at this site and also an increased amount of time during which cobbles were able to be transported alongshore on the lower beachface. Unique to this study, results demonstrate the use of PIT tags to provide direct measurement of cobble abrasion under natural processes. Repeat weight measurement on individually tracked cobbles show that after 207days the median loss was 11.3g, or 1.8% of total weight. There was a general trend of abrasion increasing with net transport distance, but longshore cobble movement was highly variable ranging from 130 to 2500m.
Article
The rock coast of northwest Ireland comprises steep cliffed headlands and more open coastal sections where bedrock shore platforms are developed. Many shore platforms are overlain by boulders; the locations on the platform from which boulders are derived are marked by ‘holes’ of fresh and unweathered rock surfaces that are not, or are poorly, covered by lichen. These areas of boulder detachment are termed sockets. This paper examines the mapped distributions and physical properties of boulders, sockets and shore platform context of an Atlantic-facing granite shore in County Donegal, northwest Ireland. Results from Schmidt hammer rebound tests show statistically-significant differences in rebound values between areas inside and outside of sockets and between sockets and boulders. Based on their distributions and physical properties, relationships between sockets and boulders are explored. We calculate that sockets are formed rapidly by winter storms but are also rapidly weathered over c. 5years, becoming indistinguishable from the surrounding bedrock platform. We argue that, in contrast to some studies, boulders here were formed during recent winter storms (episodically during the last 150–200years) rather than by more ancient waves or by tsunamis. However, a significant proportion of boulders (c. 20%) are morphometrically dissimilar to sockets; we argue that these were formed by infrequent and unusually-powerful waves that stripped whole bedrock sheets off the platform surface and which detached boulders from the lower shoreface.
Article
The Schmidt Rock Test Hammer was used to study the effect of abrasion on shore platforms in Galicia, northwestern Spain. On platforms where tidally-induced weathering (salt, wetting and drying, etc.) is dominant, rock strength is significantly lower than in areas where abrasion is, or has been active in the recent past. This suggests that abrasion removes weathered surface material, exposing the stronger, less weathered rock below. Abrasion downwearing, measured with a transverse micro-erosion meter, ranged between 0.13 and 1.8 mm yr− 1 over the last year. Most active abrasion occurs in the upper part of the intertidal zone, but weathering is slowly destroying formerly abraded surfaces at lower elevations. These abandoned surfaces were abraded by materials supplied by erosion of fluvio-nival and periglacial slope deposits that covered, or partially covered, parts of the Galician coast during the middle and late Weichselian. During the Holocene, rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level. The spatial and temporal role of abrasion on this coast is, therefore, closely associated with the exhumation and inheritance of ancient platform surfaces from beneath Weichselian deposits.
Article
This paper is concerned with the effect of sediment accumulation on shore platform development. Boulder accumulations are common on the granitic shore platforms of Galicia, northwestern Spain. Boulders are produced by erosion of shore platforms and of cliffs consisting of cold-climate deposits from the last glacial period. Measurements were made of the long axis length of more than 800 boulders, and additionally of the short and intermediate axes of 340 of these boulders, as well as of their orientation and gradient. There were two study areas. The boulders on the Barbanza Peninsula are generally a little smaller than those in southern Galicia with, respectively; mean long axis lengths of 0.98 and 1.14, and masses of 1.06 and 1.59 t. There are also some isolated, very coarse boulders and megaclasts in southern Galicia. The distribution and extent of the deposits and boulder imbrication and orientation testify to the high levels of wave energy produced by northwesterly and westerly storms in this region. Although the boulders, as well as the underlying shore platforms, were inherited, in part, from previous interglacial stages, some boulder detachment and movement is occurring today during storms, when significant deep water wave heights exceed 8 to 10 m. Despite some abrasion of the shore platforms, the primary effect of large boulder accumulations is protective. The role of sediment on shore platforms has been neglected, but this study suggests that because of arrested development under thick accumulations, platform gradient in areas with abundant sediment increases with the grain size of the material. The occurrence and type of sediment on shore platforms may therefore help to explain the distribution of sloping and subhorizontal platforms under different morphogenic and geological conditions.
Article
Abstract Five boulder beaches located along the coast of New South Wales, Australia, were examined in order to determine if beaches composed of boulders differ in basic sedimentological structure and behavior from beaches composed of cobbles or pebbles. Each beach is aligned obliquely to the approaching waves and is composed of locally derived sediment. Investigation of beach-particle size, morphology, and roundness, along with foreshore slope, reveals consistent up-beach particle fining, positive size skewness, absence of shape zoning, absence of sphericity grading, and low foreshore slope. These characteristics of the five studied boulder beaches contrast markedly with the known characteristics of beaches composed of finer sediment, which suggests that boulders appear to form fundamentally distinct coastal sedimentary assemblages.
