Article

Recording inter‐annual changes on a boulder beach in Galicia, NW Spain using an Unmanned Aerial Vehicle

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Abstract

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.

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... This typology occupies three quarters of all coastlines worldwide, and cliff sections are found in 52% of coastal areas at the global level [1,2]. While these environments could be expected to show lower variation rates than other areas, such as sedimentary systems, they have been found to be characterized by a great dynamism [3]. Although many studies have been performed on rocky coasts, the overall research on these areas has been restricted by several limitations, such as spatial and temporal resolution or the relative importance of different erosion factors, which can generate very different shapes with similar values [2]. ...
... This fact was often not possible with classic field surveys, such as topographic profiles, or with aerial images, due to their low spatial and temporal resolution. Even in a novel field such as the use of UAVs on rocky coasts, great technical and methodological advances have taken place, from an early period related to photointerpretation of high resolution images [45,46] to more recent works using photogrammetric techniques such as DSM (digital surface models) generated through SfM (structure from motion) techniques, which enhance the possibilities for quantification [3,[49][50][51]. ...
... 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. ...
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.
... Low flying UAVs have been used to obtain detailed, high resolution images in a variety of rocky coastal environments (Pérez-Alberti (Table 1). Digital surface models (DSMs) were produced for the three study areas based on the methodology described by Gómez-Pazo et al. (2019), with statistical parameters derived from statistical software R (R Core Team, 2019). The spatial resolution was homogenized, using 0.5 m as the pixel size. ...
... and Trenhaile, 2015aand Trenhaile, , 2015bGómez-Pazo et al., 2019;Horacio et al., 2019;. For the present study images were obtained during low tide using an UAV (Microdrones GmbH, Model MD4-200) flying about 30 m above the shore platforms at Caamaño(March 2, 2015), Sanxenxo (April 30, 2015), and Laxe Brava(August 8, 2016) ...
Article
Most research on shore platforms has been at fairly large spatial scales over distances ranging from hundreds to thousands of metres. Other work at much smaller scales, ranging from one to several decimetres, often corresponds to the dimensions of micro-erosion meter stations. Few studies have been concerned with platform morphology in which the basic data are acquired at intermediate or meso-scales ranging up to a few metres. This is due, in part, to terrestrial surveying at meso-scales being time-consuming while aerial surveys using LiDAR are expensive. A meso-scale study was made on three shore platforms in western Galicia, northwestern Spain using data from an Unmanned Aerial Vehicle (UAV) to produce high resolution Digital Surface Models (DSMs) and to calculate local surface elevation, roughness, slope, and joint density at a 0.5 m pixel scale, and joint orientation and length. This was supplemented by Equotip field measurements of rock hardness. A granitic platform was higher and had rougher surfaces and steeper slopes than two platforms in schist. The relationship between platform morphology and rock hardness and joint density was complex, however, reflecting in part the role of schistosity in accounting for the formation of low, regular platforms in hard schists with low joint density. The study suggested that while tidal range, inheritance, and other environmental and evolutionary factors can be dominant in determining platform morphology at the macro- or regional scale, geological, and particularly structural, factors become increasingly important in Galicia as the scale diminishes, and they are generally dominant at the local or meso-scale.
... SfM techniques allow spatially continuous DEMs to be derived, circumventing the issues of limited spatial coverage and bias that plague MEM techniques (Stephenson and Finlayson, 2009;Trenhaile, 2018). These novel SfM methods have started to be applied to study coastal boulder dynamics (Autret et al., 2018;Gómez-Pazo et al., 2019) but have not previously been applied to quantify meso-scale shore platform erosion by block detachment processes. Despite our advancements in the past decade on meso-scale platform erosion, we have very little understanding of the rate, scale, and multi-decadal patterns of block detachment from platforms. ...
... targets in each corner and the centre, with additional targets scattered systematically around the area being flown) for each of the five flights across the survey extent. The precise location of the targets was recorded using dGPS to provide ground control points (GCPs) to geolocate the resulting orthophotos and DEMs (Turner et al., 2016Gómez-Pazo et al., 2019). ...
