Modelagem matemática do sistema estuarino dos rios Mojuim e Mocajuba (Pará-BR)

Abstract

The estuaries of Mojuim and Mocajuba rivers are located in the eastern sector of the Amazon Coastal Zone and represent a peculiar and complex environment. They are connected by several channels and are receive influence of the Bay of Marajó and the Atlantic Ocean. The following research aims to implement a hydrodynamic model based on a flexible grid on the of Mojuim and Mocajuba rivers estuarine system; and to analyze the hydrological and hydrodynamic characteristics of the upper estuary of these rivers. The methodology involves the use of D-Flow Flexible Mesh pack a get simulate hydrodynamics patterns into the domain that covers the Mojuim Mocajuba rivers, the canals connecting these rivers, part of the mouth of the Bay of Marajó and the adjacent tidal flats. It was also performed an "in situ" systematic data collection, in which parameters of flow, salinity, turbidity and water level were analyzed during a tidal cycle in sites located at the upper estuary of Mojuim and Mocajuba rivers. In the Mojuim river two seasonal campaigns were made in two different sites and in the Mocajuba river only one campaign were made in the rainy season, however, a tide station was installed in this location that operated for 25 weeks. Part of the sample data were used as input to the hydrodynamic model. The upper estuary of Mocajuba river presented a macrotidal regime with maximum height of 5.8m recorded. In the Mojuim river, a gradual attenuation of the tidal wave is noticeable and, in the collection point and in the upper estuary a one-way flow discharge during the rainy season was observed. A different hydrodynamic pattern between the two rivers was also observed, with ebb speed more intense than floods and their hydrological properties directly influenced by the tide fluctuation. Finally a hydrodynamic model in flexible grid was implemented and calibrated in the researched area, where initial and boundary conditions were assigned, as well as adjustments to the border forcing. The model generated a good representation of the estuary conditions, showing acceptable tidal and hydrodynamic pattern when compared with the "in situ" measurement, once the error between the measured data and modeled data related to the water level were less than 5%, and errors related to transportation are lower than 15%.