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

The stability and survival of salt marshes is typically linked to the competing influences of sea-level rise, subsidence, and sediment accumulation and erosion. However, consideration must also be made for wind waves that regulate the erosion of salt marsh shorelines and resuspend sediments in bordering tidal flats thus providing material for marsh accretion. This thesis examines the mechanisms in which wind waves affect marsh morphology, the mechanisms of salt marsh boundary erosion, in addition to linking the processes responsible for sediment mobilization between tidal flats and adjacent salt marshes. Sediment concentration within an open-coast marsh creek along the Louisiana chenier plain is shown to be related to the local wave climate and channel velocity. Calculations of sediment fluxes during ebb and flood tides indicates that while large volumes of sediment are mobilized into the marsh when wind waves are present, only a small portion is stored during each tidal cycle. In the coastal lagoon setting of Hog Island Bay, Virginia, marsh shoreline erosion rates were estimated from direct surveys and through analysis of aerial photographs. Erosion rates averaged 1.3 m/yr, similar to the 50-year historical average determined from previous work at the same location. Based on a calibrated numerical model for wind waves, the average erosion rate was linked to the energy of the waves attacking the marsh boundary. Additionally, results suggest that the effect of large waves forming during storms on erosion rates is negligible. Variations in erosion rates were linked to shoreline sinuosity (a proxy used to describe the result of wave concentration through erosive gullies), sediment characteristics, faunal activity, and marsh elevation. The culmination of the work leads to the hypothesis that waves have two opposite effects on salt marshes. On one hand they erode marsh boundaries thus reducing marsh area; on the other hand they mobilize large volumes of sediments in nearby tidal flats which may facilitate marsh accretion thus contrasting sea-level rise. In conclusion, wind waves destabilize marshes along the horizontal direction despite their potential vertical stability.

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

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Os movimentos gravitacionais de massa se caracterizam por uma significativa dissipaÃÃo de energia responsÃvel pelo deslocamento de material nas encostas de relevos. Esses eventos decorrem de vÃrios fatores, naturais e antrÃpicos, e sÃo muito importantes na compreensÃo da evoluÃÃo geomorfolÃgica e na identificaÃÃo de Ãreas de risco morfodinÃmico. O maciÃo de Baturità (CE), localizado prÃximo à RegiÃo Metropolitana de Fortaleza, se apresenta como a mais expressiva serra Ãmida do estado, com Ãndices pluviomÃtricos que podem atingir totais acima de 1.500mm anuais e um complexo mosaico paisagÃstico, de onde se destaca a presenÃa de mata Ãmida que contrasta com o domÃnio das caatingas em que se encontra. Tendo em vista suas caracterÃsticas socioambientais, foi instituÃda uma unidade de conservaÃÃo denominada APA da Serra de BaturitÃ, na dÃcada de 1990, com o intuito de garantir a sustentabilidade dos ecossistemas Ãmidos. A altitude mÃdia desse maciÃo gira em torno de 800m, podendo ocorrer cristas acima de 1.000m. Do ponto de vista geomorfolÃgico, constata-se uma grande variedade de feiÃÃes tais como relevos dissecados nas vertentes, colinas intercaladas com planÃcies alveolares no platÃ, e superfÃcies de erosÃo e de deposiÃÃo nos setores circunvizinhos mais baixos (sertÃes e tabuleiros). Nas Ãreas mais Ãmidas evidenciam-se expressivos mantos de intemperismo, associados com a presenÃa de argissolos. A distribuiÃÃo e caracterÃsticas dos movimentos de massa em encostas variam de acordo com os fatores naturais de cada Ãrea. No maciÃo de BaturitÃ, foram identificados movimentos de massa somente nas Ãreas com declives mais significativos, que se encontram basicamente nas vertentes e no platÃ, sobretudo prÃximos de rodovias e Ãreas de cultivo agrÃcola. Na vertente dissecada Ãmida ocorrem deslizamentos rotacionais e translacionais associados com fluxos de lama e quedas de blocos. Na vertente dissecada seca acontecem deslizamentos translacionais rasos e quedas de blocos. No platà acontecem deslizamentos translacionais e rotacionais e quedas de blocos, porÃm com capacidade energÃtica inferior Ãs vertentes anteriormente citadas. Nos inselbergs e pÃes de aÃÃcar podem ocorrer quedas de blocos. Nas demais Ãreas circunvizinhas, em funÃÃo dos relevos mais planos, nÃo foram constatados movimentos de massa. Com relaÃÃo à suscetibilidade à ocorrÃncia de movimentos de massa, foram identificadas Ãreas com alta suscetibilidade, nas vertentes ocidental, meridional e parte da oriental, Ãreas com suscetibilidade mÃdia nos demais setores elevados do maciÃo, e baixa suscetibilidade nas Ãreas circunvizinhas. As informaÃÃes levantadas acerca dos movimentos de massa podem contribuir para estratÃgias de planejamento ambiental regional. O maciÃo de Baturità apresenta uma sÃrie de problemas administrativos no Ãmbito ambiental associados com licenciamentos inadequados, gestÃo de unidade de conservaÃÃo e delimitaÃÃo de Ãreas de preservaÃÃo permanente. Associado