Modelagem tridimensional da hidrodinâmica e transporte sedimentar de um lago amazônico urbano

Abstract

Lakes are critical environments for sustaining human well-being, as they regulate local climate conditions, supply potable water, and underpin a wide range of ecosystem services. The continuous monitoring of these systems is essential for elucidating their metabolic processes and for informing effective management strategies for natural resources. This study aims to develop an environmental diagnosis and prognosis for a shallow Amazonian lake located in an urban area—Lago Água Preta—through the application of a three-dimensional numerical model of hydrodynamics and sediment transport. Numerical simulations were performed using the Delft3D-FLOW model, encompassing the region’s seasonal periods: wet and dry seasons. The simulations were driven meteorological variables and physical parameters of the lake, such as air temperature, humidity, cloud cover, solar radiation, bathymetry, water temperature, current velocity, and the inflow/outflow rates. This comprehensive dataset allowed for the construction of a computational environment capable of accurately representing the hydro-sedimentary processes within the lake Model calibration was performed using a one-month time series of water temperature from February (wet season), while validation was carried out with current data and vertical temperature profiles over four months (December, February, April, and June). The simulations presented good statistical indicators, demonstrating the model's reliability. The greatest discrepancies between simulation and observation occurred at points closer to the urban center. These differences are associated with the influence of anthropogenic activities, such as the discharge of domestic effluents, or with the narrow morphology of the lake in these areas, which can generate thermal shadow zones. The analysis of circulation and temperature patterns between seasonal periods revealed relatively small differences. Notably, there was an average increase of up to 2 °C in water temperature and approximately 0.02 m/s in current velocity during the warmer period. The most significant differences in average temperature occurred in the lake's daily cycle, varying by about 3°C, with a maximum variation of up to 10°C. Since the lake is fed by an artificial water inflow, this inflow is characterized by an intense discharge with a high sediment load. As it is a shallow lake with a maximum depth of up to 4 meters, this discharge is capable of influencing the lake’s entire metabolism by promoting the resuspension of bottom sediments and redistributing nutrients into the water column. Upon entering the lake, the inflow currents are rapidly decelerated, intensifying sedimentation near the inflow point. This process increases water turbidity and alters the local biotic dynamics, resulting in an environment dominated by phytoplankton and prone to eutrophication processes, which consequently reduce water quality. Therefore, based on the diagnosis provided by the modeling of Lago Água Preta, this study highlights the need for ongoing monitoring and control of anthropogenic influences to prevent the progressive degradation of the lake's metabolism. It also underscores the importance of lakes in general, especially when located in urban contexts.