Jacques Callede

Evolution du débit de l’Amazone à Óbidos de 1903 à 1999 / Evolution of the River Amazon’s discharge at Óbidos from 1903 to 1999

Abstract Abstract The time series of 97 annual values, observed or reconstituted, of runoff of the River Amazon at Óbidos shows a slight increase of 9% in the mean annual discharges from 1903 to 1999, and of 10% for the floods. All the rupture tests indicate a break in 1970, for the mean annual discharges as well as for the floods. The evolution of the coefficients of variation indicates a reduction in the interannual variability of the mean discharges and floods, from 1927 to 1970. The comparison between the evolution of the mean annual discharges and the average annual rainfall of the basin, from 1945 to 1998, exhibits a good correlation between precipitation and runoff. Finally, the analysis of the evolution of the mean annual discharge and the average annual rainfall, expressed as a percentage of the deviation from the 1945–1998 averages, demonstrates an increase in the flow in relation to the rainfall, which could be the consequence of the Amazonian deforestation.

Discharge determination by Acoustic Doppler Current Profilers (ADCP): a moving bottom error correction method and its application on the River Amazon at Óbidos

Abstract Since 1995, hydrologists of the HiBAm (Hydrology and Geochemistry of the Amazon Basin) Research Program carried out several hundred discharge measurements in the Amazon basin. Implementation of modern discharge measurement techniques using ultrasonic devices (ADCP), give evidence of a systematic error linked to the displacement of the river bottom due to high water velocity close to the bottom. This error leads to an underestimation of discharge value. It was possible to establish a correlation between the water velocity close to the river bottom and the error between real position and position computed by ADCP when the boat returns to its starting point after a two-way crossing of the river. When there is no bottom displacement, i.e. during low flow period, this return position error is weak (less than 50 m). This has allowed quantification of river bed load speed, or bottom displacement speed. A correction method was developed on the basis of this correlation. This method, systematically applied to ADCP discharge measurements obtained at Óbidos hydrometric station, allowed all measured discharges to be corrected, especially for 1997 and 1999 floods. Another method, based on the analysis of real trajectory of the boat (obtained from topographic measurement or GPS positioning) compared with the ADCP computed trajectory, is under study.

Use of satellite communication of hydrometric data for the whole of Brazil

Abstract The difficulties of exploiting the huge Brazilian hydrometeorological network led hydrologists of the Departamento Nacional de Aguas e Energie Eletrica (DNAEE—Brazilian Department of Water and Electric Power) to use real time satellite telecommunications to improve network management. Data-gathering satellites, which are perfectly adapted to this network, were first used in 1975 and have interested DNAEE since 1980. Collaboration with ORSTOM permitted an initial evaluation of the technique in 1982. In 1984 DNAEE, together with ORSTOM, was able to set up a 20-station network in the Amazon. The results have been so encouraging that a scheme for 200 stations equipped with telecommunications facilities which use the Brazilian Satelite de Colecta de Dados number 1 (SCD1) satellite is in the final stages. This network will cover the entire country.