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Backwater and river plume controls on scour upstream of river mouths: Implications for fluvio-deltaic morphodynamics

Lamb, Michael P. and Nittrouer, Jeffrey A. and Mohrig, David and Shaw, John (2012) Backwater and river plume controls on scour upstream of river mouths: Implications for fluvio-deltaic morphodynamics. Journal of Geophysical Research F, 117 . Art. No. F01002. ISSN 0148-0227. doi:10.1029/2011JF002079.

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Sediment flux from rivers to oceans is the fundamental driver of fluvio-deltaic morphodynamics and continental margin sedimentation, yet sediment transport across the river-to-marine boundary is poorly understood. Coastal rivers typically are affected by backwater, a zone of spatially decelerating flow that is transitional between normal flow upstream and the offshore river plume. Flow deceleration in the backwater zone, as well as spreading of the offshore plume, should render rivers highly depositional near their mouths, leading to sedimentation and eventual elimination of the backwater zone at steady state. This reasoning is counter to observations of riverbed scour, erosional bed forms, and long-lived backwater zones near the mouths of some coastal rivers (e.g., Mississippi River, United States). To explain these observations, we present a quasi-2-D model of a coupled fluvial backwater and offshore river plume system and apply it to the Mississippi River. Results show that during high-discharge events the normal-flow depth can become larger than the water depth at the river mouth resulting in drawdown of the water surface, spatial acceleration of flow, and erosion of the riverbed. As proposed by Lane (1957), the transition to drawdown and erosion is ultimately forced by spreading of the offshore river plume. This points to the need to model coupled river and river plume systems with a dynamic backwater zone under a suite of discharges to accurately capture fluvio-deltaic morphodynamics and connectivity between fluvial sediment sources and marine depositional sinks.

Item Type:Article
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URLURL TypeDescription DOIArticle
Lamb, Michael P.0000-0002-5701-0504
Nittrouer, Jeffrey A.0000-0002-4762-0157
Mohrig, David0000-0003-1828-4526
Additional Information:© 2012 by the American Geophysical Union. Received 5 May 2011; revised 6 October 2011; accepted 10 October 2011; published 7 January 2012. We thank O. P. Harmar for providing access to digital Mississippi River topographic data, and we thank the U.S. Army Corps of Engineers for providing access to measurement databases. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund (grant to M.P.L.), the RioMAR Industry Consortium, and the National Science Foundation (grant EAR0948224 to J.A.N.). We thank Chris Paola, Federico Falcini, Dimitri Lague, and Alexander Densmore for their constructive reviews.
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
RioMAR Industrial ConsortiumUNSPECIFIED
Subject Keywords:backwater, erosion, river mouth, river plume.
Record Number:CaltechAUTHORS:20120203-154328575
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Official Citation:Lamb, M. P., J. A. Nittrouer, D. Mohrig, and J. Shaw (2012), Backwater and river plume controls on scour upstream of river mouths: Implications for fluvio-deltaic morphodynamics, J. Geophys. Res., 117, F01002, doi:10.1029/2011JF002079
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29140
Deposited By: Ruth Sustaita
Deposited On:06 Feb 2012 15:40
Last Modified:09 Nov 2021 17:04

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