Ocean Tide Waves Propagation along Downstream Amazon River: Measuring the Amazon Discharge at the Estuary

Physical influence of oceanic tide on downstream Amazon River can be assessed more than 1000 km upstream from the sea. In order to analyse this phenomenon, over the year recording of water levels has been ensured at 8 stations along the downstream Amazon River and flow measurement campaigns have been organised, for different river discharge rates (low flow 100,000 m³/s and mean flow 190,000 m³/s, high flow 240,000 m³/s) and sea tide amplitude ( 2 meters to 3.5 meters). During these measurement campaigns, hourly variations of water levels and discharges (using ADCP technique) during a tide cycle (13 hours) have been recorded at different stations along the downstream Amazon River. It led to observations such as local changes in discharge from 130,000 m³/s to 40,000 m³/s in 4 hours, cyclic storage of 700 million m³ 6 hours, or even local inversion of flow from 60,000 m³/s to – 22,000 m³/s in 4 hours on some branches of the Amazon 400 km from the ocean. Hourly fluctuations in suspended sediment concentrations have equally been monitored. This study is intended to contribute to increased understanding of physical processes at the interface between large rivers and the ocean, improved methodology to measure and monitor these processes, and better understanding of large rivers hydrodynamics.