Recent increase of river-floodplain suspended sediment exchange in a reach of the lower Amazon River

• Grant number: 17/18509-8
• Support type: Regular Research Grants - Publications - Scientific article
• Duration: October 01, 2017 - March 31, 2018
• Field of knowledge: Physical Sciences and Mathematics - Geosciences
• Principal Investigator: Conrado de Moraes Rudorff
• Grantee: Conrado de Moraes Rudorff
• Home Institution: Centro Nacional de Monitoramento e Alertas de Desastres Nacionais (CEMADEN). Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brasil). Cachoeira Paulista , SP, Brazil

Abstract

We analyzed variation of channel-floodplain suspended sediment exchange along a 140 km reach of the lower Amazon River for two decades (1995-2014). Daily sediment fluxes were determined by combining measured and estimated surface sediment concentrations with river-floodplain water exchanges computed with a two-dimensional hydraulic model. The average annual inflow to the floodplain was 4,088 ± 2,017 Gg y-1 and the outflow was 2,251 ± 471 Gg y-1, respectively. Prediction of average sediment accretion rate was twice the estimate from a previous study of this same reach and more than an order magnitude lower than an estimate from an earlier regional scale study. The amount of water routed through the floodplain, which is sensitive to levee topography and increases exponentially with river discharge, was the main factor controlling the variation in total annual sediment inflow. Besides floodplain routing, the total annual sediment export depended on the increase in sediment concentration in lakes during floodplain drainage. The recent increasing amplitude of the Amazon River annual flood over two decades has caused a substantial shift in water and sediment river-floodplain exchanges. In the second decade (2005-2014), as the frequency of extreme floods increased, annual sediment inflow increased by 81% and net storage increased by 317% in relation to the previous decade (1995-2004). (AU)