Tesi sul tema "Dune morphodynamics"

Coastal foredunes are natural aeolian bedforms located landward of the backshore and which interact continuously with the beach. Traditionally, coastal dunes have been associated with onshore winds, however they can be found under more complex wind regimes where offshore winds are common such as the UK East coast, Northern Ireland and New Zealand. This research investigates the ways in which foredune-beach interactions occur under a complex wind regime at a range of overlapping temporal and spatial scales and is innovative in that it explicitly links small-scale processes and morphodynamic behaviour to large scale and long-term dynamics. The study area is the north Lincolnshire coast, East England. Detailed observations of airflow at three locations under varying wind regimes revealed considerable spatial variations in wind velocity and direction, however it was possible to determine a general model of how foredune topography deflected and modified airflow and the resultant geomorphological implications (i.e. erosion and deposition). During direct offshore and onshore winds, airflow remained attached and undeflected; and distinct zones of flow deceleration and acceleration could be identified. During oblique winds airflow was deflected to become more parallel to the dune crest. The field sites used are characterized by a seasonal erosion/accretion cycle and a series of increasingly complex models was developed and tested to determine whether it was possible to predict sand volume changes in the foredune-beach system based on a limited number of variables. The model predictions were tested against detailed digital terrain models at a seasonal timescale. The model prediction that best matched the observed (surveyed) sand volume changes included wind speed, direction, grain size, fetch effect controlled by beach inundation and angle of wind approach was accurate to within ±10% for 18 out of 48 tests at the seasonal scale and 6 out of 12 tests over periods of >5 years. A key variable influencing foredune-beach sand volume is the magnitude and frequency of storm surge events and this was not factored in to the model, but may explain the model-observation mismatch over the medium-term on two occasions. Over the past 120 years historical maps and aerial photographs indicate long-term foredune accretion of approximately 2 m year-1 at the three study sites (1891-2010). At this timescale, rates of coastal foredune accretion reflect the low occurrence of severe storm surges and suggest rapid post-storm recovery. The morphological response of the foredune-beach morphology is considered to be a combination of controlling and forcing factors. Process-responses within the system, associated with nearshore interactions and sediment transfer from the littoral drift, are compiled into a multi-scale morphodynamic model. Important to match appropriate dataset to scale of research question or management plan being explored. In the case of management, long-term records of past activity are necessary to predict the future but also to understand natural responses of system to short-term impact such as storm surge.

Les dunes de sable éoliennes à différentes échelles (m-km) sont les principales formes topographiques dans les systèmes éoliens et se retrouvent sur divers corps planétaires comme la Terre, Mars ou Vénus. Elles résultent de l'interaction entre le vent, les sédiments transportés et le substratum. La forme, la taille, la disposition spatiale et le déplacement des dunes permet d'analyser les interactions entre les flux d'air et l'apport de sédiments, modulés par les conditions de surface. La production de cartes détaillées des caractéristiques individuelles des dunes couplée à une analyse statistique morphométrique spatialisée devient donc nécessaire pour mieux comprendre et caractériser l'origine de la formation et de l'évolution des dunes éoliennes.Cependant, cartographier les dunes avec précision sur de grandes étendues reste encore aujourd'hui une tâche difficile pour deux raisons. Tout d'abord, compte tenu de la disponibilité des ensembles de données de télédétection avec une résolution spatiale (et temporelle) toujours croissante, une telle cartographie nécessite des procédés automatisés car la numérisation manuelle i) est chronophage et ii) peut être d'une subjectivité et d'une qualité non-uniformes. Ces limites sont principalement dues au fait que les opérateurs humains ne peuvent pas suivre des critères de cartographie similaires sur de vastes zones d'étude, en particulier lorsqu'il s'agit de morphologies complexes. Ensuite, cette cartographie se révèle ardue ; notamment en raison de la complexité de certaines formes et de l'absence de classification universellement acceptée des dunes, malgré les efforts de recherche récents.Ce travail a donc pour objectif premier de proposer une nouvelle méthode de cartographie des dunes éoliennes axée sur une approche couplant du Deep Learning pour tracer le contour des dunes, une "squelettisation" et une analyse de réseau pour cartographier leurs crêtes et leurs connectivités (défauts). L'originalité de cette étude réside dans la capacité à cartographier ces caractéristiques à différentes échelles, allant de quelques kilomètres au désert entier. Les algorithmes développés montrent d'excellentes performances pour analyser des zones géographiques étendues et complexes avec une précision de l'ordre de 90 %. Cette méthode a permis de créer, pour la première fois, une base de données de plusieurs milliers de dunes du désert du Rub'Al Khali (le plus grand désert actif au monde), avec une fidélité élevée par rapport aux observations visuelles des dunes présentes sur le MNT.À partir de cette base de données, nous avons étudié la variabilité morphologique des dunes en les comparant avec les données de vent (ERA5 Land Reanalysis) à l'échelle du désert, afin de quantifier et de comprendre leurs changements morphologiques et leurs répartitions spatiales en lien avec la dynamique des vents. Cette analyse morphométrique spatialisée est basée sur une Analyse en Composante Principale (ACP) et met en évidence les paramètres dominants suivant : la longueur des dunes (PC1) explique plus de 50 % de la variance et décrit les dunes linéaires du SW du désert ; la hauteur (PC2) représente 18 % de la variance et décrit les dunes en croissant du NW ; et la densité de défauts (PC3) explique 14 % de la variance, représentant les dunes en étoile et en dôme au SE. Des tests de p-value ont aussi été réalisés sur ces paramètres et révèlent des valeurs inférieures à 0,05, confirmant ainsi une organisation spatiale significative des dunes à l’échelle du désert.Chaque forme archétypale de dune est dominée par l'un des trois paramètres identifiés par l'ACP, et les transitions entre ces formes représentent des étapes évolutives. En comparant ces résultats avec les données de vent, nous obtenons un modèle évolutif où la forme, la taille et l'orientation des dunes sont fortement influencées par les caractéristiques directionnelles du flux de sable associés aux vents du Shamal et du Kharif.(...)
Aeolian dunes at different scales (m-km) are the primary topographic forms in aeolian systems and are found on various planetary bodies such as Earth, Mars, or Venus. They result from the interaction between wind, transported sediments, and the substrate. The shape, size, spatial arrangement, and movement of dunes allow for the analysis of interactions between airflows and sediment supply, modulated by surface conditions. The production of detailed maps of individual dune characteristics, coupled with spatial morphometric statistical analysis, is thus necessary to understand better and characterize the origin of dune formation and evolution.However, accurately mapping dunes over large areas remains a challenging task today for two reasons. Firstly, considering the availability of remote sensing datasets with ever-increasing spatial (and temporal) resolution, such mapping requires automated processes since manual digitization i) is time-consuming and ii) can be subjective and of uneven quality. These limitations are mainly because human operators cannot maintain consistent mapping criteria across large study areas, especially when dealing with complex morphologies. Secondly, this mapping is challenging, particularly due to the complexity of some forms and the lack of a universally accepted dune classification, despite recent research efforts.The primary objective of this work is to propose a new method for mapping aeolian dunes, focusing on an approach that couples Deep Learning to delineate the dune outlines, "skeletonization," and network analysis to map their crestlines and connectivities (defects). The originality of this study lies in the ability to map these features at various scales, ranging from a few kilometers to entire deserts. The developed algorithms demonstrate excellent performance in analyzing large and complex geographic areas with an accuracy of around 90%. This method has enabled the creation, for the first time, of a database containing several thousand dunes from the Rub'Al Khali desert (the largest active desert in the world), with high fidelity compared to visual observations of the dunes present in the Digital Elevation Model (DEM).From this database, we studied the morphological variability of the dunes by comparing them with wind data (ERA5 Land Reanalysis) on a desert scale, in order to quantify and understand their morphological changes and spatial distributions in relation to wind dynamics. This spatialized morphometric analysis is based on Principal Component Analysis (PCA) and highlights the dominant parameters as follows: dune length (PC1) explains more than 50% of the variance and describes the linear dunes in the SW of the desert; height (PC2) represents 18% of the variance and describes the crescent-shaped dunes in the NW; and defect density (PC3) explains 14% of the variance, representing star and dome dunes in the SE. P-value tests were also conducted on these parameters and revealed values below 0.05, thus confirming a significant spatial organization of dunes at the desert scale.Each archetypal dune form is dominated by one of the three parameters identified by the PCA, and transitions between these forms represent evolutionary stages. By comparing these results with wind data, we obtain an evolutionary model in which dunes shape, size, and orientation are strongly influenced by the directional characteristics of sand flow associated with the Shamal and Kharif winds. The analysis of wind data to the different statistically defined dune populations also revealed two dune growth modes: an elongation mode in the west, where the crests of linear dunes align with the sediment flow, favoring their stretching, and an instability mode in the east, where isolated and crescentic dunes, perpendicular to the flow, optimize their vertical growth

