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.

A dinâmica de praia constitui conhecimento elementar em obras de engenharia e na compreensão da evolução costeira ao longo do Quaternário recente. Buscou-se avaliar a variação temporal de curto período da morfologia e do volume de sedimento em um segmento na porção sul da praia da Ilha Comprida, litoral sul de São Paulo. Os resultados permitiram algumas interpretações, tanto em escala diária, como sazonal. As morfologias e os volumes do trecho estudado apresentaram maior similaridade entre as campanhas de maio de 2005 e janeiro de 2006, com estágio morfodinâmico de praia dissipativa, e entre agosto e novembro de 2005, com estágio de praia intermediária do tipo banco e calha. As ondas de sul com alturas de até 1 m e período médio entre 7 e 8 s atuaram no processo de engordamento da praia emersa, enquanto que as ondas desta mesma direção com alturas a partir de 1,5 m e período médio entre 8 e 10 s exerceram papel erosivo. De forma inversa, as ondas de leste com até 1 m de altura e período médio entre 6 e 8 s exerceram papel erosivo e com até 1,5 m e período médio entre 6 e 7 s, papel deposicional. / The knowledge of beach dynamics is fundamental in any coastal engineering projects as well as in the coastal evolution comprehension during the Late Quaternary. The aim of this study is to evaluate the short-term variations in morphology and sediment volume in a beach segment located in the southern portion of the Ilha Comprida, southern coast of the state of São Paulo, Brazil. The results allowed us to get important conclusions on daily and seasonal variations in beach morphology and behaviour. The morphology and volume data show similarity between may/2005 and jan/2006, with dissipative morphodynamic state characteristics, as well as between aug/2005 and nov/2005, characterized by an intermediate morphodynamic state. Southerly waves reaching 1m high and mean period between 7 and 8 s acts on the emerged part of the segment in a depositional way as well as southerly waves higher than 1,5 m and period between 8 and 10 s cause erosion in the same part of the beach profile. Easterly waves act in an opposite way, with lower heights causing erosion and higher causing deposition.

Made available in DSpace on 2015-03-13T17:08:25Z (GMT). No. of bitstreams: 1 MariaFAM_reduzido_Opdf.pdf: 5528332 bytes, checksum: 355ca104cbad452325371850cf8f8051 (MD5) Previous issue date: 2009-10-02 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The Amap? State has an important natural lake system, known as The Amap? Lakes Region . Most of these lakes are on the southern part of Amap? s coastal plain, which has 300 km of extension and it s composed by holocenic sediments deposited at the northern part of Amazon River to the Orange Cape located on the northern part of Amap? state. This region is under influence of the Amazon River discharge which is the largest liquid discharge of about 209.000 m?/s and biggest sediment budget discharged on the ocean in the order 6.108 ton per day. The climate is influenced by the Intertropical Convergence Zone and El Ni?o Southern Oscillation which act mainly under precipitation, nebulosity, local rivers and tidal hidrology. In this region lake belts are Ocidental, Oriental and Meridional Lake Belts. The last one is formed by the by the lakes Comprido de Cima, Botos, Bacia, Lod?o, Ventos, Mutuco and Comprido de Baixo. These lakes are the closest to the Araguari River and are characterized by pelitic sedimentation associated with fluvial and estuarine flood plains under influence of tides. The lakes are interconnected, suffer influence of flood pulses from the Tartarugal, Tartarugalzinho and Araguari rivers and the hydrodynamic and morphodynamic know edge is poor. Volume and area reduction, natural eutrophication, anthophic influence, hidrodynamic alterations, morphological changes and are factors which can contribute to the closing of such lakes on the Meridional Lake Belt. This belt is inside the boundaries of the Biological Reserve of Piratuba Lake, created in 1980 for integral protection. Due to the fragility of the environment together with the poor knowledge of the system and with the study area relevancy it is necessary to know the hydrodynamic and geoenvironmental processes. This work aims the characterization of morphodynamic and hydrodynamic processes in order to understand the geoambiental context of the Meridional Lake Belt, from the Comprido de Baixo Lake to the dos Ventos Lake, including the Tabaco Igarape. Methodology was based on the hydrodynamic data acquisition: liquid discharge (acoustic method), tides, bathymetry and the interpretation of multitemporal remote sensing images, integrated in a Geographic Information System (GIS). By this method charts of the medium liquid discharges of Lake Mutuco and Tabacco Igarape the maximum velocity of flow were estimated in: 1.1 m/s, 1.6 m/s and 1.6 m/s (rainy season) and 0.6 m/s, 0.6 m/s and 0.7 m/s (dry period), the maximum flow in: 289 m?/s, 297 m?/s and 379 m?/s (rainy season) and 41 m?/s , 79 m?