Article
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The majority of shore platforms form in rocks that are characterised by layered stratigraphy and pervasive jointing. Plucking of weathered, joint and bed bounded blocks is an important erosion process that existing models of platform development do not represent. Globally, measuring platform erosion rates have focused on microscale (< 1 mm) surface lowering rather than mesoscale (0.1‐1 m) block detachment, yet the latter appears to dominate the morphological development of discontinuity rich platforms. Given the sporadic nature of block detachment on platforms, observations of erosion from storm event to multi‐decadal timescales (and beyond) are required to quantify shore platform erosion rates. To this end, we collected aerial photography using an unmanned aerial vehicle to produce structure‐from‐motion‐derived digital elevation models and orthophotos. These were combined with historical aerial photographs to characterise and quantify the erosion of two actively eroding stratigraphic layers on a shore platform in Glamorgan, south Wales, UK, over 78‐years. We find that volumetric erosion rates vary over two orders of magnitude (0.1‐10 m3 yr‐1) and do not scale with the length of the record. Average rates over the full 78‐year record are 2‐5 m3 yr‐1. These rates are equivalent to 1.2‐5.3 mm yr‐1 surface lowering rates, an order of magnitude faster than previously published, both at our site and around the world in similar rock types. We show that meso‐scale platform erosion via block detachment processes is a dominant erosion process on shore platforms across seasonal to multi‐decadal timescales that have been hitherto under‐investigated.
... Additionally, wave swash at the time of image capture was manually removed. A limit of detection approach was used during volumetric analysis (Gómez-Pazo et al., 2019;Ierodiaconou et al., 2016).Statistical hotspot analysis was performed using Local Moran's I index (Anselin, 1995). Neighbourhoods have been defined with a 35 m binary distance based spatial weight matrix (row-standardised), which allows for inclusion of the two adjacent transects in each Local Moran's I computation. ...
Article
Coasts are highly dynamic systems. Understanding how they respond to individual storms events and to future climate change is difficult as local boundary conditions determines their evolutionary trajectory. A lack of field data at this local scale therefore limits the ability of managers and researchers to apply existing modelling frameworks to their region of interest to ensure preservation of the natural environment. Data acquisition through low-cost Unoccupied Aerial Vehicles (UAVs) has become a viable means for obtaining high-resolution surveys (cm-scale) on the coast for whole sediment compartments (km-scale). A continued limitation however is the intensive labour costs involved in data acquisition. Here we show the power of Citizen Science in providing high quality, cost-effective data collection, when provided with adequate training and resources along a high-energy, temperate coast in Victoria, Australia. This was conducted through the Victorian Coastal Monitoring Program (VCMP), formed in 2018 as a collaboration between Australian universities and the Victorian State Government. As of 2022, this program covered 28 sites, with over 450 individual surveys taken at 6–8 week intervals. The VCMP has guided and driven significant management actions on the coast from realignment of coastal walking paths for public safety to measuring sand renourishment success. In this paper we (i) present the Citizen Science UAV program methodology, as an example that can be replicated in other jurisdictions, and (ii) illustrate, through a case-study of a sandy beach and rocky cliff, the benefits and precision achievable using our Citizen Science approach. We outline how outputs can be made widely available and applied to coastal management, with the aid of data portals and decision support systems. This data accessibility has been central to our community engagement, enabling citizen scientists to conduct their own bespoke analysis for co-creation of management solutions for their local area. It was also found to be key for facilitating continued community engagement during one of the world's longest lockdowns of the COVID-19 pandemic, impacting the program for almost two years.
... Boulder displacement appears to have been essentially chaotic, a conclusion which is consistent with the results of J o u r n a l P r e -p r o o f previous work using UAVs (Pérez-Alberti and Trenhaile, 2015a). It also supports the contention that this behaviour, involving the landward movement and deposition of boulders by high waves, followed by seaward movement, is a manifestation of perturbations that occur about a sub-equilibrium gradient (Gómez-Pazo et al., 2019). Limited boulder transport and the chaotic movement of boulders that do not move from one place to another as a loosely associated unit may therefore account for the small and inconsistent changes in beach profiles Seaward boulder movement could be primarily by backwash or reflected waves, or if they become temporarily lodged by the swash on steep slopes, by subsequent gravity-driven sliding and especially, given beach steepness and the shape of the boulders, by rolling. ...