Extreme storms are responsible for rapid changes to coastlines worldwide. During the 2013/14 winter, the west coast of Europe experienced a sequence of large, storm-induced wave events, representing the most energetic period of waves in the last 60 years. The southwest coast of England underwent significant geomorphological change during that period, but exhibited a range of spatially variable and complex morphological responses, despite being subjected to the same storm sequence. The 2013/14 storm response along the southwest coast of England was first used as a natural field laboratory to explain the variability in storm response through the introduction and evaluation of a new classification of how sandy and gravel beaches respond to extreme storms. Cluster analysis was conducted using an unique data set of pre- and post-storm airborne Light Detection and Ranging (LiDAR) data from 157 beach sites and the calculation of volumetric beach changes and a novel parameter, the longshore variation index which quantifies the alongshore morphological variability in beach response. The method used can be applied to any sandy and gravel beaches where topographic data with sufficient spatial resolution is available. Four main beach response types were identified that ranged from large and alongshore uniform offshore sediment losses up to 170 m3 m-1 (at exposed, cross-shore dominated sites) to considerable alongshore sediment redistribution but limited net sediment change (at more sheltered sites with oblique waves). The key factors in determining the type of beach response are: exposure to the storm waves, angle of storm wave approach and the degree to which the beach is embayed. These findings provide crucial information for the development of coastal studies at regional scale, especially along coastal areas where abrupt changes in coastline orientation can be observed. A 10-year time series (2007-2017) of supra- and intertidal beach volume from exposed and cross-shore transport-dominated sites was used to examine the extent to which beach behaviour is coherent over a relatively large region (100-km stretch of coast) and predictably coupled to incident wave forcing. Over the study period, 10 beaches, exposed to similar wave/tide conditions, but having different sediment characteristics, beach lengths and degrees of embaymentisation, showed coherent and synchronous variations in sediment volumes, albeit at different magnitudes. This result is crucial for studying coastal changes in remote coastal areas or in areas where only few topographic data are available. The sequence of extreme storms of the 2013/14 winter, which represents the most erosive event over at least a decade along most of the Atlantic coast of Europe, is included in the data set, and three years after this winter, beach recovery is still on-going for some of the 10 beaches. Post-storm beach recovery was shown to be mainly controlled by post-storm winter wave conditions, while summer conditions consistently contributed to modest beach recovery. Skilful hindcasts of regional changes in beach volume were obtained using an equilibrium-type shoreline model, demonstrating that beach changes are coherently linked to changes in the offshore wave climate and are sensitive to the antecedent conditions. Furthermore, a good correlation was found between the beach volume changes and the new climate index WEPA (West Europe Pressure Anomaly), which offers new perspectives for the role and the use of climatic variations proxies to forecast coastline evolution. A process based model, XBeach, was used to model storm response at one macrotidal beach characterized by the largest sediment losses during the 2013/14 sequence of extreme storms. Beach volume changes were modelled over hypothetical scenarios with varying hydrodynamics conditions and beach states to investigate the relative roles of hydrodynamic forcing (i.e., waves and tides), beach antecedent state and beach-dune morphology in beach response to extreme storms. This modelling approach is applicable to any beach system where process based models have been implemented. Beside significant wave height and peak wave period, the beach antecedent state was shown to be the dominant factor in controlling the volumes of sediment erosion and accretion along this cross-shore dominated beach. Modelled volumes of erosion were, on average, up to three times higher along an accreted beach compared to an eroded beach for the same wave conditions. The presence of a dune, being only significantly active during spring tides and storm conditions along this macrotidal beach, was shown to reduce erosion or even cause accretion along the intertidal beach. This work provides a detailed, quantitative insight of the hydrodynamic and morphological processes involved in storm response and beach recovery on a number of spatial and temporal scales. This improved understanding of the potential impact of extreme events will hopefully aid future research efforts and ensure effective management of sedimentary coastlines.

