Experimental Study of a Coupled River and River-Plume System: Backwater Controls on Source-to-Sink Sediment Transfer and Channelization on Deltas

Sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial, reservoir exploration, and unraveling global climate change and Earth history from sedimentary strata. Despite the important role of source-to-sink sediment transfer, substantial uncertainty exists about the behavior of rivers near their mouths and sediment routing from rivers to their offshore plumes. Here we aim to better understand the morphodynamics and deposits in the transitional river-to-river-plume zone that is characterized by backwater hydrodynamics by using flume experiments. Our experiments were performed in a 7.5-m flume where a 10-cm wide river channel was connected to a 1-m wide “ocean basin” allowing for offshore spreading of the experimental plume. The first experiment set shows that (1) during low flows backwater hydrodynamics cause spatial flow deceleration and sediment deposition in both the river channel and offshore plume areas, and (2) during high flows the backwater zone becomes a region of drawdown, spatial flow acceleration and bed scour. The second set of experiments shows that with a suite of flood events with different discharges and durations, a persistent backwater/drawdown zone exists and controls the patterns of deposition and erosion, which cannot be reproduced using a single characteristic discharge (as is often assumed). We find that backwater hydrodynamics can extend onto the prograding delta and that alternating periods of erosion and deposition lead to rapid formation of levees and channel elongation. This in turn confines the offshore plume, which can affect backwater dynamics upstream, delta evolution and stratigraphy generation. Results are compared to numerical simulations presented in a companion study by Lamb et al.
(2011).

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California