Chatanantavet, Phairot and Lamb, Michael P. and Nittrouer, Jeffrey A. (2012) Backwater controls of avulsion location on deltas. Geophysical Research Letters, 39 . Art. No. L01402. ISSN 0094-8276 http://resolver.caltech.edu/CaltechAUTHORS:20120210-105901002
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River delta complexes are built in part through repeated river-channel avulsions, which often occur about a persistent spatial node creating delta lobes that form a fan-like morphology. Predicting the location of avulsions is poorly understood, but it is essential for wetland restoration, hazard mitigation, reservoir characterization, and delta morphodynamics. Following previous work, we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length, i.e., the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin. To explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges. Results show that avulsion is less likely in the downstream portion of the backwater zone because, during high-flow events, the water surface is drawn down near the river mouth to match that of the offshore plume, resulting in river-bed scour and a reduced likelihood of overbank flow. Furthermore, during low-discharge events, flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel-fill timescale there. Both mechanisms favor preferential avulsion in the upstream part of the backwater zone. These dynamics are fundamentally due to variable river discharges and a coupled offshore river plume, with implications for predicting delta response to climate and sea level change, and fluvio-deltaic stratigraphy.
|Additional Information:||© 2012 by the American Geophysical Union. Received 2 November 2011; revised 30 November 2011; accepted 3 December 2011; published 12 January 2012. Acknowledgement is made to the donors of the American Chemical Society Petroleum Research fund and to Caltech for support of this work. J. Nittrouer wishes to thank the NSF Postdoctoral Fellowship (EAR0948224) for his financial support. We thank David Mohrig for insightful discussion as well as Doug Edmonds and Doug Jerolmack for formal reviews that helped strengthen the final manuscript. The Editor thanks Douglas Edmonds and Douglas Jerolmack for their assistance in evaluating this paper.|
|Subject Keywords:||Mississippi; avulsion; backwater; delta; sediment|
|Official Citation:||Chatanantavet, P., M. P. Lamb, and J. A. Nittrouer (2012), Backwater controls of avulsion location on deltas, Geophys. Res. Lett., 39, L01402, doi:10.1029/2011GL050197|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||21 Mar 2012 16:42|
|Last Modified:||26 Dec 2012 14:49|
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