Bathymetric features such as nearshore sandbars can alter local nearshore hydrodynamic processes such as the production of infragravity energy. These bathymetric features may act to reduce or increase the amount of infragravity energy that reaches the shoreline. To determine the influence of the bathymetric features on infragravity energy, the numerical nearshore processes model XBeach was used to simulate infragravity energy at the shoreline. Numerical simulations were completed for three types of bathymetric scenarios: continuous alongshore bar, bar-rip, and no-bar. The presence of the bar reduces the amount of infragravity energy at the shoreline when compared with the no-bar scenario. This reduction was characterized by modifying an empirical parameterization for significant infragravity swash developed by Stockdon et al. (2006) for barred beaches. Results show that the amount of infragravity energy in the form of swash is dependent on the bar height and depth, in addition to the offshore wave height and wavelength. The bar-rip bathymetry produces significant alongshore variation in infragravity energy. The alongshore variations may be due to refracted wave energy or the production of an edge wave by the rip. The magnitude of infragravity energy in the alongshore direction is found to be correlated with the surf zone width. Finally, erosion for the bar-rip scenario is studied qualitatively. The shape of the shoreline is modified during storm events, and is found to take the shape of the alongshore distribution of infragravity energy. Since infragravity swash influences beach erosion, results of this research may be used as part of an erosion vulnerability scale. Such information on erosion vulnerability is important for the design of coastal protection systems and the protection of coastal communities.

As desembocaduras são ambientes altamente dinâmicos com suas feições sedimentares representando a complexa interação entre as correntes de maré, descarga fluvial, ondas e a batimetria local. Essas feições arenosas possuem uma forte influência na troca sedimentar das regiões costeiras, afetando a estabilidade das regiões adjacentes como as praias e os sistemas estuarinos. O objetivo do presente trabalho é entender a relativa influência dos principais processos que controlam a evolução morfológica dos bancos arenosos e dos pontais arenosos associados a desembocadura do sistema estuarino do rio Caravelas. Este sistema é formado por diversos canais meandrantes conectados com o oceano através de duas desembocaduras, e está localizado em frente ao parcel de Abrolhos no sul da Bahia. Baseado na coleta de dados de duas campanhas de 16 dias no sistema estuarino, o modelo numérico MIKE21-FM (DHI Water \\& Environment) foi aplicado e validado a fim de avaliar quantitativamente os processos que controlam o sistema. Os módulos hidrodinâmico, propagação de ondas e de transporte de sedimentos do modelo numérico foram utilizados neste estudo. O modelo inclui a retroalimentação das mudanças morfológicas nos cálculos da hidrodinâmica, ondas e transporte de sedimentos. Os experimentos numéricos têm como objetivo avaliar a importância relativa das forçantes físicas no ambiente. Foram elaborados dez experimentos numéricos incluindo condições energéticas extremas, alta energia (alta altura de ondas, descargas e maré de sizígia) e baixa energia (pequena altura de ondas, descarga e maré de quadratura) para um intervalo de direções de ondas; e dois períodos adicionais que incluem as condições medidas na coleta de dados (Período 2008 e Período 2007). Imagens de satélites LANDSAT e CBERS também foram utilizadas para observação das mudanças morfológicas do pontal arenoso e da linha de costa adjacente ao longo dos últimos anos. Os resultados para a calibração e validação do modelo numérico aplicado demostraram que na região de interesse e na plataforma interna o modelo consegue reproduzir o padrão da hidrodinâmica de forma adequada. Os resultados mostraram que a morfodinâmica local é controlada pela interação dos principais processos físicos, entretanto a importância relativa de cada um varia ao longo das diferentes regiões do sistema. A morfologia do canal principal e o transporte de sedimentos são controlados pelos fluxos de maré. Os bancos arenosos são também controlados pela maré, porém as correntes geradas por ondas atuando sobre estes bancos, geram um transporte de sedimentos em direção à costa. O pontal arenoso Ilha do Pontal do Sul é influenciado pelas ondas e pela maré. O mecanismo de transporte de sedimentos no pontal deve-se principalmente a corrente de deriva litorânea gerada pelas ondas e a maneira como os sedimentos são depositados e transportados ao longo do pontal deve-se aos fluxos de maré. Pelas imagens de satélites, observou-se que ao longo dos anos, o pontal apresentou uma acresção em seu comprimento, um afinamento da largura e sua extremidade encurvou-se. Este formato do pontal é consequência da corrente longitudinal a qual varia em diferentes escalas de tempo: variação diária devido à maré e variação sazonal devido à mudanças na direção da incidência das