Correntes de retorno são fluxos estreitos e intensos posicionados normal ou obliquamente a linha de costa e são a chave para compreender os processos de troca de água entre a zona de surfe e a plataforma interna. O objetivo do presente estudo é avaliar a influência da morfologia e das forçantes externas nos processos de formação e manutenção das correntes de retorno na praia de Maresias (SP). Para tanto, foram integrados diversos métodos como imagens aéreas obtidas através de VANT, levantamentos topográficos e modelagem numérica. Os resultados indicam que a variação longitudinal da morfologia desempenha um papel fundamental na formação e manutenção das correntes de retorno, assim como os parâmetros de ondas incidentes. A porção leste e central da área de estudo se manteve estável quando comparada a porção oeste, em virtude de correntes de retorno controladas pela morfologia, que também intensificaram os processos de erosão e deposição na porção emersa do perfil praial. Já a porção oeste se mostrou mais suscetível a variações do parâmetros de ondas incidentes. Outro fator relevante observado foi o risco para banhistas; as correntes a leste da área de estudo representaram maior risco visto que o regime de saída foi predominante durante todo o experimento e os fluxos permaneceram estáveis por até 1 km. Os resultados mostram ainda que em se tratando dos padrões de correntes de retorno na praia de Maresias (SP), feições morfológicas geradas durante eventos extremos podem sobrepujar o efeito da variação dos parâmetros de ondas incidentes. / Rip currents are narrow and strong flows positioned normal or oblique to the coastline that represent the key to understand the processes of water exchange between the surf zone and the inner shelf. The aim of this study is to assess the influence of the morphology and the external forces in the processes of rip currents formation and maintenance at Maresias beach (SP). Therefore, we combine various methods, sucha as AUV aerial images, topographic surveys and numerical modeling. The results show that the longitudinal variation of the morphology plays a key role in the formation and maintenance of rip currents, as well as the incoming wave parameters. The central and eastern part of the study area were more stable than the west part, due to the rip currents controlled by the bathymetry, which also intensify the processes of erosion and deposition in the beach profile. The western part was more susceptible to variations of the incoming wave parameters. Another relevant factor is related to beach safety; the currents in the central and east part are more dangerous, since they show an exit flow during all the experiment and the flow remained stable up to 1 km. The results also show that in the case of rip currents at Maresias beach (SP), morphological features generated during extreme events can overcome the effect of the incoming waves.

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.