Article
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.
... Due to the high frequency of clast activation in boulder beaches, they cannot be used to interpret the age and magnitude of individual (pre-)historical events. Nonetheless, clast movements during storm events and sedimentological trends in boulder beaches have been monitored and analyzed to understand how these beaches respond to storm events, for predicting beach-morphology changes due to rising sea level and climate change Pérez-Alberti and Trenhaile, 2015;Gómez-Pazo et al., 2019). ...
Chapter
High-energy waves such as tsunamis and storm waves can dislodge and transport enormous clasts. With a growing body of literature that uses subaerial coarse clasts (individual clast sized between tens of centimetres and several metres in the intermediate axis) to interpret paleotsunamis or storms on the one hand, and characterizes coarse-clast deposits formed in recent events on the other, this chapter provides an introduction to wave-deposited coarse-clast research. It (1) addresses how to correctly identify wave-transported coarse-clast deposits; (2) provides an overview of different patterns of coarse-clast deposits, including isolated megaclasts, boulder fields, boulder ridges, coral-rubble ridges, and other gravel-sized deposits; and (3) discusses the potentials for inferring extreme-wave characteristics and deposition mechanisms (tsunami vs. storm) from coarse-clast deposits.
... Coastal boulder deposits are distributed along coasts of seas, oceans, and great lakes and include a significant amount of large clasts (true boulders and megaclasts); these deposits associate often with rocky shores and reflect influences of storms and tsunamis and the relevant clast transport (inland, above high-water mark, and even to the cliff-top position) [13,20,27]. Synonymous terms are boulderite coined by Dewey and Ryan [21], boulder beach [19,[38][39][40], and boulder field [8,41]. Finally, coastal megaclast deposits are coastal boulder deposits dominated by clasts larger than 1 m in size or, at least, bearing recognizable accumulations of such clasts. ...
Article
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Coastal megaclast deposits are dominated by detrital particles larger than 1 m in size. These attract significant attention of modern researchers because of the needs of sedimentary rock nomenclature development and interpretation of storm and tsunami signatures on seashores. If so, finding localities that exhibit coastal megaclast deposits is an important task. Field studies do not offer a quick solution, and, thus, remote sensing tools have to be addressed. The application of the Google Earth Engine has permitted to find four new localities, namely Hondarribia in northern Spain (Biscay Bay), the Ponza Island in Italy (Tyrrhenian Sea), the Wetar Island in eastern Indonesia (Banda Sea), and the Humboldt o Coredo Bay at the Colombia/Panama border (eastern Pacific). In these localities, coastal megaclast deposits consisting of blocks (1–10 m in size) and some megablocks (>10 m in size) are delineated and preliminary described in regard to the dominant size of particles, package density, mode of occurrence, etc. The limitations of such virtual surveys of coastal megaclast deposits are linked to an insufficiently high resolution of satellite images, as well as ‘masking’ effects of vegetation cover and cliff shadows. However, these limitations do not diminish the importance of the Google Earth Engine for finding these deposits. Consideration of some tourism-related information, including photos captured by tourists and bouldering catalogues, facilitates search for promising areas for subsequent virtual surveying of megaclast distribution. It is also established that the Google Earth Engine permits quantitative analysis of composition of coastal megaclast deposits in some areas, as well as to register decade-long dynamics or stability of these deposits, which is important to interpret their origin. The current opportunities for automatic detection of coastal megaclast deposits seem to be restricted.
... Thus, storm activity at Bembridge initiates geomorphic change on a larger scale than had previously been realized. This reinforces the findings of Pérez-Alberti and Trenhaile (2015), Gómez-Pazo et al. (2019) and Nagle-McNaughton and Cox (2020), who documented widespread, collective mass movement of detached clasts using unmanned aerial vehicles (UAVs). ...