Les dunes de sable sont des formes très présentes en milieu marin. Comprendre l'évolution des dunes est un enjeu important pour prévoir les caractéristiques de l'écoulement, les flux sédimentaires, et les variations de la bathymétrie. Les dunes sous-marines représentent un risque pour les activités humaines, a fortiori avec l'intérêt croissant pour les énergies marines renouvelables, pour la navigation, ou l'industrie offshore. Bien que la connaissance des dunes représente un intérêt scientifique et opérationnel de premier ordre, les processus physiques conduisant leur évolution sont toujours mal compris. En outre, la prévision de leurs caractéristiques géométriques et de leur dynamique basée essentiellement sur des formules empiriques reste peu précise. Dans ce travail de thèse, un modèle numérique est d'abord utilisée pour modéliser les dunes soumises à un écoulement stationnaire. Les simulations reproduisent l'évolution d'un fond faiblement perturbé jusqu'à un champ de dunes en équilibre avec l'écoulement et apportent des connaissances approfondies sur les processus physiques mis en jeu. Ensuite, les résultats d'un ensemble de campagnes de mesures réalisées dans la passe sud du bassin d'Arcachon permettent d'étudier la dynamique des dunes tidales in situ et relier leur asymétrie et leur migration aux résiduels de transport sédimentaire. Enfin, l'application du modèle numérique avec les conditions de forçages extraites des campagnes de mesures permet de reproduire la dynamique des dunes tidales ainsi que la génération de rides d'un ordre de grandeur comparable aux rides surimposées observées in situ. Ces résultats ouvrent des perspectives intéressantes en vue du développement d'un modèle opérationnel de prévision de la dynamique des dunes tidales
Sand dunes are ubiquitous beforms in nature within subaqueous environments. Understanding dune evolution is important issue to accurately predict the ow circulation, sediment uxes and bathymetric variations in sandy subaqueous environments. Sand dunes may pose a significant risk for offshore activities in coastal environments, especially with the growing development of renewable marine energy, for navigation or the offshore industry. Although sand dunes represent a great scientific and operational interest, their evolution is still poorly understood due to their complex behavior. The aim of the thesis work was to study the physical processes driving the evolution of subaqueous sand dunes and to understand their in situ dynamics within tidal environments. First, a numerical model was employed to simulate sand dunes under stationary current conditions. The simulations reproduced the morphodynamic evolution of a slightly perturbed bed until a steady sand dune field in equilibrium with the ow. The results offered a deeper understanding of the physical processes driving the bed evolution to equilibrium. Second, an array of in situ measurements was carried out into the Arcachon inlet, in southwest France, to study the dynamics of tidal sand dunes. For the first time their asymmetry and migration rates were linked to the sediment uxes residuals on a spring-neap tidal cycle. Finally, the numerical model was adapted both to simulate the dynamics of tidal sand dunes, and generate bedforms of the same order of magnitude as the in situ dune-superimposed ripples starting from a at bed. These results open promising perspectives for the development of a numerical tool capable of predicting the behavior of sand dunes within tidal environments

Les dunes côtières constituent un des éléments fondamentaux de la dynamique des systèmes côtiers sableux. Leur stabilité dépend essentiellement de leur capacité à résister aux effets des tempêtes et à se reconstituer après l'érosion. Dans le contexte actuel du changement climatique, la probable hausse du niveau de la mer devrait affecter considérablement les systèmes côtiers et de surcroît augmenter la vulnérabilité des cordons dunaires à l'érosion.L'objectif principal de cette thèse est d'étudier l'évolution des littoraux dunaires de la Côte d'Opale en adoptant une approche à plusieurs échelles de temps afin d'évaluer leur capacité de résistance et/ou de régénération face aux événements tempétueux. A long terme, l'étude de l'évolution du trait de côte sur près de 68 ans, à partir de photographies aériennes orthorectifiées, a révélé que plus de la moitié des littoraux dunaires de la Côte d'Opale sont stables ou en accumulation et possèdent donc une bonne capacité de résilience, malgré les nombreuses tempêtes ayant affecté ce littoral depuis le début des années 50. L'analyse de leur évolution sur un pas de temps de 5 ans a mis en évidence une forte variabilité spatiale et temporelle directement liée aux forçages météo-marins, notamment aux épisodes tempétueux associés à des hauts niveaux d'eaux. A moyen et court termes, des levés topographiques LiDAR et des mesures in-situ, couplés aux données météorologiques et hydrodynamiques, ont révélé une réponse morphologique différente entre des secteurs dunaires adjacents. Celle-ci est liée à la variation des paramètres morphologiques (altitude de pied de dune, largeur et volume du haut de plage) au cours des périodes étudiées. Les résultats montrent également que les processus de régénération peuvent être très longs sur nos sites d'étude, ce qui suggère que les dunes cotières qui, jusqu'à présent étaient relativement stables, risquent de connaître des épisodes d'érosion plus fréquents avec l'élévation contemporaine du niveau de la mer
Coastal dunes are fundamental elements of sandy coastal systems dynamic. They may experience a variable response to coastal erosion, in relation to their ability to withstand storm effects and to recover from erosion. Global sea level rise, related to global warming, would considerably affect coastal systems and hence the sensitivity of coastal dunes to erosion. The main objective of this thesis is to study the evolution of the Côte d'Opale coastal dunes at different time scales in order to evoluate their capacity to resist and/or to recover from storm impacts. Over long term periods (nearly 68 years), shoreline evolution analysis from orthorectified aerial photographs revealed that more than half of the Côte d'Opale coastal dunes are stable or prograding and thus, are resilient. Their evolution over 5-year periods highlighted a strong spatial and temporal variability which is directly linked to weather and hydrodynamic conditions, especially the occurence of storms during heigh water levels. At medium and short term scales, topographic surveys from LiDAR and in-situ measurements, coupled with metrological and hydrodynamic data, showed a different morphological response between adjacent coastal dune areas. This is related to variations in morphological parameters such as dune foot elevation, width and volume of the upper-beach during the studied periods. Results show also that coastal dunes recovery from storms can be a very long process at our study areas, suggesting that foredunes in a state of mesoscale stability may experience more frequent erosion with currents sea level rise

