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Tracking clast mobility using RFID sensors on a boulder beach in Galicia, NW Spain
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.
... 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). ...
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. ...
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.
... In other cases, there are better developed platforms, up to 50-100 m wide, with a notable uniformity and an approximate slope between 0° and 2°, and they are covered by debris that form deposits of variable amplitude and strength, composed of materials with diameters ranging from those of gravels to metric blocks. Sometimes abrasion processes are responsible for its modeling, but there is evidence that in many cases weathering processes and, consequently, differential dissection, are responsible for its construction (Gómez-Pazo et al. 2021). ...
... The existing block beaches on the Atlantic coast are relatively abundant sectors in which large accumulations of blocks dominate. They are called "coidos" in Galician, and constitute one of the most unique elements of the Galician coastline, both for its configuration and its dynamics (Pérez-Alberti et al. 2012;Pérez-Alberti and Trenhaile 2015a, b;Gómez-Pazo et al. 2021). ...
Nowadays, a traditional image of Galicia still survives showing the country as a uniform territory, but in fact there is a very different reality that materializes in a wide set of spaces with numerous contrasting landscapes. This is due to several factors: (a) firstly, the existence of an extensive coastal strip and a wide continental territory; (b) secondly, the existence of altitudinal contrasts, linked from the coast to the interior; (c) thirdly, different climatic and biogeographic environments that can be found both on the coast and inland; (d) and, fourthly, a long geomorphological and anthropic evolution affecting to this geographic area.
The contrast between the coast and the interior is, without a doubt, a first element that explains the diversity of Galicia’s landscapes. The length of its coasts-more than 2000 km-and its sinuous profile, with numerous inlets and outlets, due to the chaining of estuaries, bays, inlets, and capes, favored the genesis of contrasting spaces, with linked rocky coasts, beaches, lagoons, estuaries and rías and dune systems. In addi-tion, from the coast inland, a clear staggering of terrain levels is observed. On the same seashore stands a set of mountains, which reach 500/600 m of altitude. This is the case of A Capelada and Montes da Candieira, between the Ortigueira and Cedeira estuaries; O Barbanza, between those of Muros/Noia and Arousa; the Montes do Castrove, between those of Arousa and Pontevedra, or the Montes da Groba and O Galiñeiro, situated in the south of the Vigo estuary.
The above commented staggering becomes more relevant towards the interior. If a west–east cut is made, it is seen that the terrain rises to 1100 m in the western sierras, descends to 400/500 m in the interior of Lugo and Ourense, and reaches 2000 m again in the eastern sierras, in the limits with Asturias and Castilla y León. Also to add the existence of a wide and diverse fluvial network that is intensely embedded, with a large number of narrow and deep valleys that give rise to hills with a diversity of slopes. If lithological diversity is also added to this, it is easier to understand the reasons for the visible differences in the landscapes. From west to east, igneous and metamorphic rocks and, to a lesser extent, sedimentary rocks, are situated in a linking chain. On the Atlantic façade, granites and granodiorites are dominant. In the central regions, mafic and ultramafic rocks are present (as peridotites, eclogites, or gabbro). In the north, schists. In the center and in the south, again granites. In the eastern regions, there are slate, quartzite, limestone and dolomite bands, with small granitic intrusions.
This diversity of lithology, topography and endogenous or exogenous processes, that took place in Galicia over millions of years, has given rise to the presence of landscapes marked by geological factors and that are visible in different places in the Iberian northwest.
Keywords: Geomorphology Landscape, Galicia, Northwestern Iberian Peninsula
... The existing block beaches on the Atlantic coast are relatively abundant sectors in which large accumulations of blocks dominate. They are called "coidos" in Galician, and constitute one of the most unique elements of the Galician coastline, both for its configuration and its dynamics (Pérez-Alberti et al. 2012;Pérez-Alberti and Trenhaile 2015a, b;Gómez-Pazo et al. 2021). ...