Article
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.
... The solar cell board 1 is mounted in the lighting position of the UAV upward. The wind power generation device 2 is installed on the upper part of the UAV frame or the lower part of the power wing [3] . ...
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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
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.
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High-resolution aerial images allow detailed analyses of periglacial landforms, which is of particular importance in light of climate change and resulting changes in active layer thickness. The aim of this study is to show possibilities of using UAV-based photography to perform spatial analysis of periglacial landforms on the Demay Point peninsula, King George Island, and hence to supplement previous geomorphological studies of the South Shetland Islands.Photogrammetric flights were performed using a PW-ZOOM fixed-winged unmanned aircraft vehicle. Digital elevation models (DEM) and maps of slope and contour lines were prepared in ESRI ArcGIS 10.3 with the Spatial Analyst extension, and three-dimensional visualizations in ESRI ArcScene 10.3 software.Careful interpretation of orthophoto and DEM, allowed us to vectorize polygons of landforms, such as (i) solifluction landforms (solifluction sheets, tongues, and lobes); (ii) scarps, taluses, and a protalus rampart; (iii) patterned ground (hummocks, sorted circles, stripes, nets and labyrinths, and nonsorted nets and stripes); (iv) coastal landforms (cliffs and beaches); (v) landslides and mud flows; and (vi) stone fields and bedrock outcrops.We conclude that geomorphological studies based on commonly accessible aerial and satellite images can underestimate the spatial extent of periglacial landforms and result in incomplete inventories. The PW-ZOOM UAV is well suited to gather detailed geomorphological data and can be used in spatial analysis of periglacial landforms in the Western Antarctic Peninsula region.
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Structure-from-motion (SfM) algorithms greatly facilitate the production of detailed topographic models from photographs collected using unmanned aerial vehicles (UAVs). However, the survey quality achieved in published geomorphological studies is highly variable, and sufficient processing details are never provided to understand fully the causes of variability. To address this, we show how survey quality and consistency can be improved through a deeper consideration of the underlying photogrammetric methods. We demonstrate the sensitivity of digital elevation models (DEMs) to processing settings that have not been discussed in the geomorphological literature, yet are a critical part of survey georeferencing, and are responsible for balancing the contributions of tie and control points. We provide a Monte Carlo approach to enable geomorphologists to (1) carefully consider sources of survey error and hence increase the accuracy of SfM-based DEMs and (2) minimise the associated field effort by robust determination of suitable lower-density deployments of ground control. By identifying appropriate processing settings and highlighting photogrammetric issues such as over-parameterisation during camera self-calibration, processing artefacts are reduced and the spatial variability of error minimised.
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The measurement of topography and of topographic change is essential for the study of many geomorphic processes. In recent years, structure from motion (SfM) techniques applied to photographs taken by camera-equipped unmanned aerial vehicles (UAVs) has become a powerful new tool for the generation of high resolution topography. The variety of available UAV systems continues to increase rapidly, but it is not clear whether increased UAV sophistication translates into improved quality of the calculated topography. To evaluate the lower end of the UAV spectrum, a simple low cost UAV was deployed to calculate high resolution topography in the Daan River gorge in western Taiwan, a site with a complicated 3D morphology and a wide range of surface types, making it a challenging site for topographic measurement. Terrestrial lidar surveys were conducted in parallel with UAV surveys in both June and November 2014, enabling an assessment of the reliability of the UAV survey to detect geomorphic changes in the range of 30 cm to several meters. A further UAV survey was conducted in June 2015 in order to quantify changes resulting from the 2015 spring monsoon. To evaluate the accuracy of the UAV derived topography, it was compared to terrestrial lidar data collected during the same survey period using the cloud-to-cloud comparison algorithm M3C2. The UAV-generated point clouds match the lidar point clouds well, with RMS errors of 30–40 cm; however, the accuracy of the SfM point clouds depends strongly on the characteristics of the surface being considered, with vegetation, water, and small scale texture causing inaccuracies. The lidar and SfM data yield similar maps of change from June to November 2014, with the same areas of geomorphic change detected by both methods. The SfM-generated change map for November 2014 to June 2015 indicates that the 2015 spring monsoon caused erosion throughout the gorge and highlights the importance of event-driven erosion in the Daan River. The results suggest that even very basic UAVs can yield data suitable for measuring geomorphic change on the scale of a channel reach.