/s and 105 m?/s (dry period), respectively. From the interpretation of multitemporal satellite images, maps were developed together with the analysis of the lakes and Tobaco Igarape evolution from 1972 to 2008, and were classified according to the degree of balance in the area: stable areas, eutrophic areas, areas of gain, and eroded areas. Troughout analysis of the balance of areas, it was possible to quantify the volume of lake areas occupied by aquatic macrophytes. The study sought to understand the hydrodynamic and morphodynamic processes occurring in the region, contributing to the elucidation of the processes which cause and/or favor geoenvironmental changes in the region; all such information is fundamental to making the management of the area and further definition of parameters for environmental monitoring and contributing to the development of the management plan of the Biological Reserve of Lake Piratuba. The work activities is a part of the Project "Integration of Geological, geophysical and geochemical data to Paleogeographic rebuilding of Amazon Coast, from the Neogene to the Recent / O Estado do Amap? abrange um importante sistema lacustre natural, conhecido como A Regi?o dos Lagos do Amap? . A maioria desses lagos est? concentrada na parte sul da plan?cie costeira do Amap?. ? uma regi?o altamente influenciada pelas descargas do rio Amazonas, este considerado o maior em descarga l?quida, com cerca de 209.000 m?/s e 6.108 ton.dia-1 de aporte de sedimentos ao Oceano. Esta regi?o tamb?m ? fortemente influenciada da Zona de Converg?ncia Intertropical (ZCIT) e Oscila??o Sul-El Nino (OSEN ou ENSO) que atuam principalmente sobre precipita??o, nebulosidade, hidrologia dos rios locais e mar?. Nesta regi?o, est? localizado os principais cintur?es lacustre do Amap?: Cintur?o Lacustre Ocidental, Cintur?o Lacustre Oriental e Cintur?o Lacustre Meridional. Este ?ltimo cintur?o ? formados pelos Lagos dos Botos, Lago Comprido de Cima, Lago da Bacia, Lago Lod?o, Lago dos Ventos , Lago Mutuco e o Lago Comprido de Baixo. S?o poucos conhecidos do ponto de vista da hidrodin?mica e morfodin?mica, e correm o risco de ter seu funcionamento natural alterado, antes mesmo de serem estudados. Fatores como a redu??o do volume de ?rea, eutrofiza??o por vegeta??o aqu?tica, antropiza??o, altera??es na hidrodin?mica (vaz?o), s?o fatores j? evidenciados e podem contribuir significativamente para seu desaparecimento do Cintur?o Lacustre Meridional. Este Cintur?o est? dentro dos limites da Reserva Biol?gica do Lago Piratuba, criada em 1980, cuja finalidade ? de conserva??o e de prote??o integral. O objetivo principal deste trabalho foi a caracteriza??o dos processos morfodin?micos e hidrodin?micos, visando entender o funcionamento geoambiental do Cintur?o Lacustre Meridional, desde o Lago Comprido de Baixo at? o Lago dos Ventos, incluindo o Igarap? do Tabaco. Teve como base metodol?gica a aquisi??o de dados de descarga l?quida, mar?s, batimetria e a interpreta??o multitemporal de imagens de sensores remotos, integrados em ambiente de Sistema de Informa??o Geogr?fica (SIG). Foram estimados valores m?ximos das velocidades do fluxo e vaz?es do Lago Mutuco e Igarap? Tabaco: 1,173 m/s, 1,685 e 1,684 m/s (per?odo chuvoso) e 0,692 m/s, 0,626 m/s e 0,722 m/s (per?odo seco); as m?ximas vaz?es em: 289 m?/s, 297 m?/s e 379 m?/s (per?odo chuvoso) e 41 m?/s, 79 m?/s e 105 m?/s (per?odo seco), respectivamente. A partir da interpreta??o das imagens de sat?lites, foram elaborados mapas de an?lise multitemporal da evolu??o dos Lagos e Igarap? Tabaco de 1972 a 2008, e foram classificados de acordo com o grau de balan?o de ?rea (km? e m?) em: ?reas est?veis, ?reas eutrofizadas, ?reas de ganho, ?reas erodidas. Os resultados mostram que os tr?s lagos estudados e o Igarap? Tabaco, possuem din?micas diferentes. De 1972 at? 1999, os Lagos sofreram poucas varia??es de ?reas eutrofizadas, ?reas de ganho e ?reas est?veis. Nos per?odos de 1999 at? 2008, a din?mica mudou completamente e os Lagos tendem a reduzir consideravelmente sua ?rea ?til, e os Lagos dos Ventos e Comprido de Baixo, s?o os Lagos mais afetados pela presen?a e ocupa??o das margens pelas macr?fitas aqu?ticas: entre 1972 a 1999, o Lago dos Ventos teve uma redu??o de ?rea de 530401,1m?, de 1999 para 2008, teve redu??o de mais 2038595,3m?, equivalente a mais de 50% de ?rea reduzida em 36 anos. O Lago Comprido de Baixo, teve uma din?mica diferente de balan?o de ?rea de 1972 a 1999, sua ?rea teve aumento significativo nesse per?odo, de 2634011,8m? em 1972, para 1999 obteve um ganho de 365512,9m? aumentando para 2999524,7m?. De 1999 para 2008, sua ?rea total foi reduzida em 1225492,0m?, o equivalente a aproximadamente 60% de ?rea ocupada pelas macr?fitas aqu?ticas. Esses estudos buscaram entender os processos morfodin?micos e hidrodin?micos ocorrentes na regi?o dos Lagos e Igarap? Tabaco, com vista a contribuir na elucida??o dos processos que ocasionam e/ou favorecem as modifica??es geoambientais na regi?o. Todas essas informa??es s?o fundamentais para as tomadas de decis?es de gest?o da ?rea, defini??o posterior de par?metros para monitoramento ambiental e contribui??o para a elabora??o do plano de manejo da Reserva Biol?gica do Lago Piratuba. O desenvolvimento das atividades est? inserido no ?mbito do Projeto AMASIS, e teve apoio dos projetos PETRORISCO-FASE-2 e HIDROSEMA (REDE 05 PETROMAR/2007/CTPETRO/FINEP/PETROBRAS/CNPq)de caracter?sticas multidisciplinares e interinstitucional, em temas envolvendo o monitoramento ambiental