Galicia is a complex territory from the environmental (lithology, relief, climate) and socio-economic (population, distribution of productive activities) perspectives. Its geographical position has determined its paleoenvironmental dynamics throughout the last glacial cycle (Würm), in whose final phase a large part of the territory was under glacio-nival conditions, and has favored the emergence of favorable conditions for the domain of deciduous forests throughout the last two thirds of the Holocene. However, as a result of human colonization of most of this territory over the last 5,000 years, its vegetation cover has been greatly homogenized, first favoring the expansion of agricultural crops and scrublands (particularly heaths) and, already in recent times, forest plantations with introduced species (pines and Eucalyptus). The best examples of the characteristic vegetation of this territory take refuge in the steepest mountains, certain slightly altered coastal stretches, and some wetlands. Nonetheless, Galicia still harbors important elements (species, habitats) for the maintenance of biodiversity on a European scale. Its long-term persistence requires territorial planning and management of land use consistent with this singularity and in line with the evolving scientific knowledge and environmental regulations.KeywordsCurrent vegetationResidual forestsHeathsCoastal complexesWetlandsBiodiversity threats
... En las últimas décadas existe un gran número de ejemplos de uso de las nuevas tecnologías para estudios costeros, a partir de imágenes de satélite (Naylor et al., 2010), de datos de dron Boletín de la Asociación de Geógrafos Españoles, (96) (Hoffmeister et al., 2020;Long et al., 2016;Pérez-Alberti & Trenhaile, 2015), con el uso de dispositivos de medición en el terreno (Aoki & Matsukura, 2007;Feal-Pérez & Blanco-Chao, 2013;Viles et al., 2011) o mediante la introducción de sensores (Gómez-Pazo et al., 2021a, 2021bHastewell et al., 2020;Hastewell et al., 2019;Payo et al., 2020;Stephenson & Finlayson, 2009). ...
Coastal studies have a great relevance historically. This increase in the last with the new technologies and the possible global change impact. In this context, open-source tools represent a key element in these investigations. The present project analyzes the advantages and problems of open-source tools for estimate coastal variations and volumetric changes. For this purpose, a small sector of the Galician coast was used as an example. The open-source approaches have produced similar results to those obtained with proprietary software (ratios ≥ 0.97). In some cases, these methods improve processing times and allowing to users better possibilities for customization and decision-making.
... 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 north-west 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. ...
Open access− Billions of Radio-Frequency Identification (RFID) passive tags are produced yearly to identify goods remotely. New research and business applications are continuously arising, including recently localization and sensing to monitor earth surface processes. Indeed, passive tags can cost 10 to 100 times less than wireless sensors networks and require little maintenance, facilitating years-long monitoring with ten's to thousands of tags. This study reviews the existing and potential applications of RFID in geosciences. The most mature application today is the study of coarse sediment transport in rivers or coastal environments, using tags placed into pebbles. More recently, tag localization was used to monitor landslide displacement, with a centimetric accuracy. Sensing tags were used to detect a displacement threshold on unstable rocks, to monitor the soil moisture or temperature, and to monitor the snowpack temperature and snow water equivalent. RFID sensors, available today, could monitor other parameters, such as the vibration of structures, the tilt of unstable boulders, the strain of a material, or the salinity of water. Key challenges for using RFID monitoring more broadly in geosciences include the use of ground and aerial vehicles to collect data or localize tags, the increase in reading range and duration, the ability to use tags placed under ground, snow, water or vegetation, and the optimization of economical and environmental cost. As a pattern, passive RFID could fill a gap between wireless sensor networks and manual measurements, to collect data efficiently over large areas, during several years, at high spatial density and moderate cost.
... 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). ...
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). ...
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. ...
Billions of Radio-Frequency Identification (RFID) passive tags are produced yearly to identify goods remotely. New research and business applications are continuously arising, including recently localization and sensing to monitor earth surface processes. Indeed, passive tags can cost 10 to 100 times less than wireless sensors networks and require little maintenance, facilitating years-long monitoring with ten's to thousands of tags. This study reviews the existing and potential applications of RFID in geosciences. The major and mature application today is the study of coarse sediment transport during floods or debris flows, using tags placed into pebbles. More recently, tag localization was used to monitor landslide displacement, with a centimetric accuracy. Sensing tags were used to detect a displacement threshold on unstable rocks, and to monitor the moisture or the temperature of the soil. Propagation-based sensing was applied to monitor the properties of a volume of snow. RFID sensors, available today, can be applied to monitor other parameters, such as the vibration of structures, the tilt of unstable boulders, the strain of a material, or the salinity of water. We discuss the key challenges for using RFID monitoring more broadly in geosciences: the use of unmanned aerial vehicles to collect data or localize tags, the increase in reading range and duration, the ability to use tags placed under ground, snow, water or vegetation, and the optimization of economical and environmental cost. As a pattern, passive RFID could fill a gap between wireless sensor networks and manual measurements, to collect data efficiently over large areas, during several years, at high spatial density and moderate cost.