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Large clastic cliff-top storm deposits (called CTSDs) are one of the most remarkable signatures that characterizes extreme storm wave events on coastal cliffs. Hence, the study of CTSDs is of key importance for understanding and predicting the impacts of extreme storm wave events on rocky coasts or establishing proxies for storm intensity. The present study uses new data including hydrodynamic measurements in both deep and intertidal waters, and records of CTSDs displacement and deposition across Banneg Island during the stormy winter 2013-2014. Two drone-based surveys were carried out in January 2013 (pre-storms) and in April 2014 (post-storms). In addition, complementary field observations were carried out during the winter, providing a comprehensive and detailed dataset. Concerning the hydrodynamic measurements, nine pressure sensors deployed along four cross-shore profiles on the western coast of the island, recorded wave and water level conditions between December 2013 and April 2014. Aerial orthorectified photographs and digital elevation model of differences provide a detailed spatial description of cliff erosion and the reworking of cliff-top storm deposits. After the storms, 172 fresh scars corresponding to quarrying in the bed rock were localized above high spring tide water level, 507 blocks were transported up to 40 m inland, at altitudes of 8 to 14 meters above mean sea level, and the tracks of 170 of them were identified. The water levels and wave parameters estimated from the pressure sensor measurements provided accurate information on the maximum water elevation reached during the largest storms at the sensor locations and were extrapolated to provide run-up elevation along the four survey profiles for the whole winter 2013-2014. The results demonstrate that a large number of overwash episodes occurred, at times of high tides and energetic waves.These episodes generally correspond to morphological changes. This study confirms the major role played by extreme storm wave events on CTSDs quarrying, transport, and deposition on Banneg Island, and clearly identify the events of major evolutions.
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Aerial imagery collected before and after major storm events is ideal for the assessment of coastal landscape change driven by individual high-magnitude events. Using traditional satellite sensors and manned aerial systems can be challenging due to issues related to cloud cover, mobilization expenses and resolution. Rapid advances in unmanned aerial vehicle (UAV) technology allow for the cost-effective collection of aerial imagery and topography at centimetre resolution suitable for assessing change in coastal ecosystems. In this study we demonstrate the utility of UAV-based photogrammetry to quantify storm-driven sediment dynamics on a sandy beach on the open-coast shoreline of Victoria, Aus-tralia. UAV-based aerial photography was collected before and after a major storm event. High-resolution (< 5 cm) aerial imagery and digital surface models were acquired and change-detection techniques were applied to quantify changes in the beachface. An average beach erosion of 12.24 m 3 /m with a maximum of 28.05 m 3 /m was observed, and the volume of sand cut from the beachface and retreat of the foredune are clearly illustrated. Following the storm event, erosion was estimated at 7259.94 ± 503.69 m 3 along 550 m of beach. By combining the aerial imagery and derived topographic datasets we demonstrate the advantage of UAV-based photogrammetry techniques for rapid high-resolution data collection in semi-remote locations. Its utility in setting unlimited virtual vantage points is also illustrated and the valuable perspective it provides for tracking landscape change discussed.
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This paper reviews the common theories for determining the magnitude and distribution of wave forces on vertical walls and sloping, rubble-mound breakwaters and compares these theories, selecting the best available for use. The results of the better theories are compared with experimental data, and an outline is given of experimental investigations considered necessary to obtain data sufficient for the design of economical and safe breakwaters.
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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.