Universidade de Fortaleza / CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Esta pesquisa analisa de forma integrada os aspectos geoambientais e a dinÃmica costeira de curto e mÃdio perÃodo da planÃcie litorÃnea entre as praias do Futuro e Porto das Dunas, litoral leste do CearÃ, embasada na anÃlise multitemporal da variaÃÃo da linha de costa e mudanÃas morfolÃgicas. Aplicou-se o geoprocessamento conciliado Ãs caracterÃsticas geoambientais, morfodinÃmicas, hidrodinÃmicas, aos processos eÃlicos, Ãs aÃÃes antrÃpicas e à avaliaÃÃo dos Ãndices de vulnerabilidade à erosÃo. A Ãrea perfaz 15 km de litoral representada pelos Setores: 1 - Praia Porto das Dunas; 2 - AbreulÃndia (COFECO) e Sabiaguaba; e 3 - CaÃa e Pesca e Praia do Futuro, alÃm das desembocaduras dos rios Pacoti e CocÃ. Os aspectos metodolÃgicos foram pautados em atividades de gabinete, campo, laboratÃrio e anÃlise integrada dos dados. Elaborou-se um monitoramento sazonal durante um ano (08/10 a 08/11). Geologicamente, a Ãrea està representada por dois domÃnios geolÃgicos: unidade basal e planÃcie costeira, ambas influenciam na dinÃmica costeira das praias monitoradas, associadas Ãs condiÃÃes climÃticas. O clima à tropical chuvoso, semiÃrido e apresenta forte irregularidade pluviomÃtrica anual, com duas estaÃÃes distintas, uma seca e prolongada e outra com precipitaÃÃes curtas. Os dados modais de ondas revelam o predomÃnio do tipo deslizante, praias com relevos suaves e baixas declividades. A altura das ondas na zona de arrebentaÃÃo apresentou valor mÃdio de 1,1m, variando de 0,9m a 1,2m. Os perÃodos de ondas assumiram um padrÃo sazonal, menores na estaÃÃo seca e maiores na chuvosa, mÃximo de 15,9s e mÃnimo 6,1s. O estÃgio morfodinÃmico do Setor 1 à dissipativo, no Setor 2 varia de dissipativo a intermediÃrio e, por vezes, refletivo, e no Setor 3 predomina estÃgios intermediÃrios a dissipativos com as maiores extensÃes dos perfis praiais. O balanÃo sedimentar confirma um estado que busca o equilÃbrio entre os processos deposicional e erosional, entretanto com tendÃncia erosional para os Setores 1 e 2, e deposicional para o Setor 3, corroborando com os volumes dos sedimentos e com a variaÃÃo da linha de costa. As taxas de avanÃo e recuo da linha de costa foram obtidas utilizando-se a extensÃo Digital Shoreline Analysis System para o software ArcGIS 10.0, integrando dados georreferenciados, entre os anos de 1972 e 2010. Da praia Porto das Dunas atà a margem esquerda do rio Pacoti, definiu-se um estÃgio erosivo, taxa de variaÃÃo mÃdia de -3,53m/ano e -17,67m em 5 anos; entre a foz do rio Pacoti e a praia da AbreulÃndia, observaram-se Ãndices de erosÃo mÃdia de -0,31m/a e -2,18m em 7 anos; a praia da AbreulÃndia atà a desembocadura do rio Cocà apresentou tendÃncia erosional mÃdia de -0,07m/ano e -2,59m, em 38 anos, caracterizando uma estabilidade nesse setor, provavelmente, devido ao cordÃo descontÃnuo de rochas de praia paralelo à costa; a Praia do Futuro apresenta uma tendÃncia fortemente progradante, mÃdia de +1,43m/ano e +54,33m, em 38 anos. A anÃlise da variaÃÃo textural dos sedimentos de praia constatou o predomÃnio da fraÃÃo arenosa ao longo dos 15 km de praias, predominando areia mÃdia, moderadamente selecionada, com fraÃÃes mais finas nas praias do extremo NW e as mais grossas nas porÃÃes centrais. As caracterÃsticas granulomÃtricas sÃo fortemente condicionadas pela influÃncia dos agentes hidrodinÃmicos, eÃlicos e meteorolÃgicos, associados ao tipo, orientaÃÃo e localizaÃÃo da praia e a proximidade e tipo da Ãrea fonte de sedimentos. Os perfis morfodinÃmicos praiais estÃo associados à sazonalidade meteorolÃgica, perfis de inverno nos perÃodos de transiÃÃo e estiagem, e de verÃo no perÃodo chuvoso. A distribuiÃÃo dos sedimentos ao longo dos perfis registra para o perÃodo chuvoso a predominÃncia dos mais grossos nas Ãreas mais afastadas da linha de costa e mais finos na regiÃo subaquosa, ocorrendo uma inversÃo no perÃodo de estiagem. TrÃs fatos sÃo destacados para as velocidades dos ventos: desenvolvimento de um gradiente vertical ascendente, certa conformidade de comportamento das curvas traÃadas em alturas diferenciadas e maiores velocidades na zona de pÃs-praia. Os rios Pacoti e Cocà apresentaram estreitamento da foz e erosÃo nas faixas praiais adjacentes; nas desembocaduras observou-se uma relaÃÃo diretamente proporcional entre a faixa praial e os depÃsitos submersos, sugerindo que esses depÃsitos funcionam como suprimento de sedimentos para a faixa praial. Todos os fatores analisados condicionaram à evoluÃÃo do litoral e foram relevantes para avaliar o grau de vulnerabilidade à erosÃo costeira, inferindo-se um grau