H31D-01
Multi Satellite Radar Altimetry for the Study of Hydrological Cycle Within the Rio Negro Floodplains (Brazilian Amazon)
Frappart et al. (RSE, 2005) studied the floodplain volume variation in the Rio Negro basin, using the sole TOPEX/POSEIDON (T/P) GDR's data. In this study, river main stream and their linked floodplains could not be separated, due to the course effective resolution of these data. We have processed both data of ENVISAT RA2 altimeter, and retracked T/P data. The T/P data have been retracked with three of the ENVISAT trackers (Ocean, Ice1, Ice2). We present results of the comparison between the capability of each sensor and tracker to discriminate small water bodies including river main stream and floodplain. Using an original 3D method for defining virtual stations, we computed time series of water stage for each individual inundated area. This time series evidence the great spatial variability of the hydrological cycle, depending on the connection and the relative location between the main stream and lakes.
H31D-02
Correlation between river slope and meandering variability (obtained by DGPS data) and morphotectonics for two Andean tributaries of the Amazon river: the case of Beni (Bolivia) and Napo (Ecuador-Peru) rivers.
The Beni river drains a catchment area of 282 000 km2 of which 40 percent are located in the Cordillera of the Bolivian and Peruvian Andes, and the rest in the Amazonian plain : the studied reaches runs from Guanay (Andean Piedmont) to Riberalta (junction with Madre de Dios river) that represents a distance by the river of 1055 km. The Napo river starts in the Ecuadorian Andes and leaves Ecuador in Nuevo Rocafuerte (27 400 km2) and enters in Peru until its junction with the Amazon river : the studied section runs from Misahualli (Andean Piedmont) to this junction, that represents a distance by the river of 995 km. The GPS data were acquired using a mobile GPS embarked on a boat and 4 fixed bases located along the Beni river, 6 along the Napo river and the two rivers profile calculated from post-treated differential GPS solutions. For the Beni river, two sectors were identified: - the upstream sector (~230 km) between Guanay (414 m) and 50 km downstream Rurrenabaque (245 m) is located in Andean Piedmont, which consists in a series of thrusts associated with anticlines and synclines (the subandean zone), and presents slope values range between 135 cm/km and 10 cm/km and an average index of sinuosity (IS) of 1.29, - the downstream sector (~ 820 km) which runs in Amazonian plain (until Riberalta -165 m-), is characterized by an average slope of 8 cm/km and an average IS of 2.06 (this sector is much more homogeneous and the Beni river shows a meandering channel). For the Napo River, three sectors were identified: - the first sector (~140 km) between Misahualli (401 m) and Coca (265 m), is located in Andean Piedmont (subandean zone) and presents slope values range between 170 cm/km and 30 cm/km and an average IS of 1.6, - the second sector (~250 km) between Coca (when the Napo river enters in the Amazonian plain) and Nuevo Rocafuerte (190 m), presents slope values range between 30 cm/km and 20 cm/km and an average IS of 1.2, and a convex-up shape profile corresponding to the preserved part of the Pastaza-Napo Megafan, not yet affected by headwater erosion, - the third sector (~600 km) between Nuevo Rocafuerte and the confluence with the Amazon river (101 m), where the Napo river flows through the quaternary deposits of the Pastaza-Napo Megafan, presents slope values ranging from 20 to 10 cm/km and an average IS of 1.2, and is characterized by a more classical concave-up shape profile. Our main results established using DGPS data (an important difference between the slope and IS averages of the Napo and the Beni rivers in their Amazonian part, respectively ~20 cm/km and ~8 cm/km, ie a ratio ~2.5, 1.2 and 2.06, ie a ratio ~0.6) bring an additional explanation to the results obtained by the preceding authors, with balance methods, and confirm respectively the erosion and the sedimentation behaviour of the Napo and the Beni rivers.