Article
There is increasing evidence that shore platforms and other elements of rock coasts may be inherited, at least in part, from interglacial stages when sea level was similar to today's. Most of this evidence, which includes ancient beaches and datable terrestrial deposits, has been obtained from areas of resistant, slowly eroding rock, where the platforms often appear to be much too wide to have developed since the sea reached its present level. It is much more difficult to demonstrate that inheritance has occurred in areas of weaker rock, which generally lack any datable material. The coast of western Galicia in northwestern Spain has shore platforms in igneous and metamorphic rocks that were deeply weathered during the Tertiary. These platforms are closely associated with ancient beaches from the last interglacial stage, and associated periglacial and fluvio-nival deposits that covered and fossilized most of the Eemian platforms and cliffs during the late middle and late Weichselian glacial stage. The sedimentary processes and the thickness and facies of the sediments were determined by the height, aspect and gradient of the coastal mountains, and their distance from the coast. Radiocarbon dating, sedimentary analysis and platform morphology indicate that the shore platforms of Galicia have been inherited from at least the last interglacial stage. They were fossilized in places beneath thick Weichselian deposits and then exhumed during the Holocene transgression. The abundant evidence for inheritance in Galicia has important implications for other coasts in fairly weak rocks where such evidence is generally lacking. Copyright © 2003 John Wiley & Sons, Ltd.
Article
The dominant processes in gravel beach dynamics are reviewed, highlighting some common themes which unify the various components of the gravel beach system, the repercussions of which impart on how gravel beach dynamics might be understood conceptually. In particular, gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size, and the continual adjustments made by an active beach step, both of which act not only as the expression of changing morphodynamic conditions, but also as a controlling influence. Morphodynamics, the notion that the exchanges on beaches between the hydrodynamics, sediment transport, and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms (in such a way that they cannot be thought of or studied independently) is not a new one. Yet it appears that for the gravel beach, morphodynamics must be re-defined to describe conditions where variations in sediment size are thought to deserve parity, rather than as merely a sequent entity or boundary condition. ‘Morpho-sedimentary-dynamics’ is a phrase coined to intuit such cause and effect, detailing the co-evolution of morphology, hydro-hydraulics and sediment properties whilst acknowledging causative pluralism, feedbacks and multiplier effects. This is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach. Essentially, it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system. Therefore, it is advised that simplicity will be most expedient in our future modelling efforts, if complexity is to be adequately encapsulated.
Article
Coastal boulder accumulations are often mentioned in the literature, even though their interpretation remains difficult, especially along rock coasts affected both by storms and tsunamis. Studies on the geomorphic impact of such high-energy events are actually of great interest, since their intensity and frequency are key issues for the future evolution of coasts in the framework of the global change. The southwest coast of Iceland faces the powerful storms of the North Atlantic Ocean, with wave heights of more than 15 m. The probability for past and present tsunamis to hit this coast is very low. In this paper, we describe boulder accumulations along the volcanic rock coast of Reykjanes (southwest Iceland). They consist of cliff-top boulders, clusters and ridges, beaches, and boulder fields. Large boulders, up to 70 t in weight, have been transported and deposited up to 65 m inland (6 masl). The maximum limit of boulder deposition and driftwood was found respectively 210 m and 550 m inland. Storms appear to be a predominant factor in the geomorphic evolution of Reykjanes coasts. Our observations also give new insight for the interpretation of coastal boulder accumulations. Processes of erosion and deposition by tsunamis are a rising topic in the literature, and the effects of recurrent and powerful storms are neglected.