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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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Drainage channels are an integral part of agricultural landscapes, and their impact on catchment hydrology is strongly recognized. In cultivated and urbanized floodplains, channels have always played a key role in flood protection, land reclamation, and irrigation. Bank erosion is a critical issue in channels. Neglecting this process, especially during flood events, can result in underestimation of the risk in flood-prone areas.The main aim of this work is to consider a low-cost methodology for the analysis of bank erosion in agricultural drainage networks, and in particular for the estimation of the volumes of eroded and deposited materials. A case study located in the Veneto floodplain was selected. The research is based on high-resolution topographic data obtained by an emerging low-cost photogrammetric method (Structure-from-Motion or SfM), and results are compared to Terrestrial Laser Scanner (TLS) data. For the SfM analysis, extensive photosets were obtained using two standalone reflex digital cameras and an iPhone5® built-in camera. Three Digital Elevation Models (DEMs) were extracted at the resolution of 0.1 m using SfM and were compared with the ones derived by TLS. Using the different DEMs, the eroded areas were then identified using a feature extraction technique based on the topographic parameter Roughness Index (RI). DEMs derived from SfM were effective for both detecting erosion areas and estimating quantitatively the deposition and erosion volumes. Our results underlined how smartphones with high-resolution built-in cameras can be competitive instruments for obtaining suitable data for topography analysis and Earth surface monitoring. This methodology could be potentially very useful for farmers and/or technicians for post-event field surveys to support flood risk management.
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Coastal areas suffer degradation due to the action of the sea and other natural and human-induced causes. Topographical changes in beaches and sand dunes need to be assessed, both after severe events and on a regular basis, to build models that can predict the evolution of these natural environments. This is an important application for airborne LIDAR, and conventional photogrammetry is also being used for regular monitoring programs of sensitive coastal areas. This paper analyses the use of unmanned aerial vehicles (UAV) to map and monitor sand dunes and beaches. A very light plane (SwingletCam) equipped with a very cheap, non-metric camera was used to acquire images with ground resolutions better than 5 cm. The Agisoft Photoscan software was used to orientate the images, extract point clouds, build a digital surface model and produce orthoimage mosaics. The processing, which includes automatic aerial triangulation with camera calibration and subsequent model generation, was mostly automated. To achieve the best positional accuracy for the whole process, signalised ground control points were surveyed with a differential GPS receiver. Two very sensitive test areas on the Portuguese northwest coast were analysed. Detailed DSMs were obtained with 10 cm grid spacing and vertical accuracy (RMS) ranging from 3.5 to 5.0 cm, which is very similar to the image ground resolution (3.2–4.5 cm). Where possible to assess, the planimetric accuracy of the orthoimage mosaics was found to be subpixel. Within the regular coastal monitoring programme being carried out in the region, UAVs can replace many of the conventional flights, with considerable gains in the cost of the data acquisition and without any loss in the quality of topographic and aerial imagery data.
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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.
Article
The interactions between waves and morphology on shore platforms were investigated at four platforms located at Kaikoura Peninsula, New Zealand and the Otway coast, Victoria, Australia. Waves were measured over six tidal peaks of a spring tidal sequence at each site during a six month period (February 2007 – July 2007). This paper reports the results of an investigation into the research question: how are waves modified by platform morphology in a micro-tidal setting? Through the investigation of wave interactions on shore platforms it was found that complex hydrodynamic patterns formed on the shore platforms studied. Through direct measurement of waves on the platforms it was found that wave attenuation was not dependent on platform width, but rather influenced by platform gradient and depth of water on the platform. Spectral analysis was used to assess how wave energy was transformed across the platforms. At three of the four platforms investigated, energy gradients formed across the platform with wave energy recorded within the infragravity range.
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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.
