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Estuaries often have interconnected pathways, which may result in complex tidal dynamics that create a tidal meeting point inside the channels. Consequently, channels near urban centers could experience siltation and pollution problems due to intense human activity. Dredging is frequently employed to clean or remove material from these channels, and recover water quality and circulation conditions. However, if a water body is highly susceptible to siltation processes, dredging could be a problem instead of a solution, and lead to significant waste of economic resources. This is the case of the Fundao Canal, located in the western sector of the Guanabara Bay in Rio de Janeiro (Brazil), an area characterized by poor water and sedimentation quality conditions since its creation in 1950. A hydrodynamic model together with in situ measurements and analysis of pre-dredging (1983) and post-dredging (2014) bathymetries allowed the identification of areas with the highest deposition rates and associated water circulation patterns. The sedimentation rate calculated after dredging (finished in 2012) was close to 8 cm. year−1, approximately twice as the natural rate recorded in previous works, showing an accelerated siltation process. Siltation was favored both by the inflow of untreated sewage and of continuous sediment flows from adjacent areas, and by the formation of a convergence/divergence zone, where the tidal waves that penetrate through the two entrances of the Canal meet, generating a standing wave. This hydrodynamic pattern favors weaker currents and generates no cumulative flow or residual transport over a tidal cycle, thus contributing to the siltation process. The progressive occupation of the surrounding areas, with a 12% population growth rate between 2000 and 2020, has caused the degradation and urbanization of the basin and has contributed to a constant supply of sediments. |
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