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
This study analyzed measurements of the aeolian transport using vertical sand traps across the field dunes of Jenipabu, in the municipality of Extremoz, Rio Grande do Norte state to the North of Natal city. These measurements were used as parameters for the sand aeolian transport in the region. Before the field trips a map of landscape units was made. Three visits to the field were done in September 2011 (field a - the 13th, field b - the 21st, field c - the 29th), period of the year with the highest wind speed, and another in December 8th, 2011 (field d ) when the wind speed starts to decrease. The sand traps used were of the type "I" with collecting opening of 25 cm from the surface level, and type "S" with collecting opening of 25 cm located 25 cm from the surface level in six collecting points in two of the visits (fields a and d ), and sand traps of the type "T" with the collecting opening of 50 cm from the surface level in the other field trips (fields "b" and "c"). A set of records was also collected by using a portable meteorological station complemented with information such as frequency and intensity of winds, precipitation and relative air humidity in the region, from the Esta??o Meteorol?gica de Natal , located 12 km from the study area. The sediments collected were treated and the data obtained permitted calculating the ratio of sediment transport. In September, the sedimentation ratio varied from 0.01 to 11.39 kg.m-1.h-1 and in December this ratio varied from 0.33 to 1.30 kg.m-1.h-1 in the type T collectors. In type I collectors they ranged from 0.01 to 11.39 kg.m-1.h-1, while the same parameters varied from 0.01 to 0.73 kg.m-1.h-1 in type S collector. Based on the statistical analysis done, we concluded that the sediment transport increased proportionally to the wind speed 25 cm from the surface. However, this is not true above 25 cm from the surface. The transport of sediments is more intense near the surface where sedimentation ratios greater than 10 kg.m-1.h-1 were found, whilst a maximum value of 3 kg.m-1.h-1 was observed 25 cm below the surface. The volume of sediments collected increases with the increasing wind speed at the surface level, whereas this relationship is opposed far away from that surface
O presente estudo fez a an?lise de medidas de transporte e?lico utilizando coletores de areia verticais (Sand Traps) ao longo de um campo de dunas na praia de Jenipabu, munic?pio de Extremoz no estado do Rio Grande do Norte ao Norte da cidade de Natal. Estas medidas foram utilizadas como par?metro de avalia??o da movimenta??o e?lica nesta regi?o. Tr?s visitas a campo foram realizadas no m?s de setembro de 2011 nos dias 13 (campo "a"), 21 (campo "b") e 29 (campo "c"), per?odo do ano com maiores velocidades de vento e uma em dezembro de 2011 no dia 08 (campo "d"), per?odo onde a velocidade do vento come?a a diminuir. Utilizaram-se coletores tipo "I" com abertura de 25 cm a partir do n?vel da superf?cie e "S" com abertura de 25 cm a 25 cm da superf?cie em seis pontos de coleta em duas das visitas ? campo nos dias 13 de setembro (campo "a") e 08 de dezembro (campo "d"), e tipo "T" com abertura de 50 cm a partir do n?vel da superf?cie nas demais visitas 21 e 29 de setembro (campo "b" e "c") ao longo do Campo de Dunas de Jenipabu. Foram tamb?m coletados dados meteorol?gicos com a utiliza??o de esta??o meteorol?gica port?til e complementados com dados da Esta??o Meteorol?gica de Natal que est? localizada a cerca de 12 km da ?rea de estudo para obter informa??es sobre a frequ?ncia e intensidade dos ventos, precipita??o e umidade relativa do ar da regi?o. Os sedimentos coletados foram tratados e foi calculada a vaz?o de fluxo de sedimentos (taxa de sedimenta??o). Em setembro a taxa sedimenta??o variou de 0,01 at? 11,39 Kg m-1 h-1 e em dezembro entre 0,33 e 1,30 Kg. m-1. h-1 nos coletores tipo "T". Nos coletores tipo "I" esses valores variaram entre 0,01 e 11,39 Kg m-1 h-1, enquanto que nos coletores tipo "S" de 0,01 a 0.73 Kg. m-1. h-1. De acordo com a an?lise estat?stica realisada percebe-se que o transporte de sedimento aumentou proporcionalmente a velocidade do vento em at? 25 cm da superf?cie. Por?m, essa rela??o n?o ? verdadeira acima de 25 cm do n?vel da superf?cie. O transporte de sedimentos ? mais intenso mais pr?ximo ? superf?cie onde foram encontradas taxas de sedimenta??o maiores que 10Kg. m-1. h-1 enquanto que a 25cm de dist?ncia o m?ximo encontrado foi menor que 3Kg. m-1. h-1, a quantidade de sedimento coletados aumenta ? medida que aumenta a velocidade no n?vel da superf?cie, ao se afastar da superf?cie a quantidade de sedimento essa rela??o n?o ? verdadeira

Coastal foredune evolution involves complex processes and controls. Although a great deal is known about the effects of vegetation cover, moisture, and fetch distance on sediment supply, and of topographic forcing on airflow dynamics, the role of large woody debris (LWD) as a modulator of sediment supply and a control on foredune growth is understudied. Large assemblages of LWD are common on beaches near forested watersheds and collectively have a degree of porosity that increases aerodynamic roughness and provides substantial sand trapping volume. To date, no research has attempted to understand the geomorphic role that LWD matrices, as a whole, have as roughness elements affecting airflow and sediment transport across a beach-dune system, or, what the long-term implications of these impacts are on beach and foredune erosion recovery and evolution. This four-year research initiative investigated the role of a LWD matrix on beach-dune morphodynamics on West Beach, Calvert Island on the central coast of British Columbia, Canada. This study integrated data from research that spanned three temporal scales, 1) event-scale (10 min) flow and sediment transport patterns, 2) daily frequency and relative magnitude of landscape changing events, 3) seasonal to interannual-scale volumetric and LWD changes. An event-scale experiment to characterise airflow dynamics and related sand transport patterns showed that LWD distinctly alters wind flow patterns and turbulence levels from that of incoming flow over a flat beach. Overall, mean wind speed and fluctuating flow properties declined as wind transitioned across the LWD. Streamwise mean energy was converted to turbulent energy, however, the reductions in mean flow properties were too great for the increased streamwise turbulence to have an effect on transport. In response to these flow alterations and more limited sand transport pathways to the foredune, sediment flux was reduced by 99% in the LWD compared to the open beach, thereby reducing sand supply to the foredune. Sand grains rebounding off of the LWD were carried higher into the flow field resulting in greater mass flux recorded at 20-50 cm in the LWD as opposed to the flat beach. This effect was only recorded 6 m into the LWD. As such, LWD has the potential to modulate rates of foredune recovery, growth, and evolution. Time-lapse photography collected at 15 min intervals during the study revealed that storm events lead to wave-induced erosion of the backshore and reworking of the LWD matrix. The exposed LWD matrix subsequently traps aeolian sediment that leads to rapid burial of the LWD and building of a raised platform for emergent vegetation. However, infilling of the accommodation space within the LWD matrix is so rapid, that sediment starvation of the foredune is short-lived. While the LWD at this site does trap sediment in the backshore, helping to protect the dune from scarping, LWD at this study site maintains an overall lower impact on transport to the foredune. Critical to this relationship is the frequency and magnitude of nearshore events that erode the beach periodically and re-organize the LWD matrix, which directly impacts the ability of LWD to store sediment and modulate transport to the foredune. A conceptual model exploring these relationships is presented.
Graduate