a isso, nÃo existem estratÃgias de planejamento ambiental que incorporem estudos de movimentos de massa. Dessa forma, devem ser tomadas medidas estratÃgias, jurÃdicas e administrativas, voltadas para a soluÃÃo de alguns problemas no Ãmbito da gestÃo ambiental. / The gravitational mass movements are characterized by a significant dissipation of energy responsible for the material displacement on the slopes of relief. These events are due to many factors, both natural and anthropogenic, and are very important to understand the geomorphological evolution and identification of morphodynamic risk areas. The Baturità massif (CE), located near the metropolitan region of Fortaleza stands out as the most significant humid mountain in the state, with a rainfall indicator that can reach up to 1.500 mm annually and a complex landscape mosaic, where stands the presence of humid forest that contrasts with the area of caatinga. In view of its socio-environmental aspects, was established a protected area called âAPA da Serra de BaturitÃâ in the 1990s, in order to ensure the sustainability of humid ecosystems. The elevation of this massif is around 800m, and there may be peaks above 1,000m. From the geomorphological point of view, there is a variety of features such as relief dissected in the slopes, hills interspersed with little plains in plateau, and surfaces of erosion and deposition in the lower surrounding areas (âsertÃes and tabuleirosâ). In wetter areas is significant evidence of weathering mantles associated with the presence of acrisols. The distribution and characteristics of mass movement on slopes vary by natural factors from each area. In Baturità massif, mass movements have been identified only in areas with more significant slopes, which are basically in the hillside and on the plateau, especially near roads and areas of agriculture. In dissected wet hillside occur rotational and translational slides associated with mudflows and stone and debris fall. In dissected dry hillside occur shallow translational slides and stone and debris fall. In plateau occur translational and rotational slides and rock and debris fall, but with power capacity below the above-mentioned slopes. In inselbergs and rocky domes may occur stone falls. In the other surrounding areas, according to the most plans reliefs were not observed mass movements. Regarding susceptibility to the occurrence of mass movements, there were identified areas with high susceptibility in the west, south and part of the eastern hillsides, areas with average susceptibility in the other sectors of the massif, and low susceptibility in the surrounding areas. This information about the mass movements can contribute to regional environmental planning strategies. The Baturità massif presents a series of environmental administrative problems with inadequate licensing, management of conservation units and delineation of areas of permanent preservation. Associated with the abovementioned there is no environmental strategies that incorporate studies of mass movements. Therefore strategies must be taken, legal and administrative, aiming the solution of some problems related to environmental management.

Cette thèse traite des processus morphogénétiques au cours de l’embryogenèse pré-coce des vertébrés par le biais d’une étude mathématique et physique des lignagescellulaires spatio-temporels reconstruits à partir d’imagerie 3D+temps in vivo. Notreméthodologie repose sur une représentation de type système complexe de l’embryonavec ses différents niveaux d’organisation en interaction et l’analyse formelle des dé-placements cellulaires dans l’espace et dans le temps. Nous avons conçu et mis enœuvre une méthodologie originale pour identifier dans les lignages cellulaires la for-mation de compartiments en cohérence avec les repères anatomiques et l’organisationdes organes présomptifs. En outre, nous proposons une stratégie pour inférer les forcesbiomécaniques sous-jacentes. Nous délivrons également une interface informatique er-gonomique, d’abord déployée pour mettre en œuvre notre méthodologie, mais aussiconçue pour être extensible et versatile. Ces outils visent à construire une représenta-tion commune pour les biologistes, les mathématiciens, les physiciens et les informati-ciens explorant les processus de la morphogenèse des organismes vivants. / This thesis approaches morphogenetic processes in the early embryogenesis of verte-brates through the mathematical and physical study of spatio-temporal cell lineagesreconstructed from in vivo 3D+time images. Our methodology is based on a complexsystems representation of the embryo, with the interaction between levels of organiza-tion and the formal analysis of cell displacements in space and time. We designed andimplemented an original methodology to identify in cell lineages the formation of com-partments in consistency with anatomical landmarks and the organization of presump-tive organs. In addition, we proposed a strategy to infer the underlying biomechanicalforces. We also delivered a user-friendly computer interface, first deployed for usingour methodology but also designed to be extensible and versatile, which aims to bea common ground for biologists, mathematicians, physicists and computer scientistsinvestigating morphogenetic processes in living systems.

