Hydrodynamic Modeling as a Decision-Support Tool for Coastal Management in Large Amazonian Estuaries: A Case Study in the Pará River System, Brazil

Tropical estuaries are socioeconomically important yet highly vulnerable environments. In the eastern Amazon, the Pará River Estuary (PRE) and adjacent water bodies support the city of Belém and are increasingly affected by environmental pressures but remain underrepresented in numerical modeling efforts. The influence of key input parameters on hydrodynamic model performance in these systems remains poorly characterized, hindering the development of reliable simulation tools for this region. We present the calibration and validation of a two-dimensional hydrodynamic model for the PRE, Guajará Bay, and the Guamá River, examining how parameters such as bathymetry, roughness, and tidal and discharge forcings influence model performance. Delft3D-FM was applied using tidal harmonics and seasonal river discharge as primary forcings, with model skill evaluated against observed water levels and discharge across ten seasonally distinct scenarios over seven calibration iterations. Tidal forcing and bathymetric representation emerged as the dominant performance drivers: replacing global tidal datasets with locally derived harmonics substantially reduced simulation errors, and bathymetric refinements also improved discharge representation. Final performance met established satisfactory thresholds at the majority of observation points and cross-sections. The calibrated model provides a basis for investigating processes governed by local hydrodynamics, such as water quality assessments, contaminant dispersion, and infrastructure planning.