Hydrodynamic model and Pusher-Barge system maneuvering simulations in the Straits of the Amazon Estuarine System (Brazil)

The straits of the Amazon Estuarine System (Brazil) are a web of narrow channels that connect the Amazon river estuary (Macapá/AP, 51.0662°W, 0.0257°N) to the Pará river estuary (Belém/PA, 48.4844°W, 1.4748°S). There is significant traffic between the Amazon River and the ports in the Belém region, located at the mouth of the Tocantins River. Numerous river convoys, mostly transporting agricultural products, navigate along these channels, where local communities live in stilt houses along the riverbanks. This work aims to develop a hydrodynamic model of the currents in the straits and execute ship maneuvering simulations to assess the feasibility of larger convoys, which can improve navigation in the region.
The hydrodynamic model was generated using the software SisBaHiA (Base System of Environmental Hydrodynamics), that solves the 2DH and 3D shallow water equations with the finite element method as spatial discretization. The shallow water equations are a mathematical framework that allows solving current flows in estuaries, coastal areas, and rivers, considering several physical phenomena such as hydrologic parameters, tidal flows, bottom friction, bathymetric restrictions, pollutant dispersions, and more. In this work, bathymetry from nautical charts and satellite images were used to model the terrain. Also, daily data of river level and flow rate of gauging stations of the Amazon river, Xingu river, and the Tocantins river were used. Level variation due to astronomical tides was obtained from harmonic constituents from FEMAR database. Two modelling scenarios were chosen, one of spring tide with flood flow rate in the amazon river, and one of spring tide with drought flow rate. Results show that there is a local response to the tidal forcing, with stretches where current inversion is observed, and others where only a modulation is observed. In the straits, current intensity can reach up to 3 knots in the flood scenario. In the amazon river, currents can reach up to 5 knots.
The current fields obtained are input to the Ship Maneuvering Simulator (SMS) of TPN-USP. The SMS adopts a 6-DoF mathematical model (TPN-MM) based on a long-term experience in ship hydrodynamics. Besides, the TPN-MM follows ITTC (International Towing Tank Conference) procedures to calibrate and validate maneuvering models. The TPN-MM is based on a quasi-explicit heuristic model for estimating maneuvering forces on ships. It also comprises models for environmental forces (wind, current, waves), restricted water effects (bottom and bank interaction) and external forces (cables, tugboats, ship-to-ship). Fast-time (automatic) and real-time simulations (controlled by experienced river captains) were performed along five critical bends of the straits. The barge convoys simulated have length of 356m, breadth of 96m (7x5 arrange) or of 69m (5x5) and can be loaded (draught 4.5m) or ballasted (1m). The pusher is equipped with conventional or azimuthal propellers. The results showed in general that the navigation of the 25-barge convoy in the straits are feasible although some difficulties in adverse environmental conditions may arise. These difficulties are discussed, and recommendations are given such as limiting environmental conditions and support of tugboats in the unlikely event of blackout or rudder jam.