ondas. / Tidal inlets are highly dynamic environments with their sedimentary features representing the complex interaction of tidal currents, river discharge, waves and the local bathymetry. These sedimentary features have a strong influence in morphological changes of coastal regions, affecting the stability of the adjacent environment such as beaches and estuarine systems. The aim of this study is to better understand the relative influence of the main processes controlling the morphological evolution of sandbars and sandspits associated to the inlet system of the Caravelas estuary. The Caravelas estuarine system comprises several meandering channels connected to the ocean by a double inlet system located in front of the Abrolhos reef in the south of Bahia. Based on the data collected during two 16-day field experiments in the estuarine system, the numerical model MIKE21 FM (DHI Water \\& Environment) has been applied and validated in order to assess quantitatively the processes that control the system. The hydrodynamic, wave propagation and sediment transport modules of the numerical model were used in this study. The model includes the feedback of morphological changes on hydrodynamic, wave and sediment transport calculations. Numerical experiments aiming to assess the relative importance of the physical forcings on the environment include ten sets of boundary conditions. These include the extreme energetic conditions, for high (large wave heights, river discharge and spring tides) and low energy (small wave heights, river discharge and neap tides) under a range of wave directions; and two additional periods that include the measured conditions (2008 period and 2007 period). Satellite images (LANDSAT and CBERS) were also used to observe the morphological changes of the sandspits and adjacent coastline during the last years. The results from the calibration and validation of the numerical model showed that in the region of interest and the inner shelf the model represents the hydrodynamic patterns. Results show that the local morphodynamics is controlled by the interaction of the main physical processes, being however its relative importance variable along the different regions of the system. Tidal flows control the sediment transport and morphology of the main inlet channel. The sandbars that form the ebb-tidal delta are also tide-dominated, although wave driven currents drive an onshore sediment transport component. The sandspit is influenced by waves and tides. The sediment transport along the sandspit is controlled by longshore drift and then redistributed by tidal currents. Satellite images show the sandspit growing in length, and becoming narrower with a recurved tip. The design of the recurved spits that comprise the inlet is a consequence of the wave generated longshore drift which varies at different time scales: a daily cross-shore variation due to the varying water level and seasonally due to variations in the direction of wave incidence.

As desembocaduras são ambientes altamente dinâmicos com suas feições sedimentares representando a complexa interação entre as correntes de maré, descarga fluvial, ondas e a batimetria local. Essas feições arenosas possuem uma forte influência na troca sedimentar das regiões costeiras, afetando a estabilidade das regiões adjacentes como as praias e os sistemas estuarinos. O objetivo do presente trabalho é entender a relativa influência dos principais processos que controlam a evolução morfológica dos bancos arenosos e dos pontais arenosos associados a desembocadura do sistema estuarino do rio Caravelas. Este sistema é formado por diversos canais meandrantes conectados com o oceano através de duas desembocaduras, e está localizado em frente ao parcel de Abrolhos no sul da Bahia. Baseado na coleta de dados de duas campanhas de 16 dias no sistema estuarino, o modelo numérico MIKE21-FM (DHI Water \\& Environment) foi aplicado e validado a fim de avaliar quantitativamente os processos que controlam o sistema. Os módulos hidrodinâmico, propagação de ondas e de transporte de sedimentos do modelo numérico foram utilizados neste estudo. O modelo inclui a retroalimentação das mudanças morfológicas nos cálculos da hidrodinâmica, ondas e transporte de sedimentos. Os experimentos numéricos têm como objetivo avaliar a importância relativa das forçantes físicas no ambiente. Foram elaborados dez experimentos numéricos incluindo condições energéticas extremas, alta energia (alta altura de ondas, descargas e maré de sizígia) e baixa energia (pequena altura de ondas, descarga e maré de quadratura) para um intervalo de direções de ondas; e dois períodos adicionais que incluem as condições medidas na coleta de dados (Período 2008 e Período 2007). Imagens de satélites LANDSAT e CBERS também foram utilizadas para observação das mudanças morfológicas do pontal arenoso e da linha de costa adjacente ao longo dos últimos anos. Os resultados para a calibração e validação do modelo numérico aplicado demostraram que na região de interesse e na plataforma interna o modelo consegue reproduzir o padrão da hidrodinâmica de forma adequada. Os