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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
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
Waves are generally considered to be an important control on shore platform evolution but there have been very few detailed studies of wave dynamics on rocky coasts. This study provides a detailed description of wave transformation processes across a shore platform near Gisborne, New Zealand. A field experiment was conducted on an intertidal, 250 m-wide platform that is characterised by a sharp seaward edge. Mean platform elevation is 0.7 m below mean sea-level (MSL) and platform gradient is 0.3°. Four nearly equally spaced pressure gauges were deployed over a 24-h period during fair-weather swell conditions characterised by a mean wave height of 0.4-0.5 m and wave period of 7 s. Wave energy at the seaward edge of the platform was dominated by incident swell waves with peak frequency at 0.09 Hz. At all tidal stages waves broke at the seaward edge of the platform, but changing tidal stage exerted a strong control on the rate of wave energy attenuation across the platform. The relative importance of waves at wind-wave frequencies increased in the centre of the platform as the tidal stage and water level increased, whereas infragravity waves became dominant toward the cliff toe. Three different hydrodynamic zones were distinguished across the shore platform; (i) a breaker zone close to the seaward edge; (ii) a propagation/shoaling zone in the central region of the platform; and (iii) a zone of energy dissipation across the inner part of the platform. The spatial dimensions of the three zones varied with changing tidal stage, enabling different wave processes to operate across different parts of the platform at different times. The experiment showed that wave-height attenuation is strongly controlled by tidal stage, ranging between 93% attenuation of wave height during the initial flooding stage to 44% attenuation at high tide. Wave height was found to be depth-limited, with the ratios of H max and H m 0 to water depth calculated as 0.7 and 0.4, respectively. The findings imply that platform geometry has an important influence on wave processes on shore platforms. The geomorphic implications of gravity and infragravity waves are discussed.
Article
Coastal boulders are good evidence of high-energy events, but the distinction between storm and tsunami boulders remains difficult to identify and mathematical models are still in their preliminary stages. In a pioneering contribution, Nott (1997, 2003) developed hydrodynamic equations to assess the minimum wave height required to initiate transport of a coastal boulder by tsunamis or storm surges. These equations are widely cited and used, but they can be improved. In this study, Nott's equations have been revised: (1) the equation for the submerged boulder scenario has been revised by rearranging the lift area of the lift force, (2) the subaerial boulder scenario has been reconsidered by rearranging lift area and omitting inappropriate use of inertia force, and (3) the joint bounded scenario was revised by balancing force components in the lifting direction, and the effect of slope at the pre-transport location is tested. Calculations are performed for four case studies: boulders in Western and Eastern Australia (data after Nott, 1997, 2003), boulders in southeastern Italy (data after Scicchitano et al., 2007), storm boulders in Iceland (data after Etienne and Paris, 2010), and 2004 tsunami boulders in Sumatra (data after Paris et al., 2009).
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
This paper documents the deposition of large boulders on the Beecroft Peninsula, New South Wales, during a one in four-year swell event in October 1999. The size of the boulders in relation to the magnitude of the swell suggests that the boulder field at Whale Point on the Beecroft Peninsula is explicable in terms of storm swells alone.
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
The pre-transport environment of a coastal boulder along with its shape, size and density determines the height of wave required for it to be transported. Different forces act on sub-aerial boulders as opposed to submerged boulders when struck by a wave. Boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments. No one equation is applicable to determine the height of palaeo-waves responsible for depositing a field or ridge of imbricated coastal boulders. A range of equations and their derivation is presented here which can be applied to the respective pre-transport environment of a boulder. Such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields. ß 2003 Elsevier Science B.V. All rights reserved.
Article
Repeat topographic surveys are increasingly becoming more affordable, and possible at higher spatial resolutions and over greater spatial extents. Digital elevation models (DEMs) built from such surveys can be used to produce DEM of Difference (DoD) maps and estimate the net change in storage terms for morphological sediment budgets. While these products are extremely useful for monitoring and geomorphic interpretation, data and model uncertainties render them prone to misinterpretation. Two new methods are presented, which allow for more robust and spatially variable estimation of DEM uncertainties and propagate these forward to evaluate the consequences for estimates of geomorphic change. The first relies on a fuzzy inference system to estimate the spatial variability of elevation uncertainty in individual DEMs while the second approach modifies this estimate on the basis of the spatial coherence of erosion and deposition units. Both techniques allow for probabilistic representation of uncertainty on a cell-by-cell basis and thresholding of the sediment budget at a user-specified confidence interval. The application of these new techniques is illustrated with 5 years of high resolution survey data from a 1 km long braided reach of the River Feshie in the Highlands of Scotland. The reach was found to be consistently degradational, with between 570 and 1970 m3 of net erosion per annum, despite the fact that spatially, deposition covered more surface area than erosion. In the two wetter periods with extensive braid-plain inundation, the uncertainty analysis thresholded at a 95% confidence interval resulted in a larger percentage (57% for 2004–2005 and 59% for 2006–2007) of volumetric change being excluded from the budget than the drier years (24% for 2003–2004 and 31% for 2005–2006). For these data, the new uncertainty analysis is generally more conservative volumetrically than a standard spatially-uniform minimum level of detection analysis, but also produces more plausible and physically meaningful results. The tools are packaged in a wizard-driven Matlab software application available for download with this paper, and can be calibrated and extended for application to any topographic point cloud (x,y,z). Copyright © 2009 John Wiley & Sons, Ltd.