muito alto para o Setor 1, alto a baixo para o Setor 2 e baixo a moderado para o 3, relacionado Ãs feiÃÃes e tipos de uso. O processo de urbanizaÃÃo està bastante acelerado e ocorre de forma desorganizada, sem levar em consideraÃÃo as caracterÃsticas e fragilidades dos ecossistemas, como a ocupaÃÃo das zonas de by-pass, fato que influencia diretamente na sazonalidade natural de remoÃÃo e deposiÃÃo de sedimentos arenosos, resultando no recuo da linha de costa, em razÃo da reduÃÃo do aporte de sedimentos. Recomendam-se uma fiscalizaÃÃo mais rigorosa e a implantaÃÃo de programas de monitoramento e ordenamento territorial nessa Ãrea, importantes ao equilÃbrio dinÃmico costeiro e à preservaÃÃo de Ãcones da beleza cÃnica do litoral. / This research analyzes the geo-environmental aspects in an integrated manner and the coastal dynamics of short to medium duration of the coastal plain between the Porto das Dunas Beach and Praia do Futuro Beach, East coast of Cearà state. It is based on multitemporal analysis of shoreline variation and morphological changes. This work applied the geoprocessing reconciled to geoenvironmental characteristics, morphodynamics, hydrodynamics, aeolian processes, anthropogenic actions and assessment indices of vulnerability to erosion. The area of investigation stretches 15 km of coastline represented by 3 sectors: 1-Porto das Dunas Beach; 2-AbreulÃndia (COFECO) Beach and Sabiaguaba Beach; and 3- CaÃa e Pesca Beach and Praia do Futuro Beach, in addition to the mouths of the Pacoti River and Cocà River. Methodologically, it wasguided by activities of staff, field, laboratory and integrated analysis of the data. Seasonal monitoring was elaborated during a year (08/10 to 08/11). Geologically the area is comprised of two geological domains: basal unit and the coastal plain, both of which influence the coastal dynamics of the beaches of interest-more specifically, those related to weather conditions. The climate is rainy and tropical, semi-arid, and features strong annual rainfall irregularity that characterize two distinct seasons: one with prolonged drought and another with short rainfall. The data wave modal reveal the predominance of sliding type, beaches with soft and low reliefs declivities. The height of the waves in the surf zone presented average value of 1,1m, ranging from 0,9 m to 1,2m. The wave periods follow a seasonal pattern, with smaller waves in the dry season and larger ones in rainy season (maximum of 15,9s and minimum of 6,1s). The morphodynamic stage is dissipative in Sector 1, in Sector 2 ranges from dissipative to intermediary and, sometimes, reflective. In Sector 3 it predominates the dissipative to intermediary stages with the largest extensions of beach profiles. The sedimentary balance confirms a state seeking a balance between depositional and erosional processes, however with erosional trend for Sectors 1 and 2, and depositional trend for Sector 3. This corroborates with the sediment volumes and with the coastline variation. The rates of advance and retreat of the shoreline were obtained using the Digital Shoreline Analysis System, software for ArcGIS 10.0, integrating georeferenced data, between 1972 and 2010. From Porto das Dunas Beach to the left margin of Pacoti River it was set up an erosion stage on an average of â 3,53m/year and -17.65m in 5 years. Between the mouth of the Pacoti River and AbreulÃndia Beach erosion rates were observed, average of -0,31m/year and -2.18m in a period of 7 years. The area from AbreulÃndia Beach to the mouth of the Cocà River showed erosional average of -0.07m/year, -2,59m in a period of 38 years. This evidences stability in this sector, probably due to discontinuous cord beachrocks parallel to the coast. Praia do Futuro Beach has a strong progradational average of +1.43m/year, +54.33m in a period of 38 years. The analysis of textural variation of beach sediments noted the predominance of the sandy fraction over the 15 km of beaches with medium sand, moderately selected, with finer fractions on the beaches of the far NW and the thicker on the central portions. The grain size characteristics of this coastline is strongly conditioned by the influence of hydrodynamic, wind, and weather agents, associated with the type, orientation, and location of the beach as well as the proximity and type of sediment source area. The beach morphodynamic profiles are associated with weather seasonality, winter profiles during periods of transition and drought. Moreover, summer profiles are observed in the rainy season. The distribution of sediments along the profiles was recorded in the rainy season showing a predominance of coarse in the outlying areas of the coastline and the finest in subaqueous region. In the dry season the effect is inverse. Three facts are highlighted for the speeds of the winds: development of a vertical upward gradient, certain conformity of behavior of curves drawn in different heights, and speeds in the backshore zone. The Pacoti River and the Cocà River showed narrowing in the mouth and erosion on adjacent beach tracks. Furthermore, it