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Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie Bolivienne), en période de crue

1993; Taylor & Francis; Volume: 6; Issue: 4 Linguagem: Inglês

10.1080/09853111.1993.11105251

1778-3593

Jean‐Loup Guyot, Jean‐Marie Jouanneau, Jorge Quintanilla, J.G. Wasson,

Soil erosion and sediment transport

RésuménLe Rio Béni est l'un des principaux formateurs andins du Rio Madeira, le plus important des affluents méridionaux de l'Amazone. La station hydrométrique de "Angosto del Bala" sur le Rio Béni contrôle un bassin andin de 67500 km2, aux caractéristiques géomorpho-climatiques très contrastées.Afin de connaître l'évolution temporelle des teneurs relatives des éléments des phases dissoutes et particulaires, un suivi hydrologique et hydrogéochimique a été réalisé à cette station en mars 1988, période de hautes eaux où une crue de fréquence annuelle a été observée. Les résultats obtenus montrent l'existence d'une grande variabilité temporelle des concentrations, mais présentant un cortège hydrogéochimique stable au cours de la crue.Enfin, l'importance quantitative de cette période de hautes eaux sur le bilan moyen annuel des flux exportés est souligné.AbstractThe Béni river, located in the Rio Madeira drainage basin (Figure 1), contributes significantly to the sediment exportation from the Andes to the Amazonian basin. Although most of transport takes place during floods, the nature of the load during high flow was poorly known.To investigate this topic, an annual flood episode (10000 m3. s-1) has been sampled near Rurrenabaque, at the 'Angosto del Bala' PHICAB gauging station (Figure 1 and Table I) that controls the whole Andean catchment of the Béni river (67500 km2). This watershed presents highly contrasted geomorphic and climatic features, including some semi-arid sedimentary highly erodible basins, and crystalline, hyperhumid, densely vegetated ones. Altitude is ranging from 6400 to 250 meters.Gauging and sampling (Figures 3 & 4 and Table II) was carried out daily from March 15 to 30, 1988. Major elements (Tables III & V) and organic carbon (Table VII) were analysed in dissolved and suspended solids, clay mineralogy (Table IV) and trace elements (Table VI) in the suspended sediments.Concentrations of Total Dissolved Solids (TDS) and Total Suspended Sediments (TSS) are highly variable (Figure 4) but linked together (Figure 5) as TDS and TSS probably come from the same basins. Inversely, the chemical composition of TDS as well as TSS is relatively stable during the sampled period. Almost 90 % of organic carbon exported during this flood is particulate.Corresponding budgets are calculated. Particulate material accounts for 99 % of the total load. On an annual basis, this high flow episode (4 % of the year time) may contribute to 30 % of the Beni river mean annual sediment exportation to Amazonia.Mots-clés: AndesAmazonieHydrologieMatières en suspensionHydrochimieGéochimieKey-words: AndesAmazonieHydrologieSuspended SedimentWater ChemistryGeochemistry