A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Water surface and river bottom longitudinal profiles and characteristicsalong Amazon river mainstream in BrazilPascal Kosuth (IRD), Maximiliano Strasser (UFRJ), Ilce de Oliveira Campos (USP),Julien Nicod (IMFT), Alfredo Ribeiro Netto (UnB), Marcio Sousa da Silva (IEPA),Eurides de Oliveira (ANA)Pascal Kosuth, IRD, CP 70911 Lago Sul, CEP 711619-970 Brasilia DF Brazilkosuth.ird@apis.com.brLongitudinal profiles of Solimões, Madeira and Amazon rivers (from Tabatinga and PortoVelho downwards to Obidos and Macapa) are presented, analyzing time variable watersurface profiles, permanent mean bottom depth profiles, maximum depth profiles and riverbottom structures (dunes) characteristics.Altimetry along Amazon River mainstream has been determined, in Brazil, throughimplementation and comparison of three techniques : geometric leveling, GPS positioning andradar altimetry (TOPEX / POSEIDON). Altitudes of more than 30 hydrometric stations withreference to mean sea level (or geoïd) have been determined, allowing to translate water leveltime series to a homogeneous referential. Rivers bathymetry has been obtained throughmeasurement of transversal profiles using ADCP and/or echobathymeter coupled with GPS.Bathymetric profiles have been measured every 25km along Solimões river, every 30 kmalong Madeira river and every 10 km along Amazon river downwards to Obidos.Characterization of river bottom structures has been realized along 40 different reaches usingechobathymeters.Amazon river water profile mean slope between Manaus and Macapa varies from 5mm/km(low flow) to 15 mm/km (high flow), depending on hydrological cycle phase.Solimões river slope is almost constant in relation with time but varies from 20 mm/kmdownstream (Manacapuru) to 40 mm/km upstream (Tabatinga). Madeira river slope is 60mm/km upstream (Porto Velho) and varies from 0.6 mm/km to 10mm/km along itsdownstream reach submitted to Amazon River backwater influence. Longitudinal bathymetricprofiles enlighten differences between rivers and significant spatial variations along a givenriver, related to the morphological dynamics of the river bed. Average observed dune lengthwas about 160 m with maximum 400 m, while observed dune heights, when existing, rangedfrom 2 m to 12 m, flow depth varying from 10 to 90 m.Results contribute to a better understanding of the river valley morphological evolution and ofsediment deposition trends and processes along the main river. They are of prime interest formathematical modeling of flow hydrodynamics and sediment transport dynamics.