was observed in the mouths a relationship directly proportional between the beach range and the underwater deposits, suggesting that these deposits act as sediment suppliers to the beach range. The factors analyzed have led to the evolution of the coast and were relevant to assessing the degree of vulnerability to coastal erosion. Resulting from this process was a very high degree to the Sector 1, high to low degree to the Sector 2 and low to medium degree to the Sector 3, related to the features and types of use. The urbanization process taking place in the area is accelerated and unplanned. For example, it does not take into consideration the characteristics and weaknesses of ecosystems, such as the occupation of the by-pass areas. This latter has a direct influence on natural seasonality of removal and deposition of sandy sediments, resulting in the indentation of the coastline, due to the reduction in the contribution of sediments. Stricter supervision is recommended, and implementation of a monitoring programme and a spatial planning programme in this area are essential for the coastal dynamic balance.

Le long des littoraux sableux tels que la côte Aquitaine, les vagues et principalement les courants moyens induits par celles-ci jouent un rôle majeur dans l’évolution morphologique des plages. Que ce soit d’un point de vue socio-économique (aménagement des plages, protection de l’environnement) ou sécuritaire (noyade), comprendre la dynamique de tels environnements est devenu un réel enjeu scienti?que ces dernières années. Le développement d’une plateforme de modélisation morphodynamique opérationnelle a été menée au cours de cette thèse. Ce modèle est basé sur le couplage du modèle spectral de houle SWAN (Delft University of Technology) avec le modèle MARS 2DH (Ifremer), initialement conçu pour calculer les courants induits par la marée et les vents. Après avoir ajouté les phénomènes liés à la houle, un modèle sédimentaire a été développé pour estimer les évolutions morphodynamiques. La campagne de mesures Biscarrosse-PréECORS menée en juin 2007 sur la plage de Biscarrosse a permis de valider le modèle pour une large gamme d’état de mer. Le modèle a montré son e?cacité et sa robustesse pour décrire les courants et des circulations induites par les vagues au dessus de fortes hétérogénéités bathymétriques. Nous avons mis en évidence la forte modulation tidale des courants sagittaux qui sont intenses même pour de faibles conditions de vagues. La plateforme de modélisation morphodynamique a permis d’analyser la formation et le développement de morphologies tridimensionnelles rythmiques pour des systèmes simple et double barre. Pour les environnements à double barre comme la côte Aquitaine, l’intense couplage morphologique entre la barre externe et la barre interne a été étudié en réponse aux conditions de forçages. Nous avons mis en évidence l’in?uence de la marée sur la croissance des barres et révélé la corrélation existant entre croissance des barres et dissipation d’énergie des vagues sur les barres. Cette thèse a abouti au développement d’un modèle complet permettant d’appréhender la dynamique des environnements littoraux sableux. / Along many sandy environments as the Aquitanian Coast, waves and wave-induced currents play a key role on the beach morphodynamics. Within a socio-economic (human interventions, natural environment protection) and touristic (human safety) framework, understand the complex dynamics of these systems is a real scienti?c challenge these last decades. The development of an operational morphodynamical modeling platform was performed during this PhD thesis. The modeling strategy consists in coupling the spectral wave model SWAN (Delft Univer- sity of Technology) with the non-linear shallow water model MARS 2DH (Ifremer). The MARS model was initially designed to compute tide- and wind-induced currents. Thus, the wave processes and a sed- imentary unit were implemented inside MARS to compute morphological evolutions of wave-dominated sandy beached. The Biscarrosse-PréECORS ?eld experiment carried out in June 2007 at Biscarrosse Beach was used to validate our modeling platform for a large range of o?shore wave conditions. Results have proved the e?ciency and the robustness of our model to calculate wave-induced currents and circulations over alongshore non-uniformities. The strong tidal modulation of currents and the intense rip currents for low-energy conditions were highlighted. The morphodynamical modeling platform was also used to analyze the generation and the development of rhythmic three-dimensional morphologies for one- and double-barred systems. For double-barred en- vironments, the intense morphological coupling between the inner and outer bar was studied in the response of wave and tide forcing. We have highlighted the in?uence of the tide on the bar growth and showed the correlation between the growth and the wave dissipation over the bar. This thesis has succeeded in the development of a complete model for understanding the dynamics of sandy coastal environments.