resultados mostraram que a morfodinâmica local é controlada pela interação dos principais processos físicos, entretanto a importância relativa de cada um varia ao longo das diferentes regiões do sistema. A morfologia do canal principal e o transporte de sedimentos são controlados pelos fluxos de maré. Os bancos arenosos são também controlados pela maré, porém as correntes geradas por ondas atuando sobre estes bancos, geram um transporte de sedimentos em direção à costa. O pontal arenoso Ilha do Pontal do Sul é influenciado pelas ondas e pela maré. O mecanismo de transporte de sedimentos no pontal deve-se principalmente a corrente de deriva litorânea gerada pelas ondas e a maneira como os sedimentos são depositados e transportados ao longo do pontal deve-se aos fluxos de maré. Pelas imagens de satélites, observou-se que ao longo dos anos, o pontal apresentou uma acresção em seu comprimento, um afinamento da largura e sua extremidade encurvou-se. Este formato do pontal é consequência da corrente longitudinal a qual varia em diferentes escalas de tempo: variação diária devido à maré e variação sazonal devido à mudanças na direção da incidência das ondas. / Tidal inlets are highly dynamic environments with their sedimentary features representing the complex interaction of tidal currents, river discharge, waves and the local bathymetry. These sedimentary features have a strong influence in morphological changes of coastal regions, affecting the stability of the adjacent environment such as beaches and estuarine systems. The aim of this study is to better understand the relative influence of the main processes controlling the morphological evolution of sandbars and sandspits associated to the inlet system of the Caravelas estuary. The Caravelas estuarine system comprises several meandering channels connected to the ocean by a double inlet system located in front of the Abrolhos reef in the south of Bahia. Based on the data collected during two 16-day field experiments in the estuarine system, the numerical model MIKE21 FM (DHI Water \\& Environment) has been applied and validated in order to assess quantitatively the processes that control the system. The hydrodynamic, wave propagation and sediment transport modules of the numerical model were used in this study. The model includes the feedback of morphological changes on hydrodynamic, wave and sediment transport calculations. Numerical experiments aiming to assess the relative importance of the physical forcings on the environment include ten sets of boundary conditions. These include the extreme energetic conditions, for high (large wave heights, river discharge and spring tides) and low energy (small wave heights, river discharge and neap tides) under a range of wave directions; and two additional periods that include the measured conditions (2008 period and 2007 period). Satellite images (LANDSAT and CBERS) were also used to observe the morphological changes of the sandspits and adjacent coastline during the last years. The results from the calibration and validation of the numerical model showed that in the region of interest and the inner shelf the model represents the hydrodynamic patterns. Results show that the local morphodynamics is controlled by the interaction of the main physical processes, being however its relative importance variable along the different regions of the system. Tidal flows control the sediment transport and morphology of the main inlet channel. The sandbars that form the ebb-tidal delta are also tide-dominated, although wave driven currents drive an onshore sediment transport component. The sandspit is influenced by waves and tides. The sediment transport along the sandspit is controlled by longshore drift and then redistributed by tidal currents. Satellite images show the sandspit growing in length, and becoming narrower with a recurved tip. The design of the recurved spits that comprise the inlet is a consequence of the wave generated longshore drift which varies at different time scales: a daily cross-shore variation due to the varying water level and seasonally due to variations in the direction of wave incidence.

Le but de cette étude était de développer une méthodologie pour évaluer la résilience des littoraux aux évènements de tempêtes, à des échelles de temps différentes pour une plage située à une latitude moyenne (Biscarrosse, France). Un site pilote des tropiques, la plage de Jamestown (Ghana), non soumis aux tempêtes, a également été analysé. 