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
The Adriatic coast of southern Apulia (Italy) is marked by the presence of large boulder accumulations. Boulders are up to 8 t in weight and arranged either in small groups or rows composed of a few imbricated elements. The lower surface of some of the boulders is covered by biogenic encrustation which suggests that they were possibly carved from the mid or sublittoral zone and that they capsized during their transport. Other boulders, detached from the supratidal zone, have their surface affected by tilted rock pools. New horizontal solution pans are continually forming.A detailed survey of a large boulder accumulation was carried out at Torre Santa Sabina. Direct observations were also made concerning the carving out and transportation of one single boulder during the severe storms in that area on January 4th, 2002 and on January 12th, 2003. Collated data from both the survey and the direct observations including some radiocarbon age determinations and hydrodynamic calculations suggest that the studied accumulation was due to the superimposed effects of one or two tsunami as well as of storm waves. Tsunami would be responsible for the detachment and transportation of the largest boulders, while storm waves may have been responsible for the carving out and transportation of the newer, smaller blocks and for moving once again the largest boulders. It was in this way that a typical boulder accumulation was produced.The collated data suggest that two tsunami may have recently struck the Adriatic coast of southern Apulia. The first possibly took place on the Dalmatian coast as a result of the earthquake on April 6, 1667 which destroyed Ragusa (modern day Dubrovnik). The second tsunami would have accompanied the strong earthquake which took place in southern Apulia on February 20, 1743.
Article
The concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid-1980s and expansion in the 1990s. Much of the pioneering work was undertaken in Australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3-dimensional morphology and the Dean's parameter (Hb/WsT) was established. Subsequently, the Relative Tidal Range parameter (Hb/TR) was extended to beaches of all tidal ranges.In this paper, observations are presented from 25 beaches around the north coast of Ireland. These beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability (micro to macrotidal and low to high wave energy). Each beach was visually categorised into one of several established beach states described in the literature, on the basis of field observations. For each beach, the RTR and Dean's parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships. Observed and predicted beach states were then compared.Comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria, most other beach states did not. Lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the RTR and Dean's parameter. In addition, this study identifies geological factors as important constraints on actual beach state. In the majority of beaches studied, inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics.
Article
The tsunami hypothesis proposes that prehistoric tsunamis may have been larger than historic ones along coasts normally (historically) not associated with major tsunamis. The evidence for the hypothesis rests with the types of unusual sedimentary deposits and erosional forms along coasts where the largest historic and prehistoric storm waves do not appear capable of forming the features. This is especially the case at locations where boundary conditions, i.e. offshore water depth, coastal geomorphology and meteorological limitations, are not conducive to the propagation of sufficiently large storm waves at the shore. The tsunami hypothesis has been barely debated in the literature. This is despite the view of some, who suggest that storms have been overlooked, or underestimated, as a cause. Few comparisons have been made of the supposed tsunami generated features and the impacts on coasts of extreme intensity storms. Four of the most powerful tropical cyclones anywhere in the world in recent times struck the Western Australian coast between 1999 and 2002. The results of post-event surveys of these storms showed that none of them produced the enigmatic forms attributed elsewhere to tsunamis.
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.
Influence of Shape on the Fall Velocity of Sand Grains
  • A T Corey
Corey AT. 1949. Influence of Shape on the Fall Velocity of Sand Grains. Colorado State University: MS Thesis.