This dissertation presents the results of a multi-year interdisciplinary study of a dynamic coastal dune ecosystem restoration effort in Pacific Rim National Park Reserve in British Columbia, Canada. The research is the result of a collaboration with Parks Canada Agency (PCA) who, under the Species at Risk Act (SARA), are mandated to restore habitat for SARA listed species within the dune complex. In response, PCA committed to, and implemented, a dynamic dune ecosystem restoration program that involved widespread removal of invasive vegetation (Ammophila spp.), transplanting of native vegetation, introduction of an endangered species, and volunteer programs to prevent re-growth of Ammophila. A comprehensive monitoring program was developed with PCA and undertaken by the author and PCA collaborators from start of the project in Summer 2008 to Fall of 2012. This dissertation is the product of independent research by the author carried out under the supervision of the advisory committee and does not reproduce written materials prepared for, or by, PCA. The dissertation consists of three separate journal manuscripts (the first two published by completion of the dissertation) that stand alone as independent investigations but are structured here to provide a natural progression of research findings and allow for an overall synthesis of ideas and broader contributions of the research. The dune restoration program afforded an opportunity to review restoration trends and methods and implement a strategy and monitoring protocols based on leading edge science. Accordingly, the first manuscript, Chapter 2, summarises recent trends in coastal dune restoration, discusses relevant research surrounding beach-dune morphodynamics and coastal dune activity, and reviews preliminary data from the project. The study identifies usable control data for the project and builds the criteria for assessing the project as a whole. The second manuscript, Chapter 3, presents and analyses the core data obtained for the dissertation - 5 years of geomorphic monitoring from detailed land surveys with 3 years of analysis of beach-foredune-transgressive dune sediment budget responses derived from aerial LiDAR surveys. This chapter identifies several trends in the dune systems’ response to restoration that, with reference to the indicators developed in Chapter 2, suggest improved levels of dynamism in the landscape. Finally, Chapter 4 (manuscript 3), extends the findings of the restoration study and utilises the rich data set obtained from the restoration program to develop a dynamic mapping technique that better conveys the spatial-temporal morphodynamic behaviour of dune ecosystems. The study comments broadly on the potential to apply these data and techniques to the study of disturbance events in beach-dune systems. The dissertation is concluded (Chapter 5) with an overall summary of key research objectives and contributions, and presents recommendations for future research.
Graduate

This thesis explores the geomorphic implications of large woody debris (LWD) residing in the backshore of beach-dune systems along the northeastern coasts of Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada. Detailed topographic surveys were employed to quantify seasonal mass balance of the beach-dune systems along two distinctly different coastlines. Erosion and accretion potential models were applied to characterize sediment transport conditions. Holman’s (1986) R2% wave runup model was superimposed on total water levels, to model wave runup exceedence of the beach-dune junction elevation (6.5 m aCD). Modelled ‘erosion potential’ hours were demonstrated to correspond with observed erosion including removal of the LWD zone, resulting in decreased mass balance. Similarly, Fryberger and Dean’s (1979) Drift Potential model was used to model accretion potential hours. Modelled accretion potential hours were also able to effectively describe conditions when actual accretion occurred. The presence of LWD in the backshore offered two functions to the above processes: it acted effectively as an ‘accretion anchor’, promoting increased mass balance and rebuilding of the incipient foredune; and, it offered a mass of sediment fronting the foredune to protect the beach-dune system from storm wave attack and subsequent erosion.

This thesis presents results from spatial-temporal and volumetric change analysis of blowouts on the Cape Cod National Seashore (CCNS) landscape in Massachusetts, USA. The purpose of this study is to use methods of analysing areal and volumetric changes in coastal dunes, specifically blowouts, and to detect patterns of change in order to contribute to the knowledge and literature on blowout evolution. In Chapter 2.0, the quantitative analysis of blowout change patterns in CCNS was examined at a landscape scale using Spatial-Temporal Analysis of Moving Polygons (STAMP). STAMP runs as an ArcGIS plugin and uses neighbouring year polygon layers of our digitized blowouts from sequential air photo and LiDAR data (1985, 1994, 2000, 2005, 2009, 2011, and 2012 for 30 erosional features, and 1998, 2000, 2007, and 2010 for 10 depositional features). The results from STAMP and the additional computations provided the following information on the evolution of blowouts: (1) both geometric and movement events occur on CCNS; (2) generation of blowouts in CCNS is greatest in 1985 and is potentially related to vegetation planting campaigns by the Park; (3) features are expanding towards dominant winds from the North West and the South West; (5) the erosional and depositional features are becoming more circular as they develop, (6) the evolution of CCNS blowouts follows a similar pattern to Gares and Nordstrom’s (1995) model with two additional stages: merging or dividing, and re-activation. In Chapter 3.0, the quantitative analysis of volumetric and areal change of 10 blowouts in CCNS at a landscape scale is examined using airborne LiDAR and air photos. The DEMs of neighbouring years (1998, 2000, 2007, and 2010) were differenced using Geomorphic Change Detection (GCD) software. Areal change was detected by differencing the area of polygons that were manually digitized in ArcGIS. The changes in wind data and vegetation cover were also examined. The results from the GCD and areal change analysis provide the following information on blowout evolution: (1) blowouts generate/initiate; (2) multiple blowouts can merge into an often larger blowout; (3) and blowouts can experience volumetric change with minimal aerial change and vice versa. From the analyzes of hourly Provincetown wind data (1998-2010), it was evident that blowouts developed within all three time intervals. The percentages of comparable winds (above 9.6 m s-1) were highest in 1998, 1999, 2007 and 2010. It is speculated that tropical storms and nor'easters are important drivers in the development of CCNS blowouts. In addition, supervised classifications were run on sequential air photos (1985 to 2009) to analyze vegetation cover. The results indicated an increase in vegetation cover and decrease of active sands over time. Two potential explanations that link increased vegetation to blowout development are: (1) sparse vegetation creates a more conducive environment for the initiation of blowouts by providing stability for the lateral walls, and (2) high wind events (e.g. hurricanes and nor'easters) could cause vegetation removal, allowing for areas of exposed sand for blowout initiation and development.
Graduate
0799
0368
kimia.abhar@gmail.com