6 ans (2007-2012) de données sur la position du trait de côte,obtenues quotidiennement par imagerie vidéo, ainsi que les prévisions hydrodynamiques (ECMWF EraInterim) ont été analysées. Le climat de vagues est dominé par les tempêtes (Hs> 5% de seuil de dépassement) et leurs fluctuations saisonnières; 75% des tempêtes se produisent en hiver, et plus de 60tempêtes ont été identifiées au cours de la période d'étude. Une régression multiple, montre qu’alors que les intensités des tempêtes actuelle et précédente ont un rôle majeur sur l'impact de la tempête, la marée et les barres sableuses jouent un rôle majeur sur la récupération de plage. La position moyenne du trait de côte calculée sur la période de récupération post-tempête montre que la plage de Biscarrosse se reconstruit rapidement (9 jours) après un évènement isolé et que les séries de tempêtes (clusters) ont un effet cumulatif diminué. Les résultats indiquent que le récurrence individuelle des tempêtes est clé. Si l'intervalle entre deux tempêtes est faible par rapport à la période de récupération, la plage devient plus résistante aux tempêtes suivantes; par conséquent, la première tempête d’une série a un impact plus important que les suivantes. Le trait de côte répond, par ordre décroissant, aux évènements saisonniers,à la fréquence des tempête et aux d’échelle annuelle. La méthode EOF montre de bonnes capacité à séparer la dynamique « uniforme » et « non-uniforme » du littoral et décrit différentes variabilités temporelles: les échelles saisonnières et à court terme dominent, respectivement, la première EOF (2D)et le second mode (3D). Le littoral de Jamestown a été étudié comme base d’un projet pilote entre 2013-2014. Les fluctuations du niveau de l'eau jouent un rôle prédominant sur l’évolution de la position du trait de côte. Les vagues et les estimations des marées obtenues par l’exploitation d’images vidéo sont corrélées avec les données de prévisions. Cette étude pionnière montre que cette technique peut être généralisée à toute l’Afrique de l'Ouest en tenant compte des multiples diversités et de la variabilité du climat régional, à travers un réseau d'observations. / The aim of this study was to develop a methodology to statistically assess the shorelineresilience to storms at different time scales for a storm-dominated mid-latitude beach(Biscarrosse, France). On a pilot base, storm-free tropical Jamestown beach (Ghana) was alsoanalysed. 6-years (2007-2012) of continuous video-derived shoreline data and hindcastedhydrodynamics were analysed. Wave climate is dominated by storms (Hs>5% exceedancelimit) and their seasonal fluctuations; 75% of storms occur in winter with more than 60identified storms during the study period. A multiple regression on 36 storms shows thatwhereas current and previous storm intensity have predominant role on current storm impact,tide and sandbar play a major role on the post-storm recovery. An ensemble average on poststormrecovery period shows that Biscarrosse beach recovers rapidly (9 days) to individualstorms, and sequences of storms (clusters) have a weak cumulative effect. The results point outthat individual storm recurrence frequency is key. If the interval between two storms is lowcompared to the recovery period, the beach becomes more resilient to the next storms; and thefirst storm in clusters has larger impact than following ones. Shoreline responds in decreasingorder at seasonal, storm frequency and annual timescales at Biscarrosse. The EOF methodshows good skills in separating uniform and non-uniform shoreline dynamics, showing theirdifferent temporal variability: seasonal and short-term scales dominate first EOF (2D) andsecond (3D) modes, respectively.The shoreline at Jamestown was studied on pilot base from 2013-2014. Water level channgesplay a major role on shoreline changes. Waves estimates from video are in good agreement withhindcasts. This study shows the potential of the technique, to be replicated elsewhere in WestAfrica with all its diversity and regional climate variability through a coastal observationnetwork.

Active geomorphic features of rivers like sandbars provide habitat for endangered and threatened riparian plant and animal species. However, human development has altered flow and sediment regimes, thus impairing formation of sandbars and islands. Large scale mapping of the fluvial geomorphology in river ecosystems like the Connecticut River is are necessary to understand the dynamics of these features and preserve habitat. Orthophotographs from 2012 from United States Department of Agriculture's Farm Service Agency (FSA), National Agriculture Imagery Program (NAIP) were used to develop a model in ArcGIS Pro to identify fluvial geomorphic features in the Connecticut River and 12 of its major tributaries. This multi-stage image classification model identifies and ranks pixels of proximity and similar color to identify and map sandbars and islands. Locations of sandbars distribution were mapped and analyzed for each river. In the majority of rivers, sandbar area per reach decreases downstream. For the mainstem, sandbar area decreased towards the mouth but with three increases of sandbars due to meandering and major tributary confluences of the White and Deerfield rivers. Dams tend to decrease sandbars downstream but the effect of dams is context specific. Sandbars are stored upstream of the impoundment on the Black River as expected, sandbars appear downstream of a dam on the mainstem if a tributary confluence is present. Conservation of high sandbar area reaches and naturally eroding stream banks are necessary for preservation of endangered species. This spatial model for sandbar mapping can be applied in other river ecosystems across the region.