Extreme storm events in coastal zones play significant roles in shaping the morphology of boulder beaches. However, boulder displacement and the geomorphological evolution of boulder beaches driven by different extreme storm events, especially typhoon events, remain poorly understood. Thus, boulder displacement and the geomorphic response on a boulder beach in Fujian, southeastern China, were explored before, during and after a cold wave event (Dec. 1–7, 2020) and before and after Typhoon In-Fa (Jul. 19–27, 2021), a large tropical storm. This was achieved by tracking 42 tagged boulders distributed in the intertidal and supratidal zones using Radio Frequency Identification (RFID) and topographic surveys using real-time kinematic techniques, respectively. The results showed obvious disparities in boulder displacement in different geomorphic zones due to cold wave and typhoon events that were mainly characterized by migration magnitude, range, direction, and mode of transport. The typhoon event led to rapid and substantial changes in the overall morphology of the boulder beach, while the cold wave event impacted the intertidal morphology of the boulder beach to only a small extent. The surrounding structure of boulders, beach slope and beach elevation had a combined dominant effect on boulder displacement under the same extreme event. Hydrodynamic factors (effective wave energy fluxes, incident wave direction, storm surge and water level) had dominant effects on boulder displacement during different extreme events. In terms of a single event, the magnitude of the boulder displacement driven by the typhoon was much greater than that driven by the cold wave. However, considering the frequency and duration of cold waves in winter, the impact of multiple consecutive cold waves on the geomorphology of the boulder beach cannot be ignored in this study area. Alternating and repeated interactions between these two processes constitute the complete geomorphic evolution of the boulder beach. This study contributes to improved predictions of the morphodynamic response of boulder beaches to future storms, especially large tropical storms, and facilitates better coastal management.
Winter storms have significant morphological impacts in coastal areas, often leading to extensive infrastructure damage and socioeconomic disruption. While storm-dominated coastal environments, such as the northwest coast of Ireland, are generally attuned to highly energetic wave conditions, morphological impacts can be intensified by changes in the frequency and sequencing of storm events, particularly during storm-groups or exceptional winter seasons. Aiming to assess the variability in frequency and sequencing of wintertime wave conditions and storms in the northwest of Ireland, we combine observational records (M4 buoy) with data from two independent wave reanalyses (ERA-Interim and WAVEWATCH III) and perform a statistical analysis of wave conditions over the past six decades. Both reanalyses represent observed wave heights with very good skill. Excellent agreement between modelled data and observations was identified up to the 99th percentile, despite a slight underestimation/ overestimation by ERA-Interim/WAVEWATCH III for waves above the 90% exceedance level. The winter of 2014/15 was the most energetic on record (67 years), but not the stormiest. The results show that highly energetic and stormy winters occur in clusters during positive phases of the North Atlantic Oscillation. Significant positive temporal trends for winter wave height, number of storms per winter and average winter storm wave height, suggest that winters are becoming more energetic and stormier, with potential implications for the erosion and recovery of coastal systems in the northwest of Ireland.
The abrasion of coastal rock platforms by individual or clusters of clasts during transport has not been quantitatively assessed. We present a study which identifies the types of abrasion and quantifies erosion due to the transport of clasts during three storms in February and March 2016. We explore relationships between platform roughness, determined by the Fractal Dimension (D) of the topographic profiles, geomorphic controls and the type and frequency of abrasion feature observed. Clast transport experiments were undertaken in conjunction with the measurement of wave energy to assess transport dynamics under summer and winter (non‐storm) conditions.
