Seasonal, tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains

Journal of Geophysical Research: Earth Surface
By: , and 

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Abstract

Mainstem–floodplain material exchange in the tidal freshwater reach of ma jor rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environ ments. This knowledge gap prompts investigation of floodplain-incising tidalchannels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Seasonal, tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains
Series title Journal of Geophysical Research: Earth Surface
DOI 10.1002/esp.4616
Volume 44
Issue 9
Year Published 2019
Language English
Publisher Wiley
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description 220 p.
First page 1659
Last page 1878
Country Brazil
Other Geospatial Amazon River