Ces dernières années, de nouvelles stratégies ciblant un accompagnement de la mobilité du trait de côte plutôt que sa fixation ont vu le jour. Parmi celles-ci, les ouvrages atténuateur de houle visent à protéger la côte en dissipant l’énergie des vagues par déferlement bathymétrique, tout en restant invisibles depuis la plage. Leur utilisation a toutefois eu des effets contrastés et les processus hydro-sédimentaires induits par ces structures restent mal connus. L’objectif général de ce travail est de mieux comprendre les effets de ces atténuateurs de houle sur la morphodynamique littorale, notamment sur des sites où l’évolution de l’avant-côte est complexe et dynamique. L’observation des effets induits par un atténuateur de houle installé au lido de Sète (Golfe du Lion), sur la dynamique littorale est réalisée via un dispositif vidéo qui permet de caractériser l’évolution morphologique du système. En s’appuyant sur une méthode automatique de correction des images développée dans le cadre de cette thèse, l’estimation de la bathymétrie par inversion de la célérité des vagues et ses erreurs associées sont évaluées pour la première fois en Méditerranée. Les observations montrent que l’atténuateur de houle impacte de manière importante la morphologie et la dynamique des barres sableuses pré-littorales et révèlent que l’élargissement de la plage résulte principalement de son couplage avec la nouvelle forme de barre plus linéaire. Le modèle morphodynamique 2DBeach est ensuite implémenté sur Sète et sur un second site atelier en Australie où un récif artificiel de taille et de forme différente a été mis en place. Les simulations réalisées permettent de déterminer les circulations induites par ces ouvrages ainsi que les évolutions sédimentaires associées. Enfin, ce travail met en lumière les différents processus physiques contrôlant l’influence d’un atténuateur de houle sur les évolutions morphologiques des barres sableuses pré-littorales et du trait de côte, et renforce des connaissances essentielles à la gestion durable des plages sableuses. / In recent years, traditional coastal defense strategy has become increasingly unpopular as it is costly and lastingly scars the landscape with sometimes limited effectiveness or even adverse impact. Mimicking natural reefs, submerged breakwaters aims to protect the coast, decreasing wave energy through wave breaking offshore with the advantage of remaining invisible from the beach. The general objective of this work is to better understand the different morphodynamic processes that interact in the presence of these structures, especially for complex beach morphology with highly dynamic sandbars. The observation of the effects induced by a submerged breakwater deployed at the Lido of Sète (Gulf of Lions) on the morphological response is performed using a video monitoring system. Based on an automatic method for image correction developed in this thesis, a video-derived depth inversion algorithm was tested to infer nearshore bathymetry from remotely-sensed wave parameters. Our observations show that the submerged breakwater had a profound impact on the shoreline-sandbar system and suggest that, on barred beaches, the role of the sandbar is critical to shoreline response to the implementation of such a structure. The expected salient formation was not observed and, instead, shoreline coupled to the modified sandbar geometry, which resulted in a slight seaward migration of the shoreline in the lee of the structure. In order to characterize the nearshore circulation induced by these structures and to better assess sediment transport, the morphodynamic model 2DBeach was then implemented on Sète and at another beach in Australia where an artificial reef of different size and shape has been deployed. This work allows a better understanding of the influence of a submerged breakwater on the morphological evolution of sandbars and shoreline on time scales from storm to years, and provides new insight into nearshore system response to better design sustainable management of sandy beaches.

Understanding sandbar dynamics and variability is integral to developing a predictive capacity for nearshore flows, sediment transport, morphological change, and ultimately for determining coastline exposure to damaging storm waves. Along the high-energy U.S. Pacific Northwest (PNW) coast, sandbars typically dominate the bathymetry of the active zone. Here we report on a nearshore bathymetric data set that covers an exceptionally long stretch of coast and crosses several littoral cell boundaries. Our study area stretches from Point Grenville, Washington to Cascade Head, Oregon, including 8 littoral cells and approximately 250 km in the alongshore. We describe and quantify the morphological variability of sandbars in the PNW over large spatial scales as well as attempt to explain the inter-littoral cell variability via trends and variability in environmental parameters. From 560 bathymetric profiles (~1000 km of measurements) we have extracted over 500 distinct subtidal sandbars. The bar zone extends to over 1km from the shoreline in the northern part of the study area, but only to about 600m in the southern part. Maximum bar crest depths are typically 7m below MLLW. Bar heights range from a step in the cross-shore profile to over 3m from crest to trough. The northernmost littoral cells typically have two or more bars per cross-shore profile whereas the littoral cells in the southern part of our study area have only one bar. The mean depths of the bars, however, are much more consistent across littoral cells. The mean depths remain consistent even while the upper shoreface slope significantly increases from north to south, requiring that the maximum bar distance from the shoreline decreases from north to south. This regional gradient in upper shoreface slope is likely a response, at least in part, to a general coarsening trend in the sediment from north to south and hence linked to variations in regional geology. / Graduation date: 2013