Ces travaux de thèse concernent la morpho-dynamique d'une plage de poche sableuse, située en environnement macrotidal. L'étude est menée sur la plage de Porsmilin, une plage de type intermédiaire avec une terrasse de basse mer. Cette étude s’appuie sur des observations in situ acquises lors de campagnes de mesures, organisées au cours de cette thèse. Le principal objectif est de caractériser le rôle de la pente, dans l'équilibre dynamique existant entre les processus hydrodynamiques et la morphologie de la plage. La dynamique des niveaux d’eau, de la propagation des ondes infragravitaires et de la turbulence sont examinés et mis en regard des variations morphologiques de la plage, en particulier de la pente locale de la plage. Les niveaux d’eau sont globalement sous-estimés par les formulations empiriques proposées dans la littérature. Des formules adaptées au site de Porsmilin sont présentées. L’impact de la brisure de pente observée le long du profil de plage sur la dynamique de la plage, est étudié. La variabilité de la position de la brisure de pente est impliquée dans les processus d’accommodation à court terme de la plage. Cela se traduit par un retrait vers le haut de plage de la brisure de pente, permettant une dissipation plus efficace de l’énergie incidente par la terrasse de basse mer. En revanche, ce retrait peut conduire, à une concentration d’énergie importante en haut de plage, lors de conditions particulièrement énergétiques, associées à un marnage important. La position de la brisure de pente pourrait être un bon indicateur de l'état de vulnérabilité de la plage face à des évènements énergétiques, ce qui constitue une information primordiale dans le contexte actuel d’érosion généralisée des littoraux sableux. / This PhD work is focused on the morphodynamic of a pocket beach, located in a macrotidal environment. The beach type is intermediate, with a low tide terrace. The study is based on in situ observations, collected during field campaigns organized during the PhD. The objective is to characterize the beach slope impact on hydrodynamics processes and beach morphology. The water levels dynamic, infragravity waves propagation and turbulence generation in the swash zone, are examined and linked to the beach slope variability.The empirical formulations proposed in the literature show large under-estimations of water levels in the site. Empirical formulations adapted to the beach are proposed.The characteristic break slope presents along the cross-shore profile of low tide terrace beaches is studied. The variability of the break slope location is relevant to explain the short term accommodation of the beach. Under incident wave energy, the location of the beach slope moves shoreward, allowing higher wave dissipation by the low tide terrace. Nevertheless, the reflective part is reduced, which leads to a vulnerable state of the upper beach under strong forcing associated with high tide. The location of the beach slope is found to be a good indicator of the beach vulnerability under a given wave forcing. It provides valuable information in the globalized beach erosion context.

Les barres sableuses pré-littorales ont un rôle fondamental en morphodynamique des plages soumises à l’action des vagues. Le déséquilibre permanent entre les flux sédimentaires induits vers laplage par les non linéarités des vagues et ceux induits vers le large par le courant de retour gouverne lamigration transversale des barres. Dans cette thèse, un nouveau modèle morphodynamique de profilde plage intégrant l’état de l’art des processus hydro-sédimentaires a été développé. Le faible coûten temps de calcul de ce modèle permet de réaliser des simulations à long terme, O(mois/années),de la morphologie de plages réelles ayant des caractéristiques variées (pente, type de déferlement,granularité). La simulation sur plusieurs jeux de données, de plages réelles et expérimentales, a permisd’identifier la contribution respective des principaux processus hydro-sedimentaires dans la dynamiquede la plage suivant les conditions de houle (e.g. Tempête, temps calme). Ces avancées scientifiques ontété intégrées à un modèle 2DH, ce qui a notamment permis de simuler pour la première fois sur des casacadémiques la formation d’une barre sableuse rectiligne à partir d’une plage parfaitement plane, suiviedu développement de corps sableux tridimensionnels. Ces résultats ouvrent la voie vers l’applicationde ce type de modèle aux plages naturelles soumises à une large variabilité de régimes de houle. / Sandbars are ubiquitous patterns along wave-dominated sandy coastlines and are key elementsin the global evolution of beaches. Cross-shore sandbar migrations are the result of the permanentimbalance between sediment flux driven by wave non-linearity and mean return current. In this thesis,we developed a new process-based beach profile model integrating the recent scientific advancesin term of hydrodynamics and sediment transport developed for beach morphodynamics. The lowcomputing time allows for long-term morphodynamic simulations (O months/years) of natural beachprofiles of diverse characteristics (beach slope, sediment grain size or type of wave breaking). Modelvalidations on several data sets, encompassing natural and experimental beach profile evolutions,highlight the respective contribution of the main hydrodynamic and sediment transport processesinvolved in specific cross-shore sandbar evolution relative to various wave conditions. Finally, all thecross-shore physical processes were integrated in a 2DH morphodynamic model, resulting for the firsttime in the simulation of a quasi-complete down state sequence showing alongshore bar generationwith subsequent spontaneous formation of transverse bar and rip morphology. These very encouragingresults pave the way for using this model to simulate 3-Dimensional evolutions of natural beachesforced by irregular wave conditions

