Sediment Transport and Topographic Evolution of a Coupled River and River-Plume System: Experimental Study and Numerical Model
Chatanantavet, Phairot and Lamb, Michael P.
Sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial, land use dynamics, 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 sediment transport in the transitional river-to-river-plume zone that is characterized by backwater hydrodynamics and subject to different flow conditions. We developed a quasi-2D morphodynamic, numerical model of a coupled river and river plume system. We also conducted flume experiments to test the numerical model results as well as to directly observe morphodynamics near the river mouth. Our experiments were performed in a 7.5-m long flume where a 10-cm wide river channel was connected to a 76-cm wide “ocean basin” allowing for offshore spreading of the river plume. Both the numerical model and the flume results demonstrate that (1) during low flows backwater hydrodynamics cause spatial flow deceleration and sediment deposition in the river channel and the offshore plume areas, and (2) during high flows the backwater zone becomes a region of water-surface drawdown, spatial flow acceleration and bed scour. We also found channel levee formation offshore generated under bedload transport during low flow, and a large scour hole offshore from the river mouth that is deeper than anywhere else in the river-plume system during high flow. These two morphological characteristics may be important in developing an elongated delta in nature. Our study highlights the need to include coupled river and river plume system with a suite of flow discharges to accurately predict fluvio-deltaic morphodynamics and connectivity between fluvial sediment sources and marine sediment sinks.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013