Platform abrasion occurred extensively during the storms. We identify two types of clast abrasion trails: simple and complex. In addition, we find two forms of erosion occur on these trails: Scratch marks and Percussion marks. An estimated 13.6 m² of the platform surface was eroded by clast abrasion on simple abrasion trails during the three storms. We attribute approximately two thirds of this to scratch‐type abrasion. The total volume of material removed by abrasion was 67,808 cm³. Despite the larger surface area affected by scratch marks, we find that the volume of material removed through percussion impact was almost seven times greater. We also find that the type and frequency of abrasion features is strongly influenced by the effect of platform morphometry on transport mode, with impact‐type abrasion dominating areas of higher platform roughness. Results of the clast transport experiments indicate that abrasion occurs under non‐storm wave energy conditions with observable geomorphological effects. We suggest that abrasion by clasts is an important component of platform erosion on high energy Atlantic coastlines, particularly over longer time scales, and that the morphogenetic link between the cliff and the platform is important in this context as the sediment supplied by the cliff is used to abrade the platform.
Before-and-after photos of supratidal coastal boulder deposits (CBD) in the west of Ireland show that storms in the winter of 2013–2014 transported boulders at elevations up to 29 m above high water, and at inland distances up to 222 m. Among the clasts transported are eighteen weighing more than 50 t, six of which exceed 100 t. The largest boulder moved during those storms weighs a fairly astonishing 620 t.
The boulders moved in these recent storms provide pinning points for mapping storm-wave energies on coasts: their topographic positions mark elevations and distances inland reached by wave energies sufficient to dislocate those specific masses. Taken together, the CBD data reveal general relationships that shed light on storm-wave hydrodynamics. These include a robust correlation (inverse exponential) between maximum boulder mass transported and emplacement height above high water: the greater the elevation, the smaller the maximum boulder size, with a dependency exponent of about -0.2 times the elevation (in metres). There is a similar relationship, although with a much smaller rate-of-change (exponent -0.02), between boulder mass and distance inland, which holds from the shoreline in to about 120 m. Coastal steepness (calculated as the ratio of elevation to inland distance) seems to exert the strongest control, with an inverse power-law relationship between maximum boulder mass and slope ratio: the more gentle the topography, the larger the moved boulders.
Quantifying CBD dynamics helps us understand the transmission of wave energies inshore during high-energy storm events. The transported boulders documented here are larger than many of those interpreted to have been moved by tsunami in other locations, which means that boulder size alone cannot be used as a criterion for distinguishing between tsunami and storm emplacement of CBD. The biggest blocks—up to 620 t—are new maxima for boulder mass transported by storm waves. We predict, however, that this record will not last long: the 2013–2014 storms were strong but not extreme, and there are larger boulders in these deposits that didn't move on this occasion. Bigger storms will surely move larger clasts, and clasts at greater distances from the shoreline. These measurements and relationships emphasise the extreme power of storm waves impacting exposed coastlines, and require us to rethink the upper limits of storm wave energy at coasts.
Recent technological advances have made it possible to improve the accuracy of coastal studies through devices such as RFID (Radio Frequency IDentification). These sensors allow the monitoring of elements of the
environment at any time since its placement and offer a great level of detail. This research is developed in a boulder beach in Oia (Pontevedra), where 80 RFID sensors were installed in the natural boulders, without changing their position. The sensors were placed in lines of 5 elements perpendicular to the coastline. After the first winter, there is a general movement of the boulders. Of the 48 recovered, 81% have displaced more than 50 cm, minimum value to consider that there was movement. The greater displacements have occurred in boulders whose axes didn’t exceed 100 cm, with a maximum distance of 20,47 meters. As for the areas of greater mobility, it is clearly perceived that the central sector of the study area present greater variations in the position of the boulders, while the north and the lower part of the beach, where it is located coastal platform, are the most stable areas.
Recovery rates were obtained by radio frequency identification (RFID) technology in pebbles and cobbles at San Felipe beach, Gran Canaria. The aim of this work was to define which factors affected the recovery of tagged gravels. Several tests were performed to determine the detection depth threshold, and 16 field experiments were carried out over seventeen months after tracer deployment on the beach. Recovery rates are highly variable with time, ranging from 72.2% in the first recovery session to 25.8% in the last one. Nevertheless, a nearly stable situation was found for the final eight months. Apart from the effect of time, there were several factors that affected the recovery rate. Some of these were related to the particle, such as the position of the tag within the particle, as well as its weight, size and shape. Two environmental factors were considered. First, the elevation of the tracer on the beach showed that the recovery rate was higher with particles located above the storm berm. Second, wave height, which showed no relation with recovery rates even though during the experiment significant storms and periods of calm took place.