En la Tesis titulada "Análisis y mejoras en la evaluación de diversos términos de los modelos de evolución de playas en escalas de medio plazo" se desarrolla un modelo de evolución de playas de medio-largo plazo y se aplica a zonas de refracción-difracción. La Tesis se divide en tres secciones principales:SECCIÓN 2. Fundamentos y desarrollo del modelo de evolución de medio-largo plazoSe desarrolla y valida con datos de campo el modelo de evolución de playas de medio-largo plazo.SECCIÓN 3. Oleaje en rotura en zonas de refracción-difracción en los modelos de evolución de playasSe propone y valida un método para la determinación de las características del oleaje en rotura en zonas de refracción-difracción.SECCIÓN 4. Perfil de equilibrio en zonas de refracción-difracciónSe deriva una expresión analítica para definir el perfil de equilibrio en zonas de refracción-difracción y se calibra con datos de campo. / In this Thesis entitled "Analysis and improvements in the evaluation of several terms of medium-term beach evolution models" a medium-long term beach evolution model is developed and applied in refraction-diffraction areas. The Thesis is composed of the following main sections:SECTION 2. Fundaments and development of a medium-long term beach evolution modelIn this section a medium-long term beach evolution model is developed and validated based on field data.SECTION 3. Breaking wave characteristics in refraction-diffraction areas for beach evolution modelsIn this section a method to determine the breaking wave characteristics in refraction-diffraction areas is proposed and validated.SECTION 4. Equilibrium beach profile for refraction-diffraction areasIn this section an analytical expression to calculate the equilibrium beach profile for refraction-diffraction areas is derived, being calibrated based on field data.

Cette thèse examine les impacts sur la morphologie des tributaires du fleuve Saint-Laurent des changements dans leur débit et leur niveau de base engendrés par les changements climatiques prévus pour la période 2010–2099. Les tributaires sélectionnés (rivières Batiscan, Richelieu, Saint-Maurice, Saint-François et Yamachiche) ont été choisis en raison de leurs différences de taille, de débit et de contexte morphologique. Non seulement ces tributaires subissent-ils un régime hydrologique modifié en raison des changements climatiques, mais leur niveau de base (niveau d’eau du fleuve Saint-Laurent) sera aussi affecté. Le modèle morphodynamique en une dimension (1D) SEDROUT, à l’origine développé pour des rivières graveleuses en mode d’aggradation, a été adapté pour le contexte spécifique des tributaires des basses-terres du Saint-Laurent afin de simuler des rivières sablonneuses avec un débit quotidien variable et des fluctuations du niveau d’eau à l’aval. Un module pour simuler le partage des sédiments autour d’îles a aussi été ajouté au modèle. Le modèle ainsi amélioré (SEDROUT4-M), qui a été testé à l’aide de simulations à petite échelle et avec les conditions actuelles d’écoulement et de transport de sédiments dans quatre tributaires du fleuve Saint-Laurent, peut maintenant simuler une gamme de problèmes morphodynamiques de rivières. Les changements d’élévation du lit et d’apport en sédiments au fleuve Saint-Laurent pour la période 2010–2099 ont été simulés avec SEDROUT4-M pour les rivières Batiscan, Richelieu et Saint-François pour toutes les combinaisons de sept régimes hydrologiques (conditions actuelles et celles prédites par trois modèles de climat globaux (MCG) et deux scénarios de gaz à effet de serre) et de trois scénarios de changements du niveau de base du fleuve Saint-Laurent (aucun changement, baisse graduelle, baisse abrupte). Les impacts sur l’apport de sédiments et l’élévation du lit diffèrent entre les MCG et semblent reliés au statut des cours d’eau (selon qu’ils soient en état d’aggradation, de dégradation ou d’équilibre), ce qui illustre l’importance d’examiner plusieurs rivières avec différents modèles climatiques afin d’établir des tendances dans les effets des changements climatiques. Malgré le fait que le débit journalier moyen et le débit annuel moyen demeurent près de leur valeur actuelle dans les trois scénarios de MCG, des changements importants dans les taux de transport de sédiments simulés pour chaque tributaire sont observés. Ceci est dû à l’impact important de fortes crues plus fréquentes dans un climat futur de même qu’à l’arrivée plus hâtive de la crue printanière, ce qui résulte en une variabilité accrue dans les taux de transport en charge de fond. Certaines complications avec l’approche de modélisation en 1D pour représenter la géométrie complexe des rivières Saint-Maurice et Saint-François suggèrent qu’une approche bi-dimensionnelle (2D) devrait être sérieusement considérée afin de simuler de façon plus exacte la répartition des débits aux bifurcations autour des îles. La rivière Saint-François est utilisée comme étude de cas pour le modèle 2D H2D2, qui performe bien d’un point de vue hydraulique, mais qui requiert des ajustements pour être en mesure de pleinement simuler les ajustements morphologiques des cours d’eau. / This thesis investigates the impacts of climate-induced changes in discharge and base level on the morphology of Saint-Lawrence River tributaries for the period 2010–2099. The selected tributaries (Batiscan, Richelieu, Saint-Maurice, Saint-François and Yamachiche rivers) were chosen because of their differences in size, flow regime and morphological setting. Not only will these tributaries experience an altered hydrological regime as a consequence of climate change, but their base level (Saint-Lawrence River water level) will also change. A one-dimensional (1D) morphodynamic model (SEDROUT), originally developed for aggrading gravel-bed rivers, was adapted for the specific context of the Saint-Lawrence lowland tributaries in order to simulate sand-bed rivers with variable daily discharge and downstream water level fluctuations. A module to deal with sediment routing in channels with islands was also added to the model. The enhanced model (SEDROUT4-M), which was tested with small-scale simulations and present-day conditions in four tributaries of the Saint-Lawrence River, can now simulate a very wide range of river morphodynamic problems. Changes in bed elevation and bed-material delivery to the Saint-Lawrence River over the 2010–2099 period were simulated with SEDROUT4-M for the Batiscan, Richelieu and Saint-François rivers for all combinations of seven tributary hydrological regimes (present-day and those predicted using three global climate models (GCM) and two greenhouse gas emission scenarios) and three scenarios of how the base level provided by the Saint-Lawrence River will alter (no change, gradual decrease, step decrease). The effects on mean annual sediment delivery and bed elevation differ between GCM and seem to be related to whether the river is currently aggrading, degrading or in equilibrium, which highlights the importance of investigating several rivers using several climate models in order to determine trends in climate change impacts. Despite the fact that mean daily discharge and mean annual maximum discharge remain close to their current values in the three GCM scenarios for daily discharge, marked changes occur in the mean annual sediment transport rates in each simulated tributary. This is due to the important effect of more frequent large individual flood events under future climate as well as a shift of peak annual discharge from the spring towards the winter, which results in increased variability of bed-material transport rates. Some complications with the 1D modelling approach to capture the complex geometry of the Saint-Maurice and Saint-François rivers suggest that the use of a two-dimensional (2D) approach should be seriously considered to accurately simulate the discharge distribution at bifurcations around islands. The Saint-François River is used as a test case for the 2D model H2D2, which performs well from a hydraulics point of view but which needs to be adapted to fully simulate morphological adjustments in the channel.

Les embouchures tidales dominées par la houle sont des systèmes côtiers particulièrement dynamiques dont la morphologie est continuellement remodelée par l’action des vagues et de la marée. Les rapides évolutions morphologiques auxquelles elles sont sujettes impactent directement leurs environnements écologiques et socio-économiques. Afin de mettre en œuvre des réglementations adaptées à la gestion durable des embouchures tidales, des études environnementales systématiques sont nécessaires. L’objectif principal de cette thèse est de mieux comprendre les processus physiques qui contrôlent les évolutions morphologiques d’une embouchure tidale éphémère au Portugal - l’embouchure de la lagune d’Albufeira – à partir de l’analyse de mesures hydrodynamiques et topographiques et de résultats d’un système de modélisation morphodynamique récemment développé. Les processus qui influent sur la dynamique de l’embouchure tidale à court terme, notamment ceux liés aux interactions vague-courant, ont été étudiés à travers l’application du système de modélisation à l’embouchure. Les modulations saisonnières du climat de vagues et du niveau moyen de la mer affectent fortement la dynamique sédimentaire de l’embouchure et contribuent au comblement naturel de l’embouchure pendant l’hiver. Les processus à long terme ont également été étudiés à partir de simulations rétrospectives de paramètres moyens de vagues pour des échelles régionales et locales sur une période 65 ans. Les fortes variabilités interannuelles du climat de vagues et de la dérive littorale qui lui est associée pourraient expliquer les différences d’évolutions morphologiques du système embouchure-lagune sur des échelles de temps pluri–annuels. / Wave-dominated tidal inlets are very dynamic coastal systems, whose morphology is continuously shaped by the combined action of the waves and the tides. The rapid morphological changes they experience impact directly their ecological and socio-economic environments. In order to implement adequate regulations for the sustainable management of tidal inlets, systematic environmental studies are necessary. The main objective of this PhD research work is to gain a better understanding of the physical processes that control the morphological evolutions of an ephemeral tidal inlet in Portugal - the Albufeira Lagoon inlet - based on the analysis of hydrodynamic and topographic data and on the results of a newly developed morphodynamic modelling system. The processes that impact the dynamics of the inlet at short time-scales, particularly those related to wave-current interactions, are investigated through the application of the modelling system to the inlet. The seasonal modulations of the wave climate and mean sea level strongly affect the sediment dynamics of the inlet and contribute to the natural closure of the inlet during the winter period. Long-term processes are also investigated based on a 65-year hindcast of mean wave parameters at regional and local scales. The large inter-annual variability of the wave climate and the associated longshore sediment transport – both correlated to the North-Atlantic Oscillation – are proposed to explain the differences in the morphological behaviour of the inlet-lagoon system at pluri-annual time-scales.