Increases in the frequency and magnitude of extreme water levels and storm surges are observed along some areas of the British Columbia coast to be correlated with known climatic variability (CV) phenomena, including the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Since a shift to a positive PDO regime in 1977, the effect of ENSO events have been more frequent, persistent, and intense. Teleconnected impacts include more frequent storms, higher surges, and greater coastal erosion. Geomorphic recovery of regional beach-dune systems from erosive events is usually rapid (i.e., within a year) by way of high onshore sand transport and aeolian delivery to the upper beach and dunes. At Wickaninnish Bay on the west coast of Vancouver Island, fast progradation rates (to +1.46 m a-1) have been observed in recent decades, in part due to rapid regional tectonic uplift and a resulting fall in relative sea level of ~ -0.9 mm a-1. The Wickaninnish foredune complex has rapidly extended alongshore in response to a net northward littoral drift and onshore sediment delivery. Bar deposition and welding processes supply sediment to the foredune complex via aeolian processes, and as a result, this is forcing Sandhill Creek northward toward the prograding (+0.71 m a-1) Combers Beach system, in part maintaining active erosion (-1.24 m a-1) of a bluff system landward of the channel. Bluff erosion generates substantial sediment volumes (-0.137 m3 m-2 a-1) that feed a large intertidal braided channel and delta system as the creek purges into the Pacific Ocean. As a first step in exploring the interactions between ocean-atmosphere forcing and beach-dune responses on the west coast of Vancouver Island, British Columbia, Canada, the proposed thesis: 1) Examines and assembles the historic erosive water level regime and attempts to draw links to observed high magnitude storm events that have occurred in the Tofino-Ucluelet region (Wickaninnish Bay); and 2) Explores the geomorphic response of local shorelines by examining the geomorphology and historical evolution of a foredune-riverine-backshore bluff complex. Despite rapid shoreline progradation, foredune erosion occurs locally with a recurrence interval of ~1.53 yrs. followed by rapid rebuilding, often in the presence of large woody debris and rapidly colonizing vegetation, which drives a longer-term trend of shoreline progradation. This process is complicated locally, however, by the influence of local geological control (bedrock headlands) and backshore rivers, such as Sandhill Creek, which alter spatial-temporal patterns of both intertidal and supratidal erosion and deposition. This work is necessary to understand mechanisms responsible for erosive water levels and the process interaction responsible for subsequent coastal rebuilding following erosive periods.
Graduate
0368
derek.heathfield@gmail.com

This thesis describes the geomorphology and morphodynamics of two embayed, sandy, macrotidal beach-dune systems in the Cape St. James region of Gwaii Haanas National Park Reserve and Haida Heritage Site. Gilbert Bay beach is a small embayment with a southwest aspect that exhibits prograding dune ridges. Woodruff Bay beach, a larger system with a SE aspect, is characterized by large erosional scarps on the established foredune. Aspect to erosive conditions and embayment size control the distinct morphologic responses of these beach-dune systems. The morphodynamic regime at Cape St. James consists of high onshore sediment transport potential combined with an increasingly erosive water level regime that is forced by PDO and ENSO climatic variability events. Conceptual models of potential future responses of these beaches to sea level rise show a possible landward migration of up to 3.5 m at Gilbert Bay beach and up to 4 m at Woodruff Bay beach.

To date, there has been little research on the morphodynamics of Canada’s Pacific mesotidal beach-dune systems and their potential response to climate variability and change. Accordingly, this study examines and characterizes the morphodynamics of a mesotidal beach-dune system on western Vancouver Island (Wickaninnish Beach) and investigates its potential response to extreme seasonal storms, climate variability events, and climate change trends. This research also informs protected areas management approaches, whose effectiveness is important to the conservation of early successional and proportionately rare specialized dune species. Research methods include repeat cross-sectional surveys, repeat vantage photographs, and analysis of the wind, wave, and water level regime. Both the regional wind regime and aeolian sediment transport regime are bimodal, with a WNW (summer) component and a SE (winter) component. The nearshore littoral sediment transport regime is characterized by both longshore and rip cell circulation cells. To date, survey results are informative only of seasonal changes. Longer-term monitoring will better reveal contemporary trends of the beach-dune system. A high dune rebuilding potential (aeolian sand transport potential = 9980 m3 m‐1 a‐1, resultant aeolian sand transport = 3270 m3 m‐1 a‐1 at 356 degrees) was found based on the incident wind regime and sand grain diameter. A threshold elevation for dune erosion was defined at 5.5 m aCD. Erosive water levels were analyzed using three approaches yielding the following results. Erosive water levels are reached on average, ~3.5 times per year; with a probability of 65% in any given year; and, annual return levels are 5.59 m aCD, suggesting erosive water levels are reached annually. Statistical relations show that the positive phase of El Niño Southern Oscillation (ENSO) (El Niño) shares the most variance with the incident oceanographic regime (e.g., significant wave height, peak period), and although a causal relationship cannot be drawn, El Niño may contribute to the occurrence of erosive events on Wickaninnish Beach. Beyond El Niño, overall findings suggest climate variability signals are manifest in regional erosional water level regimes.

Mobile transgressive dune systems are often overlooked in the study of coastal morphodynamics and sediment budgets. Inundation bK sand of abutting agricultural land and infrastructure has recurred throughout the 2ot 1 century, frequently accompanied by requests by farming communities to the government to stabilise the dunes. In addition, the association of sea-beach-coastal dunes provides an attractive setting for residential I holiday developments on dune systems. Yet little is known about the pattern of dune mobility in response to changing atmospheric conditions (rainfall, air temperature and wind speed) and their effect on dune mobility and the rate of actual and predicted dune migration. The work presented in this thesis addresses the evolution of a parabolic dune, dune mobility and migration. Quantitative data were collected to determine process-response in an actively mobile long-walled asymmetric parabolic dune located on the western coastline of northeast Tasmania, Australia. The data were acquired over a period of four years from a composite of geomorphic survey techniques that incorporated repeated surveys of the ground surface topography using kinematic GPS and arrays of erosion pins, which were linked to analysis of wind flow patterns acquired from an on-site 2 m high meteorology station, and analysis of sediment that forms the dune. Wind shear velocity (u*) and roughness length (z\(_0\)) were measured close to the ground on windward slopes, and speed-up ratios were determined. Analysis of temporally spaced ortho-rectified and georeferenced aerial photography extended the duration of the survey by fifty years to establish the longer term evolution of the parabolic dune, including the downwind and lateral migration rates of the dune system. The level of accuracy (planimetric accuracies typically in the range of 2-5 cm and vertical accuracies of 3-10 cm) achieved in the six epochs of kinematic GPS surveys provided reliable GPS data that were used to construct three-dimensional topographic models of the dune system on 5 m x 5 m grids using kriging. The topographic models displayed the general patterns of displacement and accretion of sediment that maintain dune form. Using cross-sectional profiles, at representative locations across the dune, the pattern of process-response between wind speed I wind direction on the direction of sand movement and on morphodynamics was clearly evident. A series of morphological parameters were extracted from the kinematic GPS data to quantify dune migration rates, dune volumes, and dune reconstitution time. The measured migration rate of the parabolic dune head was 21.5 m/yr (mean value) measured over 4 years, and 27.3 m/yr measured from a fifty-year sequence of ortho-rectified, georeferenced, digitised aerial photography. The head of the dune reconstitutes at the rate of 8.9 years, with a volume of 100,800 m\(^3\). Volumetric change for the study site over an interval of thirty months was in the range of 656,400 m\(^3\). The majority of sand transport is generated by moderate velocity wind flows which have a higher frequency of occurrence. Forty one percent of wind events occur in the moderate velocity category (4 to< 12 m/s), twenty seven percent occur in the high velocity category of> 12 to> 20 m/s. Measurement of flow close to the ground on windward slopes indicated that shear stress does not progressively increase from toe to crest of slope due to interaction between flow and bed form. Some seventy percent of wind events are topographically aligned; across dune flow from the SW sector results in lateral migration of the trailing arms, with the smaller south trailing arm migrating ENE at more than twice the rate of the north trailing arm. This rate of lateral displacement maintains the 3: 1 length to width ratio of the asymmetric parabolic dune by maintaining the dimensions of the deflation plain which in turn maintains the dynamic equilibrium of the aerodynamic envelope of the dune form. This integrated approach has provided quantitative evidence that demonstrates the dynamic feedback between the prevailing wind regime and seasonal and discrete wind flow events on the dune bed, and the influence of atmospheric conditions on dune mobility.

