--> Abstract: The Depositional Web on the Fly River Floodplain, Papua New Guinea; #90063 (2007)

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The Depositional Web on the Fly River Floodplain, Papua New Guinea

 

Dietrich, William E.1, Geoff Day2, Joel C. Rowland1 (1) University of California, Berkeley, Berkeley, CA (2) Rio Tinto, London, United Kingdom

 

Floodplain deposition on lowland meandering rivers is usually distinguished as either occurring by lateral accretion during channel migration or by overbank deposition. Here we report the results of an intensive field study that documents the discharge of mainstem water from the Fly River, Papua New Guinea onto its floodplain and maps the spatial pattern of sediment deposition on the floodplain (using elevated particulate copper introduced into the system due to upstream mining as a tracer). Sediment laden waters are injected across the floodplain by flow reversal up low gradient tributaries and via smaller channels that link the mainstem to off river water bodies (tie channels). While sediment deposition is confined to less than 1 km either side of these channels, sediment is distributed ten's of kilometers across the plain via the tributary and tie channels. Deposition declines exponentially from the nearest channel. About 40% of the total sediment load was deposited on the floodplain, with half of that being conveyed by the floodplain channels. Levee topography along the mainstem and floodplain channels are similar, but cannot be explained by the observed exponential functions. Shear flow during extended periods of flooding my give rise to the localized levee deposition. Our study demonstrates that floodplain channels can inject large volumes of sediment-laden mainstem waters great distances across the floodplain where they spill overbank, forming a narrow band of deposition, and thereby creating a depositional web.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California