Article
Cobble transport is investigated on a mixed sand-and-gravel beach on the high-energy Oregon coast using Radio Frequency Identification technology (RFID) to detect Passive Integrated Transponder (PIT) tags inserted in the gravels. PIT tags are glass-encapsulated transponders that are activated when an antenna passes near them, with each tag characterized by its own unique identification number. The tags are sealed within the cobbles, minimizing any effect on the hydrodynamic character of the particles. The tags draw power from the antenna itself, and have a potential lifespan of up to 50 years. PIT tags are simple to use and inexpensive, permitting the release and tracking of large numbers of gravel particles. As a result, PIT tags have tremendous potential for examining the complexities of particle movement and the parameters that control their distribution on the beach. Our experiments have been conducted at Cape Lookout State Park on the northern Oregon coast, on a composite beach where a seasonally variable sand beach fronts a mixed sand-and-gravel beach, with the latter impacted by waves only during the winter when the sand beach is cut back. A total of 400 cobble tracers have been released at five different locations. Subsequent monitoring of the gravel tracers revealed that they can be detected up to 1 m below the surface of the beach using a 1.0 m diameter antenna, and up to 0.5 m below the surface using a smaller 0.3 m diameter antenna, while their positions were determined using a Trimble 5700/5800 RTK-DGPS survey system. Gravel tracer recovery rates were found to vary significantly between the different release points, from as high as 90% recovery after 8 months, to a low of 18% after 17 months. The lowest recovery rates are thought to be due to the extent of aggradation of the sandy beach during the summer, partially covering the gravel berm and burying the tracer particles to depths where they could not be detected by the antennas used with our RFID system. Relocation of the gravel tracers has revealed a predominant northward migration of the cobbles, and locally demonstrate a strong cross-shore transport (both upslope and downslope movements). Initial attempts to examine the relationship between the transport distances and particle sizes and shapes have thus far revealed that the larger gravels are tending to outrun the smaller particles. This is despite the fact that both small and large particles were found to be capable of being transported both short and long distances. In contrast, our results revealed no relationships between particle shape and distance moved. In time, it is expected that the PIT tag tracers may begin to yield more definitive patterns of sorting. The results did highlight that the gravel movement occurs predominantly near the sand/gravel beach junction on the profiles, a region dominated by a higher incidence of wave breaking and strong swash activity. Finally, our analyses revealed the potential for using PIT tags to provide field assessments of the abrasion rates of gravel particles, having already found measurable degrees of weight loss to abrasion in our experiments.
Article
A radio frequency identification system was implemented to monitor the displacement of coarse particles following runoff in two upland, ephemeral channels on the USDA-ARS Walnut Gulch Experimental Watershed in southeastern Arizona, USA. Commercially available radio frequency identification components including transponders, an antenna, a reader, and software were used to develop a system for locating particles under field conditions. During the 2003 field season, 124 particles were located following four runoff events in two ephemeral channels. The locations of 340 particle positions were measured with a real-time kinematic geopositioning system after each particle was located with the radio frequency identification system. The overall recovery rate was 96%. The passive transponder system offers the advantages of low cost, consistent results under harsh environmental conditions, and no need for a power supply in the particle. The radio frequency identification system can be used to efficiently collect data for developing sediment transport equations and improving mathematical models for simulating sediment transport under natural runoff conditions.
Article
The Grind of the Navir is an ignimbrite headland on the exposed Atlantic coast of the Shetland Islands, Scotland. During storms, offshore wave heights exceed 20 m and deep water close inshore allows high-energy waves to impact on these cliffs. The cliff top at ∼ 15 m above sea level is awash with wave water when wave heights exceed 8 m, a condition met in storms in most years. Detailed mapping, ground photography and patterns of lichen colonisation and growth allow the processes, patterns and rates of erosion to be assessed on different parts of the headland over the past 100 years.
Zonificación del litoral balear frente a un posible derrame o vertido de hidrocarburo. Establecimiento de un Índice de Sensibilidad Ambiental (ISA) de la línea de costa
  • P Balaguer
  • G Vizoso
  • M I Ferrer
  • M Ruíz
  • P Orfila
  • G Basterretxea
  • T Jordi
  • J J Fornós
  • J Satorres
  • F X Roig-Munar
  • J Tintoré
Balaguer, P., Vizoso, G., Ferrer, M.I., Ruíz, M., Orfila, P., Basterretxea, G., Jordi, T., Fornós, J.J., Satorres, J., Roig-Munar, F.X., Tintoré, J., 2006. Zonificación del litoral balear frente a un posible derrame o vertido de hidrocarburo. Establecimiento de un Índice de Sensibilidad Ambiental (ISA) de la línea de costa. In: Pérez-Alberti A, López-Bedoya J (eds). Santiago de Compostela, pp 311-322.
Influence of Shape on the Fall Velocity of Sand Grains
  • A T Corey
Corey, A.T., 1949. Influence of Shape on the Fall Velocity of Sand Grains. Colorado State University
Zonificación del litoral balear frente a un posible derrame o vertido de hidrocarburo
  • Balaguer
10.9 coastal gravel systems
  • Orford