A boulder-strewn rock platform on an Atlantic-facing coastline in Gweebarra Bay, NW Ireland, is examined using an integrated geomorphological, ecological and geotechnical methodology. Here, a steep granite shore platform is cut by intersecting subvertical and subhorizontal fractures and shows a clear biological and geomorphological zonation associated with level within the tidal frame. Minimum surface strength values of the bedrock platform (as derived from Schmidt hammer tests) corresponds to the supralittoral zone, which is dominated by Ramalina siliquosa. Bedrock surface strength increases into the littoral zone, which is characterized by a succession through Verrucaria maura, Semibalanus balanoides and Mytilus edulis communities. Granite boulders in the upper intertidal zone are clustered and stacked into ridges that have a consistent spacing and northeast-southwest alignment. Boulders within the ridges are imbricated, stacked, and have west-facing dips. Boulder surface strength is higher on northwest-facing ridge sides than on southeast-facing sides, and is higher at the landward than seaward ridge end. Variations in surface weathering across the platform show where blocks have been recently removed by storms. Pulverized bedrock and boulder surfaces show where boulders have knocked into each other and been dragged across the platform by backwash. It is likely that such boulder features are formed and destroyed on decadal or shorter time scales.
Outer sand bar dynamics on a high-energy macro-tidal beach were investigated using long-term (multi-year) field datasets of intertidal morphology and offshore bathymetry. Utilising a 15-year time-series of Argus video images, five distinct outer bar types were identified: Mega Rip, Longshore, Crescentic, Crescentic Attached and Welded. The most common classification was Crescentic Attached, with the outer bar oscillations being out of phase with the inner bar oscillations, as would be expected for the shore-normal wave approach at this site. The outer bar had a typical amplitude of 0.5-1 m and a longshore wavelength of 600 m. Changes in outer bar morphology were related to measured and modelled nearshore wave data. However, the outer bar morphology changed over a much longer timescale (monthly-to-annual) than the daily-to-weekly variations in wave height and period. An extended duration of energetic wave action was required to bring about an upstate bar transition to the Longshore or Mega Rip state, where the bar then remained arrested for a significant amount of time, requiring several months of low wave conditions to induce a down state transition through Crescentic to Welded. This slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle (several hours around low tide). The configuration and position of the outer bar were related: the more upstate (downstate) bar types being associated with a more offshore (onshore) bar position. The detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore (onshore) bar migration occurring when wave conditions were more (less) energetic that the antecedent conditions. The upstate end-member (Longshore or Mega Rip) was attained sometime during the winter months for 14 out of the 16 years of monitoring; the outer bar remained attached to the low tide shoreline over the winter 2005/2006 and 2010/2011. These two winters, with incomplete upstate cycles, were characterised by the lowest winter wave conditions and negative winter North Atlantic Oscillation (NAO) indices, suggesting that the winter NAO is correlated with both beach state and nearshore bar configuration.
In this paper we propose a further development of the STONE project, a research project based on Low Frequency RFID technology for the monitoring of coastal erosion. In the STONE project Passive Low Frequency transponders were embedded inside marble pebbles: these so called "Smart Pebbles" were positioned on a beach in Marina di Pisa, near Pisa, Italy, both on the beach, on the beachface and underwater. After a span of time and a number of storms, the Smart Pebbles were recovered using a waterproof reader through a scan of the beach and of the portion of sea close to the beach. The STONE project gave very good results and in this paper we describe the next steps of the project: first of all the use of new kinds of transponders has been experimented, in order to ease the insertion of the tag inside the pebble and to use this technique also with differently shaped kinds of pebbles. In particular we focused on the use of this technique on pebbles of very limited dimensions. Subsequently we analyze the performances of the system with pebbles of different materials, in order to widen the use of this system to new multi-material environments.