Alternate bars are large-scale bedforms characterised by an ordered sequence of scour zones and depositional diagonal fronts alternating along channel banks, which are typical of straight channelized rivers. Due to their high relief and migration properties, they represent a problem in river management, because they affect navigation, increase the flooding risk and interact with instream structures. For this reason, in the last decades many studies took the challenge of defining suitable criteria able to describe their morphometric properties. Theoretical, experimental and numerical works have clearly demonstrated that bar occurrence is a threshold process governed by the width-to-depth ratio of the channel, β. If this parameter exceeds a critical threshold, βcr, an instability mechanism amplifies the riverbed perturbations occurring due to the effect of the turbulent flow on the cohesionless riverbed, leading to the spontaneous growth of finite amplitude bars. Under steady flow conditions, alternate bars achieve an equilibrium configuration, whose amplitude value is related to the difference β-βcr. Much less information is available to describe bar characteristics under variable flow conditions, when the width-to-depth ratio changes in time and the amplitude of bars evolves depending on the duration and the shape of the hydrograph. The effect of a single idealized flood on bar amplitude evolution was successfully described by the weakly nonlinear model of Tubino (1991), which was able to capture the trajectory of bar amplitude during different stages of the flood. Supported by experimental results, he found that the response of bars crucially depends on the ratio between the flood duration and the bar-growth timescale. Nevertheless, the effect of a complex flow regime, characterised by a sequence of flow events, is to a large extent unexplored. Specifically, (i) the definition of a criterion to predict the average response of alternate bars in a river reach subject to an hydrological flow regime and (ii) the quantification of bar amplitude evolution due to a complex flow regime are still to a large extent unexplored. The goals of this work are: (i) to investigate the dependence of bar properties to variable discharge conditions; (ii) to analyse the effect of flow unsteadiness in terms of duration and sequencing of flood events and derive the main hydrological characteristics that primarily control the average response of bar amplitude; (iii) to determine the long-term bar geometry and define the "bar-forming'' discharge, which is the theoretical discharge that if maintained indefinitely would produce the same long-term bar response as the natural hydrograph; (iv) to analyse the effect that a sequence of flood events composing a complex flow series has on the evolution of bar amplitude. To pursue these purposes, we adopted a methodology primary based on theoretical models, then supported and validated through the analysis of laboratory experiments and field data. The methodology and the key results for the different parts of this thesis can be summarized as follows: 1. First, the response of bar topography to different flow stages has been investigated both theoretically and through the analysis of experimental data, observing the dependence of alternate bars to peculiar threshold conditions. The validity of weakly nonlinear model of Colombini et al. (1987), originally defined in the neighborhood of the critical condition βcr, has been extended taking into account the emersion of bars for low flows. 2. Subsequently, the average response of bars to idealized flow series has been analysed, exploring their dependence on the duration and sequencing of flood events. The probability density function has been found to be the essential hydrological information of the flow series required to determine the long-term response of bar amplitude, while the integral scale of flow sequence is a suitable metric to quantify the unsteadiness of a flow regime. 3. Then, an innovative approach has been introduced to define an occurrence criterion for alternate bars in straightened river reaches that accounts for the hydrological regime, and to determine the average bar state, with the corresponding "bar-forming'' discharge. The key novelty with respect to the classical methods adopted so far to predict the long-term equilibrium channel geometry is that in this case the morphodynamical work acted on river bars by relatively low-flow stages enhancing their formation can be reversed by high-flow stages that suppress them. Therefore, both the occurrence criterion and the average state are found from a balance between the cumulative effects of bar-forming and bar-suppressing events. 4. Finally, the weakly nonlinear model of Colombini et al. (1987), originally defined to predict the evolution of bars under steady flow conditions, has been extended to reproduce a natural flow series by considering the basic flow varying in time. This approach allows us to (i) statistically investigate the effect of flood magnitude and duration on the variations of bar amplitude and (ii) to simulate the morphological response of a river to alterations of the hydrological regime.The long-term analysis of bar amplitude, as such as its evolution subject to the hydrological flow regime, have been applied to four different study cases, each of them characterised by a distinctive average bar response: two reaches of the Alpine Rhine River, upstream and downstream the confluence of the River Ill (Switzerland), respectively, the Adige River near Trento (Italy) and the Isère River near Montmèlian (France). The theoretical model is able to capture both qualitatively and quantitatively the observed bed response. Specifically, it predicts the occurrence of high-relief bars for the upstream reach of the Alpine Rhine River and for the Isère River, while a plane configuration is predicted for the Adige River. Also the intermediate response of the downstream reach of the Alpine Rhine River is reproduced, showing a predominant flat bed morphology with sporadic low-relief bars.