Dissertação de mestrado integrado em Engenharia Civil (área de especialização em Perfil de Hidráulica e Ambiente)
A erosão costeira é um processo que afeta grande parte das praias a nível mundial, acontecendo quando a taxa de remoção dos sedimentos é maior que a taxa de deposição. Os principais fatores causadores deste desequilíbrio são: o vento, as tempestades, a elevação do nível do mar, o esgotamento das fontes sedimentares, entre outros. São diversos os estudos realizados por todo o mundo procurando soluções que mitiguem os efeitos negativos da erosão costeira. Desde 2009 que a costa de Vila Nova de Gaia tem sido objeto de um estudo relacionado com a morfodinâmica costeira e que recentemente se tem focado na componente de transporte eólico dos cordões dunares litorais sob a influência de estruturas de madeira, denominadas usualmente de paliçadas. As intervenções de defesa dos cordões dunares foram promovidas pelo Parque Biológico de Gaia. O objetivo desta dissertação consiste na caracterização da morfodinâmica em dunas onde foram instaladas paliçadas, tendo por base de estudo um programa de monitorização em locais selecionados para o efeito. As campanhas tiveram início em 9 de Março de 2011 e terminaram em 25 de Dezembro de 2012, tendo então uma duração de 10 meses. A velocidade do vento apresenta um papel essencial na quantidade de sedimentos movidos, sendo o transporte de sedimentos nas paliçadas mais significativo para velocidades acima dos 11 km/h. Os resultados obtidos nesta dissertação evidenciam também o papel desempenhado pela orientação do vento que, para além da velocidade, é determinante para o transporte dos sedimentos no interior das paliçadas, constatando-se que este transporte é mais ativo se o vento atuar do quarto quadrante.
The coastal erosion is a process largely affects the global beaches, occurring when the rate of removal of sediments is greater than the deposition rate. The main factors causing this imbalance are: wind, storms, rising sea level, the depletion of sedimentary, among others. There are several studies around the world looking for solutions that mitigate the negative effects of coastal erosion. Since 2009, the coast of Vila Nova de Gaia has been the subject of a study related to the morphodynamics and recently has focused on the transport component of the wind cords coastal dunes under the influence of wooden structures, usually called the palisades. Interventions defense of dune cordons were promoted by the Gaia Biological Park. The objective of this thesis is to characterize the morphodynamic on dunes where fences were installed, based on the study of a monitoring program in selected locations for this purpose. The campaign began on March 9, 2011 and ended on December 25, 2012, then having duration of 10 months. The wind speed has a role in the amount of sediment moved, and sediment transport in palisades most significant speeds over 11 km / h. The results obtained in this work also show the role played by the orientation of the wind, in addition to speed, is critical for the transport of sediments within the palisades, noting that this transport is more active if the wind acting in the fourth quadrant.