Extreme storm events are known to produce, entrain, transport and deposit sizable boulders along rocky coastlines. However, the extent to which these processes occur under moderate, fetch‐limited wave conditions is seldom considered. In this study we quantify boulder transport at a relatively sheltered location subject to high‐frequency, low‐magnitude storm activity. This was achieved by deploying radio frequency identification (RFID) tags within 104 intertidal limestone boulders ranging in size from fine to very coarse (intermediate axis: 0.27–2.85 m). The study was conducted over 3 years (July 2015–July 2018) and encompassed numerous storm events. Tagged boulders were relocated during 17 field surveys and their positions recorded using a differential global positioning navigation satellite system (DGNSS).
On completion, we identified boulder displacement in 69% of the tagged array. The accrued boulder transport distance amounted to 233.0 m from 195 incidents of displacement, including the movement of a boulder weighing an estimated 11.9 t. Transport was not confined to autumn and winter storms alone, as displacement was also recorded during summer months (April–September), despite the seasonally reduced wave magnitude.
Boulder production by wave quarrying was documented in three tagged clasts, confirming observations that the shore platform is actively eroding. Incidents of overturning during transport were also recorded, including multiple overturning of clasts weighing up to 5 t. We further identify a statistically significant difference (maximum p‐value ≤ 0.03) between the transport distances attributed to constrained and unconstrained boulders, suggesting that the pre‐transport morphological setting exerts considerable control over boulder transport potential.
The findings establish low to moderate storm waves as a key component in the evolution of the study site. More broadly, we claim that high‐frequency, low‐magnitude storms regularly modify these overlooked rocky coastal locations, suggesting that the hydrodynamic capability at such sites may previously have been underestimated. © 2020 John Wiley & Sons, Ltd.
An unmanned aerial vehicle (UAV) was flown over a boulder beach (area 20,000 m²) on the southern coast of Galicia (northwestern Spain) in May 2016, continuing earlier work based on flights over the same beach in July 2012, May 2013, and late March 2014. Digital Surface Models (DSMs) with 1.8 cm resolution were constructed from the 2014 and 2016 data to identify changes in beach morphology over the intervening period. Analyses were conducted using a Limit of Detection (LoD) of 0 cm and 3.71 cm. In both cases, the analyses showed that erosion dominated over 19 % of the beach area. Accretion occurred over the rest of the beach, which acquired an additional 1500 m³ of material over the study period. Re‐analysis of the data from earlier flights suggested that erosion dominated on the beach in 2012‐2013 and deposition in 2013‐2014. Without any clear relationship between beach behaviour and storm severity during each winter period, it is proposed that gravitationally induced erosion and storm‐wave induced deposition are the result of perturbations about an equilibrium beach gradient. The UAV data also suggested that an essentially random component modulates regional patterns of movement.
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.
In this paper the abrasion rate on a coarse-clastic beach was evaluated by calculating the volume loss recorded on indigenous pebbles within a 13-month timespan. The experiment was carried out at Marina di Pisa (Italy) on an artificial beach that was built to counteract the erosion processes affecting this sector of the coast. A total of 240 marble pebbles (120 rounded and 120 angular) were marked using the RFID technology and injected on the beach. The volume loss measured after consecutive recovery campaigns was progressively increasing, reaching the maximum value after 13 months (61% overall). The average volume loss is consistent between rounded and angular pebbles at any time (59.3% and 64.2% after 13 months respectively), meaning that the roundness is not a primary control factor on abrasion rate. The pebbles that did not reach such abrasion rates after 8 and 10 months (volume loss less than 20%) were found at heights equal or greater than 2 m above mean sea level, on the crest of the storm berm that formed during the strongest storms. This implies that the highest wearing is achieved in the lower portion of the backshore, which is also the area that underwent major topo-graphic modifications. Here, sea water action might also exert chemical influence on the pebbles, adding to the mechanical abrasion. The main result of this research, indicating an impressive volume loss on beach pebbles in a short timespan, could be of key importance for coastal managers. The optimization of coarse sediment beach nourishments is also relevant , taking into right consideration that the volume loss due to sediment abrasion might exceed 50% of the original fill volume just after 1 year in the most dynamic portion of the beach.
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.
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.
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.
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.
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.
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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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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