Summary: | The Patos-Mirim is the largest coastal limnological system of the world, located in southern Brazil and eastern Uruguay, which encompass over 500 km of coastline. The economical demand for the development of an international waterway brings the need for understanding the Mirim lagoon dynamics and ulterior discharge into Patos lagoon in view of establishing navigation conditions and sustainable development. In this sense, circulation and freshwater discharge dynamics were assessed by running the numerical model TELEMAC-3D for a one-year-long simulation. The model identified the wind direction and intensity as the main combined forcing modulating water circulation and transport between the northern and southern portions and conditioning the recirculation cell orientation. Predominant winds from the S-SW directions could generate adverse conditions for navigation because they would yield low water levels under northwards water transport, thus creating shallow regions for navigation. Under such conditions, the high freshwater discharge coming from the Mirim lagoon would be restricted, and the communication to the Patos lagoon would be sufficiently weakened to prevent navigation activities. Therefore, we recommend that the viability of planning and implementing an international waterway, involving the two countries (Brazil and Uruguay), must take into account wind conditions prior to setting navigation traffic and avoid economic losses.
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