Barrier islands serve as valuable resources for coastal communities by reducing backbarrier flooding, providing wildlife habitat, and creating local economic activity through opportunities for recreation and tourism. Because the benefits of these islands are linked to their morphology, coastal resource planners must consider what management alternatives will maximize these benefits, considering both short- and long-term goals. Recent advances in long-term computational modeling of barrier island, marsh, and lagoon systems have created opportunities for gaining additional insights into the morphodynamics of these systems, which may help planners make better-informed coastal management decisions. In this series of studies, a recently developed long-term barrier-marsh-lagoon model is evaluated to better understand system morphodynamics and applied to a real barrier island system in the mid-Atlantic to understand its vulnerabilities and the potential impacts of management alternatives. In the first study, a comprehensive review of advances in barrier island morphodynamic modeling was presented. In the second study, a global sensitivity analysis method, the Sobol method, was used to explore the parameter space of the barrier-marsh-lagoon model. The significant influence of initial barrier geometry, the combination of parameters required for short-term drowning to occur, and the significant role of tidal dispersion on backbarrier sediment dynamics were morphodynamic insights drawn from this study. In the third study, five global sensitivity analysis methods were evaluated based on their ability to rank parameters, converge to stable results, and their reliability. Groups of the most significant parameters were generally identified by all methods; however, the Morris method exceeded all others in terms of performance, especially its ability to converge and its reliability. VARS performed second best, on average, with better convergence and reliability results than the Sobol method, and with lower simulation counts. In the fourth study, the long-term model was applied to a mid-Atlantic barrier island and used to assess the island's vulnerabilities to sea level rise, overwash, and the impact of coastal management alternatives. Thin-layer placement and beach nourishment were found to be effective at sustaining the marsh and minimizing island retreat, respectively. / Doctor of Philosophy / Barrier islands help coastal communities by reducing flooding, providing wildlife habitat, and creating local economic activity through opportunities for recreation and tourism. Because the benefits of these islands are linked to their form, decision-makers must think about how to manage these islands to help the community both now and in the future. Recent advances in computer modeling of barrier islands, and the adjacent marshes and lagoons, over decades to hundreds of years, have created opportunities for us to learn more about how these systems behave over time, which may help planners make better-informed coastal management decisions. In this series of studies, a recently developed computer model of the barrier island, marsh, and lagoon is evaluated to learn how the system changes over time and applied to a real barrier island system in the mid-Atlantic to understand its vulnerabilities and the potential impacts of management alternatives. In the first study, a comprehensive review of advances in computer modeling of barrier island changes over time was presented. In the second study, the impact of the model parameters and their combinations with one another was explored using the Sobol global sensitivity analysis method, which is widely considered to be the standard method in practice. The significant influence of initial barrier geometry, the combination of parameters required for the barrier to be overcome by sea level in the short-term, and the significant role of sediment delivered behind the island through tidal inlets were significant insights into the system behavior that were drawn from this study. In the third study, five global sensitivity analysis methods were evaluated based on their ability to rank parameters, the number of computer simulations that were required, the ability of a method to arrive at a conclusive answer, and the consistency of a method in providing an answer. Groups of the most significant parameters were generally identified by all methods; however, the Morris method exceeded all others in terms of its ability to find conclusive and consistent answers due to its ability to identify unimportant parameters. VARS performed second best, on average, with better ability to find conclusive and consistent answers with fewer computer simulations than Sobol. In the fourth study, the long-term computer model was applied to a mid-Atlantic barrier island and used to assess the island's vulnerabilities to sea level rise, overwash (when water flows over the dunes), and the impact of coastal management alternatives. Placing thin layers of additional sediment on top of the marsh platforms and extending the shoreline toward the ocean by placing additional sediment on the beach were found to be effective at sustaining the marsh and minimizing movement of the barrier island landward, respectively.