Współczesna morfodynamika wydm, tj. zmienność ich kształtu i położenia, jest najczęściej analizowanym zagadnieniem w badaniach rozwoju akumulacyjnych form eolicznych. Ocena ich morfodynamiki polega na określeniu tempa przemieszczania się form, zmienności ich cech morfometrycznych oraz bilansu osadów. Mimo, iż badania akumulacyjnych form eolicznych prowadzone są od ponad stu lat, nieliczne prace poświęcone są kompleksowej analizie wydm gwiaździstych. Brak jak dotychczas wyników badań dotyczących zmienności ich morfodynamiki zarówno w skali sezonowej, jak i długookresowej. Głównym celem rozprawy doktorskiej było w związku z tym określenie morfodynamiki wydm gwiaździstych należących do różnego typu (prostego, złożonego i zespolonego), występujących w obszarach o bimodalnym reżimie wiatru. Celem szczegółowym rozprawy było określenie, jakie znaczenie dla morfodynamiki wydm gwiaździstych ma wielkość tego typu form (ich faza rozwoju). Celem praktycznym rozprawy było stworzenie typologii ramion wydm gwiaździstych umożliwiającej ocenę morfodynamiki tego typu form. Celem pośrednim, wynikającym z bardzo małej liczby dotychczas prowadzonych badań wydm gwiaździstych, było również określenie metod pomiarowych oraz metod analizy ilościowej, umożliwiających wykonanie i wzajemne porównanie trójwymiarowych modeli form, które uznawane są za podstawowe w badaniach współczesnej morfodynamiki form rzeźby terenu. Badania wykonano na Ergu Chebbi położonym w południowo-wschodnim Maroku. W jego obrębie występują wszystkie wydzielone dotychczas typy wydm gwiaździstych. Obszar ten cechuje występowanie bimodalnego reżimu wiatru. Analizy szczegółowe obejmowały 6 wydm gwiaździstych różnego typu i wielkości. Badania morfologii i morfodynamiki wybranych form zostały przeprowadzone pięciokrotnie w okresie od marca 2011 r. do marca 2013 r. Terminy szczegółowych pomiarów terenowych związane były z sezonową zmiennością reżimu wiatru w obszarze badań. Ze względu na małą, w porównaniu do innych typów wydm, zmienność położenia powierzchni wydm gwiaździstych, a w związku z tym konieczność precyzyjnego określenia ich kształtu, pomiary terenowe wykonano przy użyciu GPS RTK. Po każdym sezonie badawczym stworzono trójwymiarowe modele wszystkich zmierzonych form. Ich dokładność wynosiła co najmniej ±5 cm. Wzajemne ich porównanie umożliwiło przeprowadzenie szczegółowych analiz zarówno zróżnicowania jak i zmienności morfodynamiki wydm gwiaździstych. W celu określenia morfodynamiki wydm gwiaździstych przeprowadzono analizę sezonowej oraz długookresowej zmienności: cech morfometrycznych, nachylenia stoków, przebiegu i kształtu ramion oraz całkowitego i powierzchniowego bilansu osadów. Na podstawie analizy kształtu i przebiegu ramion zaproponowano ich typologię. Stwierdzono, że o morfodynamice wydm gwiaździstych w obszarach o bimodalnym reżimie wiatru decyduje kierunek natarcia wiatru w stosunku do przebiegu ramion i jego zmienność w danym okresie. Stwierdzono również, że rozkład ramion wydm gwiaździstych decyduje o tym, czy ich morfodynamika jest podobna do morfodynamiki wydm poprzecznych czy podłużnych. Uzyskane w trakcie badań wyniki wskazują, że w obszarach o bimodalnym reżimie wiatru, ramiona wydm gwiaździstych funkcjonują przeważnie jak wydmy poprzeczne odwracalne. Oznacza to, że dla morfodynamiki wydm gwiaździstych, zwłaszcza ich ramion głównych, bardzo istotną rolę odgrywa ich morfologia, w szczególności rozkład ramion drugiego rzędu, który decyduje o przepływie przypowierzchniowego strumienia powietrza w obrębie wydmy. Dzięki trójwymiarowym modelom wydm gwiaździstych, wykonanym dla kilku okresów badawczych, po raz pierwszy możliwe było określenie i analiza powierzchniowego i całkowitego bilansu osadów. Wykorzystanie bilansu osadów do badań morfodynamiki wydm gwiaździstych pozwala w szczególności na określanie kierunku rozwoju pól wydmowych, w których dominuje ten typ wydm. Kluczowym efektem badań jest model określający zależność pomiędzy reżimem wiatru, w szczególności częstością zmiany jego kierunku w skali sezonowej i długookresowej a wielkością powierzchniowego bilansu osadów wydm gwiaździstych występujących w obszarach o bimodalnym reżimie wiatru. Model ten pozwala na parametryczną analizę morfodynamiki wydm gwiaździstych występujących w innych obszarach o bimodalnym reżimie wiatru, a w konsekwencji na określanie jej sezonowej i długookresowej zmienności. Ze względu na coraz większą dokładność i dostępność zdjęć satelitarnych oraz coraz bardziej rozwinięte możliwości pomiarowe powoli otwiera się bardzo szerokie, nowe pole do badań morfodynamiki form rzeźby terenu, w tym akumulacyjnych form eolicznych. Zaproponowane w rozprawie zasady określania morfodynamiki wydm gwiaździstych, w szczególności typologia ich ramion, mogą stanowić bazę metodologiczną w dalszych badaniach morfodynamiki tego typu form.
Dunes morphodynamic i.e. their shape and position changes, is the most commonly analysed subject in the research of aeolian landforms. The assessment of their morphodynamics consists of determining the dunes migration rate, variability of their morphometric features and the sediment budget. Although the study of aeolian landforms has been made for over a hundred years, few works was made on the analysis of star dunes. None so far has brought results on the variability of their morphodynamics, in the seasonal and long-term scale. The main aim of this thesis was therefore to determine morphodynamics of star dunes belonging to different types (simple, complex and compose) in areas of bimodal wind regime. The aim of the thesis was also to determine the star dune size (their stage of development) impact on their morphodynamics. The practical aim was to create a typology of the star dunes arms, which would allowed an assessment of their morphodynamics. The aim, resulting from a small number of previously made studies of star dunes, was also to define measurement and analytical methods of quantitative analysis to complete the three-dimensional model of forms, which are regarded as essential in the study of contemporary morphodynamics landforms. The study was performed at Erg Chebbi in south-eastern Morocco. All types of previously identified star dunes are localised there. This area is characterized by bimodal wind regime. Detailed analysis included 6 star dunes of different types and size. Morphodynamics analysis of selected forms were conducted five times during the period from March 2011. to March 2013. Terms of detailed field measurements were related to the seasonal variability of wind regime in the area of research. Due to low changes of star dune surface compared to other types of dunes, and therefore the need to precisely determine their shape, field measurements were made using GPS RTK. After each research period three-dimensional models of all measured forms were made. Their accuracy is at least ±5 cm. Mutual comparison enabled to carry out detailed analyzes of both the diversity and variability of star dunes morphodynamics. In order to determine star dunes morphodynamics, the seasonal and long-term analysis included: morphometric parameters, slopes inclination, crestline direction and shape of the arms and the total and surface sediment budget. The analysis of arms shape and crestline direction was used for made their typology. It has been found that the star dunes morphodynamic in the areas of bimodal wind regime is determined by the angle of attack of wind in relation to the crestline arms direction and wind direction variability within investigated period. It was also found that the distribution of star dunes arms decides whether their morphodynamics is similar to morphodynamics of transverse or linear dunes. The results obtained during the research show that in the areas of bimodal wind regime, the star dunes arms develop mainly as reversing transverse dunes. This means that for the star dunes morphodynamics, especially the morphodynamics of their main arms, their morphology played very significant role. In particular the distribution of secondary arms determines the nearsurface air flow within the dunes. With the three-dimensional models of star dunes, made for several research periods, it was possible to identify and analyse the total and surface sediment budget for the first time. Thanks to applying the results of sediment budget study to the analysis of star dunes morphodynamics it will be possible to determine the direction of development of dune fields, in which this type of dune dominates. A key result of the study is a model of the relationship between wind regime, in particular the frequency of wind direction changes on a seasonal and long-term scale and the star dunes sediment budget, in the areas of bimodal wind regime. This model allows to made a parametric analysis of star dunes morphodynamics in other areas of bimodal wind regime, and consequently to determine its seasonal and long-term variability. Due to the increasing of accuracy and availability of satellite images and more advanced measurement capabilities a new field of research of landforms morphodynamics opens, including the aeolian one. The rules for determining the star dunes morphodynamics proposed in this thesis, in particular the typology of their arms, may form the basis for further research methodology of morphodynamics of this type of forms.