Temporal dynamics of water and sediment exchanges between the Curuai floodplain and the Amazon River, Brazil

The fluvial transport and storage of sediments within channel-floodplain systems can act as important sinks of sediments. In this study, we document the role of an Amazonian floodplain (Curuai) for sediment storage. Located on the right bank of the Amazon River, 900 km upstream of the mouth, the complex system contains more than 30 interconnected lakes linked to the mainstream by permanent and temporary channels. With an open-water area varying between 600 km^2 and 2500 km^2, it represents ~13% of the total flooded area of the Amazon River, between Manaus and Obidos. For the period 2000-2003, daily liquid and solid fluxes exchanged between the floodplain system and the Amazon River were determined using an hydrological model based on a network of gauging, meteorological and sediment monitoring stations and satellite data including radar altimetry data. Sediment accumulation occurs during the five months of the flood rise, from December to April. The export of sediments to the mainstream occurs during the low water stage while depositional processes in lakes and channels are disrupted by the wind induced re-suspension of sediments. The mean average sediment storage calculated varies between 558 and 828 × 10^3 t yr^-1 corresponding to 5.4 (±19%) × 10^3 t km^-1 yr^-1 of sediment deposited along the 130 km reach between Juruti and Santarem. This annual storage represents between 41% and 53% of the annual flux of sediments entering this floodplain through the main channels. The associated mean specific sedimentation rate is ~517 (±23%) t km^-2 yr^-1 leading to a sediment accretion rate of 1.6 mm yr^-1 ± 23%.