<p>Coherent, large-scale shapes and patterns are evident in many landscapes, and evolve according to climate and hydrological forces. For large-scale, sandy coastlines, these shapes depend on wave climate forcing. The wave climate is influenced by storm patterns, which are expected to change with the warming climate, and the associated changes in coastline shape are likely to increase rates of shoreline change in many places. Humans have historically responded to coastline change by manipulating various coastal processes, consequently affecting long-term, large-scale coastline shape change. Especially in the context of changing climate forcing and increasing human presence on the coast, the interaction of the human and climate-driven components of large-scale coastline evolution are becoming increasingly intertwined. </p><p>This dissertation explores how climate shapes coastlines, and how the effects of humans altering the landscape interact with the effects of a changing climate. Because the coastline is a spatially extended, nonlinear system, I use a simple numerical modeling approach to gain a basic theoretical understanding of its dynamics, incorporating simplified representations of the human components of coastline change in a previously developed model for the physical system. </p><p>Chapter 1 addresses how local shoreline stabilization affects the large scale morphology of a cuspate-cape type of coastline, and associated large-scale patterns of shoreline change, in the context of changing wave climate, comparing two fundamentally different approaches to shoreline stabilization: beach nourishment (in which sediment is added to a coastline at a long-term rate that counteracts the background erosion), and hard structures (including seawalls and groynes). The results show that although both approaches have surprisingly long-range effects with spatially heterogeneous distributions, the pattern of shoreline changes attributable to a single local stabilization effort contrast greatly, with nourishment producing less erosion when the stabilization-related shoreline change is summed alongshore. </p><p>Chapter 2 presents new basic understanding of the dynamics that produce a contrasting coastline type: convex headland-spit systems. Results show that the coastline shapes and spatially-uniform erosion rates emerge from two way influences between the headland and spit components, and how these interactions are mediated by wave climate, and the alongshore scale of the system. Chapter 2 also shows that one type of wave-climate change (altering the proportion of `high-angle' waves) leads to changes in coastline shape, while another type (altering wave-climate asymmetry) tends to reorient a coastline while preserving its shape. </p><p>Chapter 3 builds on chapter 2, by adding the effects of human shoreline stabilization along such a convex coastline. Results show that in the context of increasing costs for stabilization, abandonment of shoreline stabilization at one location triggers a cascade of abandonments and associated coastline-shape changes, and that both the qualitative spatial patterns and alongshore speed of the propagating cascades depends on the relationship between patterns of economic heterogeneity and the asymmetry of the wave-climate change--although alterations to the proportion of high-angle waves in the climate only affects the time scales for coupled morphologic/economic cascades.</p> / Dissertation

Numerical modelling currently cannot accurately reproduce the onshore-offshore transport asymmetry observed on gravel beaches. The role of the impulsive pressure response generated by plunging waves has been hypothesised to aid mobilisation of sediment, and thus may contribute to transport asymmetry. This process is not currently included in models. Laboratory tests were conducted across a range of wave conditions to investigate the role of plunging wave-breaker impacts on the mobilisation of sediment of gravel beaches. Pressure records were obtained at positions close to the plunging impact locations, to monitor the localised pressures that lead to sediment mobilisation. The correction of the recorded pressure to the bed surface, for further analysis, was achieved through a two stage approach. Adoption of a new technique for separating the pressure records into two components, each determined by different processes is presented. Each component is then corrected to the bed surface with the application of a pragmatic prediction of the experienced attenuation. Data covering a wide range of Iribarren values was assessed, and the impact pressure was parameterised against the wave-breaker type. This procedure identified a potential peak in the impact pressure-Iribarren space in the plunging breaker region, consistent with the previous hypothesis. Comparison of cross-shore profile records provides further limited evidence that morphological prediction fails to reproduce specific characteristics associated with profiles generated under plunging breaker action. Finally, a brief discussion is provided on how the role of the additional pressure generated under plunging impacts can be incorporated into future numerical models.

