http://repositorio.lnec.pt:8080/jspui/handle/123456789/266 2026-04-05T02:14:15Z 2026-04-05T02:14:15Z Mendes, D. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1007356 2015-07-13T16:21:13Z 2015-03-01T00:00:00Z

Study of the hydrodynamics and morhodynamics of the Óbidos Lagoon, Portugal, Mendes, D. Na lagoa de Óbidos, as ondas e as correntes de maré induzem rápidas alterações morfológicas levando ao fecho da sua embocadura. As dragagens são frequentes tendo o objetivo de manter a laguna aberta e proteger as construções marginais. No entanto, o efeito das dragagens no comportamento da embocadura é um tema pouco estudado, especialmente o impacto que poderá ter a adição de canais transversais aos tradicionais canais dragados. No interior desta laguna as ondas induzem alterações significativas nas condições hidrodinâmicas. Através da aplicação de um modelo acoplado constituído por um modelo hidrodinâmico e um modelo de agitação marítima concluiu-se que as elevações da superfície livre dentro da lagoa aumentaram para uma direcção média da onda perpendicular à linha de costa. Foi também investigado o impacto que a interacção completa entre ondas e correntes tem na dinâmica sedimentar da lagoa de Óbidos, concluindo-se que o transporte de sedimentos para o interior aumenta em 30% durante a enchente se esta interacção for tida em conta no modelo numérico. Os três planos de dragagens foram avaliados através da implementação de um modelo morfodinâmico. Os novos planos de dragagens aumentaram o prisma de maré e reduziram as diferenças de duração entre a vazante e a enchente devido aos canais principais norte e sul. Os canais transversais aumentaram o assoreamento no canal principal sul e promoveram a estabilidade do canal principal norte. No entanto, devido às baixas profundidades e a uma agitação marítima muito energética, as soluções de dragagens são incapazes estabilizar permanentemente a lagoa de Óbidos Este registo pertence ao Repositório Científico do LNEC

2015-03-01T00:00:00Z Mengual , B. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1005282 2015-04-23T17:20:42Z 2013-06-01T00:00:00Z

Modélisation numérique de la circulation hydrodynamique tridimensionnelle à la plage de Saint-Trojan Mengual , B. This fellowship aimed at studying and modeling the tridimensional hydrodynamic circulation in the case of a wavedominated dissipative beach. The studied site corresponds to Saint-Trojan Beach, located to the South-West of Oléron Island in the central part of the French Atlantic. Two instruments were deployed to characterize hydrodynamics in the surf zone: with an ADCP courantometer and a RBR pressure gauge. The modeling system used in this study is based on the coupling of the circulation model SELFE and the spectral wave model WWM-II. Model/data comparison revealed that the modeling system was capable of reproducing water levels and waves with a high accuracy compared to previously published studies. Different theories for vertical radiation stress were compared in terms of their capacity to reproduce the circulation in the surfzone. The comparison with the measurements showed that only the Mellor (2003) theory was able to reproduce the undertow in the surf zone. Besides, setup predictions in 2DH and 3D were compared with measured setup. This comparison comparisons revealed indicated that the setup predicted with the 3D approach was locally twice as large as the 2DH setup while fitting much better with the data. This interesting behavior is explained by the presence of strong undertows, which induce shoreward oriented bottom stress. Furthermore, the comparison of the relevant terms in the momentum equations showed that the bottom stress represents about 50 % of the wave-induced radiation stress gradients, which supports our hypothesis. This study confirmed the necessity of using fully coupled wave and current 3D models to properly account for the vertical current structure of currents, including undertows, which has implications on water levels along the shorelines during storms. Este registo pertence ao Repositório Científico do LNEC

2013-06-01T00:00:00Z Guerreiro, M. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1003056 2017-04-13T11:03:57Z 2010-12-01T00:00:00Z

Modelação morfodinâmica da ribeira de Aljezur Guerreiro, M. The morphology of tidal inlets is very dynamic, due to the combined action of waves, tides and river flows. The morphological changes of small and shallow inlets are particularly relevant, as even slight variations in the bathymetry may induce a dramatic effect on tidal propagation and distortion. Occasionally, these complex dynamics may lead to the closure of the inlet and thus degrade the water quality upstream. Numerical morphodynamic models constitute attractive tools to study these morphological changes, although their application is still time-consuming and requires a deep insight into the relevant processes. This study aims at analyzing the morphodynamics of the tidal inlet of a small and shallow coastal system (the Aljezur coastal stream), through the implementation, validation and exploitation of the MORSYS2D morphodynamic modeling system. The Aljezur stream is located in the south-west coast of Portugal and subject to the north Atlantic waves and winds, and tides along the Iberian shelf. The stream is about 36 km long, 1-3 m deep and 10-40 m wide. Five field campaigns were carried out between 2008-2010 to provide bathymetry, water levels, waves and currents, both in the estuary and the adjoining beach, for the understanding of the dynamics of the stream and for the application, calibration and validation of MORSYS2D. This 2D morphodynamic modeling system simulates the non-cohesive sediment transport processes and the resulting bathymetric evolution in coastal regions. The system includes a wave model (SWAN), a circulation model (ELCIRC) and a sediment transport and bottom update model (SAND2D). The application, calibration and validation of MORSYS2D were a step-by-step procedure due to the numerous variable inputs and processes involved (e.g., forcings, parameters, formulations). The procedure started with simulations forced only by the tide, and progressively were added the wave and sediment transport processes. Different data sets (water levels, velocities, wave parameters and bathymetries) were used to validate each step. Morphodynamic simulations conducted between consecutive field campaigns provided the final validation. In order to investigate the effect of the several processes on the morphodynamic evolution of the inlet (e.g., waves and peak river flows), synthetic simulations were performed. From the exploitation of the model, results show that the morphodynamic variability of the beach is dominated mostly by the waves while river flow dominates the morphodynamics of the inlet region when peak flows occur. The model system reproduces correctly the hydrodynamics (waves, levels and velocities), and produces predictions of bathymetry qualitatively correct. This study brought a new understanding of the system and its variability.

2010-12-01T00:00:00Z Pinto, L. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1003055 2017-04-13T10:28:01Z 2010-06-01T00:00:00Z

Modelação da Morfodinâmica de Estuários Pinto, L.

2010-06-01T00:00:00Z