Os processos morfodinâmicos em sistemas de desembocaduras estão relacionados a uma variedade de condições forçantes que criam condições hidrodinâmicas únicas. Correntes de maré, ondas e descarga fluvial, interagindo em diferentes níveis resultam em complexos padrões dinâmicos. O objetivo do presente trabalho é entender os processos que controlam a dinâmica da desembocadura do estuário do rio Itanhém, Alcobaça, BA. A dinâmica do ambiente foi analisada através de imagens de satélite LANDSAT5-TM e da aplicação de um modelo numérico. As imagens de satélite disponíveis, para os anos de 1987, 1990, 1996, 2007, 2008 e 2009, foram utilizadas para extrair os contornos da linha de costa que, juntamente com dados batimétricos constituíram as malhas para o desenvolvimento de uma série de experimentos numéricos. O modelo numérico utilizado foi o MIKE 21 FM. Foram utilizados três módulos: propagação de ondas, hidrodinâmico e de transporte de sedimento, com retroalimentação entre as mudanças morfológicas e a hidrodinâmica. A descrição dos processos observados pelas imagens de satélite, juntamente com os resultados dos experimentos numéricos mostraram que na região ocorreu acúmulo de sedimentos com consequente crescimento de um pontal a barlamar da desembocadura entre 1987 e 2007. Em 2007 o pontal atingiu seu tamanho máximo, e em função de um evento de alta energia, se rompeu ao norte, deixando dois canais. No período quando o canal era mais estreito, houve maior transporte pela deriva verificado pelo crescimento do banco. Já no período de canal mais largo, houve interrupção na deriva e o banco não cresceu. O mecanismo principal de transporte de sedimentos na área de estudo deve-se principalmente à incidência das ondas do quadrante nordeste, que gera uma corrente de deriva litorânea para sul. As ondas do quadrante sul e sudeste, mais energéticas, e que poderiam gerar deriva na direção oposta, são refratadas pela presença dos parcéis e da progradação da linha de costa em Caravelas, localizados a sudeste e sul da área de estudo. O novo canal formado pelo rompimento do pontal tornou-se o principal meio de fluxo das correntes. Este fluxo atua como uma barreira, interrompendo a deriva litorânea de sedimentos, aprisionando-os a barlamar e limitando o suprimento de sedimentos responsáveis pelo crescimento do banco arenoso ao sul. Nota-se que o tamanho e a largura do novo canal definem a quantidade de sedimentos que atravessa a desembocadura, controlando o crescimento deste banco. / The morphodynamic processes at inlet systems are related to a variety of forcing conditions that create unique hydrodynamic conditions. The interaction of tidal currents, wave conditions, and river discharge at different levels result in complex dynamic patterns. The present work aims to understand the processes that control the dynamics of the Itanhaém River, Alcobaça (BA). The system dynamics was analyzed through the combined application of LANDSAT5-TM satellite images, field measurements and numerical modelling. A set of satellite images (for 1987, 1990, 1996, 2007, 2008 and 2009) was used to extract the coastline contours which, combined with the bathymetric data, defined the grids for a series of numerical experiments. Three modules of the MIKE 21 FM model have been applied: wave propagation, hydrodynamic and sediment transport, including the feedback between the morphological changes and the hydrodynamics. The description of the processes observed through the satellite images and the results of the numerical experiments show that there is a spit growth driving the inlet southwards between 1987 and 2007. In 2007 the spit reached its maximum extent and a high wave energy event breached the spit leaving the system with two openings to the ocean. The sediment supply to the southern sandbar is controlled by the longshore drift, with its quantities being apparently controlled by the inlet width. The main mechanism of sediment transport in the study area is mainly due to the northeasterly waves, moving sediments southwards. The more energetic southerly waves, which could lead to transport in the opposite direction, are refracted due to the wide shelf and the presence of coral reefs in the region. The new inlet formed by the spit breach became the main flow channel. This flow interrupts part of the littoral drift, retaining sediment updrift and limiting the sediment supply downdrift. The size and width of the new inlet define the amount of sediment being bypassed, controlling the growth of the sandbar.